Materials Sciences and Applicatio ns, 2011, 2, 59-69
doi:10.4236/msa.2011.22009 Published Online February 2011 (
Copyright © 2011 SciRes. MSA
Development of Cockleshell-Derived CaCO3 for
Flame Retardancy of Recycled PET/Recycled
PP Blend
Supaphorn Thumsorn1, Kazushi Yamada2, Yew Wei Leong1, Hiroyuki Hamada1
1Department of Advanced Fibro-Science, Kyoto Institute of Technology, Kyoto, Japan; 2Future Applied Conventional Technology
Center, Kyoto Institute of Technology, Kyoto, Japan.
Received December 24th, 2010; revised January 4th, 2011; accepted January 11th, 2011.
Recycled polyethylene terephthalate (RPET) and recycle polypropylene (RPP) blends filled with a renewable filler, i.e.
cockleshell-derived CaCO3 (CS) were prepared as an environmental friendly thermoplastic composite. The effects of CS
particle size and content on thermal stability, mechanical performance and flame retardant properties of the blends
were investigated. Thermogravimetric analysis was performed to elucidate the thermal decomposition kinetics of the
filled composites. The iso-conversion of the Flynn-Wall-Ozawa was developed by the second order polynomial function
for thermal oxidative degradation of the blends while peak derivative temperature from the Kissinger method was able
to verify the mechanism of degradation in these blends. The results indicated that both CS and commercial grade
CaCO3 improved thermal stability and enhanced the stiffness as well as impact performance of the blends. However,
this could only be achieved when high filler content was present in the RPET/RPP blends.
Keywords: Cockleshell, Aragonite CaCO3, Thermal Decomposition Kinetic, Polymer Blend, Flame Retardancy
1. Introduction
According to environmental considerations, there is strong
emphasis on using recycled and biodegradable polymers
while using renewable fillers and additives to enhance
their properties. Cockle, a type of bivalve mollusk, is one
of the most popular seafood in Thailand. The large con-
sumption of cockle has resulted in the cockleshells being
left as garbage. The main mineral content in cockleshell
is calcium carbonate (CaCO3), which can be grinded into
suitable particle sizes and incorporated as fillers in ther-
moplastics. The incorporation of cockleshell-derived
CaCO3 into thermoplastics is not only value adding to the
shell but can also be a means of sustainable waste man-
agement strategy.
Polyethylene terephthalate (PET) and polypropylene
(PP) have been widely used as drinking bottles and caps,
respectively. Upon disposal, these materials are usually
separated prior to recycling since they are regarded as
immiscible. The compatibility of PET and PP blends,
however, can be improved by using a suitable compatibi-
lizer, such as styrene-ethylene-butadiene-styrene (SEBS)
co-polymers, which yielded tougher and more thermally
stable material [1-3]. However, the stiffness of the blends
remained low, especially when there is high content of
PP or compatibilizer. Therefore, one of the most promis-
ing methods to improve the mechanical performance of
the blends is by the incorporation of fillers such as
CaCO3 mineral filler has been one of the most popular
fillers used in the thermoplastic industry. CaCO3 can be
generally found in three distinct crystalline phases i.e.
calcite, aragonite and vaterite. Calcite is the most stable
and most commonly found in nature. Aragonite, however,
can only be found in precipitate CaCO3 or seashells
whereas vaterite is found from synthesized CaCO3 and
does not occur naturally [4-6]. Generally, aragonite has
higher density and hardness than calcite and vaterite,
which makes it a valuable inorganic material that can be
used as filler for armature plastic, rubber, paper, glass
fiber, print ink, paint pigment and cosmetics [7].
Apart from mechanical properties, thermal stability is
also one of the most important factors for processing of
polymeric materials. Thermal decomposition kinetics of
Development of Cockleshell-Derived CaCO for Flame Retardancy of Recycled PET/Recycled PP Blend
60 3
polymeric materials can be defined by kinetic parameters
such as activation energy (Ea), pre-exponential factor (ln
A) and reaction order (n). There are two basic thermal
decomposition kinetic models including iso-conversion
and peak derivative temperature for kinetic study, which
is generally based on the Arrhenius equation [8-17]. The
Flynn-Wall-Ozawa is a classical model of iso-conversion
that can calculate Ea as a function of sample weight loss.
On the other hand, the Kissinger model has been widely
used for peak-derivative temperature calculation, which
provides the kinetic parameters Ea, ln A and n for de-
scribing the thermal degradation stability.
