J Therm Anal Calorim (2014) 115:811 821
DOI 10.1007/s10973-013-3224-y
Influence of additives on recycled polymer blends
" " "
M. A. AlMaaded N. K. Madi A. Hodzic
C. Soutis
Received: 9 July 2012 / Accepted: 26 April 2013 / Published online: 11 June 2013
Ó Akadmiai Kiadó, Budapest, Hungary 2013
Abstract Polymer systems based on polymer waste offer Introduction
promising way to increase recycling in the society. Since
fillers play a major role in determining the properties and Plastics have become one of the materials with the greatest
behavior of polymer composites, recycled polymers can growth in terms of consumption and waste generation. The
also be combined with fillers to enhance the stiffness and growth of plastic wastes in UK and Qatar is reaching
thermal stability. In this study, blends of recycled poly- 20 % of total municipality waste with an average of
ethylene and recycled polypropylene with mica and glass 2,300 t day-1 [1]. Therefore, the environmental impact has
fiber were prepared by melt blending technique. The effect become an important challenge for many parts in the
of the particle loading, filler type, and filler matrix inter- world. Recycling of polymer waste has recently attracted a
action on thermal degradation and thermal transition of considerable attention predominantly due to the increase in
processed systems were investigated. Thermogravimetric the environmental concerns and the depletion of petroleum
analysis, differential thermogravimetric analysis, and dif- resources [2 4]. Although the recycling capacity for plas-
ferential scanning calorimetry were used in this investiga- tics has been progressively increased, the fraction of
tion. Comparative analysis shows that both fillers produced plastics that end up in a landfill is still very significant [1].
different effects on thermal properties of the processed As a consequence, there is a great interest in finding new
systems. These results were confirmed by calculating the possibilities for the use of post-consumer plastics in new
activation energy for thermal degradation and thermal products [5 7]. Several technologies have been proposed to
transition using Kissinger and Flynn Wall expressions. solve this problem and to extend the application of poly-
mers into more sectors especially as adopting them as
Keywords Polyethylene blends Polypropylene blends matrices in new composites.
Glass fiber-reinforced composites Mica-reinforced Polymers have a broad amount of applications such as
composites DSC TG packaging products, containers, and consumer goods.
Recycled polymers can be used in a growing number of
potential applications, such as boxes or pallets; however,
deterioration in thermal and mechanical properties of
polymers during repeated thermal processing limit the
applications of recycled polymers and their blends [8, 9].
During successive thermal processing steps, irreversible
M. A. AlMaaded (&) N. K. Madi
thermo-oxidative degradation in the form of chain scission,
Center of Advanced Materials (CAM), Qatar University,
cross-linking or elimination of substituent, and formation
Doha, Qatar
e-mail: m.alai@qu.edu.qa of double bond can be produced, yielding recycled mate-
rials with lower properties than that of the original batch
A. Hodzic C. Soutis
[10]. To avoid degradation, additives like compatibilities
Composite Systems Innovation Centre,
and antioxidants are added to contribute to the preservation
Department of Mechanical Engineering,
The University of Sheffield, Sheffield, UK of the original properties [11]. However, their introduction
123
812 M. A. AlMaaded et al.
normally leads to an increase in the cost of the materials. composites were analyzed using Kissinger [21] and Flynn
To improve the processing, polymer composites retaining Wall Ozawa [22, 23] kinetic methods, respectively, as
the good thermal and mechanical properties have been detailed in the following sections.
used. Incorporating inorganic fillers [12] into polymer resin
improves various materials properties such as strength and
Theoretical approach
thermal stability.
Polyolefin filled with inorganic materials has gained the
A polymer has a stable molecular structure that vaporizes,
confidence of end users because it provides excellence
performance, recyclability, design, and fabrication flexi- sublimates, or its molecular structure becomes brittle at a
high temperature to decompose into gaseous product [24].
bility. Adding the fillers has the effect of reducing the cost
This process of molecular degradation may change the
and enhancing mechanical and thermal properties of
polymer composites and, therefore, is favorable for poly- mass of the sample as a function of temperature. Since the
thermal decomposition has a direct correlation with the
mer engineering. As a result significant number of filled
and reinforced polyolefin grades have been developed and stability of the composites, TG was used to measure the
activation energy Ea of composites to determine its
successfully used in various applications in automotive,
stability.
building and construction, electronics, sport equipment,
furniture, and appliance market. The most common fillers The fundamental rate equation used in all kinetic studies
is generally described as
of PE are calcium carbonate [13], others like mica, glass
beads [14], talc [15], and clays [16] have been successfully
da
źkfa 1
used. Among traditional fillers, mica is of special interest
dt
because it can promote heterogeneous crystallization in
where k is the rate constant and fais the reaction model,
semicrystalline polymers leading to a significant change in
a function depending on the actual reaction mechanism.
