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Rheology and morphology of Polytrimethylene terephthalate/ethylene propylene diene monomer blends in the presence and absence of a reactive compatibilizer.

INTRODUCTION

Blending of polymers is a popular method of improving their end-use properties. However, most polymers are thermodynamically incompatible and phase separate on blending. Compatibilization of polymer blends is carried out to reduce the scale of dispersion and to stabilize the morphology. Rheology is one of the most frequently used methods for characterizing interfacial properties, such as interfacial tension and strength that are necessary for predicting the mechanical properties of immiscible polymer blends (1), (2). Over the last few decades rheological properties of immiscible polymer blends have been extensively studied from both theoretical and experimental points of view (1-15). Among these, Paliene's emulsion model (9) was found to be the most effective to describe the rheological behavior of the polymer blends in the linear viscoelastic range. The rheological behavior of polymer melts play a strong role in their processing and morphology and is often indicative of properties, such as molecular weight or in the case of filled systems, microstructure. Several researchers have used dynamic rheology for the evaluation of rheology/morphology relationship. There are also many reports that reactive compatibilization has extensive impact on the rheological properties (16-23). Sanchez-Solis et al. (16) investigated the influence of maleic anhydride grafting on the rheological properties of polyethylene terephthalate/styrene butadiene blends and the particle size reduction was correlated with the reduction in the shear viscosity and increase in impact properties. Brahimi et al (17) showed that the complex viscosity of polyethylene/polystyrene (PE/PS) blends was very sensitive to the concentration and the structure of the compatibilizer. The emulsion model proposed by Oldroyd (3) for two viscoelastic liquids with interfacial tension was good enough for uncompatibilized blends and not for compatibilized blends. Graebling et al. (18) studied immiscible polymer blends in the presence and absence of an externally added interfacial agent and obtained a good agreement between experimental data and theoretical predictions of a simplified version of the Palierne model. Germain et al. (19) investigated the effect of compatibilizer on the rheological behavior of polypropylene/polyamide (PP/PA) blends and concluded that the low shear rate behavior is dominated by the copolymer encapsulating the nodular dispersed phase. Remain et al. (20) showed that upon compatibilization, there occurs an additional relaxation process. Its relaxation time was related, using an expanded version of the Palierne model, to an interfacial shear modulus. The rheology of reactively compatibilized Nylon-6/maleated polypropylene blends with varying extent of interfacial reaction was investigated by Asthana and Jayaraman (21). They found that the rheology of the reactive blends is fit to the Palierne theory to infer values of the equilibrium interfacial tension. The equilibrium interfacial tension of the reactive blends is reduced in proportion to the extent of maleation of the polypropylene. Shi et al. (22) used Palierne emulsion type model to establish a relationship between the dynamic rhcological response to and morphology of PP/PA6 blends compatibilized with maleic anhydride grafted PP. Recently Jafari et al. (23) investigated the morphology and rheology of poly (trimethylene terephthalate)/metallocene linear low-density polyethylene (PTT/m-LLDPE) immiscible blends with varying extent of compatibilization and theoretically analyzed using Palierne and Coran models. A sharp reduction of complex viscosity at 10 wt% compatibilizer has been observed which is ascribed to the micelle formation in the bulk phase. Plots of the relaxation time spectrum exhibit that upon addition of the compatibilizer the magnitude of the relaxation peaks associated with interface increases owing to the increase of the interfacial area. However, the Palierne model failed to predict admissible values and reasonable trend for interfacial tension becaues of the excessively large difference between the complex shear modulus values of the dispersed and matrix phases.

Polytrimethylene terephthalate {Sorona[R]} is a new generation of polymer from Du Pont. The new polymer has exceptional properties like softness, stretch with recovery, resilience, stain resistance, easy dyeablity for fibers, and high air impermeability. However, its poor impact-strength properties at low temperature limit its application. Blending is a major tool to obtain new polymeric materials with desirable properties and relative low cost. The major studies on impact modification PTT blends included binary blends PTT/PEI (24-27), PTT/EPDM (28), (29), PTT/PEN (30), (31), ternary blends PEN/PTT/PEN, (32) and quaternary blends PET/PTT/PBT/PEI (33).