In addition to thermal stability, the composites would
also be evaluated based on their flammability, which is
important should the material be considered for automo-
tive and structural applications. The flame retardancy of
CS filled RPET/RPP blend was investigated in order to
further develop CS as an environmental friendly flame
retardant material.
2. Experimental
2.1. Materials
The RPET and RPP in the form of flake from crushed
waste bottles were provided by Yasuda Sangyo Co., Ltd,
Japan. A finely ground commercial grade CaCO3 (SOF-
TON1200) with an average particle size of 1.8 μm was
purchased from Bihoku Funka Kogyo, Co., Ltd., Japan).
Commercial grade CaCO3 is hereby known as SOFTON.
A styrene-ethylene-butadiene-styrene (SEBS) base com-
pound was used as compatibilizer, which purchased from
JSR Corporation, Japan.
Waste cockleshells were taken from Thailand and used
as original without purification. The shells were washed,
dried, ground and then sieved at 400 mesh size. Cockle-
shell derived-CaCO3 is referred as “CS”.
2.2. Sample Preparation
The ratios of RPET/RPP blends were set at 95/5, which
was then compounded with 10 wt% CS and SOFTON in
a single screw extruder (SRV-P70/62, Nihon Yuki Co.,
Ltd., Japan) with 5 phr (parts per hundred resin by
weight) of SEBS based compatibilizer. RPET was dried
by using a dehumidifying drier at 120˚C for 5 hours be-
fore compounding. The extruder barrel temperature was
set at 260-285˚C at a screw speed of 50 rpm. The blends
were dried by using an oven at 100˚C for 5 hours before
being injection molded into dumbbell specimens by us-
ing a Po Yuen UM50 injection molding machine. The
barrel temperature, injection speed and mold temperature
during injection molding were set at 280˚C, 100 mm/s,
and 30˚C, respectively.
2.3. Crystal Structure of CaCO3 Fillers
Crystal structure of filler was determined by X-ray dif-
fraction (XRD). The XRD intensity of the filler was col-
lected from a JEOL/JDX 3530 diffractometer (CuKα) at
a voltage of 30 kV and a filament current of 30 mA. The
scans were made from 2θ = 5-60˚.
2.4. Morphology Observation
Morphology of fillers and blends was characterized by
using a scanning electron microscope (JSM5200, JEOL,
Japan). Gold coating was sputtered onto the specimens
for electron conductivity.
2.5. Thermal Stability and Decomposition
Thermogravimetric analysis (TGA) (TGA2950, TA In-
struments) was performed to elucidate the thermal de-
composition kinetics. The samples weighing between 3-5
mg was subjected to heating rates of 2, 5, 10 and 20˚C/
min in nitrogen (N2) and air. The kinetic parameters of
thermal degradation of the blend was investigated by
Flynn-Wall-Ozawa (FWO), Kissinger and Coats-Redfern
methods, which the kinetic parameters are calculated
from non-isothermal technique based on the Arrhenius
equation and a solid stage reaction [8-17] by
exp a
dA f
⎝⎠ (1)
where A is the pre-exponential factor, β is a heating rate
(˚C/min), Ea is activation energy (J/mol), R is a universal
gas constant (8.314 J/mol K), T is absolute degradation
temperature (K), f(α) is the reaction model and α is con-
version of weight loss, which conversion from thermo-
gravimetric study is expressed by
= (2)
where m0 is initial mass, mT is mass at decomposition
temperature and mfinal is mass at final decomposition re-
2.6. Limiting Oxygen Index
Flame retardant property of the blends was characterized
by using limiting oxygen index (LOI) (ONI, oxygen in-
dex meter, Suga Test Instruments Co., Ltd., Japan) ac-
cording to JIS K 7201-2, specimen type IV. The mini-
mum concentration of oxygen in a flowing mixture of
oxygen and nitrogen needed to continuously burn the
sample for over 3 minutes or for a length of more than 50
mm was determined to be the LOI.
2.7. Mechanical Properties
Tensile test were performed by using an Instron 4206
Copyright © 2011 SciRes. MSA
Development of Cockleshell-Derived CaCO for Flame Retardancy of Recycled PET/Recycled PP Blend61
universal testing machine according to standard ASTM
D638. The gauge length was 115 mm at an extension rate
of 10 mm/min.
