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Compatibility studies on some rubber blend systems by ultrasonic techniques
Materials Chemistry and Physics 74 (2002) 23–32
Compatibility studies on some rubber blend systems by ultrasonic techniques M.A. Sidkey a,∗ , A.A. Yehia a,b , N.A. Abd El Malak a , M.S. Gaafar a a
National Institute for Standards, El Haram, Giza, Tersa Street, El Giza 12211, Egypt b National Research Center, Cairo, Egypt
Received 16 January 2001; received in revised form 29 April 2001; accepted 4 May 2001
Abstract Longitudinal ultrasonic velocity, and ultrasonic attenuation, were measured in Adiprene CM–NBR, Adiprene CM–NR, Adiprene E–NR, Adiprene E–NBR blend systems at room temperature, using pulse echo technique. The densities of the blend samples were measured by the immersion method. Glass transition temperatures were measured experimentally using ultrasonic and differential scanning calorimetry (DSC). Glass transition temperatures were also calculated theoretically. Results showed that the variation of both longitudinal ultrasonic velocity and density with composition is linear with Adiprene CM–NBR, Adiprene CM–NR, and Adiprene E–NBR blends indicating compatible systems. For Adiprene E–NR, the plots of ultrasonic velocity and density vs. composition deviate from linearity according to the incompatibility degree of this system. Results obtained from ultrasonic attenuation measurements showed that the excess variation of ultrasonic attenuation with composition in rubber blend samples is of relaxational type and only one maxima or minima appeared in case of compatible blends and two or more maxima or minima appeared in case of incompatible blends. The presence of a single transition temperatures observed in DSC thermograms and ultrasonic attenuation–temperature relation is a decisive confirmation of the formation of one single phase and therefore the compatibility behaviour of this blend. On the other hand, the presence of two transition temperatures is taken as evidence of phase separation and consequently the formation of two phases with incompatible behaviour of the blend system. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Ultrasonic; Adiprene; DSC; Transition temperature
1. Introduction The concept of physically blending two or more existing polymers to obtain a new product has not been developed as fully as the chemical approach to blending, but the physical approach is now attracting widespread interest and is being used commercially. Polymer blends are physical mixtures of structurally different polymers, which interact through secondary forces with no covalent bonding [1]. The manifestation of superior properties depends upon compatibility or miscibility of homopolymers at molecular levels. Compatibility of polymer blends can be examined by sophisticated experimental and theoretical techniques [2–6] to decide their practical activity. The degree of compatibility of rubber blends: natural rubber–styrene butadiene rubber (NR–SBR), acrylonitrile butadiene rubber–chloroprene rubber (NBR–CR), acrylonitrile butadiene rubber–styrene butadiene rubber (NBR– SBR), and natural rubber–chloroprene rubber (NR–CR) ∗
Corresponding author. Tel.: +20-3867-452; fax: +20-3867-451.
has been studied by Abd El-All et al. [7] using ultrasonic methods. The variation of compressional ultrasonic velocity with mole fraction percent of the blend was found to be linear in NR–SBR and NBR–CR blends indicating compatible systems while it deviates from linearity in NR–CR and NBR–SBR. Results of longitudinal ultrasonic absorption showed that compatible rubber blends exhibit only one maxima or minima. Density measurements, values of heat of mixing in these blends confirmed the ultrasonic results. Ultrasonic velocity, ultrasonic attenuation, and transition temperature investigations were measured in the blend systems CR–NBR (chloroprene–acrylonitrile butadiene rubber), CR–SBR (chloroprene–styrene butadiene rubber), and CR–EPDM (chloroprene–ethylene propylene diene monomer) by Sidkey et al. [8]. The study was carried out to examine the degree of compatibility in these rubber blend systems. Zerjal et al. [9] investigated blends of a thermoplastic polyurethane (TPU) with poly(styrene-co-acrylonitrile) (SAN) by differential scanning calorimetry (DSC) and dielectric spectroscopy. From the dielectric measurements it was concluded that the relaxation processes in the TPU/SAN
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blends occur at the same temperatures as the relaxation processes in pure components, which suggests that the motions of TPU chains are decoupled from the motions of SAN chains. Singh and Singh [3] studied the variation of longitudinal ultrasonic velocity with composition in some compatible and incompatible polymer blends in solid forms. They found that the plot of ultrasonic velocity vs. composition for PMMA–PVA blend was linear except for some curvature in the composition range of 75–85% by weight PMMA in the blend. The plot for PMMA–PS blend depicted an inverted S type of behaviour showing the multiphase nature of this system and clearly indicating the region of phase separation. Results of the variation of ultrasonic absorption with composition of polystyrene (PS) and ethylene propylene diene monomer (EPDM) blend were reported by Shaw and Singh [10]. They concluded that this blend is incompatible blend. A study carried out by Singh and Singh [3] on the compatibility of polymethyl methacrylate–polyvinyl acetate and polymethyl methacrylate–polystyrene blends in terms of phase morphology of the blends using electron microscopy aiming to give further evidence to their ultrasonic velocity measurements. They reported that PMMA–PVA blend containing 60% by weight PVA seemed to be compatible since dark and light regions representing both homopolymers were distributed homogeneously and none of the regions had phase separation. The system PMMA–PS had two phase morphology and contained darker and brighter regions depicting two homopolymeric constituents. The heterogeneity of this system showed the incompatibility of this blend. The work under report was undertaken to investigate the compatibility behaviour of some rubber blends using ultrasonic methods, DSC, and electron microscope techniques.