properties. Generally, these properties of inorganic filler
Equation (1) expresses the rate of conversion, da/dt, at
polymer composites depend strongly on size, shape, and
a constant temperature as a function of the reactant
distribution of filler in the polymer matrix and also to the
concentration loss and rate constant. In this study, the
extent of interfacial adhesion between the filler and the
degree of conversion or degradation of the material a can
matrix.
be calculated by the TG curve as:
Most polymer composites are generally subjected to
thermal degradation at elevated temperatures. The practical
Wo Wt
aź 2
use of composites requires knowledge of their thermal
Wo Wf
lifetime, which corresponds to their upper limit and the
where Wt, Wo, and Wf are time related (t), initial, and final
operating temperatures as well as thermal stability of these
mass of the sample, respectively. The rate constant k is
materials. Materials having high thermal stability can
generally given by the Arrhenius equation:
retain their mechanical integrity when exposed to elevated
temperatures [17]. It is important, therefore, to understand
E=
kźA exp 3
RT
the effect of the processing temperature on the thermal
degradation process, since the polymers are exposed to
where E is the apparent activation energy (kJ mol-1), R is
thermal degradation during the manufacturing of filler-
the gas constant (8.314 J K-1 mol-1), A is the pre-
reinforced composites. Thermal analysis is an important
exponential factor (min-1), and T is the absolute
technique for determination of the thermal stability of the
Temperature (K). Combining Eqs. (1) and (3) gives the
materials [18]. Moreover, it is a useful technique for
following correlation:
understanding structure property relationship. In addition,
da
it is possible to quantify the amount of moisture and vol- E= fa
źA exp 4
RT
dt
atiles, which can cause deterioration of the composite
properties [19, 20]. Different fillers-modified polymer
For a dynamic TG technique, introduce the heating rate,
samples were prepared in the present study by varying the
b = dT/dt, into Eq. (4), and get Eq. (5):
proportion of the filler content as well as the filler type.
da
A= E= fa
Thermogravimetric analysis (TG), differential scanning ź exp 5
b RT
dT
calorimetry (DSC), and morphological systems were used
Equations (4) and (5) are the fundamental expression of
to investigate the effect of filler type, filler loading, and
analytical methods to calculate kinetic parameters on the
filler matrix adhesion on the thermal degradation, thermal
basis of TG data. The most common model free methods
transition, and morphology of the thermoplastic compos-
used in our study are tabulated in Table 1.
ites. The DSC and TG results obtained for the studied
123
Additives on recycled polymer blends 813
Table 1 Kinetic methods used in our study to evaluate activation energy
Method Expression Plots References
Kissinger b b [22]
ln źlnAfaފEa ln vs:1=Tp
2 2
Tp RTp Tp
Flynn Wall Ozawa AEa log b vs:1=T [23, 24]
logbźlog 2:315 0:457Ea
Rga RT
Thermogravimetry
Table 2 Some physicochemical characteristics of the recycled
polyethylene, recycled polypropylene, mica and glass fibers used
Thermogravimetric analysis can be used to evaluate the
Recycled polyethylene
thermal behavior and stability parameters of the neat and
Density/g cm-3 0.92
modified thermoplastics [25]. Thermogravimetric (TG) and
Melt flow index (g/10 min, 190 C, 2.16 kg) 0.5
differential thermogravimetric (DTG) measurements were
Ash/mass% 1 2
conducted with Perkin Elmer Pyris Analyzer 6 at different
Recycled polypropylene
heating rates. Heating rates of 5, 10, 20, and 40 C min-1
Density/g cm-3 0.94
were used. Samples (*10 mg) were placed in a ceramic
Melt flow index (g/10 min, 190 C, 2.16 kg) 1.55
pan and the experiments were conducted in nitrogen
Ash/mass% 1 2
environment with N2 being supplied at a flow rate of
Mica flakes
20 mL min-1. In this work, detailed and precise factors
Aspect ratio 1 10
defining the thermal stability based on the onset tempera-
Density/g cm-3 2.9
ture of thermal decomposition (Tonset) (at conversion fac-
Chopped glass fibers
tor, a = 5 %), temperature of maximum rate of mass loss
Average length/mm 4.5
(Tpeak) (from DTG curves), the end temperature at which
Average size/lm14
the residue remains unaffected (Tend), the residue which
Density/g cm-3 2.9
presented the residual solid mass fraction percentage
detected at Tend, and the activation energy (Ea) were
investigated. The activation energies were calculated by
Experimental Flynn Wall Ozawa (Integral method) and Kissinger.