Blends of poly trimethylene terephthalate and EPDM are a new class of TPEs that combine the excellent engineering properties of PTT and the elastic, ozone resistant and weathering resistant properties of EPDM rubber. However, they are highly immiscible and incompatible owing to poor physical and chemical interaction across phase boundaries because of the high polarity difference between the component polymers. Hence, such a system requires compatibilization to improve properties.

The main aim of this work is to investigate the dynamic rheological properties and morphology of compatibilized and uncompatibilized PTT/EPDM blends. Maleic anhydride graft EPM (EPM-g-MA) was used as reactive compatibilizer precursor. Palierne and Choi-Schowalter models were used to predict the interfacial tension between the polymers. Special attention is paid to make a correlation between the phase morphology and rheology of the blends in the presence and absence of compatibilizers.

EXPERIMENTAL

Materials

PTT (Sorona[R]), EPDM and EPM-g-MA are commercially available. PTT, [[bar.M].sub.n] 36,000 and density 1.33 g/cc was supplied by DuPont Company, and EPDM was received from DSM, Netherlands EPDM (Keltan[R] 720) with E/P ratio 58/35.5 wt% and DCPD content 6.5 wt% with [[bar.M].sub.n] 120,000, was obtained from DSM (Netherlands). The compatibilizer EPM-g-MA (Royaltuf 465; MA content is 1 wt %, E/P ratio is 50/50, density = 0.88 g/mL), was supplied by Uniroyal Chemical Company, Germany. The PTT samples were dried in a vacuum oven at 105[degrees]C for 12 h before blending.

Preparation of Blends

Both uncompatibilized and compatibilized blends were prepared by two step melt mixing process in a haake mixer with a rotor speed of 60 rpm; the total mixing time was fixed as 4 min. PTT was melted first at a temperature of 230[degrees]C and then EPDM was added after 2 min. Blending was continued for 2 more minutes. The blends having PTT/EPDM concentration 90/10 to 10/90 were prepared by this type of melt blending. Blends are designated as [PTT.sub.90] to [PTT.sub.10] where subscripts denote the percentage of PTT. The samples were compression molded at 230[degrees]C with a pressure of 20 kg [cm.sup.-2] for 2 min into sheets. Similarly the compatibilized blends of PTT/EPDM were also prepared in two step melt mixing process by adding 1, 2.5, 5, and 10 wt% of EPM-g-MA onto PTT/EPDM 70/30 blends with the same mixing time and rotor speed. Calculated quantity of EPDM and the compatibilizer was melt blended for 2 min. Then PTT was added after 2 min. Blending was continued for 2 more minutes at 230[degrees]C. The blends were taken and compression molded at 230[degrees]C into thin sheets.

Phase Morphology Studies

Scanning electron microscope (SEM; Jeol 5400, Tokyo, Japan) was used to analyze the phase morphology of the blends. The specimens for phase morphology studies were cryogenically fractured in liquid nitrogen. From the cryogenically fractured PTT rich blend samples dispersed EPDM was preferentially extracted using xylene vapours (Soxhlet extraction) at 150[degrees]C for 13 h. Fracture surface was sputter coated with Au/Pd alloy in a sputter coating machine (Balzers SCD 050) for 150 s. About 200 particles were considered to determine the droplet diameter of the dispersed phase The number average ([D.sub.n]) and weight average diameters ([D.sub.w]), polydispersity index (PDI), interfacial area perunit vulume ([A.sub.i]) were determined using the following equations;

The number average diameter, [D.sub.n] = [[SIGMA]NiDi/[SIGMA]Ni] (1)

The weight average diameter, [D.sub.w] = [[[SIGMA]Ni[Di.sup.2]]/[SIGMA]NiDi] (2)

Poly dispersity index, PDI = [[D.sub.w]/[D.sub.n]] (3)

Interfacial area per unit volume, [A.sub.i] = [3[empty set]/R] (4)