The longitudinal ultrasonic velocity (V ) was measured for different solid blend samples, using the pulse echo technique, by measuring the elapsed time between the initiation and the receipt of the pulse appearing on the screen of a flaw detector (USM3—Krautkramer) by standard electronic circuit (PM3055 Philips). The velocity was therefore obtained by dividing the round trip distance by the elapsed time. Measurements were carried out at 2 MHz frequency and at room temperature. Ultrasonic absorption measurements were performed using pulse echo technique at 4 MHz frequency and at room temperature. The same transducer acted as the transmitter and receiver simultaneously. The heights of two successive echoes were measured, and the absorption coefficient (α) was then calculated according to the equation: 20 A1 α= dB/ cm, log 2d A2 where d is the thickness of the sample, and A1 and A2 are the heights of the first and second echoes, respectively. Measurements of glass transition temperatures were carried out using differential scanning calorimeter DSC 50 (Schimadzu, Japan). Measurements were carried out at a cooling rate of 4 ◦ C min−1 in the temperature range from −100 to 0 ◦ C. Liquid nitrogen was used for cooling. Besides, the transition temperature in polymer blends were measured using ultrasonic methods as described earlier by Sidkey et al. [11]. Scanning electron micrographs were obtained for Adiprene E–NR blend using JOEL-100 T scanning electron microscope.
3. Results and discussion 3.1. Density measurements
2. Experimental The ingredient rubbers used in this investigation are natural rubber (NR), nitrile butadiene rubber (NBR) manufactured by Alexandria, Egypt, and two forms of polyurethane (Adiprene CM and Adiprene E) manufactured by Uniroyal Chemica, England. These rubbers were firstly masticated separately for 1 min, then the two rubbers composing the blend were weighed according to the composition required and mastication process was then continued for 20 min. Known amount (4 part per hundred rubber) of an effective vulcanized agent (benzoyl peroxide) was added on a two roll mill and good mixing was carried out. Blocks were cut into slabs and then vulcanized in clean polished moulds in a press under pressure of about 4 × 105 kg m−2 and at temperature of 140 ◦ C for 30 min. Four rubber blends, with different compositions, were therefore prepared. The densities of the rubber blend specimens were measured using immersion technique and all measurements were taken at room temperature (298 K).
Fig. 1 shows the variation of density with the increase of polyurethanes (Adiprene CM and Adiprene E) weight percent content. The figure shows a linear relation over the entire range of composition and is represented by straight lines for the blend systems: Adiprene CM–NBR, Adiprene CM–NR, and Adiprene E–NBR. For Adiprene E–NR blend system, the variation of density with the increase in Adiprene E weight percent shows a deviation from linearity behaviour. The linear behaviour indicates greater molecular mixing and strong inter-chain inter-polymer interactions among the rubber blend components. It was reported earlier [6,7,12] that a linear relation between density and blend composition indicates the compatibility behaviour of this blend, and the complete solubility of these two rubber components in each other at all proportions [11]. On the other hand, the nonlinear behaviour shown in Fig. 1 for Adiprene E–NR blend system suggests that the mixing of these two parent rubbers is very week due to the poor inter-polymer inter-chains among the Adiprene E and NR blend components. Such behaviour
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Fig. 1. Relation between density and weight percent content of adiprene component.
indicates the presence of more than one phase and consequently the incompatibility behaviour of this blend system. A similar results were reported by Abd El-All [20]. 3.2. Ultrasonic velocity measurements The relation between longitudinal ultrasonic velocity and polyurethanes composition of the four blend systems studied is shown in Fig. 2. The plot depicts a linear relation at composition ranges of the blend systems: Adiprene CM–NBR, Adiprene CM–NR, and Adiprene E–NBR. The linearity of this relation indicates the complete solubility of the two rubber components, comprising each blend system, in each other at all proportions. This is mainly due to the strong interactions between the two macromolecular rubber components. Such behaviour may be also explained on the basis of aggregation and conformational changes of the macromolecules which leads to the formation of one homogeneous phase [5,11,13]. The linearity behaviour of ultrasonic
velocity vs. blend composition indicates the compatibility behaviour of these blend systems [8,18]. The relation between longitudinal ultrasonic velocity and weight percentage content of Adiprene E–NR in rubber blend samples shows a curvilinear type of relation at all composition ranges of the blend. The curvilinear type of this relation is mainly due to heterogeneity indicated by phase separation due to immiscibility of these two parent rubber components in each other at all proportions of Adiprene E–NR rubber blend. A behaviour of this type can be taken as an evidence for an incompatible blend system. Shaw and Singh [10], Hourston and Hughes [5], Singh and Singh [18] and Sidkey et al. [8] reported similar results. 3.3. Ultrasonic absorption measurements Fig. 3 depicts the variation of ultrasonic absorption with the change of polyurethanes (Adiprene CM and Adiprene E) weight percent content for the four investigated blends. The
Fig. 2. Variation of longitudinal ultrasonic velocity with weight percent content of adiprene component.
