Poly-Lactic Acid: Production, Applications, Nanocomposites, and Release Studies

Abstract

Environmental, economic, and safety challenges have provoked packaging scientists and producers to partially substitute petrochemical-based polymers with biodegradable ones. The general purpose of this review is to introduce poly-lactic acid (PLA), a compostable, biodegradable thermoplastic made from renewable sources. PLA properties and modifications via different methods, like using modifiers, blending, copolymerizing, and physical treatments, are mentioned; these are rarely discussed together in other reviews. Industrial processing methods for producing different PLA films, wrappings, laminates, containers (bottles and cups), are presented. The capabilities of PLA for being a strong active packaging material in different areas requiring antimicrobial and antioxidant characteristics are discussed. Consequently, applications of nanomaterials in combination with PLA structures for creating new PLA nanocomposites with greater abilities are also covered. These approaches may modify PLA weaknesses for some food packaging applications. Nanotechnology approaches are being broadened in food science, especially in packaging material science with high performances and low concentrations and prices, so this category of nano-research is estimated to be revolutionary in food packaging science in the near future. The linkage of a 100% bio-originated material and nanomaterials opens new windows for becoming independent, primarily, of petrochemical-based polymers and, secondarily, for answering environmental and health concerns will undoubtedly be growing with time.

Full text

Poly-Lactic Acid: Production, Applications,
Nanocomposites, and Release Studies
Majid Jamshidian, Elmira Arab Tehrany, Muhammad Imran, Muriel Jacquot, and St´
ephane Desobry
Abstract: Environmental, economic, and safety challenges have provoked packaging scientists and producers to partially
substitute petrochemical-based polymers with biodegradable ones. The general purpose of this review is to introduce
poly-lactic acid (PLA), a compostable, biodegradable thermoplastic made from renewable sources. PLA properties and
modifications via different methods, like using modifiers, blending, copolymerizing, and physical treatments, are men-
tioned; these are rarely discussed together in other reviews. Industrial processing methods for producing different PLA
films, wrappings, laminates, containers (bottles and cups), are presented. The capabilities of PLA for being a strong active
packaging material in different areas requiring antimicrobial and antioxidant characteristics are discussed. Consequently,
applications of nanomaterials in combination with PLA structures for creating new PLA nanocomposites with greater
abilities are also covered. These approaches may modify PLA weaknesses for some food packaging applications. Nanotech-
nology approaches are being broadened in food science, especially in packaging material science with high performances
and low concentrations and prices, so this category of nano-research is estimated to be revolutionary in food packaging
science in the near future. The linkage of a 100% bio-originated material and nanomaterials opens new windows for
becoming independent, primarily, of petrochemical-based polymers and, secondarily, for answering environmental and
health concerns will undoubtedly be growing with time.
Introduction
Today, polymers and materials used for food packaging consist of
a variety of petrochemical-based polymers, metals, glass, paper, and
board, or combinations hereof. The durability and degradability of
packaging materials are 2 contradictory subjects; the 1st is desirable
for packaging stability and protection for its contents during shelf
life and the 2nd for its rapid degradation in the environment
(Bohlaman 2005).
Advantages of petrochemical-based polymers, which encour-
aged industries to use them are: (a) low cost and high-speed
production; (b) high mechanical performance; (c) good barrier
properties; and (d) good heat sealability. On the other hand, several
disadvantages include: (a) declining oil and gas resources; (b) in-
creasing oil and gas prices during recent decades; (c) environmental
concerns for their degradation or incineration and global warm-
ing; (d) uneconomical costs and cross-contaminations in their re-
cycling; and (e) consumer toxicity risks about their monomers or
oligomers migrating to edible materials (Amass and others 1998;
Chandra and Rustgi 1998; Mohanty and others 2000; Siracusa
and others 2008).
MS 20100340 Submitted 3/29/2010, Accepted 6/10/2010. Authors are with ´
Ecole
nationale sup´
erieure d’agronomie et des industries alimentaires, Institut National Poly-
technique de Lorraine, 2 avenue de la Forˆ
et de Haye, 54501 Vandoeuvre, France. Direct
inquiries to author Jamshidian (E-mail: majid.jamshidian@ensaia.inpl-nancy.fr).
Mechanical recycling (segregated plastics, mixed plastics), bi-
ological recycling (sewage, compost, soil), and energy recovery
(incineration, pyrolysis) are 3 alternative ways for plastics waste
management, with each having some advantages and disadvan-
tages as to economical, processing, and technological aspects (Scott
2000).
The above-mentioned concerns are negligible for biopolymers
concerning the biodegradation process that takes place in nature.
Biodegradation is defined as the degradation of a polymer in nat-
ural environments that includes changes in chemical structure,
loss of mechanical and structural properties, and finally, chang-
ing into other compounds like water, carbon dioxide, minerals,
and intermediate products like biomass and humic materials. The
natural environments contain chemical, biological, and physical
forces with impinging factors like temperature, humidity, pH, O2
presence, and so on, which determine the rate and products of the
biodegradation process (Zee 2005).
Biopolymers are produced from natural resources and crude oil.
Four categories of biopolymers are recognized: (a) extracted di-
rectly from natural raw materials, such as polysacchar ides like starch
and cellulose; proteins like gelatin, casein, and silk; and marine
prokaryotes; (b) produced by chemical synthesis from bio-derived
monomers such as poly-lactic acid (PLA), also known as poly(lactic
acid) in the literature; (c) produced by microorganisms or genet-
ically modified bacteria such as polyhydroxyalkanoates (PHA),
polyhydroxybutyrate (PHB), hydroxyl-valerate (PHV), bacterial
cellulose, xanthan, and pullan; and (d) produced from crude oil like
aliphatic and aromatic polyesters, polyvinyl alcohol, and modified
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Poly-lactic acid, nanocomposites, and release studies . . .
polyolefins, which are sensitive to temperature and light (Chandra
and Rustgi 1998; Clarinval and Halleux 2005).
PLA or poly-lactide was discovered in 1932 by Carothers (at
DuPont). He was only able to produce a low molecular weight
PLA by heating lactic acid under vacuum while removing the
condensed water. The problem at that time was to increase the
molecular weight of the products; and, finally, by ring-opening
polymerization of the lactide, high-molecular weight PLA was
synthesized. PLA was 1st used in combination with polyglycolic
acid (PGA) as suture material and sold under the name Vicryl in
the U.S.A. in 1974 (Mehta and others 2005).
In comparison to other biopolymers, the production of PLA
has numerous advantages including: (a) production of the lactide
monomer from lactic acid, which is produced by fermentation
of a renewable agricultural source corn; (b) fixation of significant
quantities of carbon dioxide via corn (maize) production by the
corn plant; (c) significant energy savings; (d) the ability to recycle
back to lactic acid by hydrolysis or alcoholysis; (e) the capability of
producing hybrid paper-plastic packaging that is compostable; (f)
reduction of landfill volumes; (g) improvement of the agricultural
economy; and (h) the all-important ability to tailor physical prop-
erties through material modifications (Dorgan and others 2000).
Briefly, PLA is based on agricultural (crop growing), biological
(fermentation), and chemical (polymerization) sciences and tech-
nologies. It is classified as generally recognized as safe (GRAS) by
the United State Food and Drug Administration (FDA) and is safe
for all food packaging applications (Conn and others 1995; FDA
2002).
Production steps, general properties, applications, processing
technologies, modifications, and biodegradability of PLA are pre-
sented in this review. Consequently, migration and release stud-
ies of active compounds and PLA abilities making it a potential
active food packaging are also discussed; finally, recent different
types of nanocomposites used for improving PLA applications are
reviewed.
PLA Production
Lactic acid (2-hydroxy propionic acid), the single monomer of
PLA, is produced via fermentation or chemical synthesis. Its 2 op-
tically active configurations, the L(+) and D(−) stereoisomers are
produced by bacterial (homofermentative and heterofermentative)
fermentation of carbohydrates. Industrial lactic acid production
utilizes the lactic fermentation process rather than synthesis be-
cause the synthetic routes have many major limitations, including
limited capacity due to the dependency on a by-product of another
process, inability to only make the desirable L-lactic acid stereoiso-
mer, and high manufacturing costs (Datta and Henry 2006).
The homofermentative method is preferably used for industrial
production because its pathways lead to greater yields of lactic acid
and to lower levels of by-products. The general process consists
of using species of the Lactobacillus genus such as Lactobacillus del-
brueckii, L. amylophilus, L. bulgaricus, and L. leichmanii,apHrange
of 5.4 to 6.4, a temperature range of 38 to 42 ◦C, and a low oxy-
gen concentration. Generally, pure L-lactic acid is used for PLA
production (Mehta and others 2005).
PLA has a variable molecular weight and only its high molecular
weight polymer is used in the packaging industry. Three ways are
possible for the polymerization of lactic acid; (a) direct condensa-
tion polymerization; (b) direct polycondensation in an azeotropic
solution (an azeotrope is a mixture of 2 or more chemical liquids
in such a ratio that its composition cannot be changed by simple
distillation. This occurs because, when an azeotrope is boiled, the
resulting vapor has the same ratio of constituents as the original
mixture); and (c) polymerization through lactide formation. The
1st method is based on esterification of monomers by the aid of
some solvents and exudated water is removed using progressive
vacuum and high temperatures. Obtaining high molecular weight
polyesters with good mechanical properties via this method is not
easy, although precondensates may be of interest for the prepa-
ration of biodegradable glues or lacquers, since the –OH and
-COOH end groups allow cross-linking with suitable inorganic
or organic multivalent additives (Hartmann 1998).
Producing high molecular weight PLA polymers by direct poly-
condensation in an azeotropic solution and also application of
some catalysts is more practicable. The azeotropic solution helps
to decrease the distillation pressures and facilitates PLA separation
from the solvent by application of molecular sieves. The variety
and content of catalysts, solvent volume percentages, and the reac-
tion time on the preparation of PLA have been studied. The results
identified by using improved experimental equipment, the proper
complex catalyst, and solvent volume ratio, in order to obtain a
molecular weight of PLA of 6.6 ×104(Li and others 2006).
Polymerization through lactide formation is being industrially
accomplished for high molecular weight PLA production. Lactide
is a cyclic dimer formed by removing water under mild conditions
and without solvent. L-lactide, meso (L,D) lactide, and D-lactide
are products of L-lactic acid and D-lactic acid. The terms poly
lactide and poly (L-lactide) have been used in many references
instead of PLA.
Lactide purification is accomplished by vacuum-distillation of
high temperatures. After the vacuum-distillation of L-lactide, high
molecular weight PLA with a controlled optical and crystal purity
is formed by ring-opening polymerization. Ring-opening poly-
merization of lactide can be carried out in melt or solution by
cationic, anionic, and coordination mechanisms, depending on
the initiator utilized. The most considered active initiator for the
L-lactide ring-opening polymerization is stannous octoate (bis
2-ethyl hexanoate, SnOct2), which causes a low degree of racem-
ization at high temperature. It has a low toxicity and is accepted
by FDA (Puaux and others 2007).
A kinetics study for ring-opening polymerization of L-lactide
with stannous octoate has been done and a correlated mathematical
modeling developed for that (Mehta and others 2007).
The choice of initiator system, co-initiator as chain control
agent, catalyst concentration, monomer-to-initiator ratio, and
polymerization temperature and time significantly affect the poly-
mer properties. Properties such as molecular weight, degree of
crystallinity, and residual monomer content, in turn affect the
physico-mechanical properties of polylactide and its copolymers
(Vink and others 2004).
Figure 1 shows PLA production steps by ring-opening poly-
merization using stannous octoate as an initiator.
New ideas for decreasing PLA final price and making produc-
tion processes more eco-friendly, in comparison to earlier pro-
duction process, include usage of crop residue (stems, straw, husks,
and leaves) from corn or, potentially, other crops, and use of un-
fermentable residues as a heat source, as well as substituting some
part of electricity energy by wind power energy. These approaches
decrease the consumption of fossil fuels and corn starch as raw ma-
terials and also diminish polluting air, water, and waste emissions
to the environment (Vink and others 2003).
One of the most positive points of PLA production in compar-
ison with the other hydrocarbon-based polymers is the decrease
of CO2emission. Carbon dioxide is believed to be the most
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Poly-lactic acid, nanocomposites, and release studies . . .
Figure 1–Current production steps for PLA.
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Poly-lactic acid, nanocomposites, and release studies . . .
Figure 2–Net greenhouse gas emission of commercial PLAs and other polymers. PLA/NG =NatureWorks®PLA next generation, PLA5 =
NatureWorks®PLA in 2005, PLA6 =NatureWorks®in 2006, HIPS =high impact poly(styrene), PC =poly(carbonate), GPPS =general purpose
poly(styrene), PET am =PET amorph, PET ssp =PET solid sate polycondensed.
important contributor to global climate change and its warm-
ing. Because, carbon dioxide is absorbed from air when corn is
grown, use of PLA has the potential to emit fewer greenhouse gases
compared to competitive hydrocarbon-based polymers. “Net” or
“residual” emissions are calculated as total emissions from the cra-
dle to the factory gate minus carbon dioxide uptake that occurs
during corn production. This amount is negative for present PLA
production. It means the total CO2consumption from the cradle
to factory is more than its emission to the environment (Bo-
gaert and Coszach 2000). Vink and others (2003) concluded if
all produced PLA articles enter into composting process which
emits CO2in atmosphere; Nevertheless, their net CO2emission
is less than for other polymers. Vink and others (2007) showed
the net greenhouse gas emissions of NatureWorks®PLA polymers
decreased from 2 kg CO2eq./kg polymer in 2003 to 0.3 kg in
2006. The authors also estimated the −0.7 kg of CO2for next
PLA generation using wind energy in the near future. By this
opportunity, PLA can even become a greenhouse gas sink by the
implementation of a new process technology combined with the
use of green power to drive the production processes (Figure 2).
NatureWorks®LLC, the present leader in PLA technology,
has a 50 to 50 joint venture between Cargill incorporated
and Dow Chemical Co. and was formed in November 1997.
In 2002, they started the world’s first full-scale PLA plant in
Blair, Nebraska, U.S.A., capable of producing 140,000 metric
tons per year. NatureWorks®entered into a joint venture be-
tween Cargill and Teijin Limited of Japan in December 2007
(www.natureworksllc.com).
Other major companies involved in PLA manufacturing are
Toyobo, Dai Nippon Printing Co., Mitsui Chemicals, Shimadzu,
NEC, Toyota (Japan), PURAC Biomaterials, Hycail (The Nether-
lands), Galactic (Belgium), Cereplast (U.S.A.), FkuR, Biomer,
Stanelco, Inventa-Fischer (Germany), and Snamprogetti (China)
(Wolf 2005; Platt 2006).
Sources for lactic acid fermentation
NatureWorks®exclusively uses corn starch as raw material for
lactic acid production via lactic fermentation. Many studies have
been conducted to find other sources of carbohydrates for lac-
tic acid production. The use of a specific carbohydrate feedstock
depends on its price, availability, and purity. Some agricultural by-
products, which are potential substrates for lactic acid production
include, cassava starch, lignocellulose/hemicellulose hydrolysates,
cottonseed hulls, Jerusalem artichokes, corn cobs, corn stalks, beet
molasses, wheat bran, rye flour, sweet sorghum, sugarcane press
mud, cassava, barley starch, cellulose, carrot processing waste, mo-
lasses spent wash, corn fiber hydrolysates, and potato starch (Reddy
and others 2008).
