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Chapter 7
Thermal Degradation and Crystallisation Behaviour
,,,,
Abstract
In this chapter we discuss the thermal degradation and
crystallisation behaviour of nylonlEPDM blends. Effects of
blend ratio, compatibiliser concentration and dynamic
vulcanisation on the thermal degradation of the blends are
discussed in detail. The kinetic parameter of the degradation
process is studied. Melting and crystallisation behaviours of the
various blend systems are also evaluated. The percentage of
crystallinity of neat polymers is measured and the effects of
blend ratio and compatibilisation on the percentage of
crystallinity are determined.
Tartl, 14,32-7.
236 Chapter 7
7.1 Introduction
The study of thermal stability and crystallization behaviour of
polymers and polymer blends is of high interest to the field of science and
technology. In order to develop durable industrial products it is necessary
to investigate the thermal stability of these blends. Further, a change in heat
flow and stability of polymers will give some idea on the extent of
chemical interaction occurring between the components, their bond
strength, activation energy, melting temperature and degradation kinetics.
Polyamides have been extensively studied due to its demanding
applications where the properties of thermal stability and fire resistance are
required 11-41. Several articles are available to prove the great impact of the
thermal stability of polymers on blending [5- 161.
The thermal stability of the blends depends strongly on the
compatibility of the polymers [17-191. One of the most accepted methods
for studying the thermal properties of polymeric materials is the
thermogravimetry. Thennogravimetric curve represents the variation in the
weight (W) of the sample with temperature (T). The integral (TGA) and
derivative (DTG) therrnogravimetric curves provide information about the
nature, number of stages of thermal break down, weight loss of the
materials in each stage, threshold temperature, stability and extent of
degradation of the polymeric materials [20]. From the studies of Martuselli
et al. 1211, we could get the fundamental information about the miscibility
of blends and phase diagram of the components in the molten state.
The degree of crystallinity is the one of the most important
parameters for characterising crystalline and semicrystailine polymers. The
miscibility, melting and crystallization behaviours of polymer blends can
be analysed by differential scanning calorimeter (DSC). DSC ananlysis
Thermal D e a d o n and Crvstallisation Behaviour 237
gives the heat flow rate associated with a thermal event as function of time and
temperature to obtain quantitative information about melting and phase
transition of polymeric materials [22,23]. Some of the recent reports on thermal
studies include works of Run et al. (241, Shibata et al. [2S] and Lai et al. [261.
The measurement of polymer crystallinity has been reviewed by
Miller 1271. Several articles deal with the crystallization behaviour of
various crystalline/amorphous and crystalline/crystaslline polymer blends
128-321. It has been reported that blending of polymers has got significant
role on the crystallization properties on the individual polymers. X-ray
diffraction (XRD) is also widely used for evaluating polymer crystallinity.
The crystallinity with respect to the crystallite size and perfection can be
determined by wide angle X-ray scattering (WAXS). Many authors [33-351
have used WAXS for studying the crystallinity of polymers.
Moly et al. [36] studied the thermal and crystallization behaviour of
linear low density polyethylene (LLDPE) and ethylene vinyl acetate (EVA)
and found out that heat of fusion and crystallinity of the blends were
reduced by the addition of EVA. Santra et al.1371 investigated the effect of
compatibiliser ethylene maleic anhydride (EMA) on LDPE/ poly(dimethy1
siloxane) (PDMS) blends and found out that the thermal stability of these
blends were improved upon the compatibilisation. Yordano and Minkova
[38] reported on the fractional crystallization of compatibilised low density
polyethylene (LDPE)I polyarnide (PA6) blends. PizzoIi et al. (391 reported
the presence of low melting crystallinity in EPR rubbers. The decrease in
melting temperature for the polyamides by incorporating acrylonitrile
butadiene styrene (ABS) in blends of PA 6,PA 66 PA 6,10 with ABS have
been studied by Stolp et al. [a].
238 Chapter 7
In this chapter, attempt has been made to investigate the melting
and crystallization behaviour of nylonlEPDM blends as function of blend
ratio, compatibilisation and dynamic vulcanisation. Thermal stability and
degradation kinetics of the blends have been analysed by thermo
gravimetry (TGA). Differential scanning calorimetry (DSC) has been
employed to determine the melting and crystallisation behaviours of the
blends. XRD investigations has been used to characterize the crystalline
structure of nylon copolymerlEPDM blends. Attention has also been paid to
correlate thermal and crystallisation behaviours of the blends with the
morphology and phase structure of the blends.
7.2 Results and Discussion
7.2.1 Thermal degradation
7.2.1.1 Neat polymers
Polymers are useful in certain range of temperature-a low
temperature limit below which they are brittle and a high temperature limit
above which they soften, melt degrade and ultimately decompose. The
TGA and DTG thennograms of nylon copolymer and EPDM in nitrogen
atmosphere at a heating rate of 20°C/min are shown in the Fig. 7.1 and
Fig. 7.2 respectively. As can be seen from the Fig. 7.1, in the case of nylon
a minor weight loss at 165°C shows the elimination of water from nylon.
The second stage of degradation involves major degradation which stats at
368°C and gets completed at 500°C. Hence the sample can be considered
as stable up to 368°C in nitrogen atmosphere. Above 500°C volatilization
become very rapid and almost complete distillation occurs. So we could not
see any appreciable weight loss in the thermogram above this temperature.