Dynamic Rheology

The rheological properties of the blends were evaluated on a Rheometric Scientific ARES rheometer in plate/plate geometry. Disc shaped samples of 25 mm diameter and 1 mm thickness was prepared by compression moulding of the melt blended samples using 1 mm thick mold with 25 mm diameter placed between two parallel plates at 230[degrees]C. A temperature/frequency sweep method was selected for rheological measurements and the frequency range was taken as 0.1 to 100 rad/sec at a temperature of 230[degrees]C. The strain was taken as 10%. From the rheological measurements, the shear modulus (G'), complex viscosity ([eta]*) etc have been obtained from the instruments.

RESULTS AND DISCUSSION

Uncompatibilized Blends

Rheological and other physical properties of polymer blends are closely related to the dispersion and distribution of the particles of the dispersed phase in the matrix. Therefore, it is essential to determine the sizes of the particles and their distribution in the blends to interpret rheological data and assess rheological models. The effect of blend ratio on the complex viscosity of uncompatibilized PTT/EPDM blends is shown in Fig. 1. It can be seen that the complex viscosity decreases with increase in frequency. PTT possesses minimum viscosity, whereas EPDM has the maximum. Addition of EPDM into PTT results in sharp increase in viscosity. The viscosity ratio is very much sensitive to the frequency fluctuation because of the highly incompatible nature of PTT and EPDM. The viscosity ratio of the neat polymers at selected frequencies is presented in Table 1. The viscosity ratio decreases with increase in the frequency and the large difference in viscosity ratio with respect to frequency will reflect on the phase morphology stability of the blends and on thereby the ultimate properties. Viscosity ratio is one of the critical variables for controlling the morphology of polymer blends and its effect on blend morphology has been extensively studied (34-37). If the minor component has lower viscosity compared with the major one, it will be finely and uniformly dispersed in the major continuous phase (34) otherwise coarsely dispersed. It has been found that for a given composition of minor component, the relatively less viscous component forms smaller dispersed droplets in more viscous matrix phase when all other factors are kept constant (35, 36). Groeninckx and coworkers (38) have studied the influence of viscosity ratio on the phase morphology development in immiscible blends and showed a clear dependence of the blend phase morphology on viscosity ratio; highly viscous matrices enhance droplet break-up because of their efficient shear stress transfer toward the dispersed phase and the higher dispersive forces acting on it; low viscous matrices often act as a lubricant for the dispersed phase reducing droplet break-up. As the polymers in molten state are sensitive to frequency change and therefore to shear rate, it can be expected that the phase morphology of PTT/EPDM uncompatibilized blends will be coarse, nonuniform and unstable. The phase morphology of uncompatibilized PTT/EPDM blends can be evaluated from the SEM micrographs presented in Fig. 2. All the blend compositions except [PTT.sub.60] and [PTT.sub.50] possess a typical matrix/dispersed phase morphology of uncompatibilized blends in which the minor component exists as dispersed domains in the matrix of the major component. The influence of blend ratio on the average domain size ([[bar.D].sub.n] and [[bar.D].sub.w]) of dispersed particles is shown in Fig. 3. It is obvious from the figure that all blends exhibit a nonuniform and unstable morphology and as the wt% of the dispersed phase increases, the morphology becomes less stable. Being more viscous, EPDM imposes greater restricted diffusion effects on the coalescence of PTT dispersed particles, which in turn results in smaller PTT dispersed domains. On the other hand, when PTT forms the matrix phase, the coalescence of EPDM dispersed phase becomes relatively easy because of the lower viscosity of PTT.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]
TABLE 1. Viscosity ratio of PTT and EPDM in the blends at various
frequencies.

