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Processing of advanced green nanomaterials
Abstract
Green composites are materials having eco-friendly attributes that are technically and economically feasible while minimizing the generation of pollution. In this context, it refers to the combination of fully degradable fibers mostly cellulosic materials and natural resins to develop green composite materials. In the past decade, overdependence on petroleum products (synthetic polymers, resins, etc.) has consistently increased, and on account of this the researchers are now focusing more on green materials specially cellulosic. Green composites do not harm the environment much and could be satisfactory alternatives to petroleum-based polymers and polymer composites. The developing anxiety toward prevention of ecological destruction and the unfilled requirement for more adaptable environmental friendly materials has prompted expanding interest about polymer composites, originating from sustainable sources and biodegradable plant materials, particularly from forests. These have widened the utilization of plant fibers as reinforcements and have increased the possibility for sustainable and “biodegradable” composites, which can be called “green” composites as they satisfy the criteria of “green materials.” Thus the challenge to obtain “green” composite involves obtaining “green” polymers functioning as matrices in the production of composite materials. This chapter considers the materials and methods utilized for the fabrication and particularly the utilization of green composites in different technological fields.
... Moreover, new biodegradable thermoplastic materials, such as soy-based resin, polylactic acid and starch-based resin, are environmental-friendly because they completely degrade after disposal [27][28][29]. At the same time, it is economical as it minimises energy consumption. ...
... 7,8 These types of synthetic composites are of big concern due to their high cost and lack of environmental friendliness. 9 Furthermore, just as the synthesis of engineered polymers such as polyethylene and polypropylene is reducing fuel reserves, it is also increasing the price of fossil fuels. A remarkable amount of greenhouse gases are emitted into the environment by the manufacture of synthetic fibers and petroleum-based polymers. ...
At present, environmental sustainability is a big concern due to the limited resources and the adverse impacts of petroleum-based materials. Green composites (GCs) attracted intensive research interest for the last few decades from academicians, scientists, researchers, and practitioners both from the ecological and economic point of view and are presently being considered as one of the most promising research domains. Composites produced from renewable and/or natural resources thanks to their biodegradability and sustainability properties are envisaged as the next-generation materials to meet the growing demand worldwide. GCs are intensively investigated due to their multifunctional properties and utilization in a wide variety of fields including automobile, marine, aerospace, structural and infrastructural applications, packaging, electronics industry, sports, and biomedical applications. They also show potentials to replace the expensive as well as non-degradable petroleum-based composites. After the shelf life, it can be disposed of easily without harming the environment. The processing techniques, properties, and applications of green composites are comprehensively assessed in this review article. The feasibility of the naturally available fiber and polymers for green composites are also discussed highlighting the existing challenges with possible suggestions. It was intended to present a full overview of biodegradable polymer composites reinforced with natural fiber, as well as the necessary future directions for the concerned researchers.
Background: In recent years, food packaging has focused on two scientific pillars; adopting the biodegradable packaging materials and development of antimicrobial packaging for extended shelf life, quality and safety of food products. The bioplastic materials provide a promising application in the packaging industry to substitute environmentally deleterious petrochemical-based plastics. Scope and approach: This paper gives insights to very recent progress on the antimicrobial application of starch, polyhydroxybutyrate (PHB) and poly (lactic-co-glycolide) (PLGA) as well as their blends and nanocomposites in food packaging research. It also presents an overview of the antimicrobial application of these materials particularly in food and biomedical industry. Key findings and conclusions: PHB, starch and PLGA materials have unique properties towards novel application in foods, cosmetics, medicines as well as various composites. The materials necessitate critical studies to improve their industrial performance both for processing engineering and antimicrobial packaging due to functional and technical limitations.
In this work, the effect of both the expandable graphite (EG) and ammonium polyphosphate modified with 3-(methylacryloxyl) propyltrimethoxy silane (M-APP) on the flame retardancy and mechanical properties of the wood-polypropylene composites (WPC) were studied. Cone calorimetry results indicated that both EG and M-APP could effectively improve the flame retardancy of WPC, while the retardancy of EG was better than that of M-APP. When the flame-retardant loading was 25 wt.%, the limiting oxygen index (LOI) values of M-APP- filled WPC (M-APP/WPC) and EG-filled WPC (EG/WPC) were 30.7% and 37.9%, respectively. According to the LOI test, the optimal ratio of M-APP to EG in WPC was 1:1 by weight, at which the LOI value of WPC was 39.3%. Thermogravimetric analysis (TG) results indicated that the addition of M-APP and EG to WPC could lead to an increase of char residue. Under the same conditions, the char residue of composite filled with the mixture of EG and M-APP (at a ratio of 1:1) was greater than that of composites filled individually at the same temperature. Both the tensile strength and flexural strength decreased at a certain extent due to incorporation of EG into WPC, but with the addition of the M-APP, the mechanical properties of these composite samples increased. At the ratio of 1:1 (M-APP to EG), the mechanical properties of the composite were not obviously decreased, and the flame retardancy was higher than the M-APP-filled WPC composites.
The development and importance of inexpensive biodegradable polymeric resins were discussed. Since many of the fibers and resins are made using nondegradable, mostly petroleum-based materials, they do not degrade for several decades under normal environmental conditions. The use of composites in place of common plastics in consumer products was encouraged to improve performance and reduce weight and cost.