The peak of the DTG curves gives the temperature corresponding to
maximum degradation (T,,,). In the DTG curve of nylon, the peak
appeared at 429°C. Thermal decomposition of PA has been studied by
various researchers [4 1-49]. The degradation mechanism that is responsible
for the end products obtained can be represented as below based on the
literature reports. Kamerbeck et al. [41] suggested that thermal
decomposition of PA6 starts with homolytic scission of the N-alkylamide
bond so that primary arnide, nitrile, vinyl and alkyl chain ends are
generated (Scheme 7.1).
F'igure 7.1: Thennograms and derivative thennograms of nylon copolymer
100-
m-
E vl 60- : - 5 40- s
20 - 0
Scheme 7.1
Temperature (OC)
-1.0
- 0.5
-0.0
-4.5 2 - -1.0
5
- -1.5
-2.0
- - Nylon copolymer --.
0 100 200 300 400 5M1 Em
..........,
, , , , . - , , , , . , , . , . , , . , . , , ,
, . .
,..,....,,,..,,.,
, . , , . . , . , , . . , . . . , , , , . ,
, , . i ,
244 Chapter 7
It is also reported 142-441 that along with amines, amides and
nitriles, caprolactarn is also a major product in the degradation of PA6
(Scheme 7.2).
0
Scheme 7.2
Thermal decomposition of PA66 has been extensively reported. Wiloth and
Schnider [48,49] suggested that the main degradation mechanism of PA66
is based on the tendency of adipic acid fragment present in the polymer to
undergo cyclisation resulting in some cyclic products as we1 as carbon
dioxide (Scheme 7.3).
Scheme 7.3
Thermal Degradation and Cry stallisation Behaviour 24 1
The main feature of the degradation processes occurring in an inert
atmosphere above the melting point of nylon is the evolution of water,
carbon dioxide and cyclopentanone.
The degradation of EPDM (Fig.7.2) starts around 401 "C and almost
completed at 553°C. EPDM has got greater thermal stability in nitrogen
atmosphere than nylon, which is evident from the displacement of the
weight loss curve to much higher temperature. DTG curve (Fig.7. 2), also
supports the thermal stability of EPDM (T,, 462°C) when compared to
nylon (Tmax 429°C).
Temperature YC)
Figure 7.2: Thermograms and derivative thermograms of EPDM
IW-
81)-
3 BD- z -
5 40- s 20-
0
7.2.1.2 Uncompatibilised blends
The TGA and DTG thermograms of the blends are presented in
Figs: 7.3 & 7.4 respectively. Compared to the degradation pattern of the
individual components, the degradation behaviour of the blends is slightly
different.
0 Irn 2m m 400 sw soo
1
- 0
n - - T € - 3 - .2
-3
- EPDM
... .............. ............................ _ . , 4 : . , : : , . , , . . , , , ,
. . . , , . . . , .
.,..-- - ..... , ,
,
, . : :
, , . , , - , ,
: ! , , . , , - , , . ,
L 1 ,
242 Chapter 7
Temperature YC)
Figure 7.3: Effect of blend ratio on the thermograms (TGA) of neat nylon, EPDM and their blends
Simple Blends ( 'J I
P , O m m 4 w m a o m
Figure 7.4: Derivative thennograms (DTG) of neat nylon, EPDM and their blends
Thermal Deg-n and Crystailisdion Behviour 243
The weight loss of neat polymers and their blends at different temperatures
is given in the Table 7.1. It can be seen from Table 7.1 that degradation
temperature corresponding to different percentage weight loss decreases
gradually by the addition of rubber in blends. N30 possesses highest T,
value, which indicates that high thermaI stability than other blend systems.
Table 7.1 also gives the % weight loss of the specimen remained at two
different temperatures viz.400, and 450°C. As the weight percentage of the
rubber in the blend increases, a gradual decrease in weight loss can be
noticed indicating an increase in thermal stability. This indicates improved
thermal stability upon the incorporation of EPDM. Thermal. stability of the
polymer blends depends mainly on the morphology and miscibility of the
system. It should be noted that in N30 blends, the thermally more stable
EPDM forms the mdtrix where as in N T ~ blends nylon is the continuous phase.
The morphologies of NTO, N s ~ and N30 are shown in Fig.3.2 (Chapter 3), A
thermal degradation result suggests that even though the nylonEPDM blends
are immiscible, the thermal stability of nylon can be improved by the
addition of EPDM.
Table 7.1: Effect of blend ratio on degradation temperatures and weight losses at different temperatures of nylon EPDM blends
Sample
NIW
N7o
N ~ o
N3o
No
T,,,(*C}
368
372
380
385
40 1
Tm(OC)
422
43 9
445
452
46 1
Weight loss at
400°C (%)
20.3
12.2
10.5
8.3
1.5
Weight Ioss at
450°C (%)
94.3
62.9
57.9
45.7
22.1
T,,, ("C)
429
440
448
457
462
244 Chapter 7
The temperature at which maximum degradation occurs (T,,) from
the DTG curve and integrated procedural decomposition temperature
(IPDT) of nylon and EPDM blends are given in Table 7.2. PDT has been
employed to evaluate the relative thermal stability of blends under the
procedural conditions. IPDT of the blends was measured using Doyle's
method [50) given as:
where Ti and Tf are the initial and final experimental temperatures, A* is
the ratio of area under the curve (A1) and the total area (AI+A2) of the
thermogram and K* is the coefficient of A*. From the Table 7.2 it is clear
that there is a notable increase in thermal stability of nylon by the addition
of rubber.