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Fig. 3. Variation of ultrasonic absorption coefficient with weight percent content of adiprene component.
nature of the absorption is merely of relaxational type [6,11]. For Adiprene CM–NBR blend, one minimum appeared at about 40 wt.% Adiprene CM. For Adiprene CM–NR, only one maximum appeared at about 90 wt.% Adiprene CM. The blend system Adiprene E–NBR shows also only one maximum at about 40 wt.% Adiprene E. The presence of only one maximum or one minimum can be explained by the fact that both component rubbers of each blend system are miscible in each other forming only one single phase and consequently run a relaxation process simultaneously.
The presence of only one single minimum or maximum in the ultrasonic absorption and blend composition relation, gives an indication of the good compatibility of this blend system [6,11]. The relation between the measured ultrasonic absorption and weight percent content of Adiprene E–NR blend system shows clearly the presence of three maxima at 20, 50, and 80 wt.% Adiprene E. Moreover, two minima appeared also at about 30 and 60 wt.% content of Adiprene E. The presence of more than one maximum or minimum indicates that the two parent rubber components are
Fig. 4. Variation of attenuation coefficient of Adiprene CM–NBR blend with temperature.
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Table 1 Composition of rubber blend, values of glass transition temperatures of component rubbers, transition temperatures measured experimentally, and transition temperatures calculated theoretically Rubber composition (wt.%)
0% Adiprene CM–l00% NBR 100% Adiprene CM–0% NBR 40% Adiprene CM–60% NBR 60% Adiprene CM–40% NBR
Transition temperature (K) From references
Experimental ultrasonic
Experimental DSC
Calculated according to Fox’s equation
Calculated according to Gordon–Taylor equation
241 [14] 229 [9,24,25] – –
253 215 238 228
251.98 224.04 241.63 228.00
– – 236.05 233.65
– – 234.00 231.90
immiscible in each other and two phases occurred which undergo separate relaxation process. This blend system represents an example of the incompatible blends [6,7,11]. 3.4. Transition temperature measurements The relation between the measured ultrasonic absorption and temperature of 100% NBR, 40% Adiprene CM–60% NBR, 60% Adiprene CM–40% NBR, and 100% CM are shown in Fig. 4. The absorption is of relaxational nature and is not due to scattering of the dispersed phase. Table 1 gives the composition of the solid blend system, values for glass transition temperatures of component rubbers as given in Polymer Hand Book [14], the transition temperatures measured experimentally, and transition temperatures calculated theoretically according to the equations given by Fox [15] as Wb W1 W2 = + TgB Tg1 Tg2 where W1 , W2 and Wb represent the contents (wt.%) of components 1 and 2 and the blend, respectively, and TgB , Tg1 and Tg2 are the glass transition temperatures of the blend, components 1 and 2, respectively, and by Gordon–Taylor equation [16] as W2 TgB = Tg1 + K (Tg2 − TgB ) W1 where TgB is the glass transition temperature of the blend, Tg1 and Tg2 are those of pure components 1 and 2, respectively. W is the weight fraction and K is an empirical parameter related to the degree of curvature of the Tg composition diagram, a K value of 0.48 fitting the experimental data quite well.
It is interesting to note that Fig. 4 shows the presence of only one single transition temperature peak appeared at 228 K for 60% Adiprene CM–40% NBR blend, and also it shows only one transition temperature peak at about 238 K for 40% Adiprene CM–60% NBR blend. The presence of only one single transition temperature indicates very clearly that this blend system is a compatible blend. Moreover, the transition temperature peak appears at 228 K lies very near to the transition temperature peak of the 100% Adiprene CM rubber component which appeared at 215 K. Again, the same observation was observed for the transition temperature peak appeared at 238 K which lies nearer to the 100% NBR component transition temperature peak at 253 K. It is clear from Table 1 that the Tg values calculated theoretically from both Fox’s equation and Gordon–Taylor relation are very close to the obtained experimental values. The DSC transition temperatures of 100% Adiprene CM, 100% NBR, 40% Adiprene CM–60% NBR, and 60% Adiprene CM–40% NBR blends are given in Table 1. It can be seen that each blend displays only one single glass transition temperature (Tg ) which changes its position with blend composition. The presence of one single glass transition temperature in DSC thermograms indicates the miscibility of the two component polymers and hence the good compatibility of the blend [9,17]. Table 2 gives the composition of the Adiprene CM–NR blend system, values of glass transition temperature for component rubbers, the transition temperatures measured experimentally, transition temperatures calculated theoretically according to Fox equation and Gordon–Taylor relation. It is clear from the curves shown in Fig. 5 that the ultrasonic absorption in this blend goes through only
Table 2 Composition of rubber blend, values of glass transition temperatures of component rubbers, transition temperatures measured experimentally, and transition temperatures calculated theoretically Rubber composition (wt.%)
0% Adiprene CM–100% 100% Adiprene CM–0% 40% Adiprene CM–60% 60% Adiprene CM–40%
NR NR NR NR
Transition temperature (K) From references
Experimental ultrasonic
Experimental DSC
Calculated according to Fox’s equation
Calculated according to Gordon–Taylor equation
203.00 [14] 229.00 [9,24,25] – –
199.00 215.00 204.00 210.00
203.07 224.04 209.40 210.32
– – 212.66 217.84
– – 218.12 222.70
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Fig. 5. Variation of attenuation coefficient of Adiprene CM–NR blend with temperature.
