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ORIGINAL PAPER
Eco-friendly cellulose acetate butyrate/poly(butylene succinate)
blends: crystallization, miscibility, thermostability, rheological
and mechanical properties
Xinhang Wang
1
&Shuohan Huang
1
&Yanping Wang
1
&Peng Wei
1
&Yuwei Chen
2
&
Yumin Xi a
1
&Yimin Wang
1
Received: 19 September 2016 / Accepted: 7 December 2016 /Published online: 4 January 2017
#Springer Science+Business Media Dordrecht 2017
Abstract In this work, the crystallization, miscibility, ther-
mostability, rheological and mechanical properties of cellu-
lose acetate butyrate (CAB)/poly(butylene succinate) (PBS)
blends were investigated in detail. Differential scanning calo-
rimetry analysis confirmed that PBS could form crystalline
phase in the solution casted CAB/PBS blends with
W
CAB
≤60 wt.%. When the blends were crystallized from
melt, the crystallization of PBS was found to be severely sup-
pressed by the amorphous diluent of CAB. CAB and PBS
were confirmed to be thermodynamic miscible in molten state
by the negative value of Flory-Huggins interaction parameter
(χ
12
=−0.89) between CAB and PBS. The rheological char-
acterization results and thermogravimetric analysis revealed
that the melt viscosity and thermostability of CAB were re-
duced and improved by blending CAB with PBS, respective-
ly. Moreover, the rigid CAB became more flexible after incor-
porating with ductile PBS. The application of CAB is expect-
ed to be extended via blending the two species of eco-friendly
polymers.
Keywords Cellulose acetate butyrate .Poly(butylene
succinate) .Polymer blends .Crystallization behaviors .
Miscibility .Rheological properties .Thermostability
Introduction
The large scale use of fossil-based polymer products in our
daily life has exerted a severe impact on the environment
because the majority of them are not degradable in a natural
environment. Cellulose esters are derived from the renewable
and sustainable cellulose which is considered as the most
abundant and almost inexhaustible biomass material in nature
[1]. In addition to the excellent optical clarity, high tensile
strength, modulus and moisture transmission, cellulose esters
also possess potentially biodegradable characteristic [2–4]. As
an important commercial cellulose derivative product, cellu-
lose acetate butyrate (CAB) has been used as coating mate-
rials, optical films, filtration membranes, controlled release
materials and plastics [7]. However, the rigid rod nature of
the cellulose backbone offers CAB relative stiffness and in-
elasticity which restricts its development in applications
where stretching and elastic resilience are required.
Moreover, CAB still suffers high melt viscosity and poor ther-
mostability caused by the relative lability of the polysaccha-
ride backbone at high temperature. This supplies CAB a nar-
row thermal processing window between melt flow and de-
composition temperature [5–7]. A convenient method that
blending CAB with other polymers such as poly(ε-
caprolactone) [8], poly(propylene carbonate) [9], poly(lactide)
[10], polyestercarbonate [11] and poly(3-hydroxybutyrate-co-
3-hydroxyvalerate) [12] was employed to improve its me-
chanical properties and melt processability.
Poly(butylene succinate) (PBS) is a commercially available
biodegradable thermoplastic polyester synthesized via the
Electronic supplementary material The online version of this article
(doi:10.1007/s10965-016-1165-4) contains supplementary material,
which is available to authorized users.
*Yu m i n Xi a
xym@dhu.edu.cn
*Yimin Wan g
2389721529@qq.com
1
State Key Laboratory for Modification of Chemical Fibers and
Polymer Materials, College of Materials Science and Engineering,
Donghua University, Shanghai 201620, China
2
Key Laboratory of Rubber-Plastics, Ministry of Education/Shandong
Provincial Key Laboratory of Rubber-Plastics, Qingdao University
of Science & Technology, Qingdao 266042, China
J Polym Res (2017) 24: 16
DOI 10.1007/s10965-016-1165-4
polycondensation reaction of 1,4-butanediol and succinic acid
[13]. The biotechnological breakthrough in commercial pro-
duction of the succinic acid from biomass resources makes
PBS more eco-friendly [14]. Besides the outstanding biode-
gradability, PBS also possesses the superior flexibility and
excellent thermoplastic processability [15,16]. Therefore,
among the degradable polymers developed so far, PBS is ex-
pected to be the ideal candidate for blending with CAB in term
of decreasing its melt viscosity as well as increasing its
flexibility.