Table 7.2: Effect of blend ratio on T, and IPDT of polymer degradation in nylon, EPDM and their blends
7.2.1.3 Compatibilised blends
The TGA and DTG curves of N70 blends compatibilised with EPM-
g-MA are shown in Figs.7.5 & 7.6 respectively.
IPDT (OC) -
4 18
438
44 1
448
450
Sample
NIW
N ~ o Nso
N3o
No
Tmx (OC)
429
440
448
457
462
Figure 7.5: Thermograrns of 70/30 nylon/EPDM blend compatibilised with EPM-g-MA
Figure 7.6: Derivative thermograrns of 70/30 nylon/EPDM blend compatibilised with EPM-g-MA
Compatibiliser has substantial influence on the thermal properties of the
blends. The thermal stability of the blends was found to be increased by the
incorporation of EPM-g-MA. In Fig. 7.6, the peak corresponding to the
major weight loss is shifted to higher temperatures upon compatibilisation.
Table 7.3 shows the degradation temperature and weight loss at different
temperatures for the compatibilised blends.
246 Chapter 7
Table 7.3: Degradation temperatures and weight Ioss at different temperatures of 70/30 nylon EPDM blend compatibilised with EPM- g-MA
The addition of even 1 % of EPMp-MA resulted in the improvement of
the onset temperature for degradation. The addition of 2.5 wt % of the
compatibiliser to NTO blend (Fig.7.3) has got the maximum degradation
temperature. Further addition of the compatibiliser (5wt% and 10 wt%) aim
showed improvement in degradation temperature compared to unmodified N70.
It can also be seen from the table that the T,, to the major weight loss (DTG
Peak value) increased upon compafibilisation. The percentage weight loss at
different temperatures decreased upon compatibilisafion.
This increase in degradation temperature of cornpatibiked blends is due
to the improved interfacial adhesion between the two components as the result
of compatibilisation, which is having a direct influence on the thermal
properties. EPM-g-MA can increase compatibility of nylonlEPDM blends
through interfacial chemical reaction between its anhydride groups and the
amine end groups of nylon. The resulting copolymer will locate at the interface
and decreases interfacial tension thus provides a good interfacial adhesion
between the nylon and EPDM phases. This in turn will contribute towards the
improvement of thermal stability. Therefore the enhand thermal stability of
T,,, ("C)
440
458
460
459
461 1
Weight loss at 400°C
(%)
12.2
8.1
8.1
7 .o 9.3
T50('C)
439
452
465
453
460
Sample
N ~ o
N70.1
N70.2 s
N70,5
Nlo.10
Weight loss at 450°C
I%)
62.9
45.5
44.5
43
34.5
T,,("C)
372
375
382
379
377
T h e m 1 Degradation and Crystallisation Behaviour 247
N 7 ~ blends upon compatibilisation addition can be attributed to the
compatibilising efficiency of EPM-g-MA.
It is important to note that there is a strong link between the
thermai properties and morphology of the blends. The compatibilising
efficiency of EPM-g-MA is well evident from the finely dispersed
uniform morphology compared to uncompatibilised blend. The
morphological parameters of nylon/EPDM blends derived from SEM
micrographs are shown in the Fig. 4.5 (Chapter 4). From the micrograph
it was clear that the domain size of the dispersed EPDM in the
compatibilised system is decreased considerably. It has been revealed
from this study that this stabilization of morphology through chemical
reaction has profound effect on the thermal, properties of the blends.
7.2.1.4 Dynamically vulcanised blends
The dynamic vulcanization of rubbers generally provides a
significant improvement in the degradation temperature since more
energy is required to break the bonds formed during vulcanization.
Figs. 7.7 & 7.8 show the thermograms and derivative thermograms of
dynamically crosslinked systems using various crosslinking agents.
I I
Temperature ("C)
Figure 7.7: Thermograms of dynamically vulcanised NTO nylon/EPDM blends with different crosslinking systems
248 Chapter 7
Figure 7.8: Derivative thermograms of dynamically vulcanised N70 nylon/EPDM blends with different crosslinking systems
Both the Tonset and T,,, show increase upon vulcanization. The data
obtained from the thermograms and derivative thermograms are presented
in Table 7.4. .a.
Table7.4: Degradation temperatures and weight loss at different temperatures of dynamically vulcanised 70130 nylon /EPDM blend with different curatives
T,,, ("C)
440
47 1
448
453
469
Sample
N7n
N7oS
N7&
N 7 a S
N70DS+Compa
Weight loss at 4000C
(%I
12.2
5.9
10.5
8
7.7
Weight loss at 450°C (%)
62.9
23.3
58
49.9
26.2
T..Wt("C)
372
382
370
375
388
Tro("C)
439
466
444
449
466
Thermal Degradartion and CrystQllisation Behaviaar 249
Among the vulcanised blends the initial decomposition temperature
is highest for the sulphur crosslinked system. DCP crosslinked system has
got lowest values. This is because the usage of peroxide as curative might
cause the degradation of nylon and this results in the poor thermal stability of
blend system. These types of results have been reported by Huang et al. [51].
Mixed vulcanizing system has got intermediate thermal stability as expected.