Conversion values, a = 5 50 % at each 5 % conversion
The materials used in this study were recycled polyethyl- were used for estimating the activation energy values using
ene and recycled polypropylene supplied in pellets by local Flynn Wall Ozawa method.
plastic recycling plant (www.dohaplastic.com, Qatar),
which were derived mainly from post-consumer plastics Differential scanning calorimetry
waste. Both materials were characterized and some phys-
icochemical characteristics are summarized in Table 2. Differential scanning calorimetry analysis was carried out
Mica flakes and chopped glass fibers provided by Sheffield using a Perkin Elmer Instrument Pyris 6 DSC with a
University were used as fillers with their respective prop- sample mass of 8 10 mg. All samples were held at 30 C
erties presented in Table 2. The materials were thoroughly for 5 min, heated at a rate of 10 C min-1 to 300 C,
dried before the compounding in order to minimize the subsequently held for 5 min to erase the previous thermal
influence of moisture. Polypropylene and polyethylene history, and then cooled at a rate of 10 C min-1 to 30 C,
were dried at 60 C for one hour; the glass fiber and mica subsequently held for 5 min and heated again at a rate of
were dried at 90 C for three hours. Systems made of 10 C min-1 to 300 C under nitrogen atmosphere. The
recycled polyolefin and combinations of fillers were pre- cold crystallization temperature (Tc), melting temperature
pared using Brabender a twin-screw extruder at Qatar (Tm), and heat of fusion were determined from the second
University. The processing temperature of extruder in the heating scan. The crystallinity of samples (Xc) was deter-
feeding zone, the mixing zone, and the die were 180, 200, mined using the following expression [26]:
and 220 C, respectively. The twin screw rotating speed
DHf 100
Xcź 6
was fixed at 60 rpm. Upon completion of melt blending,
DHf w
the extruded strands were allowed to cool in the water bath
at 25 C, and then cut into pellets using a pelletizer. The value of DHf which is the heat of fusion of 100 %
Table 3 shows the designated symbol for each system and
of crystalline RPE is 293 J g-1 [27] and 209 J g-1 for RPP
the corresponding compositional ratio of each constituent.
[28], DHf is the heat of crystallization obtained from DSC
123
814 M. A. AlMaaded et al.
Table 3 Compositions of the processed samples
(a)
100
MRPE1
Designated symbol Composition and compositional ratio
MRPE2
RPE
By volume/vol % By mass/mass %
80
MRPE1 15 mica/85 RPE 35 mica/65 RPE
60
MRPE2 30 mica/70 RPE 57 mica/43 RPE
MRPP2 30 mica/70 RPP 43 mica/57 RPE
GFRPE1 15 GF/85 RPE 32 GF/68 RPE 40
GFRPP1 15 GF/85 RPP 33 GF/67 RPP
20
M mica, GF glass fiber, R recycled, PE polyethylene, PP
polypropylene
0
400 450 500 550 600
Temperature/C
curves, and w is the mass fraction of polymer in the
composite.
5
(b)
0
Results and discussions
5
Thermogravimetry
10
15
Effect of particle loading on thermal degradation
20
The thermal degradation of neat recycled polyethylene
MRPE1
MRPE2
25
(RPE), and the systems of RPE containing different
RPE
quantities of mica in nitrogen was determined by thermo-
30
gravimetry. The mass loss increases with temperature, for 400 420 440 460 480 500 520 540
heating rate of 10 C min-1, are shown in Fig. 1a, b. The Temperature/C
onset temperature of thermal degradation (Tonset), peak
Fig. 1 a TG curves of RPE and MRPEs systems at heating rate
mass loss temperature (Tpeak), end decomposition temper-
10 C min-1 and b the corresponding DTG curves
ature (Tend), and the residue at Tend are given in Table 4.
These results are obtained by averaging the results from
Table 4 Decomposition characteristics of pure RPE, pure RPP,
three runs for each sample. Tonset, Tpeak, Tend, and the res-
MRPE1, MRPE2, MRPP2, GFRPE1, and GFRPP1 systems
idue in Table 4 are the average of three values. A deriva-
Composite Tons/C Tpeak/C Tend/C Residue/%
tive mass loss curves, DTG, were used to indicate the
temperatures at which mass loss is peak (Tpeak) and ends
RPE 429.0 478.3 497.1 4.8
(Tend).