Unmodified and modified natural rubber latex (uNRL and mNRL) were used to prepare thermoplastic starch/natural rubber/montmorillonite type clay (TPS/NR/Na+-MMT) nanocomposites by twin-screw extrusion. After being dried, the nanocomposites were injection molded to produce test specimens. Scanning electron micrographs of fractured samples revealed that chemical modification of NRL enhanced the interfacial adhesion between NR and TPS; improving their dispersion. X-ray diffraction (XRD) showed that the nanocomposites exhibited partially intercalated/exfoliated structures. Surprisingly, transmission electron microscopy (TEM) showed that clay nanoparticles were preferentially intercalated into the rubber phase. Elastic modulus and tensile strength of TPS/NR blends were dramatically improved from 1.5 to 43 MPa and from 0.03 to 1.5 MPa, respectively, as a result of rubber modification. Properties of blends were almost unaffected by the dispersion of the clay except for the TPS/mNR blend loading 2% MMT. This was attributed to the exfoliation of the MMT.
A review is given of the academic and industrial aspects of the preparation, characterization, materials properties, crystallization behavior, melt rheology, and processing of polymer/layered silicate nanocomposites. These materials are attracting considerable interest in polymer science research. Hectorite and montmorillonite are among the most commonly used smectite-type layered silicates for the preparation of nanocomposites. Smectites are a valuable mineral class for industrial applications because of their high cation exchange capacities, surface area, surface reactivity, adsorptive properties, and, in the case of hectorite, high viscosity and transparency in solution. In their pristine form they are hydrophilic in nature, and this property makes them very difficult to disperse into a polymer matrix. The most common way to remove this difficulty is to replace interlayer cations with quarternized ammonium or phosphonium cations, preferably with long alkyl chains.
The objective was to characterize the properties of cellulose nanofibril/TPS based nanocomposites. The cellulose nanofibrils were extracted from wheat straw using steam explosion, acidic treatment and high shear mechanical treatment. These nanofibrils were dispersed in thermo plastic starch (TPS) using a Fluko high shear mixer in varying proportions and films were casted out of these nanocomposites. The cellulose nanofibrils were characterized using AFM, TEM, SEM, TGA, FTIR and WAXRD and the nanocomposite films were analyzed in terms of SEM, WAXRD, TGA, DSC, mechanical and barrier properties. XRD and TGA results confirmed the crystalline nature of nanofibrils. AFM and TEM images revealed fiber diameter in the range 30–70 nm. TGA depicted an increasing in residue left with increase in cellulose nanofibrils content. Mechanical properties increased with nanofiber concentration. Barrier properties also improved with addition of nanofillers up to 10% but further addition deteriorated properties due to possible fiber agglomeration.
In this work, natural fibres (sisal, kenaf, hemp, jute and coir) reinforced polypropylene composites were processed by compression moulding using a film stacking method. The mechanical properties of the different natural fibre composites were tested and compared. A further comparison was made with the corresponding properties of glass mat reinforced polypropylene composites from the open literature. Kenaf, hemp and sisal composites showed comparable tensile strength and modulus results but in impact properties hemp appears to out-perform kenaf. The tensile modulus, impact strength and the ultimate tensile stress of kenaf reinforced polypropylene composites were found to increase with increasing fibre weight fraction. Coir fibre composites displayed the lowest mechanical properties, but their impact strength was higher than that of jute and kenaf composites. In most cases the specific properties of the natural fibre composites were found to compare favourably with those of glass.
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.
Eco-friendly “green” nano composites were fabricated from potato starch and cellulose nanofibers from pineapple leaf. Nanocomposites of starch/cellulose nanofibers were prepared by solution mixing followed by casting. The investigation of the viscoelastic properties confirms starch macromolecular chain confinement around the nano scale cellulose surface, superior dispersion and very good interaction between thermoplastic starch and cellulose nanofibers. The degree of chain confinement was quantified. The chain confinement was associated with the immobilization of the starch macromolecular chains in the network formed by the nano-scale cellulose fibers as a result of hydrogen boding interactions. From the results, it was assumed that the starch glycerol system exhibits a heterogenous nature and cellulose nanofibers tend to move towards glycerol rich starch phase. Barrier properties also improved with the addition of nanofiller up to 3 wt.% but further addition depreciated properties due to possible fiber agglomeration. The kinetics of diffusion was investigated and typical kinetic parameters were determined and found that the nanocomposites follow pseudo fickian behaviour. The outcome of the work confirms that the prepared nanocomposites films can be used as a swap for packaging applications.
Novel synthesis strategy of eco-friendly bio-nanocomposite films have been exploited using cellulose nanocrystals (CNC) and polyvinyl alcohol/carboxymethyl cellulose (PVA/CMC) blend matrix as a potential in food packaging application. The CNC were extracted from sugarcane bagasse using sulfuric acid hydrolysis, and they were successfully characterized regarding their morphology, size, crystallinity and thermal stability. Thereafter, PVA/CMC-CNC bio-nanocomposite films, at various CNC contents (0.5–10 wt%), were fabricated by the solvent casting method, and their properties were investigated. It was found that the addition of 5 wt % CNC within a PVA/CMC increased the tensile modulus and strength by 141% and 83% respectively, and the water vapor permeability was reduced by 87%. Additionally, the bio-nanocomposites maintained the same transparency level of the PVA/CMC blend film (transmittance of ∼90% in the visible region), suggesting that the CNC were dispersed at the nanoscale. In these bio-nanocomposites, the adhesion properties and the large number of functional groups that are present in the CNC’s surface and the macromolecular chains of the PVA/CMC blend are exploited to improve the interfacial interactions between the CNC and the blend. Consequently, these eco-friendly structured bio-nanocomposites with superior properties are expected to be useful in food packaging applications.