Mixed system with compatibiliser EPMg-MA has got higher thermal
stability than mixed vulcanised system. The degradation temperature follows
the order N70S>N70DS+Compa>N70DS>N7&. The improvement in the
thermal stability as the result of dynamic vulcanization can be explained on
the basis of the type of crosslinks formed and the crosslink density. The
sulphur vulcanised system produces mono and polysulphide linkages, a
peroxide system gives fise to C-C linkages, a mixed system produces both
pol ysulphide linkage and C-C linkages and mixed system with compatibiliser
produces chemical bonds in addition to the polysulphide linkage and C-C
linkages. The second factor which is to be considered is the crosslink density.
The sulphur crosslinked system shows the highest crosslink density
( 4 . 2 ~ 1 0 ~ r n o ~ ~ ) . The increased crosslink density in turn increases the number
of bonds that have to be broken during the degradation process. This
naturally increases the thermal stability of the blends. The T50 dso increased
as a result of dynamic vuIcanisation (Table 7.4).
7.2.1.5 Kinetic analysis of thermal decomposition
In the present study, kinetic parameters for the thermal
decomposition of the nylon, EPDM and their blends have been determined
by applying an analytical method proposed by Coats- Redfern [52].
h the Coats-Redfern method activation energy is obtained from the
equation:
where a is the decomposed fraction at any temperature and is given as:
a = Ci - C I Ci - Cf where C i s the weight at the temperature chosen, Ci is
the weight at initial temperature and Cf is the weight at final temperature,
4 , i s the heating rate, E is the activation energy for decomposition, The
activation energy (E) and pre-exponential factor (A) was determined from
the plot of in[g(ax,] against the reciprocal of absolute temperature
(lm). Activation energy (E) can be calculated from the slope of the curve
and from the intercept value, pre-exponential factor (A) can be calculated.
The order of decomposition reaction was determined from the best linear fit
of the kinetic curve that gives the maximum correlation coefficient.
Various authors based on integral method to determine the kinetic
parameter of thermal decomposition suggest numerous mechanistic equations.
All the themo gravimetric data were analysed using nine mechanistic
equations (nine different forms of g (a)) proposed by Satara [53] and the
effects of blend ratio, compatibiliser loading and crosslinking on kinetic
parameters were studied. The form of g (a), which best represents, the
experimental data gives the proper mechanism. The nine possible equations
and the rate controlling process in each case are given in the Table 7.5. The
kinetic parameters were calculated using a computer programme. From these
calculations we found that the Mampel equation fits well in the case of various
unmodified and modified nylon/EPDM blends. This shows random nucleation
as the mechanism of degradation in the rate controlling process. The kinetic
parameters for the main stage thermal decomposition of various nylonlEPDM
blends are given in Table 7.6.
T h e m 2 D e g M o n a d Ciysballisation Behuviour 25 1
Table 7.5: Commonly used g(a) forms for solid state reactions
Table 7.6: Kinetic parameters for the thermal decomposition of various nylon/EPDM blends
Rate controlling process
Random nucleation-one nucleus on each particle- Mampel equation. Phase boundary reaction, cylindrical symmetry
boundary reaction, special symmetry
Two dimensional diffusion
Three dimensional diffusion spherical symmetry-Ginsthing-Brounshtein equation
Random nucleation-Avirami equation I Random nucleation-Avirami equation I1 Three dimensional diffusion, spherical symmetry-Jander equation One dimensional diffusion
Equation number
1.
2. 3. 4.
5.
6. 7. 8.
9.
The activation energy for degradation given in the Table 7.6
revealed that, the incorporation of EPDM resulted in the enhancement of
activation energy. From the table it is clear that the activation energy is
Form of €!(a)
-ln (1- a)
j-(1- 1 -(I- a ) l ) V h a ~ e
a + ( 1 - a) In ( t - a) ( 1 -2/3 a)-
( I - [-ln (1- a)]'' C-ln ( I - a)]'" [1-(1- ct)1/312
u2
Sample
Nloo
N ~ I I
Nso N30
Nu
Activation energy (k J/mol) (E)
114.5
135.3
141.4
158.2
181.2
highest for EPDM. Greater value of activation energy (E) indicates greater
thermal stability.
The effect of compatibilisation on the kinetic parameters is given in
Table7.7. It is interesting to note that all the compatibilised blends shows
greater activation energy (E) values as expected. This indicates that
compatibilisation using EPM-g-MA also increased the thermal stability of
NTa blend system. This shows increased interfacial interaction during
compatibilisation. Addition of 2.5% of compati biliser shows the highest
activation energy compared to other compatibilised and uncompatibilised
systems. The enhanced activation energy at 2.5% of compatibiiiser is due to
optimum cornpatibiliser concentration at this particular concentration.
Table 7.7: Effect of compatibilisation on Kinetic parameters for the thermal decomposition of various 70/30nylonEPDM blends
Sample
N7u NTO 1 % compatibilised N702.5%~~mpatibilised NT05 %Compatibilised NY0l 0% compatibilised
Activation energy (kJImo1) (El
135.3 148.5 190.6 183.9 175.3
Table 7.8: Effect of cross linking systems on Kinetic parameters for the thermal decomposition of various 70/30nylonEPDM blends
Sample Activation energy (kJ/mol) (E)
Thsrnaul Degradation and Ctystallis&'on Behaviour 253
In the case of crosslinked systems also (Table 7.8), the activation
energy increases as the result of crosslinking. Among the different cross
linking systems used, sulphur cross linked system showed higher activation
energy values. This can be attributed to the stable bonds formed during
vulcanization. The explanation given in the section 7.2.1.3 holds well here
also for the enhancement of activation energy during crosslinking using
various crosslinking systems.