Other sources of carbohydrate for lactic acid production include
kitchen wastes (Kim and others 2003; Zhang and others 2008),
fish meal wastes (Huang and others 2008), and paper sludge (Bud-
havaram and Fan 2007). By using kitchen wastes, concerns about
waste management in crowded cities could be automatically eased.
Additionally, some parts of carbohydrates from wastes will return
to the production cycle of lactic acid and, as a result, decrease a
large amount of corn consumption. By using other carbohydrate
sources rather than corn, the criticisms and debates about utilizing
a food source as packaging material will be defused (Zhang and
others 2008).
PLA Processing Technologies for Food Applications
The methods of manufacture for biopolymers are all established
polymer-manufacturing techniques, but the control and applica-
tion of these methods must be varied to cope with certain factors
associated with exploiting the advantages of biopolymers. The
manufacturing routes all show certain fundamental similarities,
with the major differences depending on whether a thermoset or
thermoplastic biopolymer is to be processed.
The conditions in biopolymer processes such as injection mold-
ing are least damaging to polymer melts, and most problematic
in continuous processes like extrusion, particularly in processes
where the extrudate is stretched, such as film blowing. The limit-
ing factors for processing conditions for biopolymers are the same
as for petrochemical-based ones: degradation at the upper limits
of temperature and shear, and lack of homogeneity at the lower
limits. However, these limits are somewhat more tightly drawn at
the upper limits for biopolymers. The results of exceeding these
upper limits are degradation of the polymer, resulting in molding
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Poly-lactic acid, nanocomposites, and release studies . . .
Table 1–Processing possibilities of typical commercial biodegradable
polymers (Clarinval 2002; Clarinval and Halleux 2005, NatureWorks®
datasheets).
Extrusion Cast Blow Fiber
Injection Extru- blow film mold- spinn- Thermo-
molding sion molding extrusion ing ing forming
Starch ×× × ×
Cellulose ×× ×
PHB ×× × × × ×
PHB-PHV ×× × × ×××
PLA ×× ××××
PBS ××
PCL ×× × ×××
PBST ×× × ×
PBAT ×× ×
PTMAT ×× × ×
PVA ×× × ××
PP,PE +
additives
×× × × ×××
Starch +
PVA
×× ×××
Starch +
cellulose
acetate
×× × × ×
PHB = Poly(3-hydroxybutyrate); PHV = Poly(hydroxyl valerate); PBS = Poly(butylenes succinate); PCL =
Poly(ε-caprolactone); PBST = Poly(butylene succinate terephthalate); PBAT = Poly(butylene adipate
terephthalate);
PTMAT = Poly(tetramethylene adipate terephthalate); PVA = Poly(vinyl alcohol).
defects such as weld lines, discoloration, or a strong odor in the
final product (Johnson and others 2003).
Processing possibilities of typical commercial biodegradable
polymers are presented in Table 1.
Commercial PLA resins are packaged in crystalline and amor-
phous pellet forms. Crystalline and amorphous pellets look signifi-
cantly different. Semicrystalline pellets are opaque and amorphous
pellets are transparent. Different types of PLA resins with different
application ranges are being produced and each customer should
specify packaging demands and match them with PLA data sheets.
In Table 2, available commercial PLA resins for food packaging
applications are characterized.
The processing technologies for producing different packaging
applications with PLA resins are mentioned here.
Drying
As PLA is sensitive to high-relative humidity and temperature
conditions, and for minimizing the risk of its molecular degrada-
tion, it is necessary to be dried less than 0.01% w/w. This value is
expressed as 0.025% w/w or below in NatureWorks®data sheets.
PLA resins normally are packaged with moisture content below
0.04% w/w in moisture-resistant foil liners to maintain that mois-
ture level, and so the drying process is essential. Drying conditions
are dependent on temperature, time, air flow rate, and dew point.
Amorphous pellets must be dried below the Tg(43 to 55 ◦C) to
prevent the resin pellets from sticking together, which can bridge
and plug the dryer (Lim and others 2008).
For crystalline types, the recommended temperatures and times
range between 80 to 100 ◦C and 4 to 2 h, respectively. Typical
drying conditions are 4 h at 80 ◦C (175 ◦F) or to a dew point of
−40 ◦C(−40 ◦F), with an airflow rate greater than 0.032 m3/
min per kg (0.5 cfm/lb) of resin throughout (NatureWorks®PLA
processing guide for biaxially oriented film 2005b). PLA is a hy-
groscopic thermoplastic and readily absorbs moisture from the
atmosphere; so its resins should not be exposed to atmospheric
Table 2–Commercial IngeoTM PLA resins adapted by NatureWorks®data
sheets.
Product
code Applications Usages
2002D Extrusion, thermoforming Dairy containers, food
serviceware, transparent
food containers, blister
packaging, cold drink
cups
3001D
3051D
Injection molding for
applications with heat
deflection temperatures
lower than 55 ◦C (130 ◦F)
Cutlery, cups, plates, and
saucers, and outdoor
novelties
3251D Injection molding, having
higher melt flow capability
than other PLA resins for
easier molding of
thin-walled parts
Injection molding
applications, both clear
and opaque, requiring
high gloss, UV resistance,
and stiffness
4032D Biaxially oriented films with
use temperatures up to
150 ◦C (300 ◦F), barrier to
flavor and grease, and oil
resistance
Laminations, printed films
with higher curing
temperatures, other
packaging applications
4042D Biaxially oriented films with
use temperatures up to
130 ◦C (265 ◦F), barrier to
flavor and grease, and
superior oil resistance
Candy twist-wrap, salad,
and vegetable bags,
window envelope film,
lidding film, label film,
other packaging
applications
4060D Heat sealant with a seal
initiation temperature of
80 ◦C
Can be coextruded with
other PLA resin to form a
sealant layer for biaxially-
oriented PLA film
7000D Injection stretch blow molding,
for 1:2 stage operations
Fresh dairy, edible oils, fresh
water
7032D Injection stretch blow molding,
for 1:2 stage operation
Fruit juices, sports drinks,
jams, and jellies
conditions after drying and the packages should be kept sealed
until ready to use and promptly be dried and resealed if not en-
tirely used.
Extrusion
The 1st major step in the conversion of plastic resin into films,
sheets, containers and so on, is to change the pellets from solid to
liquid or molten phase in an extruder.
Extrusion is a common way for melting thermoplasts and it is
the 1st step for extrusion coating, cast film extrusion, blown film
extrusion, and other polymer processes.
Screw extruders are typically used in the polymer industry. They
consist of an electrically heated metal barrel, a hopper for feeding
the resin, a motor for rotating a screw, and a die where the polymer
melt exists. So, the combination of thermal energy generated by a
heater and frictional heat due to friction between the plastic and
the screw and barrel provide sufficient heat to melt the pellets.
The L/D ratio, which is the ratio of flight length of the screw
to its outer diameter, determines the shear and residence time
of the melt. Screws with a large L/D ratio provide greater shear
heating, better mixing, and longer melt residence time in the
extruder. Another important screw parameter is the compression
ratio, which is the ratio of the flight depth in the feed section to the
flight depth in the metering section. The greater the compression
ratio a screw possesses, the greater the shear heating it provides
(Giles and others 2005).
Recommended extrusion conditions for PLA pellets include
general purpose screws with L/D ratios from 24:1 to 30:1 and
compression ratio of 2.5:1 to 3:1, melt temperature of 200 to
220 ◦C, and also smooth barrels (NatureWorks®PLA 4042 data
sheet 2006a).
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Injection molding
Injection molding involves melting a thermoplastic by extru-
sion, injecting the polymer melt into a mold, cooling the part, and
finally ejecting the part. Most polymers can be injection molded so
long as they can flow and fill the mold cavity easily. The commonly
used polymers are Poly(ethylene terephthalate) PET, Poly(styrene)
(PS), Poly(propylene) (PP), high-density poly(ethylene) (HDPE),
Low-density poly(ethylene) (LDPE), nylon, and Poly(vinyl chlo-
ride) PVC.
An injection molding machine is similar to an extruder and the
main difference between 2 machines is in their screw operation.
In an extruder, the screw rotates continuously providing output of
continuous and long product (pipe, rod, sheet), but the screw of
an injection molding machine, which is called reciprocating screw,
does not only rotate but also moves forward and backward accord-
ing to the steps of the molding cycle. The mold is equipped with
a cooling system providing controlled cooling and solidification
of the material. Injection molding may be used to manufacture a
wide variety of parts such as bottle caps, food trays, containers,
and preforms for blow molding (Rosato and others 2000).
Injection mold-grade PLA is injection molded on most con-
ventional equipment, but there could be some torque limitations
if the screw design has a high compression ratio. Compression
ratios of 2.5 to 3 should be adequate and the recommended melt-
ing temperature is 200 to 205 ◦C. Since PLA has a lower glass
transition temperature (about 58 ◦C) than PS or PET, it might
take a little longer time to set up in the mold (NatureWorks®PLA
injection molding guide for 3051D 2006b).
Physical aging occurs when a polymer is in a nonequilibrium
state and is caused by molecular relaxations that are biased in
the direction required to drive the material closer to equilibrium.
This phenomenon is very common and is encountered in thermo-
plastics moldings that have been cooled rapidly from an elevated
temperature during the shaping operation such as injection mold-
ing process (White 2006). Physical aging significantly affects the
physical properties of the amorphous phase in glassy or partly
glassy polymers. The effect of aging takes place around Tgand
can be noticed by shrinkage of specific volume, decreases in spe-
cific enthalpy and entropy, and a decrease in molecular mobility.
These effects are associated with decrease of free volume, which
controls the mobility of large segments of the polymer chains and
affects the mechanical properties of polymers such as shrinkage,
stiffness, brittleness, and decrease in damping (Ke and Sun 2003b;
Acioli-Moura and Sun 2008).
Injected molded PLA articles are relatively brittle, which caused
by rapid physical aging of polymer since ambient temperature is
approximately 25 ◦CbelowtheT
g. Cai and others (1996) studied
physical aging behavior of PLA in different times and temperatures
by DSC. The results confirmed the augmentation of endothermic
peak at Tgby increasing the aging time, which is related to the
increase of the excess enthalpy of relaxation. The rate of physical
aging was very fast initially and decreased as time increased. They
also showed that the aging temperature of 37 ◦Chadthemax-
imum enthalpy of relaxation, but by increasing the temperature
above 60 ◦C the enthalpy of relaxation was greatly reduced. How-
ever, storage conditions for injected molded PLA articles that are
especially intended for further processing (like preforms) should
be carefully controlled.
Shear-controlled orientation in injection molding (SCORIM)
is a nonconventional injection molding technique that allows for
the enhancement of the mechanical properties of semicrystalline
polymers and has additional degrees of freedom over conven-
tional injection molding. SCORIM technique manipulates the
structure development of a solidifying polymer melt through an
in-mold shearing action, thereby tailoring the morphology and
hence controls the mechanical properties of polymers (Grossman
1995). Ghosh and others (2008) investigated the effect of opera-
tive parameters of SCORIM on Poly(L-lactic acid) (PLLA). They
showed some modifications in energy at break and maximum stress
of all the SCORIM processed PLLA. The overall increments in
maximum stress and energy at break were 134% and 641%, re-
spectively.
Blow molding
Blow molding is a process of blowing up a hot thermoplastic
tube (called parison or preform, a term derived from the glass
industry) with compressed air to conform to the shape of a chilled
mold and releasing the finished product form the mold. The most
widely used materials for blow molding are LDPE, HDPE, PP,
PVC, and PET (Lee and others 2008).
There are 3 common types of blow molding: extrusion blow
molding, injection blow molding, and injection stretch blow
molding (ISBM).
Extrusion blow molding. Extrusion blow molding begins with
extruding a polymer melt into a parison. The chilled mold is
then closed, followed by blowing air through a blow pin to inflate
the parison to conform to the shape to the mold cavity. After
cooling the plastic, the mold is opened, and the part is ejected.
Containers produced by extrusion blow molding must meet mini-
mum stiffness requirements to undergo filling on automated lines.
They must avoid, or limit, unsightly bulging under weight of their
contents, both alone or when stacked. They must also withstand
normal impacts of handling, transport, and accidental dropping.
Such impact must be absorbed by the container walls, weld lines
(pinch-off and handle areas), and screw cap closure threads, often
under extremes of temperature. Basic polymers for extrusion blow
molding are HDPE, PP, and PVC. These polymers are sometimes
coextruded with Ethylene vinyl alcohol (EVOH) or nylon to pro-
vide a better gas barrier (Lee 2006).
PLA containers are not produced by this method, because of a
lack of the required physical and mechanical properties; and PLA
resins for this application have not been yet produced.
Injection blow molding. Injection blow molding is a 2-step pro-
cess for making plastic containers. This method produces a molded
parison called a preform. This method is preferred over extrusion
blow molding for making small parts that require high-production
volumes and closer quality dimensions. Injection blow molding
consists of injecting a thermoplastic material into a cavity and
around a core rod producing a hollow test tube like shape (pre-
form). The molded preform still on the core rod is transferred
to the blow mold. The mold is clamped around the preform
and air is blown into it to shape to the cavity. The preform is
injected onto a support pin or core, which forms a neck with
threads to their required dimensions. The preform is then blown
against the cavity wall to its final shape (Lee 2006; Lee and others
2008).
The use of preform allows the manufacture of bottles with more
precise detail in the neck and finish (threaded) area than extrusion
blow molding.
Injection blow molding requires lower degree of melt strength
than extrusion blow molding and its tooling costs are higher.
Common polymers for this method are PS, LDPE, Linear low-
density poly(ethylene) (LLDPE), HDPE, PP, PVC, and PET (Lee
and others 2008).
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Poly-lactic acid, nanocomposites, and release studies . . .
This process is typically limited to the production of relatively
small bottles and PLA pellets are rarely recommended to be pro-
cessed by this method.
Injection stretch blow molding. Injection stretch blow molding
(ISBM) is an extension of injection blow molding with 2 modifi-
cations: (a) the preform is significantly shorter than the bottle and
(b) a stretch rod is used to stretch the preform in the axial direc-
tion. This process became known in the blow molding industry
with the introduction of plastic or PET soft drink bottles.
While all blow molding processes involve blowing air to stretch
the parison or preform in some fashion, ISBM is designed to
achieve and retain biaxial orientation to significantly improve gas
barrier properties, impact strength, transparency, surface gloss, and
stiffness. Biaxial orientation is achieved by elongating the preform
with the stretch rod and blowing air to stretch the preform in a
direction perpendicular to the axis of the preform, while precisely
controlling a temperature warm enough to allow rapid inflation
and molecular orientation, but cool enough to retard relaxation
of its molecular structure once oriented (Rosato and others 2000)
PET bottles for carbonated soft drinks are the most common
food packaging applications of this process. The combination of
stretching by rod and blowing air at high pressure (about 4 MPa)
induces biaxial molecular orientation, thereby making the bottles
a better barrier to carbon dioxide and stronger to withstand the
internal pressure (Rosato and others 2000; Lee and others 2008).
ISBM-grade PLA resins are accessible and they are generally
used for bottles for different foods like fresh dairy liquids, fruit
juices, sport drinks, edible oils, and so on.
ISBM-grade PLA resin is typically run at lower processing tem-
peratures than bottle-grade PET and the blow molding conditions
include: preform temperature at 80 to 100 ◦C, stretch rod speed
0.8 to 1.2 m/s, and blow mold temperature at 100 to 120 ◦C. In
fact, the heating of the preforms is critical in getting a container
with good clarity and material distribution. Normal preform tem-
peratures for running on a 2-step process have been between 80
and 100 ◦C. This temperature may be lower or higher depending
on the preform design, bottle design, and reheating equipment
that is being used (NatureWorks®PLA ISBM bottle guide 2005a).