one maximum (transition temperature peak) at about 210 K for 60% Adiprene CM–40% NR blend and at about 204 K for 40% Adiprene CM–60% NR blend. This behaviour suggests the occurrence of the same thermal relaxation at some composition. The presence of only one single peak indicates very clearly that this blend system is a compatible blend. Moreover, the transition temperature of the 60% Adiprene CM–40% NR blend (210 K) lies very near to the transition temperature of the 100% Adiprene CM rubber component (215 K) while the transition temperature of the 40% Adiprene CM–60% NR blend (204 K) lies very close to the transition temperature peak of 100% NR rubber component (199 K). These observations indicate very clearly that the ultrasonic method is very successful and can be accepted as a new method for compatibility examination. The transition temperatures determined by DSC measurements, shown in Table 2, are comparable to those calculated theoretically according to Fox equation and Gordon–Taylor
relation. It was reported earlier [19] that the glass transition temperature Tg , which marks the characteristic transition of the amorphous region of the blend from glassy state to a rubbery state, is the most convenient and popular way of investigating the miscibility or immiscibility of pairs of polymers. Fig. 6 shows the relation between ultrasonic absorption and temperature for 100% NBR, 40% Adiprene E–60% NBR blend, 60% Adiprene E–40% NBR blend, and 100% Adiprene E. Only one relaxational temperature peak is observed in each investigated blend composition and its position lies between the transition temperatures corresponding to the two component rubbers. Table 3 gives the composition of the solid blend system, values of glass transition temperature of component rubbers, the transition temperatures measured experimentally, and transition temperatures calculated theoretically according to Fox equation and Gordon–Taylor relation. It is
Table 3 Composition of rubber blend, values of glass transition temperatures of component rubbers, transition temperatures measured experimentally, and transition temperatures calculated theoretically Rubber composition (wt.%)
0% Adiprene E–100% 100% Adiprene E–0% 40% Adiprene E–60% 60% Adiprene E–40%
NBR NBR NBR NBR
Transition temperature (K) From references
Experimental ultrasonic
Experimental DSC
Calculated according to Fox’s equation
Calculated according to Gordon–Taylor equation
241 [14] 216 [26] – –
253 207 237 221
251.98 211.00 246.67 243.84
– – 230.34 225.35
– – 234.94 233.65
M.A. Sidkey et al. / Materials Chemistry and Physics 74 (2002) 23–32
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Fig. 6. Variation of attenuation coefficient of Adiprene E–NBR blend with temperature.
clear from Table 3 that the Tg value theoretically calculated from both Fox’s equation and Gordon–Taylor’s relation for 40% Adiprene E–60% NBR and 60% Adiprene E–40% NBR blends, are very close to the experimental values. The presence of only one single transition temperature in Fig. 6 confirms the ultrasonic analysis indicating that this blend is a compatible blend. The Tg values obtained from DSC measurements are very close to those obtained from ultrasonic methods. It can be seen from Figs. 7 and 8 that the transition temperature peaks for 40% Adiprene E–60% NR blend appears as two transition temperature peaks at 201 and 204 K. The first transition temperature peak appeared at 201 K may be due to the relaxation of NR domain, while the second transition temperature peak at 204 K may be due to the relaxation of Adiprene E domain. The first transition peak lies very near to 100% NR transition temperature, while the second transition temperature peak lies very near to 100%
Adiprene E transition temperature peak. For the blend composition; 60% Adiprene E–40% NR, there is also two transition temperature peaks appeared at 202 and 205 K. The first transition temperature peak appeared at 202 K lies very near to 100% NR transition temperature, while the second transition temperature peak appeared at 205 K lies nearer to the transition temperature peak of 100% Adiprene E. However, the presence of two temperature peaks in the ultrasonic attenuation–temperature diagrams gives an evidence of phase separation and therefore the formation of two phases. The phase separation and consequently the formation of two phases are mainly due to the very poor intermolecular mixing between the two parent component rubbers of this blend system. Moreover, blends of incompatible rubbers that segregate into distinct phases exhibit glass transitions which may be shifted to those of the unblended components. Table 4 gives the composition of the blend system, values of glass transition temperature for component rubbers, the
Table 4 Composition of rubber blend, values of glass transition temperatures of component rubbers, transition temperatures measured experimentally Rubber composition (wt.%)
0% Adiprene E–100% 100% Adiprene E–0% 40% Adiprene E–60% 60% Adiprene E–40%
NR NR NR NR
Transition temperature (K) Polymer handbook
Experimental ultrasonic
Experimental DSC
203.00 [14] 216.00 [26] – –
199.00 215.00 201, 204 202, 205
203.07 211.00 212.83 211.72
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Fig. 7. Variation of attenuation coefficient of 40% Adiprene E–60% NR blend with temperature.