7.2.2 Melting and crystallisation behaviour
7.2.2.1 Uncompatibilised blends
The DSC heating and cooling scans can be used to determine a
number of parameters signifying the melting and non-isothermal
crystdlization behaviour of the components in the blends. The melting peak
temperature (T,,), crystallization temperature (T,), heat of fusion (AHf) and
heat of crystallization (A&) were directly obtained from these graphs. The
PA used in this study is a copolymer of PA6 and PA66 It shows a wider
melting range compared to the homopolyamides PA6 and PA66 The
melting point (T,) of the copolyamide which we used in this study depends
on both composition and the susceptibility of the mixed components. The
T, of the crystalline component in a blend i s dependent on both
morphological and thermodynamic factors [54]. This is related to
crystallization conditions like temperature, time, blend composition and
scanning rate. These factors can cause increase or decrease in T,.
Fig. 7.9 represents the second heating endothems of nylon and
some of its selected blends with EPDM.
254 Chapter 7
sb r i o 130 150 170 190 Temperature VC]
Figure 7.9: Effect of blend ratio on the heating curves of nylon and nylon/EPDM blends
The melting parameters obtained from the heating curves are
summarized in Table7.9.
Table 7.9: Melting behavior of nylon /EPDM blend systems (2nd heating cycle)
The crystalline melting point (T,) is almost same in all blends
during second heating. This reveals that blending has no effect on the
melting point of the nylon and EPDM. This also indicates that the two
polymers are high1 y immiscible and the blends are incornpati ble.
wW(J/g ,
27.8
26.9
26.3
25.1
--
endset ("c) 182.6
185.2
183.4
183.6 -a
Sample
Nloo
N7o
Nso
N3o
No
Xc %
crystallinity
30.8
29.8
29.2
27.8
--
Tm onset ("C)
158.6
162.0
163.1
161.3 --
Trn ("C)
171.2
170.2
1 70.2
169.5
--
Therml DegrutWion and CrystcrUisation Bekvwur 255
The heating curves of nylon as well as the blends show a double
melting behaviour after the onset of T,. MuItiple melting behaviour of semi-
crystalline polymers is reported by various researchers [55-621. The multiple
melting behaviour may be due to reorganization and the consequent
recrystallisation and secondary crystallisation of nylon crystals after the first
heating. Recrystallisation is a process in which the imperfect lamellae melt
and recrystallise to produce thicker and more perfect lamellae, which
will melt at a higher temperature. As a result of this process a double
melting behaviour can be observed. Recrystallisation has been observed
for neat polymers and blends (551. A complex melting behaviour is also
observed when a semi-crystalline polymer exhibits two different types of
crystal structure. The double melting peaks are quite common in DSC
measurements of nylon6 and nylon66 samples due to the presence of different
crystal line forms 16 1 -621. Therefore the multiple melting behaviour of nylon
might be due to the presence of different crystalline forms in the polymer
including pseudohexagonal, orthorhombic and monoclinic crystalline forms.
In the Fig. 7.9 an exotherm appeared at 85.5 "C corresponding to
the temperature of coId crystallization. During DSC scan crystal Iisable
polymers can exhibit a heat activated crystallization peak [63]. In the case
of nylon, those polymer chains which are crystIIisable but could not, due to
the fast processing procedure undergo reorganization upon heating. This
leads to an exothermic peak before T,, which corresponds to the cold
crystallization.
The onset of T, and the melting temperature (T,) of nylon appeared
at 158.6 and 17 1.2"C respectively. On adding EPDM, the thermogram
exhibits a different behaviour. The normalized value of enthalpy of fusion,
AHf decreased to 25.1 for rubber rich bIends (N~c)). The % crystallinity and
256 Chapter 7
enthalpies of fusion of the blends are significantly depending on the blend
composition. The glass transition values of the blends are also decreased
(-49 to-60). This can be attributed to the plasticizing effect as well as due to
the encroachment of EPDM rubber into the crystalline structure of nylon
formed as a result of strong intermolecular interaction. This causes
considerable reduction of chain rigidity, which reduces the T, of nylon due
to the increased mobility of nylon chains. The glass transition temperatures
(T,) of the sample were obtained from the inflexion of the thennograms in
the DSC trace. The T, of pure nylon and EPDM are found to be +60 and
-60 "C respectively. The heat of fusion values depend on the crystallinity
of the material. Hence % crystallinity of the blends can be calculated by
using the equation (1)
where AHqb.' is the enthalpy of fusion of the sample obtained
calorimetrically and AH; is the enthalpy of fusion the 100% pure
crystalline nylon, which is taken as 90kJ/mol. The effect of blend ratio on
the % crystallinity is given in the Fig. 7.10.