Preform design is critical in getting a container with good clar ity
and physical properties. Designing a preform for use as a PLA
container is specific to the blow mold equipment, bottle design,
and mold tooling.
Cast film extrusion
The cast film process involves extruding a molten polymer
through a slit die and drawing it around 2 or more highly polished
high-speed rolls, typically chrome-plated and water-cooled. In less
than 1 revolution, the chill roll solidifies the product as it draws
it down to the correct thickness. Cast film is used in packaging,
food wrap, substrate for coating, protective film, agricultural film
for weed control, general purpose polyethylene film as a protective
barrier to prevent scratching of parts during shipment, and many
other applications (Giles and others 2005).
Due to rapid cooling by the chilled rolls, cast films typically
have a low degree of crystallinity and transparent appearance. Be-
sides providing good optical properties, cast film extrusion has the
advantages of high production rate, good control of film thickness
and uniformity, and little or no additive is required for processing.
Similar to PP, PET, and PS films, the physical properties of PLA
films can be enhanced through orientation. Uniaxial orientation
of PLA is achieved with conventional machine direction orienta-
tion (MDO) rolls. Since PLA tends to neck in (neck in happens
by contacting the melt film with the 1st point of the die; the
hot film shrinks on its way down so its width from the die to
the chill roll is reduced. At the same time, beading or thickening
of the edges occurs) during drawing, nipped rolls are usually re-
quired. It is possible to improve both the thermal resistance and
impact resistance of PLA films or sheets by drawing, orientation,
and crystallization to the same level of strength and stiffness as
oriented polypropylene (OPP) or PET, while maintaining its high
transparency. An oriented film is obtained by stretching it to 2 to
10 times its original length at 60 to 80 ◦C, and further annealing
it at temperatures between the stretching temperature and melting
point. An oriented film may be either processed for dry lamina-
tion, printing, and heat seal or other applications including various
types of packaging (Kawashima and others 2002).
Thermoforming
Thermoforming is a generic term encompassing many tech-
niques for producing useful plastic articles from flat sheets. Ther-
moforming is a process that deals with the pressing or drawing of
pliable plastic into final shape by vacuum or air pressure. A wide
range of thermoplastics, including PP, LDPE, LLDPE, HDPE,
PET, PS, and nylon, may be thermoformed. Food packaging is the
largest application for thermoformed containers, trays, cups, and
tubs. Typical thermoforming steps are clamping, heating, shaping,
cooling, and trimming (Throne 1996)
PLA sheet can be thermoformed with vacuum, compressed
air/vacuum, or only compressed air assistance. The radiant heater
of the thermoforming line for PLA must be adjusted to very low
temperatures. Preheating is not absolutely necessary; however it has
the general advantage that the sheet is homogeneously preheated.
PLA sheet is quite brittle at room temperature and requires some
special handling and storage considerations. There is a greater risk
of cracking and breaking during transporting compared with Ori-
ented poly(Styrene) (OPS) or PET. Neither the sheet nor the
finished product can be stored at temperatures above 40 ◦Cor
greater than 50% relative humidity. These conditions minimize
moisture uptake and consequently sheet blocking, and resistance
to unwinding. Exposure to high temperatures or humidity, even
for a short period, can cause the mater ial to deform and eventu-
ally break down. Sheet and formed products must be transported
in cooled trucks and stored in a climate-controlled warehouse.
The toughness of PLA increases with orientation, and therefore,
thermoformed articles are less brittle than PLA sheet, particularly
in the regions that have been highly stretched during the form-
ing operations rather than flanges and lips. So, flange or lip areas
that receive less orientation tend to be more brittle than the rest
of the thermoformed part (NatureWorks®processing guide for
thermoforming articles 2005c; Patey 2010).
PLA is frequently thermoformed using forming ovens, molds,
and trim tools designed for PET or polystyrene. Because of higher
shrinkage of PP than PLA, the molds and trim tools designed for
PP are less optimally used for PLA.
PLA has a lower softening temperature than PET or PS. Typi-
cally oven settings are about 55 ◦C (100 ◦F) or lower than PS and
about 40 ◦C(75◦F) or lower than PET oven settings. The sheet
should be about 90 to 110 ◦C (190 to 230 ◦F) entering the mold.
Aluminum molds are recommended for thermoforming PLA.
PLA thermal properties indicate that the cooling time in the mold
will be greater for PLA than either PS or PET (NatureWorks®
processing guide for thermoforming articles 2005c).
Patey (2010) discussed some essential factors for PLA ther-
moforming process. According to his suggestions, optimizing a
558 Comprehensive Reviews in Food Science and Food Safety rVol. 9, 2010 c
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Poly-lactic acid, nanocomposites, and release studies . . .
conventional polymer thermoforming line for PLA just needs
some minor modifications in tools and equipments.
PLA crystallinity diminishes its shrinkage after thermoform-
ing process. Uradnisheck (2009) showed the shrinkage of PLA
thermoformed articles is minimized by longer dwell times and
crystallinity of polymer. He concluded that the crystallinity in
a thermoformed article dwelling in the heated mold raised to
a higher level due to supplemental crystallinity generated in the
preheat step and forming or stretching step.
PLA Thermal Stability
PLA is thermally unstable and exhibits rapid loss of molecular
weight as the result of thermal treatment at processing tempera-
tures. The ester linkages of PLA tend to degrade during thermal
processing or under hydrolytic conditions. PLA undergoes thermal
degradation at temperatures lower than the melting point of the
polymer, but the degradation rate rapidly increases above the melt-
ing point. It has been postulated that thermal degradation mainly
occurs by random main-chain scissions. Several reactions such
as hydrolysis, depolymerization, oxidative degradation, and inter-
and intramolecular trans-esterification reactions to mononmer and
oligomeric esters, are suggested to be involved in the degradation
process during thermal treatments (Taubner and Shishoo 2001;
S¨
oderg˚
ard and Stolt 2002).
Taubner and Shishoo (2001) studied 3 parameters on thermal
degradation of PLA during extrusion processing, including pro-
cessing temperature (210 and 240 ◦C), residence time in the melt
(1.75 and 7 min), and the inherent moisture content of polymer.
Their results confirmed higher polymer degradation by increas-
ing processing temperature and time. In a temperature of 210 ◦C,
the loss in Mn(Number-average molecular weights) was less de-
pendent on the residence time in the melt compared to when
processed at a temperature of 240 ◦C. The presence of moisture
in the material affected the loss in Mnto a great extent when pro-
cessing was done at 210 ◦C. The rate of degradation at 240 ◦Cand
7 min was so high that they concluded the moisture content in the
polymer probably does not contribute further to the degradation
process.
Different factors like particle size and shape of polymer, tem-
perature, moisture, crystallinity, % D-isomer, residual lactic acid
concentration, molecular weight, molecular weight distribution,
water diffusion, and metal impurities from the catalyst will affect
the polymer degradation rate. Yu and others (2003) have developed
a mathematical model to describe the molecular weight and poly-
dispersity index (Q) in PLA thermal degradations. They claimed
model ability to predict changes of the molecular weight and poly
dispersity index in the PLLA thermal degradation. Their model
was based on the random chain scission mechanism, effects of
temperature, and time on the molecular weight and polydispersity
index.
PLA Properties
PLA has unique properties like good appearance, high mechan-
ical strength, and low toxicity; and good barrier properties have
broadened its applications. Numerous researchers have studied the
different properties of PLA alone and in combination with other
polymers as blend or copolymer; and here some of them will be
introduced.
Auras and others (2003) studied mechanical, physical, and bar-
rier properties of 2 PLA films by the names of 4030-D, which was
made with nominally 98% L-lactide, and 4040-D, which was made
with nominally 94% L-lactide resins. Finally, the data from these
2 PLA film samples were compared to those of polystyrene (PS)
and polyethylene terephthalate (PET). PLA films showed good
tensile strength with higher values than PS but lower than PET.
Both 4030-D and 4040-D had lower Tm(melting point) and Tg
(glass transition temperature) than PET and PS, which makes PLA
better for heat-sealing and thermal processing. In terms of barrier
properties of PLA, the permeability coefficients of CO2and O2
were lower than those of PS and comparable to those of PET.
For tensile modulus and flexural modulus, PLA has the highest
value in comparison to PS, PP, and HDPE. For notched izod
impact (izod impact strength testing is an American society for
testing and materials [ASTM] standard method [D256 – 06ae1] of
determining impact strength. A notched sample is generally used
to determine impact strength. An arm held at a specific height is
released. The arm hits the sample and breaks it. From the energy
absorbed by the sample, its impact strength is determined), PLA
has the lowest one between PS, PP, and HDPE. The elongation
at break is low and nearly 4% that is just higher than that of PS
(Dorgan and others 2000).
Low glass transition temperature of PLA limits its usages in
thermally processed packages. Because of its deformation and its
low melting temperature, it is better to use it for heat-sealing and
thermoforming applications.
Five major properties of typical biodegradable polymers are
compared with LDPE, PS, and PET in Table 3. It is approximately
possible to predict the application fields of a polymer by these
properties and barrier properties.
The other important property of polymers is their rate of crys-
tallinity. Crystallinity is the indication of amount of crystalline
region in the polymer with respect to amorphous content. Crys-
tallinity influences many polymer properties including hardness,
modulus, tensile strength, stiffness, crease point, and melting point.
So, while selecting a polymer for a required application its crys-
tallinity plays the foremost role.
PLA crystals can grow in 3 structural positions called α,β,and
γforms. They are characterized by different helix conformations
and cell symmetries, which develop upon different thermal and/or
mechanical treatments. The αform grows upon melt or cold
crystallization, the βform develops upon mechanical stretching
of the more stable αform, and the γform, which only recently
has been reported to develop on hexamethylbenzene substrate (Di
Lorenzo 2005).
Di Lorenzo (2005) measured crystallization rates of PLA over
a wide temperature range, using both isothermal and nonisother-
mal methods. He determined that the crystallization rate of PLA at
temperatures between 100 and 118 ◦C is very high. He concluded
that the high crystallization rate of PLA below 120 ◦C has to be as-
cribed to the high rate of radial growth of the spherulites (spherical
semicrystalline regions inside nonbranched linear polymers).
By modification of the chain architecture through the intro-
duction of branching, different melt flow properties will be ob-
tained. Thermal and rheological properties of 2 commercial types
of PLA, linear and branched, were investigated by Dorgan and
others (2000). The crystallization kinetic of the branched polymer
was faster than that of the linear analog. Longer relaxation times
in the terminal region of the branched material introduced it as a
higher zero shear rate viscosity. They concluded that by utilizing
the structure modifications through polymer branching the ability
of using PLA in many processing operations will be extended.
Optical properties of PLA are important in dyeing operations
for textiles and in various packaging applications where clarity is
desirable. Hutchinson and others (2006) determined the optical
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2010 Institute of Food Technologists®Vol. 9, 2010 rComprehensive Reviews in Food Science and Food Safety 559

Poly-lactic acid, nanocomposites, and release studies . . .
Table 3–Comparison of typical biodegradable polymer properties with LDPE, PS, and PET adapted from Clarinval and Halleux (2005).
Tg(◦C) Tm (◦C) Tensile strength (MPa) Tensile modulus (Mpa) Elongation at break (%)
LDPE −100 98 to 115 8 to 20 300 to 500 100 to 1000
PCL −60 59 to 64 4 to 28 390 to 470 700 to 1000
Starch – 110 to 115 35 to 80 600 to 850 580 to 820
PBAT −30 110 to 115 34 to 40 – 500 to 800
PTMAT −30 108 to 110 22 100 700
PS 70 to 115 100 34 to 50 2300 to 3300 1.2 to 2.5
Cellulose – – 55 to 120 3000 to 5000 18 to 55
PLA 40 to 70 130 to 180 48 to 53 3500 30 to 240
PHB 0 140 to 180 25 to 40 3500 5 to 8
PHA −30 to 10 70 to 170 18 to 24 700 to 1800 3 to 25
PHB-PHV 0 to 30 100 to 190 25 to 30 600 to 1000 7 to 15
PVA 58 to 85 180 to 230 28 to 46 380 to 530 –
Cellulose acetate – 115 10 460 13 to 15
PET 73 to 80 245 to 265 48 to 72 200 to 4100 30 to 300
PGA 35 to 40 225 to 230 890 7000 to 8400 30
PEA −20 125 to 190 25 180 to 220 400
PGA = Poly(glutamic acid); PEA = Poly(ester amide).
properties of PLA with different amounts of stereoisomer propor-
tions by ellipsometric measurements. They developed an equation
for index of refraction of PLA with a wide range of stereoisomer
proportions (L-content) within the range of wavelengths from 300
to 1300 nm by using Cauchy coefficients.
There are many PLA resins for different applications with differ-
ent properties; the general characteristics of a commercial amor-
phous PLA, injection mold grade and having a 96:4 L:D ratio
content, are summarized in Table 4.
PLA barrier properties
One of the most important factors in food packaging polymers
is their barrier or permeability performance against transfer of
gases, water vapor, and aroma molecules. Gas permeation prop-
erties of PLA (L:D ratio 96:4) have been studied by Lehermeier
and others (2001) and these values have been reported: at 30 ◦C,
N2permeation in PLA was 1.3 (10−10 cm3cm/cm2scm Hg),
and the activation energy was 11.2 kJ/mol. For oxygen, the
corresponding values were 3.3 (10−10 cm3cm/cm2scm Hg) and
11.1 kJ/mol. The values for carbon dioxide permeation were 1.2
(10−10 cm3cm/cm2scm Hg) and 6.1 kJ/mol. For methane, a value
of 1.0 (10−10 cm3cm/cm2scm Hg) and an activation energy of
13.0 kJ/mol were found.
The authors concluded that polymer chain branching and small
changes in L:D stereochemical content have no effect on per-
meation properties, but film crystallinity profoundly impacted
of the permeation of mentioned gases. For example, due to
higher crystallinity of biaxially oriented PLA film, CH4perme-
ation is 4.5 times lower than that of the other films. The perme-
ation properties of PLA for all gases studied were very similar to
polystyrene.
In research done by Bao and others (2006), different results for
pure gas permeation of PLA were obtained, which disagreed with
those of previous work. They used a time-lag method for the de-
termination of PLA permeation to pure gases and also determined
diffusivity and solubility of N2,CO
2,andO
2in PLA film. For
example, at 30 ◦C, N2permeability, diffusivity, and solubility in
PLA (98.7% L, 1.3% D) were 0.05 (10−10 cm3cm/cm2scm Hg),
2.4 ×10−8cm2/s, and 2.2 ×10−4cm3/cm3(polymer) cm Hg, re-
spectively. The measured activation energy of N2permeation was
34.6 kJ/mol.
Sorption of nitrogen, oxygen, carbon dioxide, and water in PLA
has also been studied at 293.2, 303.2, and 313.2 ◦K(Oliveiraand
others 2004).
Shogren (1997) reported that the water vapor transmission rate
of crystalline and amorphous PLA in 6, 25, and 49 ◦C as 27,
82, and 333 g/m2per day for the crystalline form and 54, 172,
and 1100 g/m2per day for the amorphous form, respectively. He
reported activation energies of 5 and – 0.1 kJ/mol for amorphous
and crystalline PLA, respectively.