In general, it is of great significance to study the crystalli-
zation and miscibility of crystalline/amorphous polymer
blends because these factors could greatly affect the material
performances. Tatsushima et al. [17] obtained CAB/PBS
blend films through solution casting from chloroform solu-
tions. The composition dependences of miscibility and phase
structure of the blend films at solid state were determined. The
blends were considered to be highly miscible in an amorphous
state when PBS content ranging from 0 to 30 wt.%.
Interestingly, the mechanical performances of PBS can be
drastically changed through thermal compounding with
10 wt.% CAB due to the change in crystalline state of PBS
[18]. However, the crystallization behaviors when crystallized
form melt, the miscibility in the molten state, melt viscosity,
thermal stability and the mechanical properties of the specific
CAB/PBS blends are not well known based on previous stud-
ies. To further understand this promising biodegradable CAB/
PBS blend material, the current work affords a detailed inves-
tigation on the crystallization behaviors and miscibility of
CAB/PBS blends with the entire composition. Meanwhile,
rheological properties, thermal stability and mechanical prop-
erties of the blends were also examined in view of actual
applications.
Experimental
Materials and sample preparation
CAB (37 wt.% of butyryl, 13.5 wt.% of acetyl and 1.8 wt.% of
hydroxyl, M
n
=70000gmol
−1
) was purchased from Eastman
Co., Ltd. (USA). PBS (Bionolle
™
1001MD) was supplied by
Showa High-Polymer Co., Ltd. Chloroform (AR grade) was
purchased from Sinopharm Chemical Reagent Co., Ltd.
Cast films of pure CAB, pure PBS and CAB/PBS blends
with 10, 20, 30, 40, 50, 60, 70, 80 and 90 wt.% of CAB were
prepared by dissolving prescribed amount of CAB and PBS
(5 g in total) in hot chloroform (100 ml) at 60 °C. The solution
of both polymers (0.05 g/ml) was cast on a petri dish at room
temperature. The solvent was allowed to evaporate in a con-
trolled air stream for 1 day and the resulting films were further
dried under vacuum at 80 °C for 2 days. The CAB/PBS melt
blends with 10 and 20 wt.% of PBS were prepared on a twin-
screw DSM micro-compounder at 220 °C and 80 rpm for
5 min under dried nitrogen flow.
Characterizations
Differential scanning calorimetry (DSC) measurements were
conducted using a TA-Q20 calorimeter under nitrogen atmo-
sphere. The solution casted films were first heated from −60 to
190 °C and maintained there for 2 min (first scan), then sub-
sequently cooled down to −60 °C, followed by the second
heating to 190 °C (second scan). Both the heating and cooling
rate were 10 °C min
−1
.
Isothermal crystallization of CAB/PBS blends was also
investigated by DSC. Only pure PBS and the blends with
the weight fraction of CAB equal to or less than 20% were
studied because PBS crystallized extremely slowly or did not
crystallize when CAB content was above 20 wt.%. The sam-
ples were annealed at 190 °C for 2 min, then quenched to the
pre-set temperature (T
c
) and held at T
c
until the crystallization
completed. After that, the samples were scanned to 140 °C at
20 °C min
−1
to evaluate the melting behavior.
Spherulitic morphology of CAB/PBS blends was observed
by polarized optical microscopy (POM) (Olympus BX51).
The samples were first annealed at 190 °C for 2 min to erase
any thermal history and then cooled to the setting temperature
at 40 °C min
−1
.
Capillary rheological properties of the CAB/PBS melt
blends were investigated with a capillary rheometer
(Rosand, RH2000) using a die with a 0.5 mm diameter and
L/D = 16 at 220 °C. The melt flow index (MFI) was measured
according to the ASTM D-1238 using a Zwick 4100 equip-
ment under 2.16 kg weight at the temperature of 220 °C.