Bio-based nanocomposites have been developed from epoxidized soybean oil, diglycidyl ether of bisphenol-A (DGEBA) and organically modified montmorillonite (OMM). The organically modified montmorillonite and the nanocomposites were investigated by wide angle X-ray diffraction (WAXD) analysis and the morphology of these nanocomposites was examined by scanning electron microscopy (SEM). The exfoliated nanocomposites exhibited significant improvements in mechanical properties such as tensile strength, tensile modulus, flexural strength, flexural modulus and impact strength. Dynamic mechanical analysis (DMA) showed that nanocomposites exhibits high storage modulus and imparts rigidity upon reinforcement of the OMM. The nanocomposites were characterized for their thermal properties such as glass transition temperature, degradation stability and water absorption properties. There is almost a 24% increase in the tensile and flexural properties of the prepared nanocomposites upon reinforcement of 7wt% of the MMT. The restricted chain mobility and diffusion of oxygen and volatile products enhanced the thermal stability of the nanocomposites to a significant value.
Recently, cellulose has been re-discovered as a smart material that can be used as sensor and actuator materials, which is termed as electro-active paper. In this work we demonstrate the application of cellulose as a flexible humidity and temperature sensor. Nanoscaled polypyrrole (PPy) as a humidity and temperature sensitive layer was introduced onto cellulose surface via in situ polymerization technique without disrupting cellulose structure. Atomic force microscopy, UV–visible spectroscopy, transmission electron microscopy and secondary ion mass spectroscopic analysis revealed the successful deposition of polypyrrole nanolayer onto cellulose surface, which is referred as a cellulose–PPy nanocomposite. Effect of polymerization time on sensing behavior of cellulose–PPy nanocomposite was investigated, experimental results revealed that cellulose–PPy nanocomposite with 16h polymerization time suitable for suitable for humidity and temperature sensor.
Biodegradable nanocomposites based on 5 wt% cellulose nanowhiskers (CNW) and polylactic acid (PLA) were prepared using an extrusion process. An anionic surfactant (5, 10 and 20 wt%) was used to improve the dispersion of the CNW in the PLA matrix. The results showed that increased surfactant content resulted in improved dispersion but at the same time degraded the PLA matrix. The results from mechanical testing showed a maximum modulus for the composite with 5 wt% surfactant and as the surfactant content increased, the CNW dispersion improved and the tensile strength and elongation at break was improved compared to its unreinforced counterpart.
Polymer composites filled with natural organic fillers have gained a significant interest during the last few years, because of several advantages they can offer compared with properties of inorganic-mineral fillers. However, these composites (based, in most cases, on polyolefins) often show a reduction in some mechanical properties. This is mainly due to the problems regarding dispersion of the polar filler particles in the non-polar polymer matrix and their interfacial adhesion with polymer chains. In this work, polypropylene–wood flour composites were prepared and the effect of the addition of a maleated polypropylene was investigated. The two materials were compounded by an industrial co-rotating twin screw extruder, with two different compositions, without and with addition of Licomont AR504 (maleic anhydride-grafted polypropylene wax). The extruded material was then compression molded, which provided the specimens for tensile and impact tests. Water uptake was measured; the morphology of the fracture surfaces of the samples coming out from mechanical tests was investigated through SEM analysis. Rheological characterization was carried out as well. The addition of the adhesion promoter allowed a decrease in water uptake; mechanical properties were improved as well, especially elastic modulus and tensile strength; impact strength increased in the case of unnotched samples, while notched ones did not show remarkable differences. SEM analysis of the fracture surfaces also showed an overall change in the morphology as a consequence of the utilization of the adhesion promoter.
Rice husks (RH) were chemically modified with glycidyl methacrylate (GMA). The chemical loading of the GMA (weight percent gain, WPG) increased as the reaction time was increased. The modification of RH with GMA gave enhanced flexural, tensile and impact properties of rice husk-polystyrene (RH-PS) composites. These may be due to the increased interaction at the interfacial region between the surface of GMA-modified RH and PS. The modification improved dimensional stability and reduced water absorption of the composites.
Poly( L ‐lactide)/layered aluminosilicate nanocomposites were synthesized in bulk by ring‐opening polymerization in the presence of two organo‐modified montmorillonites. When the organo‐modifier consisted of an ammonium cation bearing primary hydroxyl groups, polymerization was initiated by the alcohol functions after adequate activation. The growing polymer chains were directly “grafted” onto the clay surface through the hydroxyl‐functionalized ammonium cations yielding exfoliated nanocomposites with enhanced thermal stability.
TEM image of a fully exfoliated Cloisite®30B‐based nanocomposite, showing delamination of the silicate layers.
magnified image TEM image of a fully exfoliated Cloisite®30B‐based nanocomposite, showing delamination of the silicate layers.
The rising concern towards environmental issues and, on the other hand, the need for more versatile polymer-based materials has led to increasing interest about polymer composites filled with natural-organic fillers, i.e. fillers coming from renewable sources and biodegradable. The composites, usually referred to as “green”, can find several industrial applications. On the other hand, some problems exist, such as worse processability and reduction of the ductility. The use of adhesion promoters, additives or chemical modification of the filler can help in overcoming many of these limitations. These composites can be further environment-friendly when the polymer matrix is biodegradable and comes from renewable sources as well. This short review briefly illustrates the main paths and results of research (both academic and industrial) on this topical subject, providing a quick overview (with no pretence of exhaustiveness over such a vast topic), as well as appropriate references for further in-depth studies.