Siparsky and others (1997) used a “solution-diffusion” model
to determine the water vapor permeability parameters of different
PLA films, PLA copolymers with caprolactone, and blends with
polyethylene glycol. These parameters included the solubility co-
efficient S, which is a measure of the equilibrium water concentra-
tion available for hydrolysis and the diffusion coefficient D, which
characterizes the rate of water vapor diffusion into the film under
specific conditions. They calculated the permeability coefficient
by the equation of P = SD. They studied S and D for PLA films
by different percent of L and D Lactide. They found the degree
of crystalline had little influence on the measured permeability
parameters.
In a more detailed research done by Tsuji and others (2006),
the effects of D-Lactide content, degree of crystallinity (% Xc),
and molecular weight of PLA films on water vapor transfer rate
(WVTR) were studied. They observed the WVTR of PLA
films decreased monotonically with increasing Xc from 0% to
20%, while leveled off for Xc exceeding 30%; so they sug-
gested this change due to the higher resistance of restricted
amorphous regions to water vapor permeation compared with
that of the free amorphous regions. They also concluded that
changes in Mnof PLA films in the range of 9 ×104to 5 ×
105g/mol and D-lactide unit content of PLA films in the
range of 0% to 50% have insignificant effects on their WVTR
values.
Some aforementioned PLA permeability parameters are sum-
marized in Table 5.
Orientation changes the barrier properties. In a study done by
Auras and others (2005), oriented PLA (OPLA) was investigated
with PET and oriented polystyrene (OPS) with regard to physical,
mechanical, and barrier properties. They concluded, in terms of
water vapor barrier, that PET gave the best performance, followed
by OPS and OPLA. In the case of oxygen barrier properties, PET
showed the lowest oxygen permeability coefficients, followed by
OPLA and OPS that showed very poor oxygen barrier perfor-
mance.
According to these results, the barrier properties of PLA are
remarkable and better than those of OPS. As a consequence, PLA
560 Comprehensive Reviews in Food Science and Food Safety rVol. 9, 2010 c
2010 Institute of Food Technologists®

Poly-lactic acid, nanocomposites, and release studies . . .
Table 4–General characteristics of commercial amorphous poly L-lactid
acid film, injection mold grade, 96:4 L:D, produced by NatureWorks®
Co.
Characteristics Unit Amount Reference
Physical:
Molecular weight g/mol 66000 Garlotta (2001)
Specific gravity – 1.27
Solid density g/cm31.2515
Melt density g/cm31.0727
Glass transition
temperature
◦C 55 Mehta and others
(2005)
Melting temperature ◦C 165
Specific heat (Cp) J/Kg ◦C
190 ◦C 2060
100 ◦C 1955
55 ◦C 1590
Thermal conductivity W/m ◦C
190 ◦C 0.195
109 ◦C 0.197
48 ◦C 0.111
www.nature
worksllc.com
(technical data
sheet)
Optical:
UV light transmission: Auras and others
190 to 220 nm <5% (2004)
225 to 250 nm 85%
>300 nm 95%
Visible light
transmission
95%
Color
L∗90.64 ±0.21
a∗−0.99 ±0.01
b∗−0.50 ±0.04
Mechanical:
Tensile strength MPa 59
Elongation at break % 7.0
Elastic modulus MPa 3500
Shear modulus MPa 1287 www.nature
works.com
(technical data
sheet)
Poissons ratio – 0.3600
Yield strength MPa 70
Flexural strength MPa 106
Unnotched izod impact J/m 195
Notch izod impact J/m 26
Rockwell hardness HR 88
Heat deflection temp. ◦C55
Vicat penetration ◦C59
Ultimate tensile
strength
MPa 73
Percent of elongation % 11.3
Young’s modulus MPa 1280
Rehological:
Cross WLF Viscosity Model:
n 0.2500 www.nature
worksllc.com
(technical data
sheet)
Tau Pa 1.00861e +
005
D1 Pa-s 3.31719e +
009
D2 K 373.15
D3 K/P 0
A1 20.194
A2 K 51.600
is suitable for packaging a wide range of foods that are mentioned
in the section of PLA applications.
Studies on Migration from PLA
Lactic acid is the lone monomer in the PLA structure and so, mi-
grated agents are lactic acid monomers, dimmers, and oligomers.
Conn and others (1995) investigated the safety of PLA as a food
contact polymer under different conditions and studied the mi-
gration of most probable species from PLA. They concluded: (1)
Very limited migration can be expected from PLA into foods that
it contacts during the intended conditions of use. (2) The small
amount of any material that might migrate from PLA into food
will be lactic acid, or its dimers (lactoyl lactic acid and lactide)
Table 5–PLA permeability parameters.
L:D, 96:4 (30 ◦C) L:D, 98.7:1.3 (30 ◦C)
(Lehermeier and (Bao and
others 2001) others 2006)
CO210−10 cm3cm/ 1.2 1.1
O2cm2scm Hg 3.3 0.26
N21.3 0.05
Water vapor permeation
property
(Shogren 1997) 6 ◦C25
◦C49
◦C
Crystalline, 66%
crystallinty
g/m2/day 27 82 333
Amorphous 54 172 1100
(Siparsky and
others 1997) 20 ◦C40
◦C50
◦C
L:D (100:0), 39%
crystallinity
cm3cm/cm2sPa 1.6 1 2
L:D (100:0),
Amorphous
1.9 0.8 2.1
L:D (95:5) 1.4 2.2 2.1
L:D (50:50) 2.2 8.7 6.1
and oligomers that will be subsequently hydrolyzed in aqueous
systems to lactic acid. Based on these findings, they concluded
that PLA is safe and GRAS for its intended uses in fabricating
articles intended for use in contact with food. The authors also
mentioned that the projected intake of lactic acid from PLA is
approximately 700 times less than the estimated daily lactic acid
intake of a breast-fed infant.
Mutsuga and others (2008) determined the PLA migration
products for 4 different PLA sheets, which are used in lunch
boxes in Japan. They applied 3 food simulants such as water,
4% acetic acid, and 20% ethanol at temperatures of 40, 60, and
95 ◦C for different periods of time. They concluded that the rate
of migration is augmented by high temperatures. The total mi-
grated levels, including lactic acid, lactide, and oligomers, at 40 ◦C
after 180 d were 0.28 to 15 μg.cm−2and 0.73 to 2840 μg.cm−2
for 60 ◦C after 10 d. The migration test at 95 ◦C for 30, 60, and
120 min mimicked the use of lunch boxes in a microwave oven at
100 ◦C or above, and the total migrated levels for 120 min were
2.04 to 49.63 μg.cm−2.
So, for a PLA much of the concerns about migrations of po-
tential dangerous materials, which exist for petrochemical-based
polymers are resolved. These results are only for pure PLA poly-
mer and more studies are needed for its blends and copolymers,
also for all the compounds that are applied or added for improving
physical, mechanical, and barrier properties of PLA.
PLA Applications
PLA has potential for use in a wide range of applications;
Table6showsanoverviewofNatureWorks
TM PLA and IngeoTM
fibers, PLA opportunities, and examples of commercially available
products. As be seen, PLA food packaging applications are ideal
for fresh products and those whose quality is not damaged by PLA
oxygen permeability.
PLA is a growing alternative as a “green” food packaging poly-
mer. New applications have been claimed in the field of fresh
products, where thermoformed PLA containers are used in retail
markets for fruits, vegetables, and salads. The market capacity of
these products packaged in PLA is unlimited.
The major PLA application today is in packaging (nearly 70%);
the estimation for 2020 shows the increase of other applications
especially in fibers and fabrics (Table 7).
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2010 Institute of Food Technologists®Vol. 9, 2010 rComprehensive Reviews in Food Science and Food Safety 561

Poly-lactic acid, nanocomposites, and release studies . . .
Table 6–Business segments for products based on IngeoTM plastic and
IngeoTM fibers PLA (NatureWorks®) adapted from Vink and others (2004).
Business segment Commercially available applications
1- Ingeo plastic applications
Rigid thermoforms Clear fresh fruit and vegetable clamshells
Deli meat trays
Opaque dairy (yogurt) containers
Bakery, fresh herb, and candy containers
Consumer displays and electronics packaging
Disposable articles and cold drink cups
Biaxially oriented
films
Candy twist and flow wrap
Envelope and display carton windows
Lamination film
Product (gift basket) overwrap
Lidding stock
Die cut labels
Floral wrap
Tapes
Shrink sleeves
Stand-up pouches
Cake mix, cereal, and bread bags
Bottles Short shelf-life milk
Edible oils
Bottled water
2- Ingeo fiber applications
Apparel Casual (sports-), active, and underwear fashion
item
Nonwovens Wipes, hygiene products, diapers, shoe liners,
automotive head and door liners, and paper
reinforcement
Furnishings Blankets and panel, upholstery, and decorative
fabrics
Industrial carpets Agricultural and geotextilesa
Residential/institutional broadloom and carpet
tiles
Fiberfill Pillows, comforters, mattresses, Duvets, and
furniture
aGeotextiles are permeable fabrics which, when used in association with soil, have the ability to
separate, filter, reinforce, protect, or drain. Usually geotextiles are placed at the tension surface to
strengthen the soil.
Table 7–Main applications of PLA in 2003 and the estimation for 2020
(Wolf 2005).
Percent of total
production
(2003)
Estimated
percent of total
production
(2020)
Cargill Cargill
Sector Dow Hycail Dow Hycail
Packaging 70 70 20 55
Building
Agriculture 1 12 6
Transportation 20 2
Furniture
Electric appliance and electronics 1 1 10 10
Houseware 12 6
Other (fibers and fabrics) 28 3 to 5 50 21
Other (analytics)
Total 100 100 100 100
In the field of packaging, 2 specific areas have received close
attention, namely high-value films and rigid-thermoformed con-
tainers. PLA brings a new combination of attributes to pack-
aging, including stiffness, clarity, deadfold and twist retention,
low-temperature heat sealability, as well as an interesting combi-
nation of barrier properties including flavor, and aroma barrier
characteristics. The functional properties and benefits of PLA in
these areas are presented in Table 8.
Commercialized PLA products demonstrate this fact that PLA
is not being used solely because of its degradability, nor be-
cause it is made from renewable resources; it is being used be-
cause it functions very well and provides excellent properties
Table 8–PLA functional properties for packaging (Kawashima and others
2002).
Functional property
Packaging
improvement Comment
Dead fold, twist, and
crimpaImproved folding and
sealing
OPLA has excellent
dead fold and twist
retention
High gloss, and clarity Package aesthetics Comparable with PET
and cellophane, 3
times more than
nylon and PP, 10
times more than
LDPE
Barrier properties Grease and oil resistance Good resistant to oils
and terpens
Renewable resource Made from CO2and H2O
Flavor and aroma
properties
Reduced taste/odor
issues
Low temperature
heat seal
Stronger seals at lower
temperatures
PLA can provide an
“easy-open”
package
High tensile and
modulus
Wet paper strength,
ability to down guage
coating
Low coefficient of
friction, polarity
Printability Excellent printability,
metallizable,
antifogging ability
GRAS status Food contact approved
aThe ability to hold a crease or fold, or the ability to retain a twist that is imparted in order to close the
edges of the film around a small object.
Table 9– Some commercialized PLA products (Platt 2006; www.nature
worksllc.com).
Product Company namea
Packaging
Films and trays for biscuits, fruit, vegetables,
and meat
Treophan, Natura, IPER,
Sainsburys, Sulzer,
Ecoproducts, RPC
Yogurt cup Cristallina/Cargill Dow
Rigid transparent packaging of batteries
with removable printed film on back side
Panasonic
Trays and bowls for fast food McDonalds
Envelope with transparent window, paper
bag for bread with transparent window
Mitsui, Ecocard
Agriculture and horticulture
Mulching films Novamont, Cargill Dow
Long life consumer good
Apparel (T-shirt, socks) FILA/Cargill Dow, Kanebo
Gosen
Blanket Ingeo
Casing of walkman Sony
CD (compact disk) Sanyo Marvic Media/Lacea
Computer keys Fujitsu
Small component of laptop housing Fujitsu/Lacea
Sapre wheel cover Toyota
aList is not exhaustive.
at a competitive price. There are many commercialized PLA
products in today’s market and their variety and consumption
are increasing rapidly (Table 9). The reader can find the part-
ners and consumers of PLA from the NatureWorks®Co. website
(www.natureworksllc.com).
PLA is also used in biomedical applications, with various uses
as internal body components mainly in the of restricted load for
example, interference screws in ankle, knee, and hand; tacks and
pins for ligament attachment; rods and pins in bone, plates and
screws for craniomaxillofacial bone fixation (Lim and others 2003);
and also for surgical sutures, implants, and drug delivery systems
(Furukawa and others 2005; Mills and others 2006).
562 Comprehensive Reviews in Food Science and Food Safety rVol. 9, 2010 c
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Poly-lactic acid, nanocomposites, and release studies . . .
PLA as an Active Packaging Material
Release studies from PLA
Active packaging is defined as an intelligent or smart system
that involves interactions between package or package components
and food or internal gas atmosphere and complies with consumer
demands for high quality, fresh-like, and safe products (Labuza and
Breene 1989).
Active packaging is an innovative approach to change the con-
dition of the packaging to extend shelf-life or improve safety or
sensory properties while maintaining the quality of the food. Tra-
ditional packaging concepts are limited in their ability to prolong
shelf-life of food products. The most important active packag-
ing concepts are O2and ethylene scavenging, CO2scavengers
and emitters, moisture regulators, antimicrobial packaging con-
cepts, antioxidant release, release or adsorption of taste, and aroma
molecules (Ver meiren and others 1999; Lopez-Rubio and others
2004; Kerry and others 2006).
As a GRAS and biodegradable material, and also because of its
biosorbability and biocompatible properties in the human body,
PLA and its copolymers (especially poly-glycolic acid) is attractive
to pharmaceutical and medical scientists as a carrier for releasing
various drugs and agents like bupivacaine (Sokolsky-Papkov and
others 2009), rapamycin (Miao and others 2008), melittin (Cun
and others 2008), 5-fluorouracil (Liu and others 2008), amoxicillin
(Xu and Czernuszka 2008), human nerve growth factor (rhNGF)
(Gu and others 2007), and gentamicin (Schnieders and others
2006) and many others.
In food domains, little research has been done studying the
ability of PLA as an active packaging material. PLA is a relatively
new polymer and needs time to become an acceptable and an
effective active packaging in the market.
Antioxidants have been added to food packaging material for
the intentional purpose of migration into food, because proox-
idant effects are often seen to a high extent and could be re-
duced by antioxidants. Van Aardt and others (2007) studied the
release of antioxidants from loaded poly (lactide-co-glycolide)
(PLGA) (50:50) films, with 2% α-tocopherol, and a combina-
tion of 1% butylated hydroxytoluene (BHT) and 1% butylated
hydroxyanisole (BHA), into water, oil (food simulant: Miglyol
812), and milk products at 4 and 25 ◦C in the presence and
absence of light. They concluded that in water medium PLGA
(50:50) showed hydrolytic degradation of the polymer and release
of BHT into water. In Miglyol 812, no degradation or antioxidant
release took place, even after 8 wk at 25 ◦C. Milk fat was stabilized
to some extent when light-exposed dry whole milk and dry but-
termilk were exposed to antioxidant-loaded PLGA (50:50). The
authors also suggested potential use of degradable polymers as a
unique active packaging option for sustained delivery of antiox-
idants, which could be a benefit to the dairy industry by limit-
ing the oxidation of high-fat dairy products, such as ice cream
mixes.