Thermogravimetric analysis (TGA) (Netzsch 209 F1) was
conducted from 50 to 600 °C with the heating rate of
20 °C/min under air atmosphere.
Tensile tests were performed on an electronic universal
material testing machine (INSTRON 5969) at 25 °C
with gauge length of 30 mm and crosshead speed of
20 mm min
−1
. The data provided is the average values based
on 10 replicates.
Results and discussion
Melting and crystallization behavior
Figure 1presents the DSC thermograms taken in the first
heating process of the solution casted CAB/PBS blends with
various compositions. It is clearly shown that pure PBS is a
crystalline polymer with a melting temperature of 115 °C
while pure CAB is an amorphous polymer. No melting peak
was detected for the blends with W
CAB
≥0.7 (Hereafter, the
blend composition is denoted by weight fraction of CAB,
16 Page 2 of 9 J Polym Res (2017) 24: 16
W
CAB
, too), indicating that PBS component in the blends does
not crystallize if incorporating a large proportion of CAB,
which leads to the transformation of the solution casted blends
from a crystalline state at W
CAB
< 0.7 into an amorphous state
at W
CAB
≥0.7.
The crystallization behavior of the crystallizable compo-
nent was usually influenced by the second amorphous com-
ponent in miscible blends [19–21]. In order to gain insight
regarding the crystallization behavior and miscibility, the
CAB/PBS blends were subjected to the second DSC heating
scan after cooling from their molten state. As shown in
Fig. 2b, DSC thermograms in the second heating scan are
totally different with that in the first heating scan. The melting
endothermic peak can be seen only for the blends with
W
CAB
≤0.3 and shifts toward a lower temperature with the
increase of W
CAB
. For the blends with W
CAB
≥0.4, crystalli-
zation of PBS is simply prevented. Moreover, cold crystalli-
zation occurs in the blends with W
CAB
=0.2and0.3.Thiscan
be fully understood if one considers the different crystalliza-
tion kinetics of PBS in the CAB/PBS blends with different
composition. As shown in Fig. 2a, pure PBS crystallized rap-
idly during the cooling process and thus enough crystalliza-
tion could be achieved under the experimental condition
employed (cooling from melt at 10 °C min
−1
). Therefore,
there was no necessity to undergo the secondary crystalliza-
tion during the subsequent heating scan. Similarly, when in-
corporating with 10 wt.%CAB, PBS still underwent sufficient
crystallization in spite of the reduction in crystallization rate.
However, once W
CAB
was increased further, the blends either
did not undergo sufficient crystallization (e.g. W
CAB
=0.2)or
just did not have time to crystallize (e.g. W
CAB
=0.3) during
the DSC cooling scan because of the remarkable decline of
crystallization rate. Hence they underwent the cold crystalli-
zation in the second heating scan. The blends with W
CAB
≥0.4
were unable to crystallize under the experimental condition,
either because of their extremely slow crystallization rate, or
due to the lost ability of crystallization induced by the exces-
sive amorphous CAB diluent. It is worth noting that a well-
defined double melting peak can be identified for the blend
with W
CAB
=0.1 (see Fig. 2b), indicating that a melt-
recrystallization process occurred during the DSC second
heatingscanforthisblend[22,23](seeSupporting
Information).
Figure 3shows the melting behavior of CAB/PBS blends
crystallized from melt at 60 °C for 14 days. It is clear that the
blends with W
CAB
≤0.5 could form PBS crystals when iso-
thermally crystallized at 60 °C for quite a long time. It must be
noted that the blends with W
CAB
= 0.4 and 0.5 exhibit melting
endotherms but no crystallization or melting occurs in the
same blends during the DSC measurement as shown in
Fig. 2. This phenomenon indeed illustrates the quite low crys-
tallization rate of PBS in the CAB/PBS blends comprising
higher W
CAB
.