This study aims to synthesize and characterize a biodegradable scaffold with a cellulose/nano-hydroxyapatite base for bone tissue engineering. At first, nano particles of hydroxyapatite were synthesized via precipitation method; furthermore scaffolds were fabricated by solvent casting/particulate leaching technique, where poly(methyl methacrylate) were utilized as porogen. The 1-n-allyl-3-methylimidazolium chloride ionic liquid was used for dissolution of cellulose as well. Scaffolds with 3 different compositions (5, 15, and 30wt.% of nano-hydroxyapatite) had 85–90% porosity. Also, the morphology of the samples was studied employing SEM. Images showed that pore sizes of the scaffolds were nearly 250–450μm. Meanwhile, sample bioactivity was determined via MTT assay and ALP test. Bioactivity and compatibility of the samples were confirmed; in addition, no toxicity was observed after 14days. SEM studies demonstrated that the cells can attach to the surface of the nanocomposite samples. This behavior revealed osteoconductivity of the composite surface.
Thermoformed natural fiber filled polyolefin composites are becoming increasingly important because of their combination of low cost, good formability and high strength-to-weight ratio. During thermoforming, ex truded sheets are stretched into a mold by either mechanical force or pressure/ vacuum. As the sheet stretches into the mold it thins. Hence, it is important to optimize the process in order to form an acceptable final part. Often, optimiza tion is an expensive and time-consuming trial-and-error process. However, with microcomputers, numerical simulation of the thermoforming process is becom ing increasingly accurate and powerful. In this study, a one-dimensional finite element simulation was developed to predict the thinning of axisymmetric and rectangular thermoformed parts. This simulation uses an empirical model de veloped from experimental data to represent the temperature-dependent stress-strain behavior of wood flour filled polypropylene. To predict sheet thin ning, the simulation solves the virtual work equation including normal, bend ing and shearing stresses in the sheet during stretching. To solve the governing equations, one-dimensional finite element theory is used. Based on the ex perimental results, an empirical model that represents the material behavior of wood flour filled polypropylene was developed. The simulation was compared to an analytical solution and experimentally measured thickness profiles. Also, the effects of non-isothermal heating and elastic versus elastic-plastic material behavior were studied and a part was optimized using the simulation.
Wood flour (WF) and talc-filled polylactic acid (PLA) composites are prepared by melt compounding and injection molding. The effects of filler loading and silane treatment, the thermal and mechanical properties of the composites are studied. Loading of WF and WF/talc mixture into neat PLA results in a small decrease in the glass transition and crystalline temperatures of the composites. The use of WF, talc and silane in the composites causes successively larger decreased in the composite crystallinity. The addition of talc and silane to PLA/WF composites improved the tensile modulus. The tensile strength of the composites decreases slightly with the addition of talc, but it considerably improves with the use of 1 wt% silane. Morphological analysis shows improved interfacial bonding with silane treatment for the composites.
In this paper, several starch/polyvinyl alcohol (PVA)/nano-silicon dioxide (nano-SiO2) biodegradable blend films were prepared by a solution casting method. The physical and biodegradable properties of this film were also studied. From the results, SPS5 was found to have the best tensile strength at about 15.0MPa, and its elongation at break was 120%. With the increase in nano-SiO2 content, the water resistance of the films was also improved. Additionally, SPS5 had the best optical transparence in all of the films. The soil burial test showed that the addition of nano-SiO2 has no significant influence to the biodegradability of the films. Moreover, the results indicated that an intermolecular hydrogen bond and a chemical bond COSi were formed in the nano-SiO2 and starch/PVA. Therefore, the miscibility and compatibility between starch and PVA were increased, and the physical properties of the additional nano-SiO2 were improved.
Forward recoil spectrometry was used to obtain the tracer (D*) and mutual (D̃) diffusion coefficients in a miscible polymer blend of poly(methyl methacrylate) (PMMA, Tg=136°C) and poly(styrene-co-acrylonitrile) with ∼23 wt% acrylonitrile content (SAN, Tg=112°C). For blends with SAN weight fraction w of 0.2 and 0.5, the temperature dependence of D* for both species was nearly identical. Tracer diffusion coefficients D*PMMA and D*SAN were determined for matrices consisting of 176 000 molecular weight SAN (w=0.5) and various molecular weights of PMMA ranging from 27 000 to 840 000. The results were consistent with those expected from the mechanisms of reptation and constraint release. Analysis of the tracer diffusion coefficients D* showed that SAN has a monomer friction coefficient, ζ0,PMMA, about five times smaller than that of PMMA (ζ0,PMMA) in a matrix of pure PMMA, but the difference decreased monotonically as w increased, so that the ζ0 values were nearly equal when w=1. Corresponding to this relative change in ζ0, the glass transition process is broad for PMMA-rich blends and narrow for SAN-rich ones, raising the possibility that the difference in ζ0 in the PMMA-rich blends is due to the existence of two local glass transitions, one for each species in the blend. For blends at the composition of w=0.5, the D̃ was measured as a function of PMMA molecular weight. The data followed closely the predictions of the fast theory, the result expected if D̃ is ultimately controlled by the diffusion of the faster moving species. From the measurements of D̃ and D* at 187°C, the composition dependence of the Flory interaction parameter was also obtained, which showed good agreement with the recent small angle neutron scattering results by Hahn et al.
The successful manufacture of natural fiber reinforeced thermoplastic composites is complicated by the hygroscopic and hydrophylic nature of cellulosic fillers, as well as by their limited thermal stability at typical melt processing temperaures. This study examines the processability and properties for several wood flour (WF)-polypropylene (PP) composites. Other studies on natural fiber reinforced thermoplastics have concentrated on the properties of these composites rather than on their processability, as such, relatively more is known about the hydrophylic consequences of cellulosic fillers relative to the hygroscopic consequences. A focus of this study was to carefully evaluate the positive and negative implications of absorbed moisture (within the WF) on the mechnical and rheological behavior of such composites. Filler-matrix dry blends of 45wt% WF-PP and 55wt% WF-PP were compounded/pelletized on a 38 mm single screw extruder. The pelletized feedstock was subsequently melt-processed on a 667 kN/108 cm3 injection molding machine (into a standard tesile bar mold) and on a 19 mm single screw extruder (therough a capillary die). The results from an analysis of process monitoring and material property data were then used to identify the impact of absorbed moisture on the processability and performance of cellulosic/thermoplastic composites.