Fig. 8. Variation of attenuation coefficient of 60% Adiprene E–40% NR blend with temperature.
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Fig. 9. Scanning electron micrographs of (500×) for: (A) 100% NR; (B) 100% Adiprene E; (C) 40% Adiprene E–60% NR blend; (D) 60% Adiprene E–40% NR blend.
transition temperatures measured experimentally by ultrasonic technique and DSC. It can be observed from Table 4 that there is only one transition temperature peak measured experimentally by DSC technique, which lies at 212.83 K for 40% Adiprene E–60% NR blend. Moreover, only one transition temperature peak appeared at 211.72 K for the blend system 60% Adiprene E–40% NR. Although the use of Tg in determining polymer compatibility is based on the judgement that the observation of two transition temperature peaks between those of pure components is taken as evidence of incompatibility [20,21], there are certain circumstances under which the transition temperature criterion may be inapplicable or even misleading. The application of the single transition criterion requires that the transition temperature of the parent components to be sufficiently displaced from each other so that the resolution is possible. The limits of resolution of transition temperatures less than about 20 K apart between the two parent components is very poor [22]. The closeness of blend components transi-
tion temperatures may be even a more severe problem for detecting by DSC technique [23]. The electron microscopy analysis of Adiprene E–NR blend system shown in Fig. 9 may confirm qualitatively the behaviour shown by ultrasonic measurements. The micrographs show dark and bright regions for 100% NR, large and elongated lines forming some sort of large opaque domains for 100% Adiprene E, some aggregates of dark and transparent domains for both blends 60% Adiprene E–40% NR and 40% Adiprene E–60% NR. The last two micrographs depict two homopolymeric constituents and can be roughly classified into two groups.
4. Conclusion The present investigations indicate clearly that the compatibility of rubber blends can be studied successfully in solids by ultrasonic techniques. It may be concluded that the
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simple measurement of ultrasonic velocity, ultrasonic absorption, and glass transition temperature by ultrasonic technique provide clue to the compatibility of blends which is in general obtained by sophisticated techniques of the DSC and scanning electron microscopy. References [1] M. Shen, H. Kawai, Am. Chem. Eng. J. 24 (1978) 1. [2] S. Krause, in: D.R. Paul, S. Newmann (Eds.), Polymer–Polymer Compatibility in Polymer Blends, Vol. 1, Academic Press, New York, 1978. [3] Y.P. Singh, R.P. Singh, Eur. Polym. J. 19 (1983) 529. [4] Y.P. Singh, S. Das, S. Maiti, R.P. Singh, J. Pure Appl. Ultrasonic 3 (1981) 1. [5] D.J. Hourston, I.D. Hughes, Polymer 19 (1978) 1181. [6] M.A. Sidkey, A.M. Abd El-Fattah, A.A. Yehia, N.S. Abd El-All, J. Appl. Polym. Sci. 43 (1991) 1441. [7] N.S. Abd El-All, A.A. Yehia, S.H. El-Sabbagh, J. Pure Appl. Ultrasonic 16 (1994) 103. [8] M.A. Sidkey, N.S. Abd El-Aal, A.M. Eid, The Specific Conference on Rheology and Polymer Processing (PCR), September 26–30, 1994, Kyoto, Japan, p. 345.
[9] B. Zerjal, Z. Jelcic, T. Malavasic, Eur. Polym. J. 32 (1996) 1351. [10] S. Shaw, R.P. Singh, Eur. Polym. J. 23 (1987) 547. [11] M.A. Sidkey, A.M. Abd El-Fattah, Z. Abdel Aziz, A.Z. Mohamed, N.S. Abd El-Aal, J. Pure Appl. Ultrasonic 15 (1993) 1. [12] A.H. Al-Salah, Polym. Bull. 40 (1998) 477. [13] D.J. Hourston, I.D. Hughes, Polymer 18 (1977) 1175. [14] J.E. Brandrup, Polymer Hand Book, Wiley/Interscience, New York, 1960. [15] T.G. Fox, Bull. Am. Phys. Soc. 1 (1956) 123. [16] M. Gordon, J.S. Taylor, J. Appl. Chem. 2 (1952) 493. [17] M. Song, A. Hammiche, H.M. Pollock, D.J. Hourston, M. Reading, Polymer 36 (1995) 3313. [18] Y.P. Singh, R.P. Singh, Eur. Polym. J. 20 (1984) 201. [19] R.P. Singh, J. Acoust. Soc. Ind. 21 (1993) 159. [20] N.S. Abd El-All, Ph.D. Thesis, Ain Shams University, Cairo, Egypt, 1992. [21] S. Zheng, J. Huang, Y. Li, Q. Guo, J. Polym. Sci. B 35 (1997) 1383. [22] S. Krause, N. Roman, J. Polym. Sci. A 3 (1965) 1631. [23] V.R. Landi, Rubber Chem. Technol. 45 (1972) 222. [24] M.M. Pohl, R. Dany, R. Mix, J. Gahde, G. Hinrichsen, Polymer 37 (1996) 2173. [25] A. Ferry, P. Jacobson, J.D. Van Heumen, J.R. Stevens, Polymer 37 (1996) 737. [26] C.J. Spaans, J.H. De Groot, F.G. Dekens, A.J. Pennings, Polym. Bull. 41 (1998) 131.