Based on above observations, it is reasonable to conclude a
greater inhibition on crystallization of PBS with increasing
W
CAB
. The severe suppression of crystallization can be pre-
dominantly ascribed to the restricted mobility of PBS
Fig. 1 DSC thermograms in the first heating scan of the CAB/PBS
blends
Fig. 2 DSC thermograms ofthe CAB/PBS blends in (a) the cooling scan
and (b) the second heating scan
J Polym Res (2017) 24: 16 Page 3 of 9 16
macromolecules during crystallization caused by the homoge-
neously diffused CAB component which is considered as a
rather stiff and immobile amorphous diluent. It is believed that
the retarded crystallization also leads to crystalline imperfec-
tions of PBS crystals which are responsible for the melting
temperature depression (see Fig. 2b).
Spherulitic patterns and spherulite growth rate
Figure 4shows the spherulitic morphology of pure PBS
and its blends with CAB isothermally crystallized at var-
ious temperature under POM. It is seen that PBS in the
blends formed well–organized spherulites with periodical-
ly banded extinction rings and typical Maltese cross fea-
tures, while the irregular and coarse spherulites are ob-
served for pure PBS due to the much higher crystalliza-
tion temperature employed [24,25]. When the CAB/PBS
blends were molted in the hot stage of the POM, the melt
appeared to be homogeneous for all composition investi-
gated. However, with the dropping of temperature, liquid–
solid phase separation occurred in CAB/PBS blends dur-
ing the crystallization process of PBS. As observed in
Fig. 4, the spherulites ultimately impinged upon their
neighbors and no space left between adjacent spherulites,
suggesting that the CAB component was located in the
interlamellar and/or interfibrillar regions of PBS spheru-
lites during solidification of the blends. These behaviors
are common to crystalline/amorphous blends [25–27].
As depicted in Fig. 5, the PBS spherulite radius increases
linearly with time at 60 °C. The slope of the linear fitted lines
or the PBS spherulite growth rate was calculated to be 0.96,
0.09 and 0.01 μms
−1
for the blends with W
CAB
= 0.1, 0.2 and
0.3, respectively. Such drastic change of spherulite growth rate
implies that PBS crystallized from a mixed phase where the
macromolecules of CAB and PBS were intimately
intermingled. This as well reveals the good miscibility be-
tween CAB and PBS in the molten state because the spherulite
growth rate of the crystallizable polymer in the miscible bina-
ry blend is usually lowered by the second amorphous compo-
nent [28]. It is inferred that the dilution effect of non-
crystallizable CAB on PBS, the suppressed segmental mobil-
ity of PBS and the decreased undercooling induced by the
depression of melting temperature work together to lower
the crystallization rate of the CAB/PBS blends.
Fig. 4 Polarized optical micrographs of CAB/PBS blends after PBS
crystallized to saturation (Same magnification, scale bar = 50 μm)
Fig. 5 Spherulite radius as a function of time for CAB/PBS blends
isothermally crystallized at 60 °C
Fig. 3 Melting behavior of CAB/PBS blends isothermally crystallized
from melt at 60 °C for 14 days
16 Page 4 of 9 J Polym Res (2017) 24: 16
Equilibrium melting temperature and interaction
parameters
Analysis of the melting temperature of a crystalline polymer
blended with an amorphous polymer is an important way of
assessing the miscibility. However, the melting temperature of
a polymer is influenced not only by the thermodynamic factor
but also by the morphological factor. The equilibrium melting
point (T
m
°), which may be defined as the melting temperature
of perfect crystals with infinite large lamella, can separate the
morphological effect from the thermodynamic effect and thus
is frequently employed to estimate the miscibility of polymer
blends [20,27,29,30]. Hoffman and Weeks revealed a rela-
tionship between the apparent melting temperature T
m
and the
isothermal crystallization temperature T
c
:
Tm¼Tc
ηþ1−1
η
T
mð1Þ
Where ηis the ratio of the initial to final lamellar thickness.
T
m
° can be obtained from the intersection of this line with the
T
m
=T
c
equation.
The melting behavior of CAB/PBS blends was studied
using DSC after PBS crystallized to saturation at various T
c
.