Izod impact strength was determined for 2 mm-deep
notched specimens, which was cut from the parallel re-
gions of the dumbbell specimens. The tests were con-
ducted by using a Toyo Seiki Izod impact tester accord-
ing to ASTM D256 with a pendulum of 5.50 J.
3. Results and Discussion
3.1. Characterization of Cockleshell-Derived
The average particle size of CS was measured from
scanning electron microscopy (SEM) images. Figure 1
shows SEM photographs and XRD patterns of CaCO3
filler including CS and SOFTON. The average particle
size of these fillers is presented in Table 1 . It can be seen
that the average particle size of CS after sieving was
about 25 µm, which was larger than SOFTON.
The CaCO3 content in CS was determined by heating
the sample until 900˚C in a thermogravimetric analyzer
at a heating rate of 20˚C/min under nitrogen atmosphere.
A calculation of weight loss from CaCO3 decomposition
reveal that CS contains 97 wt% of CaCO3, which is
similar to that of SOFTON. Characterization of CS by
X-ray diffraction revealed peaks at 2θ = 26.16˚ corre-
sponding to (111) reflections from aragonite crystal
structure of CS aragonite structures, as shown in Figure
1(a). SOFTON, on the other hand, revealed peaks at 2θ =
29.44˚ corresponding to the (104) reflections of the cal-
cite crystal structure as shown in Figure 1(b) .
3.2. Morphology of Filled RPET/RPP Blends
Figure 2 presents the SEM photographs of unfilled and
filled RPET/RPP blend. All photographs exhibited good
dispersion of RPP dispersed particles on RPET matrix,
which attributed to compatibilization of the blend. The
image J software was used to measure the sizes of the
RPP dispersed phase in the blends. The average RPP
dispersed particle sizes were 0.65, 0.48 and 1.60 µm for
unfilled, SOFTON filled and CS filled RPET/RPP blends,
respectively. The difference of RPP dispersed size should
be considered due to the difference of interfacial tension
between RPET/RPP and compatibilizer. The presence of
filler in the blend increased the interfacial tension of
RPET/RPP and compatibilizer due to interaction between
filler and compatibilizer thus effect on coalescence of
RPP dispersed phase particle. Therefore, CS filled RPET/
RPP blend exhibited larger of RPP dispersed sizes as
compared to others. However, smaller size of SOFTON
would breakage RPP dispersed phase during compound-
ing resulting in smaller RPP dispersed phase.
Figure 1. Structure and morphology of (a) CS and (b)
Table 1. Particle size and content of filler included thermal
stability and Ea by Coats-Redfern equation.
SOFTON97.9 1.80 636.4 703.7 218.1
CS 97.5 25.2 608.1 697.1 180.6
3.3. Thermal Stability of Fillers
The effect of CaCO3 filler particle size on its thermal sta-
bility and decomposition kinetic was determined through
the Coats-Redfern equation by using a single heating rate
at 20˚C/min in N2. Thermal degradation temperature (Td)
and Ea values of the fillers are tabulated in Table 1. The
results revealed that SOFTON exhibited better thermal
stability than CS, as can be seen from the higher degra-
dation temperature as well as Ea value. Low thermal sta-
bility of CS could be attributed to its lower heat transfer
efficiency, which less capability for withstand high tem-
perature, and corresponding to lower thermal stability of
its aragonite than calcite CaCO3 structure [4,6].
3.4. Thermal Decomposition Kinetic Study of
The typical effect of heating rate on non-isothermal deg-
radation of the blends is presented in Figure 3. A shift in
the conversion of weight loss (α) and peak derivative
weight (dα/dt) towards a higher temperature could be ob-
Copyright © 2011 SciRes. MSA
Development of Cockleshell-Derived CaCO for Flame Retardancy of Recycled PET/Recycled PP Blend
62 3
Figure 2. SEM photographs of (a) Unfilled (b) SOFTON
filled and (c) CS filled RPET/RPP blends.
Figure 3. (a) Conversion and (b) Derivative weight TGA
thermogram of CS filled RPET/RPP blend in N2.
served when increasing heating rates. This was due to the
lag in heat absorption by the specimens due to their rela-
tively low thermal conductivity. However, the heating
rates would significantly affect the thermal degradation
of the samples. Therefore, it is necessary to use mul-
ti-heating rates when performing thermal decomposition
kinetic studies.