In the preparation of polymer/clay nanocomposites, organoclay plays an important role in lipophilizing and dispersing the clay into less polar polymer matrixes. Organic modifiers of various chain lengths were examined in different types of clays, smectite, montmorillonite (MMT), and mica, to prepare their corresponding organoclays. The layered structure and gallery spacing of organoclays and polylactide (PLA) nanocomposites shows that, with a modifier of the same chain length, the gallery spacing of the organoclay was largest for mica and smallest for smectite because of the higher ion-exchange capacity of mica and physical jamming of the modifier due to a restricted conformation at the core part of the clay of larger size. The increment of the modulus in a smectite nanocomposite, compared to that of PLA, is higher than MMT or mica nanocomposite due to better dispersion in a smectite system for the same clay loading. Being a well-dispersed system, smectite nanocomposites have better gas barrier properties than the MMT or mica systems, which are larger in size but stacked in nature in their nanocomposites. A new idea for obtaining porous ceramic material from layered silicate/polymer nanocomposites by burning is unveiled using various clays and the mechanism of their formation is elucidated.
Organophilic montmorillonite was obtained by the reaction of montmorillonite (MON) and distearyldimethylammonium chloride (DSAC). The modified clay and poly(l-lactide), (PLLA), were solvent-cast blended using chloroform as cosolvent. The structure and properties of the PLLA-clay blends were investigated. Thermal measurements revealed that cold crystallization took place in the as-cast PLLA, and that the clay served as a nucleating agent. From small and wide-angle x-ray scattering measurements, it was found that silicate layers forming the clay could not be individually well dispersed in the PLLA-clay blends prepared by the solvent-cast method. In other words, the clay existed in the form of tactoids, which consist of several stacked silicate monolayers. However, these tactoids formed a remarkable geometrical structure in the blend films. That is, their surfaces lay almost parallel to the film surface, and were stacked with the insertion of PLLA crystalline lamellae in the thickness direction of the film. During the blend drawing process, fibrillation took place with the formation of plane-like voids developed on the plane parallel to the film surface. Furthermore, delamination of the silicate layers did not occur even under the application of a shearing force. Finally, Young's modulus of the blend increased with the addition of a small amount of the clay. © 1997 John Wiley & Sons, Inc.
The addition of organic fillers into thermoplastic polymers is an interesting issue, which has had growing consideration and experimentation during the last years. It can give rise to several advantages. First, the cost of these fillers is usually very low. Also, the organic fillers are biodegradable (thus contributing to an improved environmental impact), and finally, some mechanical and thermomechanical properties can be enhanced. In this study, the effect of the addition of different organic fillers on the mechanical properties and processability of an extrusion-grade polypropylene were investigated. The organic fillers came from natural sources (wood, kenaf, and sago) and were compared to short glass fibers, a widely used inorganic filler. The organic fillers caused enhancements in the rigidity and thermomechanical resistance of the matrix in a way that was rather similar to the one observed for the inorganic filler. A reduction in impact strength was observed for both types of fillers. The use of an adhesion promoter could improve their behavior. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1906–1913, 2005
The application of microwave heating for the separation of stabilizers from polypropylene and polyethylene was studied. Additives examined were the antioxidants IRGANOX 1010 and IGRAFOS 168 and the light stabilizer CHIMASSORB 81. The polymer samples were kept in sealed vessels and irradiated in a laboratory microwave oven. Fairly quantitative (>90% of the expected content) extraction of the stabilizers from powered polymer was achieved within 3 to 6 minutes using 1, 1, 1 -trichloroethane or the 1:1 mixture of acetone and n-heptane as the extracting solvent.Die Abtrennung von Stabilisatoren aus Polypropylen und Polyethylen mit Hilfe des Mikrowellenheizens wurde untersucht. Die untersuchten Additive waren die Antioxidantien IRGANOX 1010 und IRGAFOS 168 und das Lichtschutzmittel CHIMASSORB 81. Die Polymerproben wurden in Geschlossenen Geflen in einem Laboratoriumsmikrowellenherd bestrahlt. Eine nahezu quantitative Extraktion (>90% des erwarteten Gehalts) der Stabilisatoren aus dem gepulverten Polymer wurde innerhalb von 3 – 6 min mit 1,1,1-Trichlorethan oder einer 1:1-Mischung aus Aceton und n-Heptan erzielt.
Addition of organic fillers to post-consumer recycled plastics can give rise to several advantages. First of all, the cost of these fillers is usually very low, the organic fillers are biodegradable contributing to an improved environmental impact and, last but not least, some mechanical and thermomechanical properties can be enhanced. Organic fillers are not widely used in the plastic industry although their use is increasing. Bad dispersion into the polymer matrix at high-level content and poor adhesion with the matrix are the more important obstacles to this approach. In this work various organic fillers have been used with a post-consumer plastic material originating from films for greenhouses. The properties of these green composites have been compared with those of materials filled with a conventional inorganic filler. The organic fillers cause slightly worse processability, due to an increase of viscosity, an enhancement of the rigidity and of the thermomechanical resistance similar to that measured for the inorganic filler, while a reduction of the impact strength is observed. Copyright © 2004 Society of Chemical Industry
This article presents study of melt rheological properties of composites of polypropylene (i-PP) filled with wood flour (WF), at filler concentrations of 3–20 wt%. Results illustrate the effects of (i) filler concentration and (ii) shear stress or shear rates on melt viscosity and melt elasticity properties of the composites. Incorporation of WF into i-PP results in an increase of its melt viscosity and a decrease of melt elasticity such as die swell and first normal stress differences; these properties, however, depend on filler concentration. Processing temperature of the filled i-PP increases as compared to the nonfilled polymer.