As shown in Fig. 6, two melting endothermic peaks or one
main melting peak with one shoulder are observed regardless
of T
c
for the melting behavior of pure PBS and CAB/PBS
blends with W
CAB
= 0.05, 0.1 and 0.2.The lower melting peak
shifts to higher temperature range with the increase of T
c
,
while the higher one remains almost constant. Such melting
behavior can be ascribed to the recrystallization effect as men-
tioned above. Therefore, the lower melting temperature corre-
sponding to the melting of crystals formed during the isother-
mal crystallization process should be used for the analysis of
the Hoffman–Weeks equation. Figure 7gives the best-fit T
m
vs. T
c
lines for CAB/PBS blends, from which the T
m
°isesti-
mated to be 139.0, 138.4, 138.0 and 136.9 °C for the blends
with W
CAB
= 0, 0.05, 0.1 and 0.2, respectively. The downward
temperature shift of T
m
° of PBS with the addition of CAB
confirms that CAB is miscible with PBS in the molten state.
It is generally known that miscibility of polymer
blends is controlled by a thermodynamic process. To
evaluate the thermodynamic miscibility of CAB/PBS
blends, the Flory–Huggins interaction parameter (χ
12
)
was determined using the Nishi–Wang equation, based
on the Flory–Huggins theory
33
:
1
T
mb
−1
T
mp
¼−RV2
ΔHV1
lnϕ1
m2
þ1
m2
−1
m1ϕ1þχ12ϕ2
1
ð2Þ
Where the subscripts 1 and 2 represent the amorphous and
crystalline polymer, respectively. V
1
and V
2
are the molar
volumes of repeating units of the polymers. T°
mb
and T°
mp
refer to the equilibrium melting points of the blends and the
pure crystalline component, respectively. ΔH° is the enthalpy
of fusion of the perfectly crystallizable polymer. m is degree of
polymerization and ϕis the volume fraction of the component
in the blends. R is the universal gas constant. Considering m
1
and m
2
are large for high molecular weight polymers, related
terms in Eq. [2] vanish and thus Eq. [2] can be rewritten as
ΔHV1
RV2
1
T
mb
−1
T
mp
!
¼−χ12ϕ2
1ð3Þ
To calculate the left-hand side term of Eq. [3], several pa-
rameters are taken as follow: ΔH° = 19.0 kJ mol
−1
[31],
V
1
=267.0 cm
3
mol
−1
(the molar mass of repeating unit of
CABis320gmol
−1
and the density of CAB is 1.2 g cm
−3
),
V
2
= 145.9 cm
3
mol
−1
[32]. The plot of (ΔH°V
1
/RV
2
)
[(1/T°
mb
) - (1/T°
mp
)] vs. ϕ
2
is shown in Fig. 8.Theχ
12
was
calculated to be −0.89 from the slope of the straight line. The
negative value of the χ
12
for CAB/PBS blends further indi-
cates that the two components are thermodynamically misci-
ble in the molten state. The similar chemical structure of the
repeating units in PBS (−O(CH
2
)
4
OCO(CH
2
)
2
CO-) and the
butyryl groups (−OCO(CH
2
)
2
CH
3
) in CAB, as well as the
hydrogen bonding interaction between the residual OH groups
in CAB and C=O groups in PBS, are expected to be respon-
sible for the good miscibility of CAB/PBS blends.
Melt rheological properties
Figure 9a illustrates the dependence of melt apparent
shear viscosity (η
a
)onshearrare(γ)at220°Cforpure
CAB and CAB/PBS blends with W
CAB
=0.9 and 0.8. As
show in Fig. 9a, the melt apparent shear viscosity of CAB
and CAB/PBS blends melt declines with the increase of
shear rate, indicating that the CAB and CAB/PBS blends
melt are both pseudoplastic. It is worth noting that the
melt apparent shear viscosity of CAB/PBS blends is much
lower than that of pure CAB at low shear rate. For exam-
ple, the melt apparent shear viscosity for pure CAB, CAB/
PBS blends with W
CAB
= 0.9 and 0.8 at the shear rate of
100 s
−1
is 448, 399 and 292 Pa·s, respectively. This indi-
cates that PBS actually acts as the plasticizer for CAB and
higher amount of PBS causes higher degrees of plastici-
zation. The melt rheological properties of CAB and its
blends with PBS were also investigated by MFI at
220 °C. As shown in Fig. 9b, the MFI rapidly increases
from1.4g/10minforpureCABto3.8and6.8g/10min
for CAB/PBS blends with W
CAB
= 0.9 and 0.8, respec-
tively. This confirms again that the melt shear viscosity
of CAB can be reduced by mixing CAB with PBS.