PLA and antimicrobial packaging trends
The innovative strength of PLA antimicrobial packaging has
a direct impact on consumer health by creating safer and more
wholesome packaged foods. Active packaging realizes certain ex-
traordinary and vital functions other than providing an inert barrier
between product and external conditions.
Active substances that are important and considered for novel
bioactive packaging include antimicrobials, vitamins, phytochem-
icals, prebiotics, marine oils, and immobilized enzymes (Lopez-
Rubio and others 2006).
Figure 3–Schematic representation of PLA film with nisin as an active
agent incorporated and release thereof.
A whole range of active additives, including silver-substituted
zeolite, organic acids and their salts, bacteriocins such as nisin
and pediocin, enzymes such as lysozyme, a chelator like ethylene-
diaminetetraacetic acid (EDTA), lactoferrin, and plant extracts
have already been successfully incorporated in antimicrobial active
packaging (Joerger 2007).
The most widely used bacteriocin in active food packaging is
nisin due to its GRAS status (FDA 2001). Successful introduc-
tion of a new active packaging requires careful attention to the
interactions in the active agent, packaging, and food triangle.
Notion of controlled release. In particular for active packaging,
the major complexity emerges for migration/diffusion as either
slow release of package component itself or as an active agent
being incorporated. In both contexts, the evaluation of materials
compliance with regulations includes migration monitoring for
package component (monomer) and additives (active agent). A
schematic representation is showed in Figure 3 for release of an
active agent (nisin) alone and in conjunction with packaging ma-
terial. Recently, the predictive mathematical modeling for active
agent-controlled release and its various approaches were excel-
lently reviewed by Poc¸as and others (2008).
On the contrary, to study an additive’s release from a package,
active agent desorption from the multilayer biodegradable film
and diffusion in agarose gels were monitored. The data attained
after 2 or 6 d of contact between antimicrobial films and agarose
gels were employed to find out nisin mass transfer by numerical
modeling following Fick’s 2nd law. The values were in the range
from 0.87 ×10−3m/s to 4.30 ×10−3m/s and 6.5 ×10−11 m2/s
to 3.3 ×10−10 m2/s, for nisin apparent desorption and diffusion
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Poly-lactic acid, nanocomposites, and release studies . . .
coefficients, respectively. The diffusion process was governed by
interactions between nisin, package, and food matrix simulant
(Chollet and others 2009).
Mode of incorporation. The customized direct incorporation
of active agents may result in a loss of activity due to interactions
with food components, thus showing from a diminution of active
concentration and dilution into bulk foods (Kim and others 2002;
Coma 2008). The incorporation of antimicrobial agents into PLA
packaging material slows down their release and helps to maintain
high concentrations of the active compounds against pathogenic
bacteria like Listeria monocytogenes (Jin and others 2009).
In the last decade, the above-mentioned slow release approach
has been used for PLA. In this regard, major antimicrobial agents
include bacteriocins, predominantly nisin (Ariyapitipun and oth-
ers 1999; Jin and others 2009), lactic acid (Ariyapitipun and oth-
ers 1999), lysozyme (Del Nobile and others 2009), and chitosan
(Torres-Giner and others 2008).
Novel PLA active packaging potential approaches
Although the above-mentioned PLA systems reduced resistant
bacterial strain development and guaranteed a higher level of mi-
crobial protection for certain food products, their casting and
preparation was complicated and inactivation of the active pro-
teins was observed. Active agent modification by attachment to
a polymer did not yield biologically active derivatives. Up till
now, a literature study reveals that relatively low attention has
been given to micro-encapsulated active agents in foods. Active
agent-loaded polymeric micro-/nanoparticles give the impression
of being promising formulations to achieve long-lasting antimicro-
bial activity (Salmaso and others 2004; Sanchez-Garcia and others
2007).
Thus, this particular controlled release concept can be enlarged
to the applications of other active agents like antioxidants for oil-
rich foods and antisticking/antifogging agents for cheese slices and
fresh fruits, respectively.
PLA Modifications
The special characteristics of PLA can make it a good fit for
some applications but may also require modifications for some
others. For example, the oxygen and moisture permeability of
PLA is much higher than for most other plastics, such as PE,
PP, and even PET. However, the applications of PLA are limited
by several factors such as low glass transition temperature, weak
thermal stability, and low toughness and ductility (Harada and
others 2007).
For extending PLA applications, the properties like impact
strength or flexibility, stiffness, barrier properties, thermal stability,
and production costs must be improved. Generally, modifiers have
been studied to improve stiffness at elevated temperatures, reduce
cost, or increase the degradation rate of PLA.
Some efforts of PLA modifications in the field of packaging are
presented in Table 10.
A large number of investigations have been performed on the
blending of PLA with various polymers, for example, thermo-
plastic starch, poly (ethylene oxide), poly (ethylene glycol), poly
(ε-caprolactone), poly (vinyl acetate), poly (hydroxy butyrate),
cellulose acetate, poly (butylene succinate), and poly (hexamethy-
lene succinate). Low molecular weight compounds have also been
used as plasticizers for PLA, for example, oligomeric lactic acid,
glycerol, triacetine, and low molecular weight citrates (Ljungberg
and others 2005).
The choice of polymers or plasticizers to be used as modifiers
for PLA is limited by the requirements of the application. For
packaging and hygiene applications, only nontoxic substances ap-
proved for food contact and personal care can be considered as
plasticizing agents. The plasticizer should be miscible with PLA,
thus creating a homogeneous blend. The plasticizer should not
be too volatile, because this would cause evaporation to occur at
the high temperature used during processing. Furthermore, the
plasticizer should not be prone to migration into the materials in
contact with the plasticized PLA. It would also cause the blended
materials to regain the brittleness of pure PLA (Ren and others
2006).
There is a tendency for plasticizers to migrate to the surface of
a polymer. A possible way to prevent this migration would be to
increase the molecular weight of the plasticizers.
However, increasing the molecular weight too much would
eventually decrease the solubility causing phase separation and
formation of a 2-phase system.
The final properties of these blends depend on the chemical
structure of the original components, the mixing ratio of the
constituent polymers, the interaction between the components,
and the processing steps to which they are then subjected.
Amorphous PLA exhibits lower modulus above the glass tran-
sition temperature and poor heat resistance, which limits the wide
application of PLA in the general plastic use. Thus, how to im-
prove the crystallization behavior or enhance the degree of crys-
tallinity (% Xc) of PLA becomes the main problem that must be
solved. Decreasing the cooling rate of PLA from melt and pro-
viding an annealing process for PLA articles is believed to be the
most efficient way to enhance the (% Xc) of PLA. It has been
reported that the smaller the cooling rate, the higher the (% Xc).
Annealing endows PLA chain segments enough activation energy
and promotes the crystallization through the reorganization pro-
cess. Especially, in a certain condition, the annealing process also
induces the polymorphic transition in PLA (Li and others 2009).
Other kinds of modifications, such as surface modifications, are
being applied in biomedical uses for improving polymer release
properties (Janorkar and Hirt 2004; Koo and Jang 2008).
Nanotechnology and PLA Food Packaging
Nanotechnology and its applications in food science have re-
cently been studied by several researchers. The use of nanoparti-
cles, such as micelles, liposomes, nanoemulsions, biopolymeric
nanoparticles, and cubosomes, as well as the development of
nanosensors aimed at ensuring food safety, are some novel nano-
food applications.
Nanoparticles can be used as bioactive compounds in functional
foods. Bioactive compounds that can be found naturally in certain
foods have physiological benefits and might help to reduce the risk
of certain diseases, including cancer. Omega-3 and omega-6 fatty
acids, probiotics, prebiotics, vitamins, and minerals have found
their applications in food nanotechnology as bioactive compounds
(Sozer and Kokini 2009).
Nanotechnology is also applicable in food packaging in the form
of elementary components of food packaging. This approach in-
cludes improving packaging performances like its gas, moisture,
ultraviolet, and volatile barriers, increasing mechanical strength,
decreasing weight, and increasing the heat resistance and flame
retardancy of the packaging material. Nanoadditives, intelligent
packaging (using nanosensors), delivery and controlled release of
neutraceuticals, antibacterial agents, self-cleaning packaging, and
systems to monitor product conditions during transportation are
other novel nano-approaches in food packaging (Ray and Bous-
mina 2005; Sozer and Kokini 2009).
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Poly-lactic acid, nanocomposites, and release studies . . .
Table 10–Summary of PLA modifications for packaging applications.
Type of
modification Treatment or added material Effect Reference
Modifier Citrate esters Lowering the Tg and improving the
elongation at break
Labrecque and others (1997)
Triacetine or tributyl citrate Decrease in Tg and increase in crystallinity Ljungberg and Wessl´
en (2002)
Oligomeric malonate esteramides Decrease in Tg and improvement of the
strain at break
Ljungberg and others (2005)
4,4-Methylene diphenyl diisocyanate Tg value increased to 64 ◦C, tensile strength
increased from 4.9 to 5.8 MPa good
nucleating agent for PLA crystallization
Li and Yang (2006)
Polyglycerol esters Improving the elongation at break Uyama and others (2006)
Polyethylene glycol and acetyl triethyl
citrate
Decrease in Tg and increase in
crystallization rate
Li and Huneault (2007)
Talc Increase the ductility at more than 10% Li and Huneault (2007)
Bifunctional cyclic ester Enhance PLA toughness Jing and Hillmyer (2008)
Poly(1,3-butylene adipate) Decrease in storage modulus and glass
transition temperature but increase in
elongation at break
Wang and others (2008)
Polycarbodiimide Improve the thermal stability at 210 ◦Cfor
up to 30 min
Yang and others (2008)
Blending with: Polyvinyl acetate Increase in tensile strength and percent
elongation
Gajria and others (1996)
Poly ethylene oxide (PEO) Elongation at break of more than 500% Nijenhuis and others (1996)
Poly ε-caprolactone (PCL) High improvement in mechanical properties Tsuji and Ikada (1996)
Poly ethylene glycol (PEG) Enhance the crystallinity of PLA and
biodegradability
Sheth and others (1997)
Starch with different plasticizers Lowering the price, decreasing Tg, and
increasing crystallinity and
biodegradability
Ke and Sun (2001); Jacobsen and Fritz
(1996); Ke and others (2003)
Polyvinyl alcohol and starch Increase in tensile strength Ke and Sun (2003a)
Ethylene vinyl alcohol (EVOH) Improvement of mechanical, thermal, and
biodegradability properties
Lee and others (2005)
Polycarbonate Improvement of mechanical properties and
biodegradation rate
Wang and others (2007)
Poly ethylene glycidyl methacrylate
(PEGMA)
Production of super-tough PLA materials Oyama (2009)
Copolymerization
of PLA and:
DL-mandelic acid Increasing Tg and improving mechanical
properties
Kylm¨
a and others (1997)
ε-Caprolactone Improving the decomposition temperatures
and crystallinity
Park and others (1998)
Polyvinyl chloride Improving strength and toughness Lu and others (2008)
Acrylonitrile–butadiene–styrene Improved impact strength and elongation
at break with a slight loss in modulus and
tensile strength
Li and Shimizu (2009)
Physical treatment Vacuum compression-molding and
solid-state extrusion techniques
Flexural strength and flexural modulus were
improved up to 221 MPa and 8.4 GPa,
respectively
Lim and others (2001)
Orientation Significant improvement in tensile and
impact properties
Grijpma and others (2002)
Annealing Increasing the toughness Park and others (2004)
Aging Increasing the Tg Quan and others (2004)
Drawing Improvement in tensile and fracture
properties
Todo (2007)
Addition of different fillers to polymers for improving their per-
formances like their strength and stiffness, barrier properties, resis-
tance to fire and ignition, and also decreasing their price has always
been a common objective in packaging technology. Traditionally,
mineral fillers such as clay, silica, and talc are incorporated in film
preparations in the range of 10% to 50% by weight to reduce film
cost or to improve its performance in some way. However, me-
chanical strength of such films, in general, decreases when fillers
are present. Recently, nanocomposites have received significant
attention as an alternative to conventional filled polymers (Rhim
2007).
Nanocomposites
Nanocomposites are a new class of composites that are particle-
filled polymers for which at least 1 dimension of the dispersed par-
ticles is in the nanometer range. Three types of nanocomposites
include isodimensional nanoparticles (with 3 nano dimensions),
nanotubes or whiskers (with 2 nano dimensions), and polymer-
layered crystal nanocomposites (with 1 nano dimension) (Alexan-
dre and Dubois 2000).
Although several nanoparticles have been recognized as possible
additives to enhance polymer performance, the packaging industry
has focused its attention mainly on layered inorganic solids like
clays and silicates, due to their availability, low cost, significant
enhancements, and relative simple processability (Azeredo 2009).
These nanocomposites exhibit markedly improved mechanical,
thermal, optical, and physicochemical properties when compared
with the pure polymer or conventional (microscale) composites.
The layered silicates commonly used in nanocomposites consist of
2-dimensional layers, which are 1-nm thick and several microns
long depending on the particular silicate (Alexandre and Dubois
2000).
The commonly used layered silicates for the preparation of
polymer-layered silicate (PLS) nanocomposites are montmoril-
lonite (MMT), hectorite, and saponite (Sinha Ray and Okamoto
2003).
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Poly-lactic acid, nanocomposites, and release studies . . .
The matrix of polymer/clay nanocomposites consists mainly of
synthetic polymers including thermosets such as epoxy, thermo-
plastics like poly (methyl methacrylate), nonpolar polymers like
polyethylene and polypropylene, polar polymers like nylon, and
conductive polymers like polyaniline. In addition, biodegradable
polymers such as PLA and polycaprolactone (PCL) have also been
tested for the manufacture of nanocomposites with layered silicate
(Rhim 2007).
PLA nanocomposites
The combination of PLA and montmorillonite-layered silicate
may result in a nanocomposite with good barrier properties that is
suitable for film packaging material. The modulus of PLA would
be increased by the addition of montmorillonite. However, the in-
corporation of the montmorillonite clay into PLA could decrease
the toughness of the PLA composites. There are various technical
approaches to achieve a balance of good strength and toughness
for PLA nanocomposites. The addition of poly ethylene glycol
could act as a good plasticizer in a PLA/clay systems (Shibata and
others 2006).
A comprehensive review is provided by Sinha Ray and
Okamoto (2003) for the preparation, characterization, materi-
als properties, crystallization behavior, melt rheology, and foam
processing of pure polylactide (PLA) and PLA/layered silicate
nanocomposites. They concluded this new family of compos-
ite materials frequently exhibits remarkable improvements in its
material properties when compared with those of virgin PLA.
Improved properties can include a high storage modulus both in
the solid and melt states, increased tensile and flexural properties,
decreased gas permeability, increased heat distortion temperature,
and increased rate of biodegradability of pure PLA.
In a complementary review, Sinha Ray and Bousmina (2005)
presented recent developments on the above-mentioned prop-
erties for many biodegradable polymers’ nanocomposites. They
described 2 types of biodegradable polymers: (a) originating from
renewable sources like PLA, poly (3-hydroxybutyrate), thermo-
plastic starch (TPS), plant-based polymers, cellulose, gelatin, or
chitosan; and (b) originating from petroleum sources like poly
(butylene succinate), aliphatic polyesters, poly(ε-caprolactone), or
poly (vinyl alcohol).
Recent research on PLA nanocomposites
The potential applications of PLA-based nanocomposites are in
food packaging, medical applications, and tissue cultures. Some
research conducted on PLA nanocomposites in the field of food
packaging after the year 2005 is presented here.