Figures 4(a) and (b) compares the dα/dt curves of the
samples degraded in N2 and air, respectively. It was
noted that the incorporation of both CS and SOFTON
into RPET/RPP blends have resulted in a slight increase
in the peak degradation temperature (Td peak). Further-
more, it can be seen that degradation rate (dα/dt) of the
blends decreased with the presence of both CS and
SOFTON fillers. The increment of Td peak and reduction
of dα/dt results indicated an improvement of thermal
Copyright © 2011 SciRes. MSA
Development of Cockleshell-Derived CaCO for Flame Retardancy of Recycled PET/Recycled PP Blend63
Figure 4. Derivative weight TGA thermograms of unfilled
and filled RPET/RPP blends in (a) N2 and (b) Air.
stability of the RPET/RPP. An obvious difference in
thermal degradation mechanism could be observed, i.e. a
single-step degradation in N2 and two-step degradation in
air. The decomposition mechanism of the blends can be
explained by using thermal decomposition kinetics, whi-
ch corresponds to solid state reaction models as tabulated
in Table 2. The various kinds of models could be classi-
fied by isothermal plot between rate of reaction and con-
version of the reaction. The shapes of the plot are corre-
sponding to kinetic models and can be classified by ac-
celeratory, decelerator, linear or sigmodal models, which
are related to solid state kinetic models of nucleation,
geometrical contraction, diffusion or reaction-order mo-
dels as reviewed by Khawam et al. [11].
Figure 5 illustrates the isothermal plot of dα/dt and
conversion of thermal decomposition (α) for the unfilled,
CS- and SOFTON-filled RPET/RPP blends. The iso-
thermal plot of dα/dt and α revealed a bell shaped curve
whereby an initial increment of reaction rate was immi-
nent with increasing conversion until a maximum de-
composition reaction was reached, thereafter the reaction
rate decreased until the decomposition process ended.
The shape of these plots could be classified as sigmoidal
models, which corresponds to reaction-order models [11].
Therefore, thermal decomposition kinetic of CS and
SOFTON filled RPET/RPP blend can be evaluated based
on the first-order reaction model by using Flynn-Wall-
Ozawa and Kissinger model.
3.5. Thermal Decomposition Kinetic from
Thermal decomposition kinetic of Flynn-Wall-Ozawa
(FWO) is an iso-conversion or model-free method, which
can be calculated from the kinetic parameter by integral
method through following equation
log log2.315a
=−− (3)
At constant heating rate, the kinetic parameter of acti-
vation energy can be calculated by using the slope of
linear plots of log heating rate (β) and the inverse tem-
perature (1/T) at various weight losses by
0.457 1
The thermal decomposition kinetic from Flynn-Wall-
Ozawa yields linear plots between log β and 1/T based on
Arrhenius relationship and their slopes are used for the
calculation of kinetic parameters. Figure 6 presents the
linear relationship of unfilled, SOFTON filled and CS
filled RPET/RPP blends during decomposition in N2.
The activation energy, Ea was directly evaluated from the
slope of these plots.
Figure 7 shows the Ea values as a function of weight
loss conversion of unfilled and filled RPET/RPP blends
for thermal degradation in N2. The Ea values at initial
stage of decomposition (Ea 0.05) are 225, 218 and 191
kJ/mol while Ea values at 50% weight loss (Ea 0.50) are
237, 225 and 227 kJ/mol as tabulated in Table 3 for un-
filled, SOFTON filled and CS filled REPT/RPP blends,
respectively. The Ea values are almost constant from the
initial stage until 50% weight loss, which indicates that a
similar one-step thermal decomposition mechanism was
true when the blends were degraded in N2 thus confirm-
ing earlier decomposition profiles shown in Figure 4(a).
However, Ea values of CS filled RPET/RPP blend were
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Development of Cockleshell-Derived CaCO3 for Flame Retardancy of Recycled PET/Recycled PP Blend
Copyright © 2011 SciRes. MSA
Table 2. Solid state reaction and integral expressions for different reaction models.