Frequency (Hz)  Viscosity ratio ([[eta].sub.EPDM]/[[eta].sub.PTT])

  0.1                                  170.1
  0.25                                 119.1
  0.5                                   90.3
  1                                     67.5
  2.5                                   43.1
  5                                     31.7
 10                                     23.1
 25                                     14.1
 50                                      9.9
100                                      7.1


Figures 4 and 5 demonstrate the effect of blend ratio on the polydispersity index and domain distribution of the dispersed phase, respectively in PTT/EPDM uncompatibilized blends. These figures clearly indicate that the dispersed PTT phase has more narrow distribution than that of the dispersed EPDM phase as expected. Also, it is evident from the figures that PTT/PEPDM uncompatibilized blends possess a broad, nonuniform and unstable morphology. It can also be seen that as the wt% of the minor component in the blends increases, the nonuniformity increases with simultaneous depletion in the stability. The interfacial area per unit volume ([A.sub.i]) of dispersed particles presented in Fig. 6 implies that [A.sub.i] decreases with increase in dispersed phase content for both EPDM and PTT dispersed blends. On the basis of [A.sub.i] values, it is evident that blends with lower [A.sub.i] exhibit maximum unfavourable interactions (derived from maximum interfacial tension) at the interface and thus associated with more coarse, non-uniform and unstable morphology. We can see that PTT dispersed particles possess relatively higher values. Thus, we can see a good correlation between the phase morphology and rheological properties of uncompatibilized blends.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

The effect of blend ratio on the storage (G') modulus of uncompatibilized PTT/EPDM blends is shown in Fig. 7. The storage modulus (G') values of EPDM is greater compared with PTT. The storage modulus increases with increase in frequency. This is due to the fact that with increase in frequency, polymer chains get less relaxation time and consequently moduli increased. All the blends give intermediate values for storage modulus and is due to the highly incompatible nature of the blends and this behavior is reported for immiscible polymer blends, such as PS/PMMA (18), (39), liquid crystalline polymer/polyethylene terephthalate (LCP/PET), (40) and PP/styrene acrylonitrile (SAN) (41).

[FIGURE 7 OMITTED]

Compatibilized Blends

Compatibilization Strategy. The present compatibilization strategy involves the compatibilization of PTT with the second immiscible phase, EPDM, by the introduction of a compatibilizer precursor (EPM-g-MA), which is physically miscible with the second phase (EPDM) but has chemical functionality (maleic anhydride group) which can react with the hydroxyl end group of PTT to form a graft copolymer at the interface as shown in reaction Scheme 1. This situation is expected to lead to a reduction in particle size through a reduction in interfacial tension and an increased resistance to coalescence through stabilization of the interface. Similar reactions of hydroxyl group of polyester with anhydrides have been reported (28), (29), (42), (43), where the reaction is claimed to be of moderate nature. We can also expect intermolecular dipole-dipole interactions and interchange reactions between OH,--COOH, and ester groups in the case of maleic anhydride modified polymers and polyesters (44).

[ILLUSTRATION OMITTED]

Dynamic Rheology and Phase Morphology. The effect of compatibilization on the complex viscosity ([eta]*) of [PTT.sub.70] blends is shown in Fig. 8. In all cases, we found that the complex viscosity increases with increase in the addition of compatibilizer up to a critical compatibilizer concentration (CMC) in the whole frequency range. The increase in [eta]* is taken as an evidence for the compatibilizing action of EPM-g-MA by interfacial chemical reaction. This interfacial chemical reaction enhances the favourable interactions between the polymer chains at the interface, consequently, the viscosity of the system increases. Similar observations were reported by Brahimi et al. (17), Sung et al. (41) and Macaubas and Demarquette (45) for PE/PS blends compatibilized with styrene-butadiene (SB) diblock copolymer, PS/SAN blends compatibilized with PS-g-SAN graft copolymer, PP/PS blends compatibilized with a triblock copolymer, respectively.