Biodegradability of polymers through photodegradation has
been studied by using TiO2nanoparticles as photocatalysts that
decompose various organic chemicals like aldehyde, toluene, and
polymers such as PE, PP, PVC, and PS.
In a study done by Nakayama and Hayashi (2007), TiO2
nanoparticles were prepared and the surface of TiO2was modified
using propionic acid and n-hexylamine, with the modified TiO2
uniformly dispersed into PLA matrixes without aggregation. They
studied the PLA-TiO2nanocomposite’s photodegradation under
UV light and concluded photodegradability of nanocomposites
can be efficiently promoted.
Melt intercalation is a method where the blending of polymer
and silicate layers is followed by molding to form a polymer-
layered silicate nanocomposite. In general, for intercalation, poly-
mers and layered hosts are annealed above the softening point of
the polymer. Chow and Lok (2009) used this method for study-
ing the effect of maleic anhydride-grafted ethylene propylene
rubber (EPMgMA) on the thermal properties of PLA/organo-
montmorillonite nanocomposites. They concluded that the ad-
dition of OMMT (Organo-montmorillonite) and EPMgMA did
not influence much the Tgand Tm(melting temperature) of PLA
nanocomposites. The degree of crystallinity of PLA increased
slightly in the presence of OMMT; it had been supposed that
OMMT could act as a nucleating agent to increase the crys-
tallinity of PLA. In contrast, the addition of EPMgMA may restrict
the crystallization process and crystal formation of PLA, which
subsequently reduces the degree of crystallinity of PLA/OMMT
nanocomposites. Finally, they claimed that the thermal stability of
PLA/OMMT was greatly enhanced by the addition of EPMgMA.
Kim and others (2009) studied the effect of bacterial cellulose on
the transparency of PLA/bacterial nanocomposites, since bacterial
cellulose had shown good potential as reinforcement or preparing
optically transparent materials due to its structure, which consists
of ribbon-shaped fibrils with diameters in the range from 10 to 50
nm. They found that light transmission of the PLA/bacterial cel-
lulose nanocomposite was quite high due to the size effect of the
nanofibrillar bacterial cellulose. Additionally, the tensile strength
and Young’s modulus of the PLA/bacterial cellulose nanocom-
posite were increased by 203% and 146%, respectively, compared
with those of the PLA.
Carbon nanotubes (CNTs) have been the subject of much atten-
tion because of their outstanding performance including excellent
mechanical, electrical, and thermal properties. The most promis-
ing area of nanocomposite research involves the reinforcement of
polymers using CNTs as reinforcing filler (Kim and others 2007).
Li and others (2009) introduced functionalized multiwalled car-
bon nanotubes (f-MWCNTs) into PLA to investigate the effect of
such filler on the crystallization behavior of PLA. They concluded
that the addition of f-MWCNTs accelerates the crystallization
of PLA dramatically and induces formation of homogeneous and
very small spherulites. The results of polarized optical microscopy
showed that the average spherulite diameter is about 200 μm,
but for nanocomposites it was very difficult to differentiate the
spherulites one by one.
Numerous studies have also been done on PLA nanocomposites
in medical science regarding drug delivery systems, tissue engi-
neering, and bone fixation (Jo and others 2004; Sakata and others
2006; Chen and others 2007).
PLA Degradability, Biodegradability, and Recyclability
Almost all the conventional plastics such as PE, PP, PS, and PVC
are resistant to microbial attack; on the contrary aliphatic polyesters
like PLA are readily degraded by microorganisms present in the
environment. According to ASTM D6400–04, a biodegradable
plastic is ‘‘a plastic that degrades because of the action of naturally
occurring microorganisms such as bacteria, fungi, and algae,’’ and
a compostable plastic is ‘‘a plastic that undergoes degradation by
biological processes during composting to yield carbon dioxide,
water, inorganic compounds, and biomass at a rate consistent with
other known compostable materials and leaves no visually distin-
guishable or toxic residues.
PLA degradation was studied in animal and human bodies for
medical applications like implants, surgical sutures, and drug deliv-
ery materials (Vainionpaa and others 1989). In these environments,
PLA is initially degraded by hydrolysis and the soluble oligomers
formed are metabolized by cells. PLA degradation upon disposal
in the environment is more challenging because PLA is largely
resistant to attack by microorganisms in soil or sewage under
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Poly-lactic acid, nanocomposites, and release studies . . .
ambient conditions. The polymer must 1st be hydrolyzed at ele-
vated temperatures (about 58 ◦C) to reduce the molecular weight
before biodegradation can commence. No degradation was ob-
served on PLA sheets after 6 wk in soil, thus PLA will not degrade
in typical garden compost (Brandrup and others 1999; Ohkita and
Lee 2006). Urayama and others (2002) reported that the molecu-
lar weight of PLA films with different optical purity of the lactate
units (100% L and 70% L) decreased by 20% and 75%, respectively,
after 20 mo in soil.
Kale and others (2007) studied the degradation of PLA bottles
in a real composting condition (compost containing cow manure,
wood shavings, and waste feed) at 65 ◦C for 30 d. They observed
major fragmentation, which produces decomposition of the poly-
mer chain into shorter oligomer chains and monomers since the
4th day, and on the15th day, the bottles were already in pieces and
mostly consisted of parts from cap threads, and neck (bottle parts
having higher thickness) and finally on the 30th day the bottles
were completely degraded.
Microbial and enzymatic degradation of PLA have recently been
studied by many researchers because these types of degradations
usually do not need the high temperatures to be accomplished.
Williams (1981) 1st reported the degradation for PLLA by pro-
teinase K from Tritirachium.album., afterward many studies were
done for finding different enzymes corresponding PLA degrada-
tion. Reported enzymes that enable to degrade PLA in different
scale include, alkaline protease (Oda and others 2000), serine pro-
teases such as subtilisin, trypsin, elastase, and α-chymotrypsin (Lim
and others 2005), Cutinase-like enzyme (Masaki and others 2005).
Lipase could hydrolyze low molecular weight PLLA and some
copolymers such as PDLLA (poly D,L-lactic acid) and, poly(D-
lactid-co-glycolide) but not PDLA (poly D-lactic acid) and high
molecular weight PLLA (Fukuzaki and others 1989). Pranamuda
and others (2001) found an enzyme from Amycolatopsis sp. cultures
and named it PLLA depolymerase. The optimum pH and temper-
ature for this enzyme were 6.0 and 37 to 45 ◦C, respectively. PLLA
depolymerase can also hydrolyze casein, silk fibroin, succinyl-p-
nitroanilide, but not PHB and PCL. The enzymatic degradation
of aliphatic polyesters by hydrolysis is a 2-step process. The 1st
step is adsorption of the enzyme on the surface of the substrate
through surface-binding and the 2nd step is hydrolysis of the ester
bond (Tokiwa and Calabia 2006).
Pranamuda and others (2001) 1st isolated a PLA-degrading mi-
croorganism of Amycolatopsis strain from soil environment, which
was capable of degrading 60% of the PLA film after 14 d. Suyama
and others (1998) reported that PLA-degrading microorganisms
are not widely distributed in the natural environment and, thus,
PLA is less susceptible to microbial attack in the natural envi-
ronment than other synthetic aliphatic polyesters like PHB, PCL,
and Poly(butylenes succinate) (PBS). Several PLA-degrading mi-
croorganisms, their enzymes, and substrate specificities are re-
ported in Table 11. Upon disposal in the environment, PLA is
hydrolyzed into low molecular weight oligomers and then miner-
alized into CO2and H2O by the microorganisms present in the
environment.
Microbial degradation of PLA should be studied for packaging
of foods containing microorganisms including lactic acid bacteria,
and fungi for their probable abilities of PLA degradation. Torres
and others (1996) reported the ability of assimilation of lactic acid
and racemic oligomer products of PLA for 2 strains of Fusarium
moniliforme (widely distributed in soil) and on strain of Penicillium
roqueforti (the main fungus in blue cheese, and can be isolated from
soil).
Recycling diverts material from alternative waste streams such
as land filling or incineration, as well as conserves natural resources
and energy. PET and HDPE make up a large percentage of the
plastic bottles that get recycled. Sorting PLA in recycling facilities
is difficult due to low volumes and in many cases, the PLA con-
tainer looks like PET. Because of this, the possibility of mixing the
different materials together exists. As a result, there is concern in
the recycling community that PLA bottles, at high enough levels,
would contaminate the PET recycle stream due to chemical and
thermal property differences. The National Association for PET
Container Resources (NAPCOR) recently announced its concern
for potential contamination of the PET recycling stream associ-
ated with PLA bottles. This trade association for the PET plastic
industry in the U.S. and Canada cited its concerns involving cost
of separation, increased contamination, yield loss, and impact on
recycled PET (RPET) quality and processing (www.napcor.com).
Consequently, NatureWorks®and Primo Water Corp. con-
ducted a commercial scale bottle recycling evaluation to demon-
strate that automated systems being used today in the recycling
industry are capable of separating PLA bottles from PET bot-
tles with good accuracy and efficiency (93%). In this evaluation,
near-infrared equipment was used since it is a common sorting
technology in large recycling operations and can accurately iden-
tify many different types of polymers (NatureWorks®2009).
Recycled bottles crushed, chopped into flakes, and pressed into
bales. They enter to final recycling step and are changed to PLA
monomers; L-lactic acid or L-lactide. There are 2 methods for
PLA recycling, primarily hydrolysis or solvolysis to L-lactic acid
or L-lactic acid-based compounds and, 2nd, depolymerization to
the cyclic dimer, L-lactide. Both methods have problems with low
yield of monomers in a short period and require the removal of
catalysts and additives used for hydrolysis, solvolysis, or depoly-
merization (Tsuji and others 2003).
High-temperature hydrolysis, normally above the melting point,
is an effective way to hydrolyze PLA rapidly to L-lactic acid with-
out the aid of catalysts. The highest maximum yield of L-lactic
acid (about 90%) in a high temperature and high pressure wa-
ter was attained at 250 ◦C for 10 to 20 min (Tsuji and others
2001).
Conclusion
In previous years, the most negative point of PLA was its price
in comparison with petrochemical-based polymers. Today, by us-
ing other sources of dextrose, optimizing lactic acid production
processes and its costs, substituting electricity energy by wind and
solar energy for PLA production, optimizing PLA production pro-
cesses, and increasing PLA demands, reduction of its price can be
attained. The present PLA price is much lower than in previous
years, but it is not fixed and it even will be considerably lower in
the future because, according to expert forecasts, beyond 2010 the
global demand for biodegradable plastics will continue to increase
by 30% each year and PLA will take a large part of this market
because of its valuable properties (Bastioli 2005).
The linkage of a 100% bio-originated mater ial and nano-
materials opens new windows for becoming independent from
petrochemical-based polymers and also free of environmental and
health concerns.
Substituting PET with PLA in food packages, which require
high-barrier properties, is not feasible unless some modifications
are applied to develop its permeability. Also, the brittleness of
PLA may also limit its applications where toughness and impact
resistance are critical. However, with the help of nanotechnology
c
2010 Institute of Food Technologists®Vol. 9, 2010 rComprehensive Reviews in Food Science and Food Safety 567

Poly-lactic acid, nanocomposites, and release studies . . .
Table 11–PLA-degrading microorganism, their enzymes substrate specificities, and detection methods used in degradation tests.
Microorganism Enzyme Substrate specificity Detection method for PLA degradation
Amycolatopsis sp. strain HT 32 Protease L-PLA Film-weight loss; monomer production (lactic acid)
Amycolatopsis sp. strain 3118 Protease L-PLA Film-weight loss; monomer production
Amycolatopsis sp. strain KT-s-9 Protease Silk fibroin, L-PLA Clear-zone method
Amycolatopsis sp. strain 41 Protease L-PLA, silk powder, casein,
Suc-(Ala)3-pNA
Film-weight loss; monomer production
Amycolatopsis sp. strain K104–1 Protease L-PLA, casein, fibrin Turbidity method
Lentzea waywayandensis (formerly
Saccharothrix waywayandensis)
Protease L-PLA Film-weight loss; monomer production
Kibdelosporangium aridum Protease L-PLA Film-weight loss; monomer production
Tritirachium album ATCC 22563 Protease L-PLA, silk fibroin, elastin Film-weight loss; monomer production
Brevibacillus (formerly Bacillus brevis)∗Protease L-PLA Change in molecular weight and viscosity
Bacillus stearothermophilus∗Protease D-PLA Change in molecular weight and viscosity
Geobacillus thermocatenulatus∗Protease L-PLA Change in molecular weight and viscosity
Bacillus sinithii strain PL 21∗Lipase
(Esterase)
L-PLA, pNP-fatty acid esters Change in molecular weight
Paenibacillus amylolyticus strain TB-13 Lipase DL-PLA, PBS, PBSA, PES,
PCL, triolein, tributyrin
Turbidity method
Cryptococcus sp. strain S-2 Lipase
(Curtinase)
L-PLA, PBS, PCL, PHB Turbidity method
Adapted from Tokiwa and Calabia (2006).
and providing safe PLA nanocomposites, many of its weakness
compared to petrochemical-based polymer will be resolved.
According to its safety, biodegradability, and ability for being
improved in a tailor-made fashion, the authors predict the substi-
tuting of many petrochemical-based polymers by PLA for almost
all pharmaceutical and direct food contact packaging materials in
the near future.
Nomenclature
ASTM = American society for testing and materials;
EVOH = Ethylene vinyl alcohol;
GPPS = General purpose poly(styrene);
HDPE = High-density poly(ethylene);
HIPS = High-impact poly(styrene);
LDPE = Low-density poly(ethylene);
LLDPE = Linear low-density poly(ethylene);
MMT = Montmorillonite;
MWCNT = Multiwalled-carbon nanotube;
OMMT = Organo-montmorillonite;
OPLA = Oriented poly(lactic acid);
OPP = Oriented poly(propylene);
OPS = Oriented poly(Styrene);
PBAT = Poly(butylene adipate terephthalate);
PBS = Poly(butylenes succinate);
PBST = Poly(butylene succinate terephthalate);
PC = Poly(carbonate);
PCL = Poly(ε-caprolactone);
PEA = Poly(ester amide);
PEG = Poly(ethylene glycol);
PEGMA = Poly(ethylene-glycidyl methacrylate);
PEO = Poly(ethylene oxide);
PET = Poly(ethylene terephthalate);
PGA = Poly(glutamic acid);
PHB = Poly(3-hydroxybutyrate);
PHV = Poly(hydroxyl valerate);
PLLA = Poly(L-lactic acid);
PP = Poly(propylene);
PS = Poly(styrene);
PTMAT = Poly(tetramethylene adipate terephthalate);
PVA = Poly(vinyl alcohol);
PVC = Poly(vinyl chloride);
TPS = Thermoplastic starch.
References
Acioli-Moura R, Sun XS. 2008. Thermal degradation and physical aging of
poly(lactic acid) and its blends with starch. Polym Eng Sci 48:829–36.
Alexandre M, Dubois P. 2000. Polymer-layered silicate nanocomposites:
preparation, properties and uses of a new class of materials. Mater Sci Eng
R: Rep 28:1–63.
Amass W, Amass A, Tighe B. 1998. A review of biodegradable polymers:
uses, current developments in the synthesis and characterization of
biodegradable polyesters, blends of biodegradable polymers and recent
advances in biodegradation studies. Polym Int 47:89–144.