Weight % of Nylon
Figure 7.10: Effect of blend ratio on the % crystallinity of nylonlEPDM blends
Thermal Degradah'on and CrystQUisation Behaviour 257
It can be seen from the Table 7.9 and Fig. 7.10 that the crystallinity of
the system does not have appreciable change with increase in the rubber
concentration in the blend. Percentage crystallinity of the blends follow& the
same trend as enthalpies of fusion and crystallization. Martuscelli et d. [a] have
made a detailed investigation on the effect of elastomer phase on the
crystallization behaviour of thermoplastic elastomers, and observed that rubber
particles are present in the intra sperulitic region of the crystalline plastic phase.
This limits the mobility of the chains and thereby the growth of the crystalline
lamella into a more spherulitic structure, especially for the nylonlEPDM with a
high amount of rubber. This may be the reason for the marginal decrease in the
crystallinity.
Among the several methods for studying polymer miscibility DSC has
been mainly used for analyzing the compatibility of two polymers on molecular
scale. In this case as the one of the polymers is crystallisabk, DSC will hardly
provide direct and reliable information of the polymer T,. The presence of two
T,' s in the blends indicated the incompatibility of the polymers.
Crystallization behaviour of neat nylon and its blends with EPDM
can be evaluated from the cooling curves given in Fig. 7.1 1 .
Figure 7.11: Effect of blend ratio on the cooling curves of nylon and Nylon EPDM blends
For this we anneded the samples at 200°C for 3 minutes to make sure the
complete melting of the crystals. The crystallization parameters obtained
from the cooling curves are summarised in Table 7,10.
Table 7.10: Effect of blend ratio on the crystallization characteristics of uncompatibilised nylon /EPDM blends (Cooling cycle)
T, onset, TC and AHc of virgin nylon are found to be 143A°C, 136.3"C,
-32.2.J/g, respective1 y. It is important to note that the T, slightly increases
upon the incorporation of EPDM into nylon. This is because EPDM phase
act as nucleating agent for nylon crystallization in this region. Addition of a
nucleating agent increases the peak temperature [65]. It is reported in the
case of iPPPolyhedra1 oligomeric silsesqui oxanae (POSS) blends the
addition of POSS has a nucleating effect on iPP and also it accelerates the
crystallization process during non-isothermal cooling [66]. The
crystallization during the cooling process is completed at 135°C. All the
cooling curves show the same behaviour. The lower area of exotherm
values indicates a narrow distribution of crystallite size.
Sample
Ntoo
N70
Nso
N3o
The comparatively low crystallinity values of the rubber rich blends
(N3()) can be explained on the basis of morphology. From the SEM
micrographs demonstrated in Fig. 3.2 (Chapter 3) one can see that nylon
rich blends exhibited matrix/droplet type morphology in which nylon forms
TC onset (O C)
143.6
142.1
146.2
143.7
Tc (OC)
136.3
137.6
140.9
139.1
Tc cndmt
("c)
128.9
132.1
134.3
133.7
(AHc 1 (Jig) Normalised
-32.2
-30.7
-28.1
-25.6
Thermal Degradation and Crysalisation Behaviour 259
the continuous phase. On the other hand, Nso shows a typical co-continuous
morphology. N30 also possesses a dispersed morphology where EPDM
forms the matrix. Thus in N30, the continuous rubbery phase interferes with
the crystallization of the nylon phase thereby causing a marginal reduction
in crystallinity. It should be noted that the blend ratio has immense impact
on the morphology of the blends.
7.2.2.2 Compatibilised blends
The heating and cooling curves of NTO blend is shown in the
Fig. 7.12 and 7.1 3 respectively. The data obtained from DSC thermograms
are tabulated in Table 7.1 1. The observed values indicate that
compatibilisation does not show appreciable effect on the melting and
crystallization behaviour of the N70 blends. It is well evident from the figure
and table that compatibilisation does not have much contribution towards
melting and crystallsation parameters.
Figure 7.12: Effect of different level of compatibiliser on the heating curves N70 blend
260 Chapter 7
Figure 7.13: Effect of different level of compatibiliser on the cooling curves N ~ o blend
Table 7.11: Effect of compatibiliser EPM-g-MA on the melting and crystalisation parameters on 70130 nylon/EPDM blend
The possible explanation for this observation is based on the fact that, an
efficient compatibiliser locates at the interface and hence the probability to
interfere with the crystallization of the component polymers is very less. The
interfacial chemical reactions taking place during the incorporation of
wmpatibiliser in the present system usually occur at the amorphous phase and
therefore it doesn't contribute towards the appreciable change in the me1 ting and
crystallisation behaviour. Therefore it is quite expected that cornpatibilisation is
unable to produce any effect on the melting and crystallization behaviour of the
N70
N7o I
N702.5
NXIS
N-,OID
Tm ( O C )
170.2
171.6
173.9
172.3
172.5
Tc'O
137.6
133.0
135.6
136.3
137.6
(Am) (Jig) Normalised
26.9
28.6
29.2
29.1
24.3
( AHc (Jig) Normalid
-30.7
-31.3
-30.7
-28.1
-26.6
XC sa Crystallinity
29.8
32.8
32.4
32.3
27 .O
T k e m l De~ra&tion a d CrvsiWisation Behaviour 261
blends. However, it is important to note a marginal increase in crystallinity at
2.5% level of the compatibiliser concentration. Similarly T, (peak) value is
higher for N7a2.s blend. This can be explained on the basis of morphological
transformations occurring during compatibilisation. The SEM micrographs are
presented in the Fig. 4.5 (Chapter 4). Significant size reduction of the EPDM
domains can be observed at 2,5% level of compatibiliser. These small EPDM
parhcles act as heterogeneous nuclei for crystallisation thereby causing an
increase in crystallinity. The crystallinity is slightly reduced for 5 and 20% level
of compatibiliser. This observation reveals that, there is some critical size for the
nuclei for accelerating crystallization.