RPP 415.5 459.8 493.0 7.0
It is evident from TG curves that, the mass loss of RPE
MRPE1 428.3 479.8 496.8 29.0
occurred in a one-step degradation process from 400 Cto
MRPE2 442.8 483.1 500.8 51.9
below 500 C. This result is confirmed by the presence of
MRPP2 442.6 473.4 479.8 56.0
single peak in DTG curve, at temperature of 478.3 C
GFRPE1 434.9 479.4 495.5 32.3
(Table 4). The mass loss of RPE starts at about 400 C.
GFRPP1 404.9 458.2 478.7 40.1
Above 450 C, this process accelerates rapidly and the
quantity of RPE residue is relatively low (equal to 4.8 %).
This is due to further break down of RPE into gaseous result is also confirmed by the presence of the single peak
products at high temperature. The relatively higher amount from DTG curves, which might have been the result of
of residue in RPE is due to thermally stable additives that random chain scission process and subsequent pyrolysis of
were added during the recycling process. the samples.
On the other hand, the thermal degradation of RPE The effect of particle loading can be observed also from
composites with mica increases gradually up to approxi- Fig.1a, b, in which the thermal stability of recycled RPE is
mately 400 C, and then a more marked mass loss occurs sensitive to a large quantity of inorganic fillers. This
between 400 and 500 C. All samples showed a peak mass clearly appears in the obtained values of Tonst, Tpeak, and
loss on reaching about 480 C more or less (Table 4). This Tend (Table 4). The onset temperatures of the thermal
123
Mass loss/%
1
Derivative mass loss/% min
Additives on recycled polymer blends 815
degradation processes of the system that contains higher
(a)
content of fillers (30 % of mica) were increased compared MRPE1
100
GFRPE1
to that of system containing 15 % of mica. For Tpeak and
Tend of thermal degradation process of studied systems, the
80
temperature difference between low and higher content is
slightly changed. Decomposition temperature increases
60
with the increase in filler content in the system due to the
relatively high molecular weight and crystalline nature of
40
the modifier, which increases their thermal resistance.
Effect of filler type on the thermal degradation of systems 20
These experiments were designed to measure the effect of
0
400 450 500 550 600
GF loading on the thermal properties of RPE in comparison
Temperature/C
to the effect of mica. This was examined in non-isothermal
TG and DTG. The TG and the corresponding DTG curves (b) 5
obtained at a heating rate of 10 C min-1 for GFRPE1 and
MRPE1 are shown in Fig. 2a, b. TG curves correspond to
0
single-stage degradation with well-defined initial and final
degradation temperatures. The rapid mass loss steps of both
5
systems start at 430 C. The thermal degradation of samples
can take place through random chain scission and a radical
chain mechanism. The onset temperature of thermal deg-
10
radation (Tonset), the peak temperature where the maximum
decomposition rate was obtained (Tpeak), the end tempera-
ture at which the residue remains unaffected (Tend), and the 15
residue which presented the residual solid mass fraction
percentage detected at Tend are tabulated in Table 4. Evi-
20
400 450 500 550 600
dently, the onset temperature of thermal degradation of the
Temperature/C
GFRPE1 system is higher than that of MRPE1. This is
indicative of improved fiber matrix interaction and the
Fig. 2 a TG curves of MRPE1 and GFRPE1 systems at 10 C min-1
effectiveness of glass fiber as reinforcing agent.
and b DTG curves for the same systems
It is also seen from Table 4 that even after complete
(Tonset), when comparing thermal degradation of RPE
degradation, char residue is very high for both systems
composite with mica and mica-filled RPP system. Appar-
filled with GF and mica whereas for neat RPE char residue
ently, there is little compatibility and interfacial adhesion
is only 5 %. This is due to the presence of thermally stable
between inorganic fillers and RPP matrix. Some studies
glass fiber and solid inorganic filler. Moreover, the residue
have reported [29] that the uncoupled glass fiber creates a
solid of both systems were found to be consistent with the
poor interfacial adhesion with polypropylene resin.
composition in the molding compounders suggesting good
dispersion of the fillers in the matrix.