Compatibility studies on some rubber blend systems by ultrasonic techniques M.A. Sidkey a,∗ , A.A. Yehia a,b , N.A. Abd El Malak a , M.S. Gaafar a a
National Institute for Standards, El Haram, Giza, Tersa Street, El Giza 12211, Egypt b National Research Center, Cairo, Egypt
Received 16 January 2001; received in revised form 29 April 2001; accepted 4 May 2001
Abstract Longitudinal ultrasonic velocity, and ultrasonic attenuation, were measured in Adiprene CM–NBR, Adiprene CM–NR, Adiprene E–NR, Adiprene E–NBR blend systems at room temperature, using pulse echo technique. The densities of the blend samples were measured by the immersion method. Glass transition temperatures were measured experimentally using ultrasonic and differential scanning calorimetry (DSC). Glass transition temperatures were also calculated theoretically. Results showed that the variation of both longitudinal ultrasonic velocity and density with composition is linear with Adiprene CM–NBR, Adiprene CM–NR, and Adiprene E–NBR blends indicating compatible systems. For Adiprene E–NR, the plots of ultrasonic velocity and density vs. composition deviate from linearity according to the incompatibility degree of this system. Results obtained from ultrasonic attenuation measurements showed that the excess variation of ultrasonic attenuation with composition in rubber blend samples is of relaxational type and only one maxima or minima appeared in case of compatible blends and two or more maxima or minima appeared in case of incompatible blends. The presence of a single transition temperatures observed in DSC thermograms and ultrasonic attenuation–temperature relation is a decisive confirmation of the formation of one single phase and therefore the compatibility behaviour of this blend. On the other hand, the presence of two transition temperatures is taken as evidence of phase separation and consequently the formation of two phases with incompatible behaviour of the blend system. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Ultrasonic; Adiprene; DSC; Transition temperature
1. Introduction The concept of physically blending two or more existing polymers to obtain a new product has not been developed as fully as the chemical approach to blending, but the physical approach is now attracting widespread interest and is being used commercially. Polymer blends are physical mixtures of structurally different polymers, which interact through secondary forces with no covalent bonding [1]. The manifestation of superior properties depends upon compatibility or miscibility of homopolymers at molecular levels. Compatibility of polymer blends can be examined by sophisticated experimental and theoretical techniques [2–6] to decide their practical activity. The degree of compatibility of rubber blends: natural rubber–styrene butadiene rubber (NR–SBR), acrylonitrile butadiene rubber–chloroprene rubber (NBR–CR), acrylonitrile butadiene rubber–styrene butadiene rubber (NBR– SBR), and natural rubber–chloroprene rubber (NR–CR) ∗
Corresponding author. Tel.: +20-3867-452; fax: +20-3867-451.