Model Differential form f(
) = 1/k d
/dt Integral form g(
) = kt
Nucleation models
Power law (P2) 2α1/2 α1/2
Power law (P3) 3α2/3 α1/3
Power law (P4) 4α3/4 α1/4
Avrami-Erofeyev (A2) 2(1α)[ln(1α)]1/2 [ln(1α)]1/2
Avrami-Erofeyev (A3) 3(1α)[ln(1α)]2/3 [ln(1α)]1/3
Avrami-Erofeyev (A4) 4(1α)[ln(1α)]3/4 [ln(1α)]1/4
Prout-Tompkins (B1) α(1α) ln[α/(1α)]+ca
Geometrical contraction models
Contracting area (R2) 2(1α)1/2 1(1α)1/2
Ontracting volume (R3) 3(1α)2/3 1(1α)1/3
Diffusion Models
1-D diffusion (D1) 1/(2α) α2
2-D diffusion (D2) [1/ln(1α)] ((1(1α)ln(1α))+α
1-D diffusion-Jander (D3) [3(1α)2/3]/[2(1(1α)1/3)] (1(1α)1/3)2
Ginstling-Brounshtein (D4) 3/[2((1α)/1/31)] (1(2/3)α(1α)2/3
Reaction order models
Zero-order (F0/R1) 1 α
First-order (F1) (1α) ln(1α)
Second-order (F2) (1α)2 [1/(1α)]-1
Third-order (F3) (1α)3 (1/2)[(1α)21]
(a) (b)
Figure 5. Isothermal plot of degradation rate and conversion decomposition of unfilled and filled RPET/RPP blends in
(a) N2 and (b) Air.
Development of Cockleshell-Derived CaCO for Flame Retardancy of Recycled PET/Recycled PP Blend65
Figure 6. Flynn-Wall-Ozawa plot of (a) Unfilled (b) SOF-
TON filled and (c) CS filled RPET/RPP blends in N2.
Figure 7. Activation energy of unfilled and filled RPET/
RPP blends in N2.
lower than unfilled and SOFTON filled blends at the
initial stage of decomposition, which suggest lower
thermal stability of CS than SOFTON.
On the other hand, thermal oxidative degradation of
these blends exhibited non-linear relationship between
log β and 1/T of FWO plots for decomposition in the
presence of O2 as illustrated in Figure 8. Generally, the
Flynn-Wall-Ozawa kinetic model enables the determina-
tion of Ea from the linear relationship of log β and 1/T
from non-isothermal degradation at various heating rates.
Nevertheless, thermal oxidative decomposition of unfilled
and filled RPET/RPP blends from the FWO indicated
some drawback of this method. Therefore, in this study
the non-linear plot was successfully developed by using
polynomial fitting data. These results are considered that
Ea of thermal oxidative degradation was dependent on
the slow heating rate and complex degradation mecha-
nism [18]. The non linear relationship of these FWO
plots can be fitted by using the second order polynomial
function as described by
log ab
where a is polynomial coefficient, b is linear coefficient
and c is constant.
The fitting plots revealed the curve of FWO plot at
low heating rates, which was clearly seen at low weight
loss decomposition. These results could be considered on
the effect of particle size of filler as well as RPP dis-
persed phase particles on these blends, which attributed
to their different surface areas. It can note that the de-
composition reaction is significantly influenced by low
heating rate, which this low heating rate decomposition
can be explained and controlled the mechanism of the
Copyright © 2011 SciRes. MSA
Development of Cockleshell-Derived CaCO for Flame Retardancy of Recycled PET/Recycled PP Blend
66 3
Figure 8. Flynn-Wall-Ozawa plot of (a) Unfilled (b) SOF-
TON filled and (c) CS filled RPET/RPP blends in air.
thermal oxidative decomposition.
The Ea of kinetic parameter for thermal oxidative deg-
radation of these blends can be evaluated by using poly-
nomial and linear coefficient from polynomial fitting
data as shown in Figure 9. The Ea values at initial stage
of thermal oxidative decomposition (Ea 0.05) are 124,
157 and 141 kJ/mol while Ea values at 50% weight loss
(Ea 0.50) are 200, 214 and 162 kJ/mol as presented in
Table 3 for unfilled, SOFTON filled and CS filled
REPT/RPP blends, respectively. The Ea values as a func-
tion of weight loss in Figure 9 exhibited a two-step deg-
radation profile of thermal oxidative degradation in air.
The Ea values increased from the initial stage at 2.5 to
10% weight loss, which can be described as the first step
of degradation. The Ea values gradually came to a plateau
with further weight loss.
Thermal stability of the blends was improved with the
incorporation of CS and SOFTON, which prompted an
increment in Ea values, especially at the initial stages of
degradation. This could be attributed to interaction be-
tween filler and polymer matrix and filler would act as
barrier to protect volatile substance during decomposi-
Figure 9. Activation energy of unfilled and filled RPET/
RPP blends in air.