Determination of activation energy
Effect of polymer filler interaction on the thermal
F W O method
degradation of systems
TG curves for the MRPE1, MRPE2, MRPP2, GFRPE1,
Figure 3a shows the thermal stability when mica is added
and GFRPP1 systems at different four heating rates are
to RPE and RPP. While, Fig. 3b shows when GF is added
to RPE in comparison to GF-filled RPP. In GF- and mica- shown in Fig. 4a e, respectively. It is observed that the
increase in the heating rate results in a higher degradation
filled RPP, the decomposition temperature and the thermal
temperature, and a higher decomposition temperature
stability are reduced as shown in Fig. 3a, b and presented
(Tonst). The possible explanation is that the polymer
in Table 4. Also, the shifting of the peak values of (Tonst),
absorbs more heat energy during exposure to slow heating
(Tpeak), and (Tend) is observed with GF-filled RPE in
rates [30]. To obtain activation energy (Ea kJ mol-1) of
comparison to GF-filled RPP. Same trend is observed for
thermal decomposition using Flynn and Wall expression
(Tpeak) and (Tend), while there is no significant change in
123
Mass loss/%
1
Derivative mass loss/% min
816 M. A. AlMaaded et al.
Fig. 4 shows a series of such lines created from the six
(a)
MRPE2
curves shown in Fig. 4a e, respectively, by plotting the
100
MRPP2
data at different conversion levels.
It is shown in the insets of Fig. 4a e that the fitted lines
80
are nearly parallel, which indicates approximate activation
energy values at different conversion rates, and conse-
60
quently implies the possibility of single reaction mecha-
nism (or the unification of multiple reaction mechanisms).
40 The reaction mechanism, however, also might change in
comparatively higher conversion periods according to
slopes at a = 0.6 in Fig. 4a e. The change of reaction
20
mechanism in higher conversion might be caused by the
complex reactions in decomposition process of the main
0
filler components. Generally, the decomposition conver-
400 450 500 550 600
Temperature/C
sion when conversion rate is higher than 0.6 becomes
meaningless for polymer systems due to high temperature
(b)
and sample mass loss.
GFRPE1
100
Figure 5 shows the plots of activation energy Ea as a
GFRPP1
function of conversion a obtained for the thermal degra-
80
dation of RPE, MRPE1, MRPE2, MRPP2, GFRPE1, and
GFRPP1 systems calculated by Flynn Wall Ozawa
method. As the thermal decomposition process proceeded
60
in the inorganic filler, the activation energy was slightly
changed after the initial stage and then remained nearly
40
constant within a certain range of a. This range is system
dependent and after that range, Ea was slightly decreased.
20
Also shown, the presence of low values of Ea for low
conversion and high Ea in high conversion might imply the
different decomposition mechanisms in the whole process.
0
400 450 500 550 600
Whenever filler is added into a polymer, the interaction
Temperature/C
between polymer and filler may lead to many processes
Fig. 3 a TG curve of MRPE2 in comparison to that of MRPP2 and like bound rubber formation, rubber shell formation,
b TG curve of GFRPE1 in comparison to TG curve of GFRPP1 (at
occlusion, and filler networking. Based on the nature of
10 C min-1)
filler, polymer, and particle loading one or more of the
above process can take place and have effect on the deg-
[22, 23], the first step is the choice of level of decompo- radation of the polymer [31 33].
sition. Typically, a value early in the decomposition profile
is desired since the mechanism is more likely to be that of Isoconversional Kissinger method
the actual product failure. On the other hand, taking the
value too early on the curve may result in the measurement Free isoconversional Kissinger method [21] is used to cal-
of some volatilization (e.g., moisture) which is not culate the activation energy as an alternative way in this
involved in the failure mechanism. A value of 5 % con- study. The maximum degradation temperature (Tpeak) for
version level is a commonly chosen value. Therefore, the different systems has been determined first from DTG curves
fixed conversions, a were selected from 0.05 with incre- of each system and hence ln(b/Tpeak) against 1,000/Tpeak
ment of 0.05 until the temperature at which the mass loss plots are prepared and presented in Fig. 6. Figure 6 shows
change remains stable. After the final conversion level, that the fitting straight lines are nearly parallel and thus
there is only the presence of residue not considered in the improve the applicability of this method. The activation
calculation of Ea. Using the selected value of conversion, energy is determined from the slope of the straight line.