Moreover, as shown in Fig. 9c,inalgη
a
-lgγbi-logarithm
coordinate system, the lgη
a
declines almost linearly with the
J Polym Res (2017) 24: 16 Page 5 of 9 16
increase of lgγ. Therefore, the relationship between the melt
apparent shear viscosity and the shear rate roughly obeys the
power law which can be written as:
ηa¼Kγn−1ð4Þ
Where K is the consistency index and n is the non-
Newtonian index. By means of the linear regression analysis
method, the non-Newtonian index of pure CAB and CAB/
PBS blends with W
CAB
= 0.9 and 0.8 was determined to be
0.28, 0.40 and 0.41, respectively. It can be seen that the non-
Fig. 7 Hoffman-Weeks plots of pure PBS and its blends with CAB for
the estimation of the equilibrium melting temperature (Inset: magnified
views)
Fig. 8 Nishi-Wang plot for the calculation of the Flory-Huggins
interaction parameter of CAB/PBS blends
Fig. 6 Melting behavior of CAB/PBS blends isothermally crystallized at various temperature from melt
16 Page 6 of 9 J Polym Res (2017) 24: 16
Newtonian indexes of CAB/PBS blends melt are much bigger
than that of the pure CAB. It means that the sensitivity of melt
apparent shear viscosity to the shear rate for CAB/PBS blends
melt is lower than that for pure CAB melt. Generally speak-
ing, polymer melts show the declined apparent shear viscosity
with increasing shear rate caused by the reduction of entan-
glement density of polymer chains and the orientation of poly-
mer chains along flow direction. Furthermore, the entangle-
ment density is dependent of the destruction rate and the cre-
ation rate for the network junctions of the polymer melts. As
the linear aliphatic polyester, PBS is much more flexible than
CAB with rigid cellulose backbone, and hence the relaxation
time of PBS polymer chain is much shorter than that of CAB
polymer chain. Therefore, compared with the entanglements
formed among the CAB macromolecules, the entanglements
formed between CAB and PBS macromolecules (polymer
chains of CAB and PBS melt are expected to be closely
entangled since the CAB/PBS blends are miscible in molten
state as confirmed above) are much easier to rebuild after the
entanglements are destructed by the shear force. As a result,
the variation of entanglements density or the melt apparent
shear viscosity of CAB/PBS blends melt is not as sensitive
as that of pure CAB melt with the increase of shear rate.
Consequently, CAB/PBS blends melt show the higher non-
Newtonian indexes compared to the pure CAB melt.
Fig. 10 Thermogravimetric curves for CAB/PBS blends under air
atmosphere
Fig. 9 Shear rate dependencies of melt viscosity (a,c) and melt flow index (b) at the temperature of 220 °C for pure CAB and CAB/PBS blends with
W
CAB
= 0.9 and 0.8
J Polym Res (2017) 24: 16 Page 7 of 9 16
Thermostability of CAB/PBS blends
Thermostability is of particular importance for any materials
in the melting-process. However, it is well-known that the
decomposition temperature of cellulose esters is very close
to their melt flow temperature. As a kind of cellulose esters,
CAB also suffers thermal decomposition during melt process-
ing [18,33]. This makes the melt processing of CAB harder
and results in poor mechanical performance of CAB products,
therefore, it is significant to improve the thermostability of
CAB. Since the melt processing is usually not conducted un-
der inert environment, the thermostability of CAB/PBS blends
was investigated under oxidative atmosphere by thermogravi-
metric analysis.
Figure 10 shows the thermal degradation behaviors of
CAB/PBS blends under air atmosphere, and T
d(5%)
,
T
d(10%)
,T
dmax
(see Table 1) are employed to evaluate
the thermostability. As seen in Fig. 10 and Table 1,
T
d(5%)
,T
d(10%)
and T
dmax
of pure PBS are about 13, 18
and 32 °C higher than pure CAB, respectively, indicating
that pure PBS is much more stable than pure CAB when
they are subjected to heating in air. Overall, T
d(5%)
,
T
d(10%)
and T
dmax
of CAB/PBS blends increase with in-
creasing PBS content. These results indicate that the
thermostability of CAB is improved by blending CAB
with PBS.