[FIGURE 8 OMITTED]

The phase morphology of the compatibilized blends clearly establishes the efficiency of EPM-g-MA as interfacial emulsifying agent. The SEM micrographs given in Fig. 9 shows the effect of compatibilization on the phase morphology PTT/EPDM blends. The influence of EPM-g-MA on the dispersed particle size of these blends is presented in Fig. 10. There is a reduction in particle size with increase in compatibilizer concentration can be seen and is due to reduction in interfacial tension and coalescence rate as a result of emulsification. It can be seen that, after the initial sharp decline in particle size, a quasi-equilibrium state is attained beyond a critical compatibilizer concentration called critical micelle concentration, CMC owing to micelle formation of the excess compatibilizer in one of the phases as well as the change in its molecular state at interface (5 wt% of compatibilizer in the present case). Variation of polydispersity index of [PTT.sub.70] blends with increase in EPM-g-MA is shown in Fig. 11a. PDI decreases with increase in compatibilizer content. Effect of compatibilizer concentration on the distribution of dispersed particles [PTT.sub.70] blends is given in Fig. 11b. Domain distribution becomes narrower in presence of compatibilizers indicating a more fine, uniform and stable morphology of the compatibilized blends. Beyond CMC (5 wt%), there is little change in distribution of particles. From Fig. 12, we can see that there is appreciable increase in interfacial area per unit volume ([A.sub.i]) of dispersed particles with increase in compatibilizer concentration up to 5 wt% of compatibilizer (CMC). Beyond that limit, an almost levelling off in [A.sub.i] is observed.

[FIGURE 9 OMITTED]

[FIGURE 10 OMITTED]

[FIGURE 11 OMITTED]

[FIGURE 12 OMITTED]

However, it should be noted that, beyond CMC, the complex viscosity decreases as shown in Fig. 8. The decrease in viscosity above CMC is due to the fact that excess compatibilizer forms micelle and forms separate phase which could contribute to the total viscosity. Thus, it can be concluded that the addition of compatibilizer increased the complex viscosity up to CMC because of compatibilizing effect derived from enhanced interfacial interactions due to the generation of EPM-g-PTT copolymer as a result of interfacial chemical reactions. Beyond CMC, a levelling off is seen. This is an indication of interfacial saturation followed by micelle formation by compatibilizer molecules. Thus, it can be stated that both the morphology and rheology are in perfect correlation.

Figure 13 shows the effect of compatibilization on the storage modulus of the blends. It is obvious from the Fig. that G' shows a linear increase with compatibilizer addition up to CMC. The increase in G' is an indication of the pronounced elastic properties of the blends because of enhanced interfacial adhesion in the presence of compatibilizer. However, G' decreases beyond CMC. The reason is that at higher concentration compatibilizer forms micelles.

[FIGURE 13 OMITTED]

Interfacial Tension Measurements

Palierne model and Choi-Schowalter model were used for interfacial tension measurements. We used approximate methods obtained from these two models for interfacial tension measurements. The interfacial tension was calculated based on the weighted relaxation spectrum ([tau][H.sub.([tau])]) with the relaxation time ([tau]). To get the weighted relaxation spectrum the following equations were used:

[G'.sub.([omega])] = [[integral].sub.-[infinity].sup.[infinity]][([H.sub.(r)][[omega].sup.2][[tau].sup.2])/(1 + [[omega].sup.2][[tau].sup.2])]d(ln [tau]) (5)

[G".sub.([omega])] = [[integral].sub.-[infinity].sup.[infinity]][([H.sub.(r)][omega][tau])/(1 + [[omega].sup.2][[tau].sup.2])]d(ln [tau]) (6)

the relaxation spectrum can be determined using Tschoegle approximation (46) as given in following equation:

[H.sub.(r)] = G'[{[(d(log G')/d(log [omega])) - 0.5[(d(log G')/d(log [omega])).sup.2]] - [[(1/4.606)[[d.sup.2](log G')/d(log [omega]).sup.2]]}.sub.[1/[omega] = [tau]/[square root of 2]]] (7)

where [omega] is the frequency and [tau] is the relaxation time. It should be noted for neat polymer one will get one relaxation time where as for blends two [tau] ([[tau].sub.1] and [[tau].sub.2]) will be there corresponding to the component polymers. The difference in the values ([[tau].sub.1]--[[tau].sub.2]) was used to calculate the interfacial tension between the polymers in the presence and absence of compatibilizers. The interfacial tension ([alpha]) was calculated using two methods: Interfacial tension ([alpha]) between the polymers in the melt was calculated using the following equations:

i. Palierne (9) (Eq. 8)

[alpha] = [[[R.sub.v][[eta].sub.m]/4[tau]]][[[(19K + 16)(2K + 3 - 2[empty set](K - 1))]/[(10(K + 1)) - (2[empty set](5K + 2))]]] (8)

ii. Choi-Schowalter (6) (Eq. 9).