Table 3. Kinetic parameters of unfilled and filled RPET/
RPP blends from the Fly nn-Wall-Ozawa method.
Nitrogen Air
Ea 0.05 Ea 0.50 Ea 0.05 Ea 0.50
(kJ/mol) (kJ/mol) (kJ/mol) (kJ/mol)
- 225.1 237.5 124.2 200.3
95/5 SOFTON218.6 220.4 157.8 214.8
CS 191.7 227.8 141.6 162.3
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Development of Cockleshell-Derived CaCO3 for Flame Retardancy of Recycled PET/Recycled PP Blend
Copyright © 2011 SciRes. MSA
are shown in Table 4. tion of these blends. The degradation of the blends would
also depend on the state of dispersion of the RPP phase
as well as the filler in the RPET matrix. Due to the low
thermal stability of RPP in the presence of oxygen, the
degradation of the blends would be slower when RPP is
well dispersed and embedded within in the RPET matrix
since the latter could become a good oxygen barrier.
Moreover, well dispersed filler particles could also retard
or inhibit thermal oxidative degradation by acting as a
barrier to prevent attacks by volatile substances on the
polymeric phases. However, thermal stability of the CS
filled blends was slightly inferior to the unfilled and
SOFTON filled blends, which could be due to the large
CS particle size that prevented the formation of an effec-
tive barrier.
From the results, Ea and ln A of the blends was lower
when decomposed in air than in N2, which was due to
thermal oxidative degradation in the presence of oxygen.
The highest thermal stability, as determined from the
Kissinger model, was observed in SOFTON filled
RPET/RPP blend, which exhibited high activation energy
and pre-exponential factor. Similar to the results obtained
through FWO, the CS filled composites also exhibited
lower thermal stability than SOFTON filled composites
as can be deduced from the lower Ea and ln A values
determined by the Kissinger method. Nevertheless, both
CS and SOFTON filled blends exhibited lower rate of
degradation (dα/dt) as compared to the unfilled blends.
According to thermal decomposition kinetic study, ki-
netic parameter including activation energy, pre-expo-
nential factor and reaction order of the blends can be
influenced by various factors such as the kinetic methods,
the sample mass and size, and the operating conditions
[12]. Therefore, the kinetic compensation effect was de-
veloped in order to determine the effect from the differ-
ent specimens or experimental conditions in a change of
activation energy calculation [9]. In this circumstance,
kinetic parameter of pre-exponential factor, A would
vary with the activation energy, Ea. Form kinetic pa-
rameters of Kissinger models, linear plots between ln A
and Ea of the unfilled and filled RPET/RPP blends is
illustrated in Figure 10 The compensation effect of these
blends are based on thermal degradation under N2 and air
as determined by Equations (8) and (9), respectively
3.6. Thermal Decomposition Kinetic from
Kissinger Model
Thermal decomposition kinetics based on the Kissinger
method is calculated through the derivation from hetero-
geneous chemical reactions and widely used without
considering the reaction order (n) or conversion function,
f(α) [19]. The kinetic equation of the Kissinger model is
expressed as
ln lna
where , αm is maximum conversion
of weight, n is reaction order and Tdm is the highest deg-
radation temperature of the first derivative of material at
constant heating rate. The activation energy can be in-
vestigated by using the slope of ln (β/T2
dm) versus 1/Tdm
of Kissinger plot by
ln11.370.17 a
−+ (8)
−+ (9)
These linear relationships from thermal degradation
and thermal oxidative degradation suggest that an iso-
kinetic relationship between pre-exponential and activa-
tion energy was established whereby the thermal de-
composition mechanisms of unfilled and filled RPET/
RPP blends were similar [9]. It is interesting to note that
decomposition atmosphere plays an important role on
thermal decomposition kinetic of unfilled and filled
The pre-exponential factor can be obtained from the
intercepts of the Kissinger plot.
The Ea values and pre-exponential factor (ln A) from
Kissinger model as well as the degradation rate (dα/dt)
Table 4. Kinetic parameters of unfilled and filled RPET/RPP blends from the Kissinger method.