7.2.2.3 Dynamically vulcmised blends
The effect of crosslinking systems on the DSC therrnograms in the
heating and cooling modes are represented in the Figs. 7.14 and 7.15.
Additional information regarding the melting and crystallisation behaviour
of crossslinked N ~ o nylon/EPDM blends with different crosslinking systems
is given in the Table 7.12.
I
*I T?w.EL& %a Figure 7.14: Effect of crosslinking systems on the heating curves of N70
blend
262 Chapter 7
Figure 7.15: Effect of crosslinking systems on the cooling curves of NTO blend
The Table 7.12 revels that there is no significant reduction in crystllinity
with the crosslinking systems. Normally the crosslinks provides some
hindrance to the ordered arrangement of the polymer chains. These
chemical crosslinks restricts the diffusion and alignment of nylon
molecules. The type of the crosslinks formed also reflect on the melting
and crystallization values of the blends. The type of crosslinks formed is
well explained in Chapter 5.
Table 7.12: Effect of crosslinking systems on the thermal and crystallisation behaviour of 70130 nylon/EPDM blend
Sample
N ~ o
N7oS
N70D
N7oDS
N70DS+Comp
( AHF) (Jig)
Nomdjwd
26.9
28.1
23.2
25.1
24.6
Tm ('C)
170.2
168.6
166.4
167.3
1 67.1
(AH3 (J/g)
Normalised
-30.7
-29.9
-26.5
-27.7
-28.2
Tc ("C)
137.6
133.0
124.6
127.38
1 30.69
X, % Cr~shllinity
29.8
31.2
25.7
27.8
27.3
Thermal DearaiWora and Crvstallisation Behaviour 263
The morphologies of N 7 ~ and with different crosslinking
systems are given in the Fig. 5.2 (Chapter 5). One can visualize the domain
size reduction of the dispersed phase during dynamic vulcanization. The
crosslinking restricts the ordered arrangement of the chains and as a result
of this, crystallinity decreases. The schematic representation of the nylon
spherulites in N70 before and after dynamic vulcanization is shown in the
Fig. 7.16. In N70, rubber is dispersed as large domains. So only a few large
rubber particles are presented in N70. This favours the crystalline growth
process resulting in the formation of large nylon spherulites. Since the
rubber particles are easily deformable, the spheruilites can grow by
sqeezing the rubber particles. During dynamic vulcanization, a large
number of small crosslinked rubber particles are formed, which can hinter
the spherulite growth process. Hence interspherulitic area increases. After
dynamic vulcanization, the rubber particles become resistant to deformation
and the growth of the spherulite cannot be proceeded when a growing
spherulite touches a rubber particle.
Unvulcanised Dynamically vulcanised
Figure 7.16 Schematic represen tations of the nylon spherulites before and after dynamic vulcanisation of NTO blend
264 Chupter 7
7.2.3 Wide angle X-ray scattering
7.2.3.1 Uncompatibilised blends
The properties of thennoplastic elastomers with crystallisable
component depend on crystalline structure and crystallinity of the blends. XRD
is proved to be a more successful method for the determination of some
structural changes occurring as a result of blending. The amount of crystallinity
very much depends on the method of preparation of the sample and also on the
technique of measurement. PA exhibits basically two crystalline modifications,
namely a and y forms depending on the crystallization conditions [67-711. The
crystalline unit a l l for the a form is rnonwlinic and for the y form
pseudohexagonal. Among this a is the stablest configuration. The presence of
water facilitates the transformation of a to y structure. The XRD scans of
nylonlEPDM blends and the parent polymer nylon, as a function of Bragg angle
(20) are shown in Fig. 7.1 7. WAX diagram of partially crystalline polymers
shows peaks of high intensity corresponding to their crystalline regions and
peaks of low intensity corresponding to their amorphous regions. Integration of
the area under the two portions of the curve gives a measure of the crystalline to
amorphous ratio.
Scattering angle,2eo Figure 7.17: Wide angle X-ray diffractograms of nylon and nylon/EPDM
blends
Thennut Degradation and Crystallisation Behaviour 265
From the figure it is clear that the incorporation of EPDM into the nylon phase
does not cause considerable reduction in the crystaliinity of PA. The variation in
the peak height may be also due to the variation of the mean spherulite size or
their distribution, deformation at the spherulite boundaries by the incorporation
of EPDM. The Table7.13 shows the results obtained from the analysis of WAX
diffractograms of nylon and binary blends. From the table it is ciear that the d-
values (inter planer distance) increase slightly as the concentration of the rubber
in the blend increases. This indicates that rubber particles may be present in the
intra sphemlitic structure of nylon. The crystallinity of the blend can be
calculakd using the equation
where I, and Z, are the intensities corresponding to the crystalline and
amorphous phase respectively. The percentage crystallinity is given in the
Table 7.13. In the uncompatibilised blends crystallinity decreases slightly
with the EPDM content. The addition of more amorphous EPDM to nylon
causes the migration of amorphous phase into the crystalline phase of
nylon, which hinders the ordered arrangement of nylon and thus reduces its
crystalinity. From the table it is seen that, the values are higher than that
obtained from the DSC measurements.