the temperature (in Kelvin) at that conversion level is
measured for each thermal curve. A plot of log b versus DSC analysis
1,000/T at constant conversion is produced. The plotted
data should produce a straight line, and the activation DSC has been carried out to evaluate interaction of par-
energy is determined from the slope of each line. Inset of ticulate components in the polymer composites. The effect
123
Mass loss/%
Mass loss/%
Additives on recycled polymer blends 817
2.5
ą = 5 %
(a) (c)
ą = 10 %
100 2.5
ą = 15 %
ą = 20 %
100
ą = 25 % ą = 5 %
2.0
ą = 30 %
ą = 10 %
80 ą = 35 % 2.0
ą = 15 %
ą = 40 %
80 ą = 20 %
ą = 45 %
ą = 25 %
1.5
ą = 50 %
ą = 30 %
60 ą = 55 % 1.5
ą = 35 %
60
ą = 60 %
1.0
40 1.0
40
= 5 C min 1
0.5
= 5 C min 1 = 10 C min 1
20 0.5
20
= 10 C min 1
= 20 C min 1
= 20 C min 1
= 40 C min 1
= 40 C min 1
0 0.0 0 0.0
400 450 500 550 1.25 1.30 1.35 1.40 1.45 1.50 400 450 500 550 1.2 1.3 1.4 1.5
Temperature/C Temperature/C
1000/T/K 1 1000/T/K 1
2.5
ą = 5 %
= 5 C min 1
ą = 10 %
(b) 2.5 (d)120
= 10 C min 1
ą = 15 %
= 20 C min 1 ą = 20 %
100 ą = 5 %
ą = 25 % 2.0
= 40 C min 1
100
ą = 30 %
ą = 10 %
2.0 ą = 35 %
ą = 15 %
ą = 40 %
80
ą = 20 %
ą = 45 %
80
1.5
ą = 50 %
ą = 25 %
ą = 55 %
1.5
ą = 30 %
60
ą = 35 %
60
ą = 40 %
1.0
1.0
40
40
= 5 C min 1
= 10 C min 1
0.5
0.5
= 20 C min 1
20
20
= 40 C min 1
0.0
0 0.0 0
400 450 500 550 1.2 1.3 1.4 1.5
400 450 500 550 1.3 1.4 1.5 1.6
Temperature/C Temperature/C
1000/T/K 1
1000/T/K 1
2.5
(e)
ą = 5 %
100
ą = 10 %
ą = 15 %
2.0
ą = 20 %
ą = 25 %
80
ą = 30 %
ą = 35 %
ą = 40 %
1.5
ą = 45 %
60
ą = 50 %
ą = 55 %
1.0
40
= 5 C min 1
= 10 C min 1
0.5
20
= 20 C min 1
= 40 C min 1
0 0.0
400 450 500 550 1.30 1.35 1.40 1.45 1.50
Temperature/C
1000/T/K 1
Fig. 4 TG curves for a MRPE1, b RPE2, c MRPP2, d GFRPE1, and e GFRPP1 systems at different heating rates. The insets are the
isoconversional curves of each system by F W O expression derived from the corresponding figures
of filler type and filler content on the Tm, Tc, DHf, and the heat of enthalpy of melting peak at 127.8 C is pre-
crystallinity (XC) of each system obtained from Fig. 7a, b valent as compared to the heat of enthalpy of the shoulder
are illustrated in Table 5. The endotherm between 100 and peak at 110 C, which designates that the waste plastic
140 C and between 150 and 180 C represents the melting contains major percentage of high molecular mass grades.
of the crystallites in the RPE and RPP matrix, respectively. Also, the incorporation of mica-filled RPE has significant
As shown in Fig. 7a, b, DSC curves of RPE revealed effect on both Tm and Tc (Table 5). Two melting endo-
one sharp melting peak at 127.8 C and peak shoulder at therms still have been observed for mica-filled RPE sys-
110 C. These indicated the presence of different types of tem, one sharp around 130 C and a broad shoulder peak
polymer grades in plastic waste. Evidently from Fig. 7a, b, appears at about 110 C. This shoulder peak becomes