has been studied by Abd El-All et al. [7] using ultrasonic methods. The variation of compressional ultrasonic velocity with mole fraction percent of the blend was found to be linear in NR–SBR and NBR–CR blends indicating compatible systems while it deviates from linearity in NR–CR and NBR–SBR. Results of longitudinal ultrasonic absorption showed that compatible rubber blends exhibit only one maxima or minima. Density measurements, values of heat of mixing in these blends confirmed the ultrasonic results. Ultrasonic velocity, ultrasonic attenuation, and transition temperature investigations were measured in the blend systems CR–NBR (chloroprene–acrylonitrile butadiene rubber), CR–SBR (chloroprene–styrene butadiene rubber), and CR–EPDM (chloroprene–ethylene propylene diene monomer) by Sidkey et al. [8]. The study was carried out to examine the degree of compatibility in these rubber blend systems. Zerjal et al. [9] investigated blends of a thermoplastic polyurethane (TPU) with poly(styrene-co-acrylonitrile) (SAN) by differential scanning calorimetry (DSC) and dielectric spectroscopy. From the dielectric measurements it was concluded that the relaxation processes in the TPU/SAN
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blends occur at the same temperatures as the relaxation processes in pure components, which suggests that the motions of TPU chains are decoupled from the motions of SAN chains. Singh and Singh [3] studied the variation of longitudinal ultrasonic velocity with composition in some compatible and incompatible polymer blends in solid forms. They found that the plot of ultrasonic velocity vs. composition for PMMA–PVA blend was linear except for some curvature in the composition range of 75–85% by weight PMMA in the blend. The plot for PMMA–PS blend depicted an inverted S type of behaviour showing the multiphase nature of this system and clearly indicating the region of phase separation. Results of the variation of ultrasonic absorption with composition of polystyrene (PS) and ethylene propylene diene monomer (EPDM) blend were reported by Shaw and Singh [10]. They concluded that this blend is incompatible blend. A study carried out by Singh and Singh [3] on the compatibility of polymethyl methacrylate–polyvinyl acetate and polymethyl methacrylate–polystyrene blends in terms of phase morphology of the blends using electron microscopy aiming to give further evidence to their ultrasonic velocity measurements. They reported that PMMA–PVA blend containing 60% by weight PVA seemed to be compatible since dark and light regions representing both homopolymers were distributed homogeneously and none of the regions had phase separation. The system PMMA–PS had two phase morphology and contained darker and brighter regions depicting two homopolymeric constituents. The heterogeneity of this system showed the incompatibility of this blend. The work under report was undertaken to investigate the compatibility behaviour of some rubber blends using ultrasonic methods, DSC, and electron microscope techniques.
The longitudinal ultrasonic velocity (V ) was measured for different solid blend samples, using the pulse echo technique, by measuring the elapsed time between the initiation and the receipt of the pulse appearing on the screen of a flaw detector (USM3—Krautkramer) by standard electronic circuit (PM3055 Philips). The velocity was therefore obtained by dividing the round trip distance by the elapsed time. Measurements were carried out at 2 MHz frequency and at room temperature. Ultrasonic absorption measurements were performed using pulse echo technique at 4 MHz frequency and at room temperature. The same transducer acted as the transmitter and receiver simultaneously. The heights of two successive echoes were measured, and the absorption coefficient (α) was then calculated according to the equation: 20 A1 α= dB/ cm, log 2d A2 where d is the thickness of the sample, and A1 and A2 are the heights of the first and second echoes, respectively. Measurements of glass transition temperatures were carried out using differential scanning calorimeter DSC 50 (Schimadzu, Japan). Measurements were carried out at a cooling rate of 4 ◦ C min−1 in the temperature range from −100 to 0 ◦ C. Liquid nitrogen was used for cooling. Besides, the transition temperature in polymer blends were measured using ultrasonic methods as described earlier by Sidkey et al. [11]. Scanning electron micrographs were obtained for Adiprene E–NR blend using JOEL-100 T scanning electron microscope.
3. Results and discussion 3.1. Density measurements
2. Experimental The ingredient rubbers used in this investigation are natural rubber (NR), nitrile butadiene rubber (NBR) manufactured by Alexandria, Egypt, and two forms of polyurethane (Adiprene CM and Adiprene E) manufactured by Uniroyal Chemica, England. These rubbers were firstly masticated separately for 1 min, then the two rubbers composing the blend were weighed according to the composition required and mastication process was then continued for 20 min. Known amount (4 part per hundred rubber) of an effective vulcanized agent (benzoyl peroxide) was added on a two roll mill and good mixing was carried out. Blocks were cut into slabs and then vulcanized in clean polished moulds in a press under pressure of about 4 × 105 kg m−2 and at temperature of 140 ◦ C for 30 min. Four rubber blends, with different compositions, were therefore prepared. The densities of the rubber blend specimens were measured using immersion technique and all measurements were taken at room temperature (298 K).
Fig. 1 shows the variation of density with the increase of polyurethanes (Adiprene CM and Adiprene E) weight percent content. The figure shows a linear relation over the entire range of composition and is represented by straight lines for the blend systems: Adiprene CM–NBR, Adiprene CM–NR, and Adiprene E–NBR. For Adiprene E–NR blend system, the variation of density with the increase in Adiprene E weight percent shows a deviation from linearity behaviour. The linear behaviour indicates greater molecular mixing and strong inter-chain inter-polymer interactions among the rubber blend components. It was reported earlier [6,7,12] that a linear relation between density and blend composition indicates the compatibility behaviour of this blend, and the complete solubility of these two rubber components in each other at all proportions [11]. On the other hand, the nonlinear behaviour shown in Fig. 1 for Adiprene E–NR blend system suggests that the mixing of these two parent rubbers is very week due to the poor inter-polymer inter-chains among the Adiprene E and NR blend components. Such behaviour
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Fig. 1. Relation between density and weight percent content of adiprene component.