This study describes the design and synthesis of bacterial cellulose/hydroxyapatite nanocomposites for bone healing applications using a biomimetic approach. Bacterial cellulose (BC) with various surface morphologies (pellicles and tubes) was negatively charged by the adsorption of carboxymethyl cellulose (CMC) to initiate nucleation of calcium-deficient hydroxyapatite (cdHAp). The cdHAp was grown in vitro via dynamic simulated body fluid (SBF) treatments over a one week period. Characterization of the mineralized samples was done with X-ray Photoelectron Spectroscopy (XPS) and Field Emission Scanning Electron Microscopy (FESEM) with Energy Dispersive Spectroscopy (EDS). The amount of cdHAp observed varied among different samples. XPS demonstrated that the atomic presence of calcium and phosphorus ranged from 0.44 at.% to 7.71 at.% Ca and 0.27 at.% to 11.18 at.% P. The Ca/P overall ratio ranged from 1.22 to 1.92. FESEM images showed that the cdHAp crystal size increased with increasing nanocellulose fibril density. To determine the viability of the scaffolds in vitro, the morphology and differentiation of osteoprogenitor cells was analyzed using fluorescence microscopy and alkaline phosphatase gene expression. The presence of cdHAp crystals on BC surfaces resulted in increased cell attachment.
This communication focuses to unveil the molten behaviour of biodegradable polyvinyl alcohol (PVOH) blending with native cassava starch (CSS). Different percentages of CSS were blended with glycerol plasticized PVOH (PPV) to study the shear rate–viscosity at 190 °C and the thermal transition state at 200 bar (20.265 MPa). The outcomes showed that the viscosities of PPV–CSS compounds reduced as the PPV composition increased. This indicates that the addition of PPV helps to improve the processability of thermoplastic starch compound. On the other hand, a higher percentage of CSS would disrupt the transition of specific volumes at the molten stage (160–180 °C) of PPV–CSS compounds. The transition was lowered due to the loss of crystallinity in PPV. It is postulated that injection moulding of PPV–CSS blends has lower volume shrinkage than PPV due to lower thermal transition and crystallinity of the compounds.
This letter describes the preparation and characterization of a novel porous ceramic material via the burning of the polylactide/layered silicate nanocomposite. WAXD patterns indicate that an amorphous structure was developed in the porous ceramic material after sintering the nanocomposite. SEM observation revealed a morphology in which individual silicate layers stacked together to form platelet structure and produce house of cards structure porous ceramic material. The stress−strain curve of the porous ceramic material shows elastic-like property in the elastic region (e8% strain) under compression test.
This review aims at highlighting on recent developments in preparation, characterization, properties, crystallization behaviors, melt rheology, processing, and future applications possibilities of biodegradable polymers and their layered silicate nanocomposites. These materials are attracting considerable interest in materials science research. Montmorillonite and hectorite are among the most commonly used smectite-type layered silicates for the preparation of nanocomposites. In their pristine form they are hydrophilic in nature, and this property makes them very difficult to disperse into biodegradable polymer matrices. The most common strategy to overcome this difficulty is to replace the interlayer clay cations with quarternized ammonium or phosphonium cations, preferably with long alkyl chains. A wide range of biodegradable polymer matrices is described in this review with a special emphasis on polylactide because of more eco-friendliness from its origin as contrast to the fully petroleum-based biodegradable polymers and control of carbon dioxide balance after their composting. Preparative techniques include (i) intercalation of polymers or prepolymers from solution, (ii) in situ intercalative polymerization method, and (iii) melt intercalation method. This new family of composite materials frequently exhibits remarkable improvements of mechanical and material properties when compared with virgin polymers or conventional micro- and macro-composites. Improvements can include a high storage modulus both in solid and molten states, increased tensile and flexural properties, a decrease in gas permeability and flammability, increased heat distortion temperature and thermal stability, increase in the biodegradation rate, and so forth.
This letter describes the preparation, characterization, material properties, and biodegradability of polylactide (PLA)-layered silicate nanocomposite. Montmorillonite modified with trimethyl octadecylammonium cation was used as an organically modified layered silicate (OMLS) for the nanocomposite preparation. WAXD and TEM analyses respectively confirmed that silicate layers of the montmorillonite were intercalated and nicely distributed in the PLA-matrix. The material properties of neat PLA improved remarkably after nancomposite preparation. The biodegradability of the neat PLA and corresponding nanocomposite was studied under compost, and the rate of biodegradation of neat PLA increased significantly after nanocomposite preparation.
The use of natural organic fillers in addition to postconsumer recycled polymers is getting a growing interest during the last years; this is due to many advantages they can provide in terms of cost, aesthetic properties, environmental impact. In this work, several types of wood flour (differing each other with regard to production source and particle size) were added to a recycled polyethylene coming from films for greenhouses and the effects of filler type, content, and size were investigated. Investigation was then focused on the improvement of mechanical properties, through the addition of polar copolymers (ethylene-co-acrylic acid, ethylene-vinyl acetate) and a maleic anhydride-grafted-grafted polyethylene (Licocene® PE MA 4351 TP), in order to try to overcome the poor adhesion between polar filler particles and nonpolar polymer chains. Investigation was also based on SEM micrographs. An overall positive influence of these additives was observed. Polym. Eng. Sci. 46:1131–1139, 2006. © 2006 Society of Plastics Engineers.