Table 7.13: WAX datas of nylon and nylon/EPDM blends
Sample
Ntoo
N ~ o
N5o
N3o
20"
21.75
21.51
21.33
18.3
d(A)
4.08
4.12
4.16
4.83
Crystallinity (%I 36.3
32.1
30.2
28.4
7.2.3.2 Compatibilised blends
The effect of compatibilisation of NTO nylon/EPDM blend with EFM-g-
MA as the compahbiliser on the WAXS pattern is shown in the Fig. 7.1 8. From
the f i p it is clear that addition of cornpatibilker does not show appreciable
change in the crystallization pattern. The compatibilised system also shows
similar molecular structure as that of uncompatibilised blends. During reactive
compatibilisation the interface is modified. From the Table 7.14 it is seen that,
there is a slight reduction in the interplanar distances during compatibilisation
even though there is no appreciable change in the 20 values corresponding to the
highest peak point. The compatibiliser concentration of 2.5wt% gives
comparatively better crystallization behaviour for 7 W30 nylonlEPDM
compatibilised blends.
Scattering angle,20°
Figure 7.18 Wide angle X-ray diffractograms of EPM-g-MA compatibilised nylon/EPDM blends
T h e d Degradation and Crystal&saflafloro Bdhaviour 267
Table 7.14: WAX datas of 70130 nylonlEPDM compatibilised blends
7.2.3.3 Dynamic vulcanisation
Sample
N ~ o
N70.1
N70.2.5
N70.s
X-ray diffraction patterns of uncrosslinked and dynamically
crosslinked NTO blends are shown in the Fig. 7.19.
There is no change for the 20 values corresponding to the maximum
peak height. The influence of the crosslinking agents on crystallinity and
lattice distance of the blends are given in the Table7.15.
28"
21.51
21 -22
21.80
2 1.28
Scattering angle,%
Figure 7.19: X-ray scattering pattern of uncrosslinked and dynamically crosslinked 70/30nyloniEPDM blends
dl&
4.12
4,lO
4.07
4.06
CrystaIIini ty f %)
32.1
31.2
31.6
31.4
268 Chapter 7
Table 7.15: WAX datas of 70130 nylonlEPDM dynamically vulcanised blends
WAX studies reveal that crosslinking slightly reduces the
crystallinity of the system. By crosslinking the regular arrangements of the
crystalline regions in the system is blocked. Rizzo et al. 1721 have reported
similar trend in the case of crosslinked samples.
7.3 Conclusions
Thermal degradation, melting and crystallization behaviour of
nylon, EPDM and their blends were studied as a function of blend ratio,
cornpatibilisation and dynamic vulcanization, by using thermo gravirnetric,
differential scanning calorimetry and X-ray diffractometry. The TGA
studies revealed that EPDM was thermally more stable than nylon. The
addition of EPDM into nylon improved the thermal stability of the blends
significantly. Even though the blends are heterogeneous with two-phase
morphology, we obtained single degradation peak for all the blends. Phase
morphology was found to be one of the decisive factors that affected the
thermal stability since the thermal stability depends on the stability of the
matrix phase. The EPM-g-MA has been found to be an effective
cornpatibiliser in nylonEPDM systems as it improves the thermal stability
of the systems by providing improvement in the interfacial interaction
between nylon and EPDM. The compatibiliser increased the decomposition
Width at half height (cm)
1.7
1.8
1.9
2.0
Crystallinity (%I
32.1
28.7
27.0
28.0
Sample
N 70
N7oS
N7oD
N7oSD
20"
21.51
21.5
2 1.49
21.48
d(A)
4.12
4.1 1
4.12
4.12
T h e m 1 Degradation and CtystWisatiort Behaviaar 269
temperature of these systems especiaIIy at a critical value of its
concentration in the blends. Dynamic vulcanization using sulphur and DCP
also found to provide improvement in the decomposition temperature.
sulphur cured system showed higher decomposition temperature. Attempts
have also been made to correlate the thermal behaviour of the dynamically
crosslinked systems with the type of the crosslinks and the crosslink
density. Activation energy was calculated using Coats-Redfern method.
The kinetic study of degradation showed random nucleation as the
mechanism of degradation in the rate controlling process.
The melting and crystallisation behaviour of the Mends revealed
that blend ratio, compatibilisation and dynamic vulcanization have no
remarkable effect on the melting and crystallisation temperatures,
enthalpies of fusion and crystdlisation and percentage crystallinity of nylon
and EPDM. Compatibilisation has only marginal impact on the melting and
crystallisation behaviour of the nylon/EPDM blends owing to the fact that
compatibilisers are interfacial agents and their action is restricted only at
the interfacial area. Therefore the spherulite formation and their growth are
not affected by the presence of compatibilisers. A slight decrease in the
crystallinity on crosslinking is due the hindrance provided by the
crosslinks, which prevents the ordered arrangement of the polymer chains.
X-ray diffraction studies of the uncompatibilized blends revealed a
slight reduction in crystallinity and increase in interplaner distance of the
nylon as the incorporation of EPDM. Compatibilisation did not show much
appreciable change in the crystallization pattern. In the case of dynamic
vulcanisation crosslinking reduced the crystallinity of the system.
270 Chapter 7
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