123
log
log
Mass loss/%
Mass loss/%
log
log
Mass loss/%
Mass loss/%
log
Mass loss/%
818 M. A. AlMaaded et al.
220
(a) (b)
RPP
RPE
215
210
MRPE1
205
200
MRPE2
195
MRPP2
190
MRPE1
RPE MRPE2 GFRPE1
185
MRPP2
GFRPP1
180
0 20 40 60 0 20 40 60 0 20 40 60
Conversion rate/%
GFRPE1
GFRPP1
Fig. 5 A comparison of apparent activation energy as a function of
40 60 80 100 120 140 160 180 200
40 60 80 100 120 140 160 180 200
decomposition conversion rate (a) for all investigated composites
Temperature/C
calculated by F W O method. The solid lines are drawn to guide the
eyes
Fig. 7 DSC endothermic melting curves and exothermic cold
crystallization for a RPE, MRPEs, GFRPE1, and b RPP, MRPP2,
9.0 and GFRPP2 systems at heating rate of 10 C min-1
MRPE1
GFRPE1
MRPE2
9.5 Table 5 DSC curves data of RPE, RPP, MRPEs, MRPP2, GFRPE1,
GFRPP1
MRPP2
and GFRPP1 systems at heating rates of 10 C min-1
10.0 Composite Tm/C Tc/C (DHf)polymer/J g-1 (Xf)polymer/%
RPE 127.4 114.8 98.7 33.7
10.5
MRPE1 131.1 111.8 106.5 36.4
MRPE2 130.1 112.5 120.7 41.2
11.0
GFRPE1 128.6 114.2 120.0 41.0
RPP 162.0 119.1 80.0 38.3
11.5
MRPP2 164.9 122.0 46.3 22.2
GFRPP1 166.6 123.5 54.2 26.9
12.0
1.28 1.30 1.32 1.34 1.36 1.38 1.30 1.32 1.34 1.36 1.38 1.40 1.42
1.28
1000/Tm/K 1
The results were different for RPP and its composite
with mica. As shown in Fig. 7b, two melting peaks have
Fig. 6 Kissinger non-isothermal plot of heating rate versus reciprocal
of temperature for MRPE1, MRPE2, MRPP2, GFRPE1, and GFRPP1
been observed, one sharp around 160 C and a second
at DTG peak temperature
smaller melting peak appears at about 150 C. This would
indicate that mica-filled RPP system exhibited a bimodal
less pronounced when mica content increases by 30 % by
crystal distribution after processing. This also appears in
volume indicating that the bimodal crystal distribution
the low crystallinity level obtained after incorporation of
disappears by increasing the filler content. Furthermore, the
mica into RPP when compared to pure RPP crystallinity
width of the cold crystallization and melting curves for
(Table 5).
both systems is narrow and becomes narrower at higher
In addition, Fig. 7a, b shows DSC thermograph of RPE
filler content. Thus, in the case of mica-filled RPE, it seems
composite with GF. Table 5 shows the variation of melting
that there is some level of compatibility in these systems
temperature, crystallization temperature, and crystallinity
especially at higher content of the filler. The increase in
of polymer matrix with GF addition. Compared with the
perfection or crystallinity (Table 5) is due to enhancement
pure polymer, the new morphology has not changed the
of crystal nucleation in the region surrounding the rein- position of melting peak and cold crystallization signifi-
forced particles [34]. This is strongly recommended by the
cantly. The peaks shape has changed only due to the
observed decrease in Tc values (Table 5) for these two
presence of GF filler. As shown in Table 5 the crystallinity
systems indicating the mica as an effective nucleating
of GF-reinforced RPE is increased predominantly. This
agent.
increment is due to the small and uniform crystallite size
123
1
a
E
/kJ mol
Heat flow endo up/mW
2
m
ln( /
T
)
Additives on recycled polymer blends 819
(a) 45 (b)
MRPE1 MRPE2 MRPP2 GFRPE1 GFRPP1
= 5 C min 1
40 = 10 C min 1
= 20 C min 1
= 40 C min 1
35
30
25
= 5 C min 1
= 10 C min 1
20
= 20 C min 1
= 40 C min 1
15
40 80 120 160 40 80 120 160 40 80 120 160 200 80 120 160 80 120 160 200
Temperature/C Temperature/C Temperature/C
Fig. 8 a DSC curves for MRPE1, MRPE2 and MRP2 systems and b GFRPE1, and GFRPP1 systems at different heating rates (5, 10, 20, and
40 C min-1)
(a) 8.0 8.0 8.0
(b)
GFRPE1
MRPP2
GFRPP1
8.5 8.5 8.5
2
R = 0.824
2
R = 0.990
9.0 9.0 9.0
R2 = 0.909
9.5 9.5 9.5
R2 = 0.938
R2 = 0.995
10.0 10.0 10.0
MRPE1
MRPE2
10.5 10.5 10.5
2.44 2.46 2.48 2.50 2.44 2.48 2.52 2.40 2.44 2.48 2.24 2.26 2.28 2.30
2.40
1000/Tm/K 1 1000/Tm/K 1 1000/Tm/K 1 1000/Tm/K 1
Fig. 9 Kissinger non-isothermal plot of heating rate versus reciprocal of temperature for a MRPE1, MRPE2, and MRPP2 systems and
b GFRPE1, and GFRPP1 at DSC peak (B) temperature derived from Fig. 7a, b, respectively
Compared with the neat RPP, the composite with GF
Table 6 The value of Ea/kJ mol-1 for the polymer degradation in
has higher melting peak temperature and also crystalliza-
each system obtained by Kissinger method from TG analysis and
compared with average values of activation energy obtained by F W tion peak temperature. Since untreated GF does not exhibit
O methods obtained at different conversion ratios
good adhesion or dispersion in the RPP matrix, one
observes the deterioration in the crystallinity of RPP
System Activation energy/kJ mol-1 obtained by
composite with GF (Table 5). However, the final statement
F W O method Kissinger method
about the effect of filler on thermal stability requires more
TG TG DSC
study of thermal history and filler characteristics which will
be presented in the future work.