Nanocomposites of starch were prepared via different addition sequences of plasticizer and clay by the solution method. The extent of dispersion of the filler was evaluated by wide angle X-ray diffractometry (WAXD) in the resulting composites. Thermal stability, mechanical properties and water absorption studies were conducted to measure the material properties whereas FT-IR spectroscopy was used to study the microdomain structure of composites. The sequence of addition of components (starch /plasticizer (glycerol) / clay) had a significant effect on the nature of composites formed and accordingly properties were altered. Glycerol and starch both have the tendency to penetrate into the silicate layers but penetration of glycerol is favored owing to its smaller molecule size. The filler dispersion becomes highly heterogeneous and the product becomes more brittle when starch was plasticized before filling with clay due to the formation of a bulky structure resulting from electrostatic attractions between starch and plasticizer. It was concluded that best mechanical properties can be obtained if plasticizer is added after mixing of clay in the starch matrix.
Natural cellulose fibers with cellulose content, strength, and elongation higher than that of milkweed floss and between that of cotton and linen have been obtained from the stems of common milkweed plants. Although milkweed floss is a unique natural cellulose fiber with low density, the short length and low elongation make milkweed floss unsuitable as a textile fiber. The possibility of using the stems of milkweed plant as a source for natural cellulose fibers was explored in this research. Natural cellulose fibers extracted from milkweed stems have been characterized for their composition, structure, and properties. Fibers obtained from milkweed stems have about 75% cellulose, higher than the cellulose in milkweed floss but lower than that in cotton and linen. Milkweed stem fibers have low % crystallinity when compared with cotton and linen but the strength of the fibers is similar to cotton and elongation is higher than that of linen fibers. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers
Sustainability, industrial ecology, eco-efficiency, and green chemistry are guiding the development of the next generation of materials, products, and processes. Biodegradable plastics and bio-based polymer products based on annually renewable agricultural and biomass feedstock can form the basis for a portfolio of sustainable, eco-efficient products that can compete and capture markets currently dominated by products based exclusively on petroleum feedstock. Natural/Biofiber composites (Bio-Composites) are emerging as a viable alternative to glass fiber reinforced composites especially in automotive and building product applications. The combination of biofibers such as kenaf, hemp, flax, jute, henequen, pineapple leaf fiber, and sisal with polymer matrices from both nonrenewable and renewable resources to produce composite materials that are competitive with synthetic composites requires special attention, i.e., biofiber–matrix interface and novel processing. Natural fiber–reinforced polypropylene composites have attained commercial attraction in automotive industries. Natural fiber—polypropylene or natural fiber—polyester composites are not sufficiently eco-friendly because of the petroleum-based source and the nonbiodegradable nature of the polymer matrix. Using natural fibers with polymers based on renewable resources will allow many environmental issues to be solved. By embedding biofibers with renewable resource–based biopolymers such as cellulosic plastics; polylactides; starch plastics; polyhydroxyalkanoates (bacterial polyesters); and soy-based plastics, the so-called green bio-composites are continuously being developed.
This paper reviews the thermal processing of starch-based polymers, including both fundamental science such as microstructure, phase transition and rheology, as well as processing techniques, conditions and formulations. The unique microstructure of starch and its multiphase transitions during thermal processing provide an outstanding model system to illustrate our conceptual approach to understanding the structure–processing–property relationships in polymers. One of the unique characteristics of starch-based polymers is their thermal processing properties, which are much more complex than conventional polymers, since multiple chemical and physical reactions may occur during processing, such as water diffusion, granular expansion, gelatinization, decomposition, melting and crystallization. Among these phase transitions, gelatinization is particularly important because it is closely related to the others, and it is the basis of the conversion of starch to a thermoplastic. Furthermore, the decomposition temperature of starch is higher than its melting temperature before gelatinization. Various conventional processing techniques such as extrusion, injection compression molding, and casting, as well as some new techniques such as reactive extrusion, have been adapted for processing starch-based polymers. The achievements in this area have increased our knowledge of polymer science, in particular that of natural polymers.
In this work we have studied the utilization of kaolin as filler reinforcement for thermoplastic starch in order to improve its mechanical properties. The composites were prepared with regular cornstarch plasticized with glycerin and reinforced with hydrated kaolin. All the components were pre-mixed and processed in an intensive batch mixer at 170°C. Compounds with 0, 10, 20, 30, 40, 50 and 60 phr — parts of kaolin per hundred parts of thermoplastized starch — were prepared. The mechanical tests were performed from dumb-bell shaped specimens conditioned in ambient for 14 days. The material were also evaluated by DSC, TGA analysis and water sorption experiments. The composite filled with 50 phr kaolin showed an increase in the tensile strength from 5 to 7.5 MPa. The modulus of elasticity increased from 120 to 290 MPa and the tensile strain at break decreased from 30 to 14%. Scanning Electron Microscope of fractured surface revealed the occurrence of strong bonding between kaolin and the matrix. Besides the good mechanical properties, the utilization of these clays leads to an increase in the water resistance of thermoplastic starch compounds also.