Mechanical properties of CAB/PBS blend films
The rigid feature of CAB prevents its development in many
application fields. This detrimental property is expected to be
modified through mixing CAB with ductile PBS. The tensile
test results of the solution casted CAB/PBS blend films are
summarized in Fig. 11. The breaking elongation of the CAB/
PBS blend films shows a rapid increase as the PBS content is
increased to 60 wt.%, at which point the breaking elongation
reaches 89%, a 432% increase compared with the pure CAB.
Meanwhile, the reduction in tensile strength of the blends are
tolerable, from 32 MPa for pure CAB to 22 MPa for the blends
comprising 60 wt.% of PBS, indicating that CAB becomes
more flexible and ductile after incorporating with PBS. It
should be noted that the blend with 80 wt.% of PBS shows
the minimal breaking elongation and tensile strength among
the samples. This may be ascribed to the occurrence of relative
severe phase separation between CAB and PBS due to the
very high crystallinity of the solid blend film comprising
80 wt.% of PBS.
Fig. 11 Te nsi le pro pe rti es o f t he
solution casted CAB/PBS blend
films
Tabl e 1 TGA results of CAB/PBS blends
Materials Pure CAB CAB/PBS 80/20 CAB/PBS 60/40 CAB/PBS 40/60 CAB/PBS 20/80 Pure PBS
T
d(5%)
(°C) 336.2 341.8 343.7 343.4 345.1 348.7
T
d(10%)
(°C) 349.2 356.1 359.5 360.4 360.3 367.3
T
dmax
(°C) 380.2 381.1 380.5 390.7 405.9 412.5
T
d5%
,T
d10%
and T
dmax
represent the temperature of thermal degradation for 5%, 10% weight loss and the temperature at maximum weight loss rate,
respectively
16 Page 8 of 9 J Polym Res (2017) 24: 16
Conclusions
The CAB/PBS blends were studied in detail with regard
to the crystallization behavior, miscibility, rheological
property, thermostability and mechanical performances,
and it is found that PBS is an ideal candidate for blend-
ing with CAB in term of improving the melt processabil-
ity and mechanical properties of CAB. DSC results re-
vealed the presence of crystalline phase in the solution
casted CAB/PBS blends with W
CAB
≤0.6. When the
blends were crystallized from melt, the crystallization
of PBS was severely suppressed by CAB. Nevertheless,
if given sufficient crystallization time, PBS still crystal-
lized in the blends with W
CAB
≤0.5. The suppressed
crystallization of PBS shown during DSC measurements
was consistent with the striking decline in the spherulites
growth rate of PBS observed under POM with the in-
crease of W
CAB
. Additionally, it was found that the ad-
dition of CAB to PBS resulted in a depression of the
equilibrium melting point of PBS. According to the
Nishi-Wang equation, the Flory-Huggins interaction pa-
rameter between CAB and PBS in the molten state was
calculated to be −0.89, a negative value was obtained.
These facts verified that CAB and PBS are miscible in
the molten state.
The CAB/PBS blends exhibited much lower melt vis-
cosity and better thermal stability than pure CAB. This
suggests that incorporating CAB with PBS is beneficial
for improving the melt processability of CAB which
always suffers from a relative narrow window between
the melt flow temperature and the thermal decomposi-
tion temperature. Moreover, the CAB/PBS blends ap-
peared to be tougher and more ductile compared with
the rigid pure CAB. A series of CAB/PBS blend mate-
rials with tailored mechanical properties are achievable
by simply changing the composition, which makes CAB
and PBS more attractive among the environment-
friendly materials.
Acknowledgements The authors gratefully acknowledge the valuable
help and great support from National Natural Science Foundation of
China (No.21404024), China Postdoctoral Science Foundation
(No.2016 M591573) and the Fundamental Research Funds for the
Central Universities (No.2232015G1-11 and No.2232014D3-20).
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