RPE h207.7ią 9 90.4
MRPE1 h213.9ią 29 268.9 372.6
MRPE2 h236.3ią 43.4 295.8 458.1
Determination of activation energy for investigated systems
MRPP2 h228.9ią 40.7 227.5 233.1
GFRPE1 h244.8ią 68.3 320.5 221.0
Since many transitions (evaporation, crystallization,
GFRPP1 h214.0ią 19.9 247.9 87.3
decomposition, etc.) are kinetic events, they are function of
The values of Ea obtained by Kissinger method from DSC analysis
both time and temperature. DSC, therefore, was used with
are also presented
four scanning rates (5, 10, 20, and 40 C min-1) to ana-
lyze, MRPE1, MRPE2, MRPP2, GFRPE1, and GFRPP1
distribution. Also it indicates that there is a good adhe- systems and compare their characteristics for thermal
sion between GF and RPE matrix. The size of crystallites transition. The effects of heating rate on melting behavior
is determined by the type and volume fraction of added of studied systems are shown in Fig. 8a, b. It can be seen
filler [31]. that the lower the heating rate, the higher the peak
123
Heat flow undo up/mW
Heat flow undo up/mW
Heat flow undo up/mW
2
2
2
2
m
m
m
m
ln( /
T
)
ln( /
T
)
ln( /
T
)
ln( /
T
)
820 M. A. AlMaaded et al.
resolution, and consequently the shoulder peak still exists. (2) TG and DTG results revealed that:
This may be interpreted that the slower heating rates enable
(a) TG curves of RPE and RPP and their composites
a semicrystalline polymer to have more time for crystal
with mica and GF showed a single stage of mass
growth prior to final melting. At higher heating rate, there
loss. The severe mass loss from 400 to 500 Cis
is no sufficient time for crystal rearranging and the shoul-
due to break down of polymer into gaseous
der peak, representing two populations of RPE and RPP
product.
crystals in the polymer composites, disappeared. For this
(b) MRPE2 showed better thermal stability com-
reason, high heating rates should normally be used when
pared with MRPE1 indicating that the effect of
trying to measure small transitions as they provide large
filler reinforcement increased with filler loading.
heat flow signals. It is also shown that distinguishing peaks
(c) The glass fiber is more effective as reinforcing
are shifted to higher temperatures with an increase in
agent than mica particles.
heating rate [26].
(d) Inorganic organic filler exhibited weak interac-
The peak temperatures of the main endothermic curves
tion with RPP matrix than that observed with
in the DSC signals at different heating rates were used with
RPE polymer.
the Kissinger model for determination of the activation
(e) With the TG carried out at four different heating
energy of thermal transition which can be calculated from
rates, the F W O method was used to analyze
2
the slope of the graph by plotting ln (b=Tm) as a function of
the pyrolysis kinetics of systems. It was found
(1,000/Tm) [21]. Figure 9a, b shows the Kissinger plots for
that the presence of low values of Ea for low
the studied systems.
conversion and high Ea in high conversion might
The values of Ea for the polymer degradation in each
imply the different decomposition mechanisms
system obtained by Kissinger method from TG analysis are
in the whole decomposition process. It was also
presented in Table 6 and compared with average values of
found that higher heating rate provides the better
activation energy obtained by F W O methods obtained at
thermal stability, resulting from the decelerated
different conversion ratios. It is noticed that the values
decomposition rate.
obtained by Kissinger s method are overall higher than
(3) DSC analysis revealed that:
those obtained by isoconversional method. Accordingly, an
appropriate apparent activation energy range should be
(a) The melting endotherms of RPE and its com-
obtained by combining all values from the two methods
posite with mica can be considered as bimodal.
and consequently a general activation energy range is
Also, mica has the influence on crystallinity
suggested for most inorganic fillers for the purpose of
degree of RPE matrix. These trends are depen-
polymer composites processing. The obtained values of
dent on loading level.
activation energy by Kissinger method from DSC analysis
(b) GF promotes the crystallinity degree of RPE
are also presented in Table 6 and, therefore, can be com-
matrix.
pared with the corresponding values obtained from TG
analysis.
Acknowledgments The authors acknowledge the financial support
from Qatar Science and Technology Park (QSTP). We would like also
like to thank Center of Advanced Materials and office of research at
Conclusions
Qatar University for their support.
In this study, detailed experimental analyses of thermal
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