Plastic lumber is being used to replace wooden lumber in some construction applications, especially in outdoor applications where the plastic lumber is presumed to weather better than the wood. However, the structural properties of the plastic lumber are not well understood, and the use of plastic lumber in structural applications is not authorized in the common building codes. In this research effort, standard 2×6 plastic lumber planks were tested for many different structural properties. The plastic lumber tested was a blend of recycled plastic and sawdust. The tests were conducted at −23.3°C to simulate winter conditions, and at 40.6°C to simulate summer conditions. In all cases the high temperature strength and stiffness was lower than at low temperature, so the high temperature values would determine the allowable strength and stiffness for design. The high temperature modulus of the plastic lumber was 5.79, 1.03, and 1.12 GPa in compression, flexure and tension respectively. High temperature strength values were 16.8, 12.0, and 1.45 MPa in compression, flexure and tension respectively. The high temperature shear strength of the plastic lumber was 5.31 MPa. Strength tests were also performed for nail and screw connections typically used with lumber, and the pull-out and lateral load were comparable to wooden lumber. The plastic lumber performed well under sustained load tests at high temperature. Slip resistance tests were performed, and it was found that the plastic lumber is more slippery than wooden lumber, but probably does not represent a safety hazard. The conclusion was that the plastic lumber is a good structural material, but it is not appropriate to simply substitute plastic lumber for wooden lumber pieces of the same dimension in structural applications. Plastic lumber structures must be designed using the structural properties of the plastic lumber.
Our study was to clarify the intercalation of polymer chains to organoclays and to improve the thermo-mechanical properties. Two organoclays were synthesized. One was a montmorillonite modified with hexadecylamine (C16-MMT); the other was a fluorinated-mica modified with hexadecylamine (C16-Mica). Dispersions of organoclays with poly(lactic acid) (PLA) were by using the solution intercalation method at different organoclay contents to produce nano-scale composites. The maximum ultimate tensile strength was observed for blends containing 4 wt% of either of the two organoclays and decreased with further increases in the organoclay content. The initial modulus increased with increasing organoclay content up to 4 wt% for C16-MMT. When the C16-MMT content was greater than this critical wt%, the modulus of the hybrids started to decrease. In contrast, the initial modulus of the hybrids using C16-Mica increased continually with increasing clay content from 2 to 8 wt%. The tensile properties of the C16-Mica hybrids were higher than those of the hybrids containing C16-MMT. The optical translucency was not affected by the organoclay content up to 6 wt%; however, the films containing 8 wt% organoclays were slightly more cloudy.
An investigation is described in which the morphology of hemp stem was examined by optical and scanning electron microscopy. We reported the results concerning steam-explosion treatment either on bast fibers impregnated with alkaline liquor or on woody hemp chènevotte samples impregnated under neutral, acidic and alkaline conditions. The influence of steam-explosion treatment parameters were followed by optic and scanning electron microscopy, chemical composition and evolution of the average (DPv) values of the purified samples. Hemp bast fibers purified by steam treatment were compounded with polypropylene (PP), either directly or after surface treatment with polypropylene-maleic anhydride co-polymer (PPMA). Polypropylene/hemp fibers composite films with various amount of fibers were prepared and their mechanical properties were improved, in particular when fibers treated with PPMA were used.
In this study binary and ternary blends of polylactide (PLA), polycaprolactone (PCL) and thermoplastic starch (TPS) are prepared using a one-step extrusion process and the morphology, rheology and physical properties are examined. The morphology and quantitative image analysis of the 50/50 PLA/TPS blend transverse phase size demonstrate a bimodal distribution and the addition of PCL to form a ternary blend results in a substantial number of fine dispersed particles present in the system. Focused ion beam irradiation, followed by atomic force microscopy (AFM) shows that dispersed PCL forms particles with a size of 370 nm in PLA. The TPS phase in the ternary blends shows some low level coalescence after a subsequent shaping operation. Dynamic mechanical analysis indicates that the temperature of the tan δ peak for the PLA is independent of TPS blend composition and that the addition of PCL in the ternary blend has little influence on the blend transitions. Both the α and β transitions for the thermoplastic starch are highly sensitive to glycerol content. When TPS of high glycerol content is blended with PLA, an increase in the ductility of the samples is achieved and this effect increases with increasing volume fraction of TPS. The ternary blend results in an even greater ductility with an elongation at break of 55% as compared to 5% for the pure PLA. A substantial increase in the notched Izod impact energy is also observed with some blends demonstrating three times the impact energy of pure PLA. The mechanical properties for the ternary blend clearly indicate a synergistic effect that exceeds the results obtained for any of the binary pairs. Overall, the ternary blend approach with PLA/TPS/PCL is an interesting technique to expand the property range of PLA materials.
Steady state flow of wood/high density polyethylene (HDPE) composites was studied using capillary rheometry to approach a fundamental understanding of the rheology of wood–polymer composite melts. Mooney slip analysis was applied to examine the nature of shear flow, indicating that the flow of wood/HDPE melts consist of contributions from both wall slip and viscous flow. Both simple viscous flow and yield stress behavior were observed, depending on wood species and content. It was observed that the dependence of wall slip velocity on shear stress in maple (Acer spp.) formulations resembles that of neat HDPE. In pine (Pinus spp.) formulations, however, wall slip rate is influenced by wood content. A converging flow technique was used to study the extensional flow. In contrast to shear flow properties, the extensional viscosity was found to depend much less on wood species. The effects of both wood content and species were observed through Trouton ratio. Strong inter-particle interaction was recorded for some filled melts as yield stress in shear flow and apparent strain hardening in extensional flow.
Copyright: 2008 Elsevier Ltd This review deals with a recent study of the literature on the various aspects of cellulosic fibres and biocomposites. Cellulosic fibre reinforced polymeric composites are finding applications in many fields ranging from construction industry to automotive industry. The pros and cons of using these fibres are enumerated in this review. The classification of composites into green composites, hybrid biocomposites and textile biocomposites are discussed. New developments dealing with cellulose based nanocomposites and electrospinning of nanofibres have also been presented. Recent studies pertaining to the above topics have also been cited. Finally, the applications of cellulosic fibre reinforced polymeric composites have been highlighted