[alpha] = [[[R.sub.v][[eta].sub.m]/[tau]]][[[(19K + 16)(2K + 3)]/[40(K + 1)]]] x [1 + [empty set]([[5(19K + 16)]/[4(K + 1)(2K + 3)]])] (9)

where [[eta].sub.m] is the viscosity of the matrix, [empty set] is the volume fraction of the dispersed phase, K is the viscosity ratio and is given as K = [[eta].sub.d]/[[eta].sub.m] ([[eta].sub.d] is the viscosity of the dispersed phase).

Table 2 gives the interfacial tension between PTT and EPDM in [PTT.sub.90], [PTT.sub.80] and [PTT.sub.70] blends. The difference in the interfacial tension values between these blends indicate that the interfacial tension change with blend composition. However, this is unlikely as the interfacial tension between two polymers is believed to be the same for the whole composition range. The difference arises from the viscosity and average particle size parameters used in the equations since the final morphology is determined by drop break-up process and coalescence.
TABLE 2. Interfacial tension values of uncompatibilized PTT/EPDM
blends.

                 Interfacial tension (mN/m)

Blend           Palierne    Choi-Schowalter

[PTT.sub.90]       8.5            9.7
[PTT.sub.80]       9.4           10.5
[PTT.sub.70]      12.7           13.4


The relative importance of applied viscous force and counteracting interfacial force can be expressed by Taylor equation derived from the studies of deformation and disintegration of the dispersed phase for Newtonian systems in simple shear fields in the absence of coalescence effects (47).

Ca = [[eta].sub.m][gamma]R/[sigma] (10)

where [[eta].sub.m] is the viscosity of the matrix, p the viscosity ratio of the droplet phase to the matrix, R the radius of the droplet, [gamma] the shear rate and [sigma] the interfacial tension. If Ca is small, the interfacial forces dominate and a steady drop shape develops. When Ca exceeds a critical value, [Ca.sub.crit] the droplet will deform and subsequently breaks up under the influence of interfacial tension. Later, Wu (48) modified this equation as:

D = [[4[sigma][p.sup.[[+ or -]0.84]]]/[gamma][[eta].sub.m]] (11)

The exponent is positive for p > 1 and negative for p < 1.

From Taylor equation it is seen that the size of dispersed particles is directly related to the interfacial tension between the two phases. Also, it is important to note that it is the Taylor equation that forms the basis for both Palierne equation and Choi-Schowalter equation.

Effect of compatibilization on the interfacial tension between the two polymers is presented in Table 3. It is well known that compatibilization decreases the interfacial tension between the component polymers (49-51) by decreasing unfavourable interfacial interaction. Anastasiadis et al. (49) have observed a sharp decrease in interfacial tension with the addition of small amount of compatibilizer followed by a levelling off as the copolymer concentration is increased above the apparent CMC. Asthana and Jayaraman (21) have investigated the rheology of reactively compatibilized PA6/PP blends with varying extent of interfacial reaction and reported that the increasing extent of maleation leads to increasing extent of interfacial reaction and hence "progressive crowding" at the interface.
TABLE 3. Effect of compatibilization on the interfacial tension between
PTT and EPDM in [PTT.sub.70] blends.