Ariyapitipun T, Mustapha A, Clarke AD. 1999. Microbial shelf life
determination of vacuum-packaged fresh beef treated with polylactic acid,
lactic acid, and nisin solutions. J Food Prot 62:913–20.
Auras R, Harte B, Selke S, Hernandez R. 2003. Mechanical, physical,
and barrier properties of poly(lactide) films. J Plastic Film Sheet 19:123–35.
Auras R, Harte B, Selke S. 2004. An overview of polylactides as packaging
materials. Macromol Biosci 4:835–64.
Auras RA, Singh SP, Singh JJ. 2005. Evaluation of oriented poly(lactide)
polymers vs. existing PET and oriented PS for fresh food service containers.
Packag Technol Sci 18:207–16.
Azeredo HMCD. 2009. Nanocomposites for food packaging applications.
Food Res Int 42:1240–53.
Bao L, Dorgan JR, Knauss D, Hait S, Oliveira NS, Maruccho IM. 2006. Gas
permeation properties of poly(lactic acid) revisited. J Membr Sci
285:166–72.
Bastioli C. 2005. Handbook of biodegradable polymers. 1st ed. Shropshire,
U.K.: Rapra Technology Limited. 5 p.
Bogaert JC, Coszach P. 2000. Poly(lactic acids): a potential solution to plastic
waste dilemma. Macromol Symp 153:287–303.
Bohlaman GM. 2005. General characteristics, processability, industrial
applications and market evolution of biodegradable polymers. In: Bastioli C,
editor. Handbook of biodegradable polymers. 1st ed. Shropshire, U.K.:
Rapra Technology Limited. p 183–218.
Brandrup J, Immergut EH, Grulke EA. 1999. Polymer handbook. 4th ed.
New York: John Wiley and Sons. 163 p.
Budhavaram NK, Fan Z. 2007. Lactic acid production from paper sludge
using thermophilic bacteria. AIChE Annual Meeting.
Cai H, Dave V, Gross RA, McCarthy SP. 1996. Effects of physical aging,
crystallinity, and orientation on the enzymatic degradation of poly(lactic
acid). J Polym Sci, Part B: Polym Phys 34:2701–8.
Chandra R, Rustgi R. 1998. Biodegradable polymers. Prog Polym Sci
23:1273–335.
Chen C, Lv G, Pan C, Song M, Wu C, Guo D, Wang X, Chen B, Gu Z.
2007. Poly(lactic acid) (PLA)-based nanocomposites—A novel way of
drug-releasing. Biomed Mater 2:L1–4.
Chollet E, Swesi Y, Degraeve P, Sebti I. 2009. Monitoring nisin desorption
from a multi-layer polyethylene-based film coated with nisin-loaded HPMC
film and diffusion in agarose gel by an immunoassay (ELISA) method and a
numerical modeling. Innov Food Sci Emerg Technol 10:208–14.
568 Comprehensive Reviews in Food Science and Food Safety rVol. 9, 2010 c
2010 Institute of Food Technologists®

Poly-lactic acid, nanocomposites, and release studies . . .
Chow WS, Lok SK. 2009. Thermal properties of poly(lactic acid)/organo-
montmorillonite nanocomposites. J Therm Anal Calorim 95:627–32.
Clarinval AM. 2002. Classification and comparison of thermal and
mechanical properties of commercialized polymers. International Congress
& Trade Show, The Industrial Applications of Bioplastics, 2002 February
3–5; York, UK.
Clarinval AM, Halleux J. 2005. Classification of biodegradable polymers. In:
Smith R, editor. Biodegradable polymers for industrial applications. 1st ed.
Boca Raton, FL, USA: CRC Press. p 3–31.
Coma V. 2008. Bioactive packaging technologies for extended shelf life of
meat-based products. Meat Sci 78:90–103.
Conn RE, Kolstad JJ, Borzelleca JF, Dixler DS, Filer LJ, LaDu BN, Pariza
MW. 1995. Safety assessment of polylactide (PLA) for use as a food-contact
polymer. Food Chem Toxicol 33:273–83.
Cun D, Cui F, Yang L, Yang M, Yu Y, Yang R. 2008. Characterization and
release mechanism of melittin-entrapped poly (lactic acid-co-glycolic acid)
microspheres. J Drug Deliv Sci Technol 18:267–72.
Datta R, Henry M. 2006. Lactic acid: recent advances in products, processes
and technologies: a review. J Chem Technol Biotechnol 81:1119–129.
Del Nobile MA, Conte A, Buonocore GG, Incoronato AL, Massaro A,
Panza O. 2009. Active packaging by extrusion processing of recyclable and
biodegradable polymers. J Food Eng 93:1–6.
Di Lorenzo ML. 2005. Crystallization behavior of poly(l-lactic acid). Eur
Polym J 41:569–75.
Dorgan JR, Lehermeier H, Mang M. 2000. Thermal and rheological
properties of commercial-grade poly(lactic acids)s. J Polym Environ 8:1–9.
FDA. 2001. FDA/CFSAN/OPA: Agency response letter: GRAS Notice No.
GRN 000065.
FDA. 2002. Inventory of Effective Food Contact Substance (FCS)
Notifications No. 178. http://www.accessdata.fda.gov/scripts/fcn/
fcnDetailNavigation.cfm?rpt=fcsListing&id=178.
Fukuzaki H, Yoshida M, Asano M, Kumakura M. 1989. Synthesis of
copoly(D,L-Lactic acid) with relatively low molecular weight and in vitro
degradation. Eur Polym J 25:1019–26.
Furukawa T, Sato H, Murakami R, Zhang J, Duan YX, Noda I, Ochiai S,
Ozaki Y. 2005. Structure, dispersibility, and crystallinity of
poly(hydroxybutyrate)/poly(L-lactic acid) blends studied by FT-IR
microspectroscopy and differential scanning calorimetry. Macromol
38:6445–54.
Gajria AM, Dav´
e V, Gross RA, McCarthy SP. 1996. Miscibility and
biodegradability of blends of poly(lactic acid) and poly(vinyl acetate).
Polymer 37:437–44.
Garlotta D. 2001. A literature review of poly(lactic acid). J Polym Environ
9:63–84.
Ghosh S, Viana JC, Reis RL, Mano JF. 2008. Oriented morphology and
enhanced mechanical properties of poly(l-lactic acid) from shear controlled
orientation in injection molding. Mater Sci Eng A 490:81–9.
Giles FH, Wagner JR, Mount EM. 2005. Extrusion, the definitive processing
guide and handbook. 1st ed. New York: William Andrew Publishing. 547 p.
Grijpma DW, Altpeter H, Bevis MJ, Feijen J. 2002. Improvement of the
mechanical properties of poly(D,L-lactide) by orientation. Polym Int
51:845–51.
Grossman EM. 1995. Annual Technical Conference—ANTEC 95,
Conference Proceedings. SCORIM- principles, capabilities and
applications. Society of plastic engineers 1995 p 461–76.
Gu H, Song C, Long D, Mei L, Sun H. 2007. Controlled release of
recombinant human nerve growth factor (rhNGF) from poly[(lactic
acid)-co-(glycolic acid)] microspheres for the treatment of
neurodegenerative disorders. Polym Int 56:1272–80.
Harada M, Ohya T, Iida K, Hayashi H, Hirano K, Fukuda H. 2007.
Increased impact strength of biodegradable poly(lactic acid)/poly(butylene
succinate) blend composites by using isocyanate as a reactive processing
agent. J Appl Polym Sci 106:1813–20.
Hartmann MH. 1998. High-molecular-weight polylactic acid polymers. In:
Kaplan DL, editor. Biopolymers from renewable resources. Berlin: Springer.
p 367–411.
Huang L, Sheng J, Chen J, Li N. 2008. 2nd International Conference on
Bioinformatics and Biomedical Engineer ing, iCBBE 2008. Direct
fermentation of fishmeal wastewater and starch wastewater to lactic acid by
Rhizopus oryzae. 2008.
Hutchinson MH, Dorgan JR, Knauss DM, Hait SB. 2006. Optical properties
of polylactides. J Polym Environ 14:119–24.
Jacobsen S, Fritz HG. 1996. Filling of poly(lactic acid) with native starch.
Polym Eng Sci 36:2799–804.
Janorkar AV, Hirt DE. 2004. Annual Technical Conference—ANTEC,
Conference Proceedings. Surface modification of poly(lactic acid) films via
grafting hydrophilic polymers. 2004.
Jin T, Liu L, Zhang H, Hicks K. 2009. Antimicrobial activity of nisin
incorporated in pectin and polylactic acid composite films against Listeria
monocytogenes. Int J Food Sci Technol 44:322–9.
Jing F, Hillmyer MA. 2008. A bifunctional monomer derived from lactide for
toughening polylactide. J Am Chem Soc 130:13826–7.
JoYS,KimMC,KimDK,KimCJ,JeongYK,KimKJ,MuhammedM.
2004. Mathematical modelling on the controlled-release of
indomethacin-encapsulated poly(lactic acid-co-ethylene oxide) nanospheres.
Nanotechnology 15:1186–94.
Joerger RD. 2007. Antimicrobial films for food applications: a quantitative
analysis of their effectiveness. Packag Technol Sci 20:231–73.
Johnson RM, Mwaikambo LY, Tucker N. 2003. Biopolymers. Rapra Rev
Rep 43:1–26.
Kale G, Auras R, Singh SP, Narayan R. 2007. Biodegradability of polylactide
bottles in real and simulated composting conditions. Polym Test 26:1049–61.
Kawashima N, Ogawa S, Obuchi S, Matsuo M, Yagi T. 2002. Poly lactic acid
“LACEA.” In: Doi Y, Steinbuchel A, editors. Biopolymers polyesters III
applications and commercial products. Weinheim: Wiley–VCH Verlag
GmbH. p 251–74.
Ke T, Sun X. 2001. Thermal and mechanical properties of poly(lactic acid)
and starch blends with various plasticizers. Trans Am Soc Agric Eng
44:945–53.
Ke T, Sun XS. 2003a. Starch, poly(lactic acid), and poly(vinyl alcohol)
blends. J Polym Environ 11:7–14.
Ke T, Sun XS. 2003b. Thermal and mechanical properties of poly(lactic
acid)/starch/methylenediphenyl diisocyanate blending with triethyl citrate. J
Appl Polym Sci 88:2947–55.
Ke T, Sun SX, Seib P. 2003. Blending of poly(lactic acid) and starches
containing varying amylose content. J Appl Polym Sci 89:3639–46.
Kerry JP, O’Grady MN, Hogan SA. 2006. Past, current and potential
utilisation of active and intelligent packaging systems for meat and
muscle-based products: a review. Meat Sci 74:113–30.
Kim YM, An DS, Park HJ, Park JM, Lee DS. 2002. Properties of
nisin-incorporated polymer coatings as antimicrobial packaging materials.
Packag Technol Sci 15:247–54.
Kim KI, Kim WK, Seo DK, Yoo IS, Kim EK, Yoon HH. 2003. Production
of lactic acid from food wastes. Appl Biochem Biotechnol 107:637–48.
Kim JY, Park HS, Kim SH. 2007. Multiwall-carbon-nanotube-reinforced
poly(ethylene terephthalate) nanocomposites by melt compounding. J Appl
Polym Sci 103:1450–7.
Kim Y, Jung R, Kim HS, Jin HJ. 2009. Transparent nanocomposites
prepared by incorporating microbial nanofibrils into poly(l-lactic acid). Curr
Appl Phys 9:S69–71.
Koo GH, Jang J. 2008. Surface modification of poly(lactic acid) by
UV/ozone irradiation. Fibers Polym 9:674–8.
Kylm ¨
aJ,H
¨
ark¨
onen M, Sepp¨
al¨
a JV. 1997. The modification of lactic
acid-based poly(ester-urethane) by copolymerization. J Appl Polym Sci
63:1865–72.
Labrecque LV, Kumar RA, Dav´
e V, Gross RA, McCarthy SP. 1997. Citrate
esters as plasticizers for poly(lactic acid). J Appl Polym Sci 66:1507–13.
Labuza TP, Breene W. 1989. Application of ‘active packaging’ technologies
for the improvement of shelf-life and nutritional quality of fresh and
extended shelf-life foods. Bibl Nutr Dieta 43:252–9.
Lee NC. 2006. The extrusion blow moulding system. In: Practical guide to
blow moulding. Shawbury, U.K.: Rapra Technology Limited. p 81–98.
Lee CM, Kim ES, Yoon JS. 2005. Reactive blending of poly(L-lactic acid)
with poly(ethylene-co-vinyl alcohol). J Appl Polym Sci 98:886–90.
Lee DS, Yam KL, Piergiovanni L. 2008. Food packaging science and
technology. 1st ed. New York: Taylor and Francis 631 p.
Lehermeier HJ, Dorgan JR, Way JD. 2001. Gas permeation properties of
poly(lactic acid). J Membr Sci 190:243–51.
Li H, Huneault MA. 2007. Effect of nucleation and plasticization on the
crystallization of poly(lactic acid). Polymer 48:6855–66.
Li Y, Shimizu H. 2009. Improvement in toughness of poly(l-lactide) (PLLA)
through reactive blending with acrylonitrile-butadiene-styrene copolymer
(ABS): Morphology and properties. Eur Polym J 45:738–46.
c
2010 Institute of Food Technologists®Vol. 9, 2010 rComprehensive Reviews in Food Science and Food Safety 569

Poly-lactic acid, nanocomposites, and release studies . . .
Li BH, Yang MC. 2006. Improvement of thermal and mechanical properties
of poly(L-lactic acid) with 4,4-methylene diphenyl diisocyanate. Polym Adv
Technol 17:439–43.
Li L, Tang SC, Wang QH, Pan YK, Wang TL. 2006. Preparation of poly
(lactic acid) by direct polycondensation in azeotropic solution. J East China
Univ Sci Technol 32:672–5.
Li Y, Wang Y, Liu L, Han L, Xiang F, Zhou Z. 2009. Crystallization
improvement of poly(L-lactide) induced by functionalized multiwalled
carbon nanotubes. J Polym Sci Part A: Polym Chem 47:326–39.
Lim JY, Kim SH, Lim S, Kim YH. 2001. Improvement of flexural strengths
of poly(L-lactic acid) by solid-state extrusion. Macromol Chem Phys
202:2447–53.
Lim JY, Kim SH, Lim S, Kim YH. 2003. Improvement of flexural strengths
of poly(L-lactic acid) by solid-state extrusion, 2: extrusion through
rectangular die. Macromol Mater Eng 288:50–7.
Lim HA, Raku T, Tokiwa Y. 2005. Hydrolysis of polyesters by serine
proteases. Biotechnol Lett 27:459–64.
Lim LT, Auras R, Rubino M. 2008. Processing technologies for poly(lactic
acid). Prog Polym Sci 33:820–52.
Liu FT, He R, Zhao YD, Gao F, Zhang YX, Cui DX. 2008. Modified
biodegradable poly(D, L-lactic-co-glycolic acid) film implants for sustained
release of 5-fluorouracil. Shanghai Jiaotong Daxue Xuebao/J Shanghai
Jiaotong Univ 42:822–6,30.
Ljungberg N, Wessl´
en B. 2002. The effects of plasticizers on the dynamic
mechanical and thermal properties of poly(lactic acid). J Appl Polym Sci
86:1227–34.
Ljungberg N, Colombini D, Wessle´
en B. 2005. Plasticization of poly(lactic
acid) with oligomeric malonate esteramides: dynamic mechanical and
thermal film properties. J Appl Polym Sci 96:992–1002.