Nitrogen Air
Ea ln A Ea ln A
Blend Filler
(kJ/mol) (min–1)
(%/min) (kJ/mol) (min–1)
- 225.1 27.53 10.43 159.0 16.54 9.27
95/5 SOFTON 206.4 24.26 9.03 175.9 19.20 6.72
CS 203.4 23.60 9.08 159.3 15.53 6.52
Development of Cockleshell-Derived CaCO for Flame Retardancy of Recycled PET/Recycled PP Blend
68 3
Figure 10. Linear relationship of ln A and Ea of unfilled and
filled RPET/RPP blends in N2 and air.
RPET/RPP blends, whereby the kinetic parameters dur-
ing decomposition in N2 were significantly higher than
those recorded during thermal oxidative decomposition
in the presence of oxygen.
3.7. Flame Retardant Property
Flame retardant property of CS and SOFTON filled
blends was investigated by using the limiting oxygen
index (LOI). The LOI values decreased with increasing
filler concentration indicating higher flammability, as
shown in Table 5. It was observed in the unfilled speci-
men that the region under the flame would melt instan-
taneously to cause dripping, which prevented the flame
from spreading towards other parts of the specimen. The
incorporation of CaCO3, however, prevented this drip-
ping thus causing the specimens to continue burning. It
should be noted that flame retardants are generally added
into polymers at high contents of up to 60 wt%. There-
fore, it is thought that the amount of CaCO3 incorporated
into the blends may be insufficient to dilute the combus-
tible portion of the blends. The thermal oxidative de-
composition kinetic of the filled blends can also be useful
to explain their flame resistance. The second step of
thermal oxidative decomposition in the filled blends
when exposed to air can be related to the deterioration of
carbonaceous elements or char formed from the initial
decomposition of organic substances. The presence of
CaCO3 would accelerate the decomposition of aromatic
groups in the blend during degradation leading to faster
formation of char, which would provide better flame re-
sistance to the RPET/RPP blend. However, at low con-
tent of filler could not yield efficiency flame retardancy
of the filled blends.
3.8. Mechanical Properties of CaCO3 Filled
Table 5 summarizes the mechanical properties of un-
filled and CaCO3 filled RPET/RPP blends. The incorpo-
ration of fillers, both CS and SOFTON enhanced the
stiffness and impact performance of the blend. The in-
crement of tensile modulus (E) of the filled blend was
due to the high rigidity of the filler particles whereas
cavitation caused by the poor interfacial adhesion be-
tween fillers and the matrix could enhance their impact
performances. Incidentally, the reduction in yield strength
(σ) of the filled blends would also be due to the lack of
interfacial adhesion between fillers and the blend matrix.
It could be noted that CS filled blend exhibited highest
modulus values due to the presence of aragonite crystal
4. Conclusions
Thermal oxidative decomposition kinetics based on the
FWO model was developed by using the second order
polynomial equation, which fitted well with experimental
data. The activation energy during thermal oxidative
degradation was dependent on the size of fillers and RPP
dispersed particles in the blends. According to the FWO
model, a two-step degradation mechanism was observed
when the samples were degraded in air. The incorpora-
tion of SOFTON provided higher thermal resistance to
the blends especially at the first phase of degradation
involving the deterioration of organic compounds. CS,
however, did not act as an efficient thermal oxidative
degradation barrier due to the large particle sizes. Mean-
while, the Kissinger kinetic model was able to suggest
similar decomposition mechanisms in these blends th-
rough the linearity of the compensation plots. The incor-
poration of CS and SOFTON improved the thermal sta-
bility of RPET/RPP blends. However, char formation of
both fillers was not enough for yield flame retardancy of
the RPET/RPP blends. It is interesting to note that arago-
nite CaCO3 of CS significantly enhance stiffness of the
Table 5. Mechanical properties of unfilled and filled RPET/
RPP blends limiting oxygen index (LOI).
BlendFiller E (GPa)σ (MPa)
LOI (%)
- 1.54 46.5 1.54 23.5
SOFTON1.78 43.0 1.77 20.3
CS 1.99 42.6 1.09 20.4
Copyright © 2011 SciRes. MSA
Development of Cockleshell-Derived CaCO for Flame Retardancy of Recycled PET/Recycled PP Blend69
5. Acknowledgements
The authors gratefully acknowledge Dr. Hiroyuki Inoya,
Yasuda Sanyo Co., Ltd., Japan for supporting materials
and compounding system, Department of Industrial En-
gineering,Pathumwan Institute of Technology, Thailand
for preparing cockleshell and Dr. Koji Yamada and Dr.
Joji Kodata from Osaka Municipal Research Institute,
Japan for limiting oxygen index measurement.
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