                                    Interfacial tension (mN/m)

Blend                              Palierne    Choi-Schowalter

[PTT.sub.70]                         12.7           13.4
[PTT.sub.70] + 1.0 wt% EPM-g-MA      10.3           11.5
[PTT.sub.70] + 2.5 wt% EPM-g-MA       8.7            9.5
[PTT.sub.70] + 5.0 wt% EPM-g-MA       6.8            7.4
[PTT.sub.70] + 10 wt% EPM-g-MA        6.9            7.8


It is clear from the Table 3 that there is a linear reduction in interfacial tension up to CMC because of the addition of the compatibilizer. The interfacial tension reduction is an indication of enhanced interfacial interactions due to chemical reactions. As the extent of interfacial reaction increases, the interface is progressively occupied. In terms of interfacial tension, the CMC was found to be 5 wt% for [PTT.sub.70] blends, respectively. It is seen that beyond CMC, the interfacial tension increases slightly in both cases. This means that 5 wt% compatibilizer is sufficient for interfacial saturation as suggested by the phase morphology studies. Willis and Favis (52) reported that about 5 wt% of ionomer is sufficient for polyolefin/PA blend system for interfacial saturation. Thomas and Groeninckx (53) also observed 5 wt% of compatibilizer was the optimum compatibilizer concentration for PA/ethylene propylene rubber (EPM) blends. Further addition of compatibilizer is not only able to reduce the interfacial tension but also tends to form micelle.

Finally, the particle size reduction and interfacial tension reduction in [PTT.sub.70] blend is shown in Fig. 14. It can be seen that in the blend, a perfect relation is seen between particle size reduction which is evaluated from the phase morphology and interfacial tension values computed from rheology. Thus, it can be concluded like uncompatibilized blends, morphology and rheology of compatibilized blends are in perfect correlation.

[FIGURE 14 OMITTED]

CONCLUSIONS

In this study we performed a detailed investigation of the phase morphology and dynamic rheology of poly trimethylene terephthalate (PTT) and ethylene propylene diene monomer (EPDM) blends in the presence and absence of reactive compatibilizer and established a relationship between the rheology and morphology of the blends. The complex viscosity and the elastic properties of EPDM were found to be greater than that of PTT and the viscosity ratio between the polymers was sensitive to frequency which gave an idea about the unstable morphology. It was shown that the rheology and phase morphology of the uncompatibilized and compatibilized blends were intimately related. The effect of compatibilization on the rheological properties of the blends revealed that the complex viscosity increased with increase in compatibilizer concentration up to critical micelle concentration (CMC). Beyond CMC a reduction in complex viscosity is observed since the compatibilizer formed a third phase at higher concentration, which also contributed to the total viscosity. Storage modulus also increased with increase in compatibilizer concentration up to CMC and thereafter a decrease was seen. The interfacial tension between the polymers in the melt is calculated using Palierne and Choi-Schowalter models. Although both methods gave reasonably good values, there was a difference between the interfacial tension values. The interfacial tension is decreased due to the addition of the compatibilizer up to CMC and beyond which a slight increase in the values because of interfacial saturation followed by micelle formation. Finally, we made a comparison between phase morphology and rheology of compatibilized blends and obtained a perfect correlation between them.

ACKNOWLEDGMENTS

The authors thank Dr. Joseph V. Kurian and Sorona R&D, Bio-Based Materials, E. I. du Pont de Nemours and Company, Inc. Wilmington, Delaware, USA, for providing PTT polymers for the study.

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Correspondence to: Indose Aravind; e-mail: indosearavind@gmail.com

Contract grant sponsor: CSIR, New Delhi, India.

View this article online at wileyonlinelibrary.com.

[C]2010 Society of Plastics Engineers

Indose Aravind, (1) Seno Jose, (2) Kyung Hyun Ahn, (3) Sabu Thomas (1)

(1) School of Chemical Sciences, Mahatma Gandhi University, Priyadarshini Hills, Kottayam, Kerala, India

(2) Department of Chemistry, Government College, Kottayam, Kerala, India

(3) School of Chemical and Biological Engineering, Seoul National University, Seoul, 151-744 Korea

DOI 10.1002/pen.21723
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Author:Aravind, Indose; Jose, Seno; Ahn, Kyung Hyun; Thomas, Sabu
Publication:Polymer Engineering and Science
Article Type:Report
Geographic Code:9INDI
Date:Oct 1, 2010
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