Lopez-Rubio A, Almenar E, Hernandez-Munoz P, Lagaron JM, Catala R,
Gavara R. 2004. Overview of active polymer-based packaging technologies
for food applications. Food Rev Int 20:357–87.
Lopez-Rubio A, Gavara R, Lagaron JM. 2006. Bioactive packaging: turning
foods into healthier foods through biomaterials. Trends Food Sci Technol
17:567–75.
Lu D, Zhang X, Zhou T, Ren Z, Wang S, Lei Z. 2008. Biodegradable poly
(lactic acid) copolymers. Prog Chem 20:339–50.
Masaki K, Kamini NR, Ikeda H, Iefuji H. 2005. Cutinase-like enzyme from
the yeast Cryptococcus sp. strain S-2 hydrolyses polylactic acid and other
biodegradable plastics. Appl Environ Microbiol 7:7548–50.
Mehta R, Kumar V, Bhunia H, Upadhyay SN. 2005. Synthesis of poly(lactic
acid): a review. J Macromol Sci Polym Rev 45:325–49.
Mehta R, Kumar V, Upadhyay SN. 2007. Mathematical modeling of the
poly(lactic acid) ring-opening polymerization using stannous octoate as a
catalyst. Polym Plast Technol Eng 46:933–7.
Miao LF, Yang J, Huang CL, Song CX, Zeng YJ, Chen LF, Zhu WL. 2008.
Rapamycin-loaded poly (lactic-co-glycolic) acid nanoparticles for
intraarterial local drug delivery: preparation, characterization, and in
vitro/in vivo release. Acta Acad Med Sinicae 30:491–7.
Mills CA, Navarro M, Engel E, Martinez E, Ginebra MP, Planell J, Errachid
A, Samitier J. 2006. Transparent micro- and nanopatterned poly(lactic acid)
for biomedical applications. J Biomed Mater Res 76:781–7.
Mohanty AK, Misra M, Hinrichsen G. 2000. Biofibres, biodegradable
polymers and biocomposites: an overview. Macromol Mater Eng
276–277:1–24.
Mutsuga M, Kawamura Y, Tanamoto K. 2008. Migration of lactic acid,
lactide and oligomers from polylactide food-contact materials. Food Addit
Contam Part A, Chem, Anal, Control, Expo Risk Assess 25:1283–90.
Nakayama N, Hayashi T. 2007. Preparation and characterization of
poly(l-lactic acid)/TiO2nanoparticle nanocomposite films with high
transparency and efficient photodegradability. Polym Degrad Stab
92:1255–64.
NatureWorks. 2005a. PLA ISBM bottle guide. Minnetonka, Minn.:
NatureWorks LLC.
NatureWorks. 2005b. PLA processing guide for biaxially or iented film.
Minnetonka, Minn.: NatureWorks LLC.
NatureWorks. 2005c. Processing guide for thermoforming articles.
Minnetonka, Minn.: NatureWorks LLC.
NatureWorks. 2006a. PLA 2002D, 3001D, 3051D, 3251D, 4032D, 4042D,
4060D, 7000D, 7032D data sheets. Minnetonka, Minn.: NatureWorks LLC.
NatureWorks. 2006b. PLA injection molding guide for 3051D. Minnetonka,
Minn.: NatureWorks LLC.
Natureworks. 2009. Using near-infrared sorting to recycle PLA bottles.
Minnetonka, Minn.: Natureworks LLC.
Nijenhuis AJ, Colstee E, Grijpma DW, Pennings AJ. 1996.
High-molecular-weight poly(L-lactide) and poly(ethylene oxide) blends:
thermal characterization and physical properties. Polymer 37:5849–57.
Oda Y, Yonetsu A, Urakami T, Tonomura K. 2000. Degradation of
polylactide by commercial proteases. J Polym Environ 8:29–32.
Ohkita T, Lee SH. 2006. Thermal degradation and biodegradability of
poly(lacticacid)/cornstarch biocomposites. J Appl Polym Sci 100:3009–17.
Oliveira NS, Oliveira J, Gomes T, Ferreira A, Dorgan J, Marrucho IM.
2004. Gas sorption in poly(lactic acid) and packaging materials. Fluid Phase
Equilib 222–223:317–24.
Oyama HT. 2009. Super-tough poly(lactic acid) materials: reactive blending
with ethylene copolymer. Polymer 50:747–51.
Park S, Chang Y, Cho JH, Noh I, Kim C, Kim SH, Kim YH. 1998.
Synthesis and thermal properties of copolymers of L-lactic acid and
ε-caprolactone. Polymer 22:1–5.
Park SD, Todo M, Arakawa K. 2004. Effect of annealing on fracture
mechanism of biodegradable poly(lactic acid). Key Eng Mater
261–263:105–10.
Patey W. 2010. Thermoforming PLA: how to do it right. Plastics Technol
56:30–1.
Platt K. 2006. The global biodegradable polymers market. In: Biodegradable
polymers. Shawbury, UK: Smithers Rapra Technology Limited. p 31–48.
Poc¸ as MF, Oliveira JC, Oliveira FAR, Hogg T. 2008. A critical survey of
predictive mathematical models for migration from packaging. Crit Rev
Food Sci Nutr 48:913–28.
Pranamuda H, Tsuchii A, Tokiwa Y. 2001. Poly(L-lactide)-degrading
enzyme produced by Amycolatopsis sp. Macromol Biosci 1:25–9.
Puaux JP, Banu I, Nagy I, Bozga G. 2007. A study of L-lactide ring-opening
polymerization kinetics. Macromol Symp 259:318–26.
Quan D, Liao K, Zhao J. 2004. Effects of physical aging on glass transition
behavior of poly(lactic acid)s. Acta Polym Sinica 5:726–30.
Ray SS, Bousmina M. 2005. Biodegradable polymers and their layered
silicate nanocomposites: in greening the 21st century materials world. Prog
Mater Sci 50:962–1079.
Reddy G, Altaf M, Naveena BJ, Venkateshwar M, Kumar EV. 2008.
Amylolytic bacterial lactic acid fermentation—A review. Biotechnol Adv
26:22–34.
Ren Z, Dong L, Yang Y. 2006. Dynamic mechanical and thermal properties
of plasticized poly(lactic acid). J Appl Polym Sci 101:1583–90.
Rhim JW. 2007. Potential use of biopolymer-based nanocomposite films in
food packaging applications. Food Sci Biotechnol 16:691–709.
Rosato DV, Rosato DV, Rosato MG. 2000. Injection molding handbook.
3rd ed. Boston: Kluwer Academic Publishers 1488 p.
Sakata S, Kei T, Uchida K, Kaetsu I. 2006. Nano-particle of hydrophobic
poly lactic acid for DDS. Polym Preprints Japan 55:2074.
Salmaso S, Elvassore N, Bertucco A, Lante A, Caliceti P. 2004. Nisin-loaded
poly-L-lactide nano-particles produced by CO2anti-solvent precipitation
for sustained antimicrobial activity. Int J Pharm 287:163–73.
Sanchez-Garcia MD, Gimenez E, Lagaron JM. 2007. Novel PET
nanocomposites of interest in food packaging applications and comparative
barrier perfor mance with biopolyester nanocomposites. J Plastic Film Sheet
23:133–48.
Schnieders J, Gbureck U, Thull R, Kissel T. 2006. Controlled release of
gentamicin from calcium phosphate-poly(lactic acid-co-glycolic acid)
composite bone cement. Biomaterials 27:4239–49.
Scott G. 2000. ‘Green’ polymers. Polym Degrad Stab 68:1–7.
Sheth M, Kumar RA, Dav´
e V, Gross RA, McCarthy SP. 1997.
Biodegradable polymer blends of poly(lactic acid) and poly(ethylene glycol).
J Appl Polym Sci 66:1495–505.
Shibata M, Someya Y, Orihara M, Miyoshi M. 2006. Thermal and
mechanical properties of plasticized poly(L-lactide) nanocomposites with
organo-modified montmorillonites. J Appl Polym Sci 99:2594–602.
Shogren R. 1997. Water vapor permeability of biodegradable polymers. J
Environ Polym Degrad 5:91–5.
Sinha Ray S, Okamoto M. 2003. Polymer/layered silicate nanocomposites: a
review from preparation to processing. Prog Polym Sci 28:1539–641.
Siparsky GL, Voorhees KJ, Dorgan JR, Schilling K. 1997. Water transport in
polylactic acid (PLA), PLA/polycaprolactone copolymers, and
PLA/polyethylene glycol blends. J Environ Polym Degrad 5:125–36.
570 Comprehensive Reviews in Food Science and Food Safety rVol. 9, 2010 c
2010 Institute of Food Technologists®

Poly-lactic acid, nanocomposites, and release studies . . .
Siracusa V, Rocculi P, Romani S, Rosa MD. 2008. Biodegradable polymers
for food packaging: a review. Trends Food Sci Technol 19:634–43.
S¨
oderg˚
ard A, Stolt M. 2002. Properties of lactic acid based polymers and
their correlation with composition. Prog Polym Sci (Oxford) 27:1123–63.
Sokolsky-Papkov M, Golovanevski L, Domb AJ, Weiniger CF. 2009.
Prolonged local anesthetic action through slow release from poly(lactic acid
co castor oil). Pharm Res 26:32–9.
Sozer N, Kokini JL. 2009. Nanotechnology and its applications in the food
sector. Trends Biotechnol 27:82–9.
Suyama T, Tokiwa Y, Ouichanpagdee P, Kanagawa T, Kamagata Y. 1998.
Phylogenetic affiliation of soil bacteria that degrade aliphatic polyesters
available commercially as biodegradable plastics. Appl Environ Microbiol
64:5008–11.
Taubner V, Shishoo R. 2001. Influence of processing parameters on the
degradation of poly(L-lactide) during extrusion. J Appl Polym Sci
79:2128–35.
Throne JL. 1996. Technology of thermofor ming. 1st ed. New York: Hanser
Publishers. 922 p.
Todo M. 2007. Effect of unidirectional drawing process on fracture behavior
of poly(l-lactide). J Mater Sci 42:1393–6.
Tokiwa Y, Calabia BP. 2006. Biodegradability and biodegradation of
poly(lactide). Appl Microbiol Biotechnol 72:244–51.
Tor res A, Li SM, Roussos S, Vert M. 1996. Screening of microorganisms for
biodegradation of poly(lactic acid) and lactic acid-containing polymers.
Appl Environ Microbiol 62:2393–7.
Tor res-Giner S, Ocio MJ, Lagaron JM. 2008. Development of active
antimicrobial fiber-based chitosan polysaccharide nanostructures using
electrospinning. Eng Life Sci 8:303–14.
Tsuji H, Ikada Y. 1996. Blends of aliphatic polyesters. I. Physical properties
and morphologies of solution-cast blends from poly(DL-lactide) and
poly(ε-caprolactone). J Appl Polym Sci 60:2367–75.
Tsuji H, Nakahara K, Ikarashi K. 2001. Poly(L-lactide), high-temperature
hydrolysis of poly(L-lactide) films with different crystallinities and crystalline
thicknesses in phosphate-buffered solution. Macromol Mater Eng
286:398–406.
Tsuji H, Daimon H, Fujie K. 2003. A new strategy for recycling and
preparation of poly(L-lactic acid): hydrolysis in the melt. Biomacromol
4:835–40.
Tsuji H, Okino R, Daimon H, Fujie K. 2006. Water vapor permeability of
poly(lactide)s: effects of molecular characteristics and crystallinity. J Appl
Polym Sci 99:2245–52.
Uradnisheck J. 2009. Annual Technical Conference—ANTEC 2009,
Conference Proceedings. Improved dimensional stability of thermoformed
polylactic acid articles. 2009 June 22–26; Chicago IL, USA, p 1612–5.
Urayama H, Kanamori T, Kimura Y. 2002. Properties and biodegradability
of polymer blends of poly(l-lactide)s with different optical purity of the
lactate units. Macromol Mater Eng 287:116–21.
Uyama H, Ueda H, Doi M, Takase Y, Okubo T. 2006. Plasticization of poly
(lactic acid) by bio-based resin modifiers. Polym Preprints Japan 55:5595.
Vainionpaa S, Rokkanen P, Tor mall P.1989. Surgical application of
biodegradable polymers in human tissues. Prog Polym Sci 14:679–
716.
Van Aardt M, Duncan SE, Marcy JE, Long TE, O’Keefe SF, Sims SR. 2007.
Release of antioxidants from poly(lactide-co-glycolide) films into dry milk
products and food simulating liquids. Int J Food Sci Technol 42:1327–
37.
Vermeiren L, Devlieghere F, Van Beest M, De Kruijf N, Debevere J. 1999.
Developments in the active packaging of foods. Trends Food Sci Technol
10:77–86.
Vink ETH, Rabago KR, Glassner DA, Gruber PR. 2003. Applications of life
cycle assessment to NatureWorks®polylactide (PLA) production. Polym
Degrad Stab 80:403–19.
Vink ETH, Rajbago KR, Glassner DA, Springs B, O’Connor RP, Kolstad J,
Gruber PR. 2004. The sustainability of NatureWorks polylactide polymers
and ingeo polylactide fibers: an update of the future. Initiated by the 1st
International Conference on Bio-based Polymers (ICBP 2003), November
2003, Saitama, Japan. Macromol Biosci 4:551–64.
Vink ETH, Glassner DA, Kolstad JJ, Wooley RJ, O’Connor RP. 2007. The
eco-profiles for current and near-future NatureWorks®polylactide (PLA)
production. Ind Biotechnol 3:58–81.
Wang S, Tao J, Guo T, Fu T, Yuan X, Zheng J, Song C. 2007. Thermal
characteristics, mechanical properties and biodegradability of
polycarbonates/poly(lactic acid) (PPC/PLA) blends. Lizi Jiaohuan Yu
Xifu/Ion Exch Adsorp 23:1–9.
Wang N, Zhang X, Yu J, Fang J. 2008. Study of the properties of plasticised
poly(lactic acid) with poly(1,3-butylene adipate). Polym Polym Compos
16:597–604.
White JR. 2006. Polymer ageing: physics, chemistry or engineering? Time
to reflect. C.R Chimie 9:1396–408.
Williams DF. 1981. Enzymatic hydrolysis of polylactic acid. Eng Med 10:5–
7.
Wolf O. 2005. Techno-economic feasibility of large-scale production of
bio-based polymers in Europe. Institute for Prospective Technological
Studies, Spain: European Communities. p 50–64.
Xu Q, Czernuszka JT. 2008. Controlled release of amoxicillin from
hydroxyapatite-coated poly(lactic-co-glycolic acid) microspheres. J Control
Release 127:146–53.
Yang L, Chen X, Jing X. 2008. Stabilization of poly(lactic acid) by
polycarbodiimide. Polym Degrad Stab 93:1923–9.
Yu H, Huang N, Wang C, Tang Z. 2003. Modeling of poly(L-lactide)
thermal degradation: theoretical prediction of molecular weight and
polydispersity index. J Appl Polym Sci 88:2557–62.
Zee MV. 2005. Biodegradability of polymers–Mechanisms and evaluation
methods. In: Bastioli C, editor. Handbook of biodegradable polymer. 1st
ed. Shropshire, U.K.: Rapra Technology Limited. p 1–22.
Zhang B, He PJ, Ye NF, Shao LM. 2008. Enhanced isomer pur ity of lactic
acid from the nonsterile fermentation of kitchen wastes. Bioresour Technol
99:855–62.
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