indicates the presence of more than one phase and consequently the incompatibility behaviour of this blend system. A similar results were reported by Abd El-All [20]. 3.2. Ultrasonic velocity measurements The relation between longitudinal ultrasonic velocity and polyurethanes composition of the four blend systems studied is shown in Fig. 2. The plot depicts a linear relation at composition ranges of the blend systems: Adiprene CM–NBR, Adiprene CM–NR, and Adiprene E–NBR. The linearity of this relation indicates the complete solubility of the two rubber components, comprising each blend system, in each other at all proportions. This is mainly due to the strong interactions between the two macromolecular rubber components. Such behaviour may be also explained on the basis of aggregation and conformational changes of the macromolecules which leads to the formation of one homogeneous phase [5,11,13]. The linearity behaviour of ultrasonic
velocity vs. blend composition indicates the compatibility behaviour of these blend systems [8,18]. The relation between longitudinal ultrasonic velocity and weight percentage content of Adiprene E–NR in rubber blend samples shows a curvilinear type of relation at all composition ranges of the blend. The curvilinear type of this relation is mainly due to heterogeneity indicated by phase separation due to immiscibility of these two parent rubber components in each other at all proportions of Adiprene E–NR rubber blend. A behaviour of this type can be taken as an evidence for an incompatible blend system. Shaw and Singh [10], Hourston and Hughes [5], Singh and Singh [18] and Sidkey et al. [8] reported similar results. 3.3. Ultrasonic absorption measurements Fig. 3 depicts the variation of ultrasonic absorption with the change of polyurethanes (Adiprene CM and Adiprene E) weight percent content for the four investigated blends. The
Fig. 2. Variation of longitudinal ultrasonic velocity with weight percent content of adiprene component.
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Fig. 3. Variation of ultrasonic absorption coefficient with weight percent content of adiprene component.
nature of the absorption is merely of relaxational type [6,11]. For Adiprene CM–NBR blend, one minimum appeared at about 40 wt.% Adiprene CM. For Adiprene CM–NR, only one maximum appeared at about 90 wt.% Adiprene CM. The blend system Adiprene E–NBR shows also only one maximum at about 40 wt.% Adiprene E. The presence of only one maximum or one minimum can be explained by the fact that both component rubbers of each blend system are miscible in each other forming only one single phase and consequently run a relaxation process simultaneously.
The presence of only one single minimum or maximum in the ultrasonic absorption and blend composition relation, gives an indication of the good compatibility of this blend system [6,11]. The relation between the measured ultrasonic absorption and weight percent content of Adiprene E–NR blend system shows clearly the presence of three maxima at 20, 50, and 80 wt.% Adiprene E. Moreover, two minima appeared also at about 30 and 60 wt.% content of Adiprene E. The presence of more than one maximum or minimum indicates that the two parent rubber components are
Fig. 4. Variation of attenuation coefficient of Adiprene CM–NBR blend with temperature.
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Table 1 Composition of rubber blend, values of glass transition temperatures of component rubbers, transition temperatures measured experimentally, and transition temperatures calculated theoretically Rubber composition (wt.%)
0% Adiprene CM–l00% NBR 100% Adiprene CM–0% NBR 40% Adiprene CM–60% NBR 60% Adiprene CM–40% NBR
Transition temperature (K) From references
Experimental ultrasonic
Experimental DSC
Calculated according to Fox’s equation
Calculated according to Gordon–Taylor equation
241 [14] 229 [9,24,25] – –
253 215 238 228
251.98 224.04 241.63 228.00
– – 236.05 233.65
– – 234.00 231.90
immiscible in each other and two phases occurred which undergo separate relaxation process. This blend system represents an example of the incompatible blends [6,7,11]. 3.4. Transition temperature measurements The relation between the measured ultrasonic absorption and temperature of 100% NBR, 40% Adiprene CM–60% NBR, 60% Adiprene CM–40% NBR, and 100% CM are shown in Fig. 4. The absorption is of relaxational nature and is not due to scattering of the dispersed phase. Table 1 gives the composition of the solid blend system, values for glass transition temperatures of component rubbers as given in Polymer Hand Book [14], the transition temperatures measured experimentally, and transition temperatures calculated theoretically according to the equations given by Fox [15] as Wb W1 W2 = + TgB Tg1 Tg2 where W1 , W2 and Wb represent the contents (wt.%) of components 1 and 2 and the blend, respectively, and TgB , Tg1 and Tg2 are the glass transition temperatures of the blend, components 1 and 2, respectively, and by Gordon–Taylor equation [16] as W2 TgB = Tg1 + K (Tg2 − TgB ) W1 where TgB is the glass transition temperature of the blend, Tg1 and Tg2 are those of pure components 1 and 2, respectively. W is the weight fraction and K is an empirical parameter related to the degree of curvature of the Tg composition diagram, a K value of 0.48 fitting the experimental data quite well.
It is interesting to note that Fig. 4 shows the presence of only one single transition temperature peak appeared at 228 K for 60% Adiprene CM–40% NBR blend, and also it shows only one transition temperature peak at about 238 K for 40% Adiprene CM–60% NBR blend. The presence of only one single transition temperature indicates very clearly that this blend system is a compatible blend. Moreover, the transition temperature peak appears at 228 K lies very near to the transition temperature peak of the 100% Adiprene CM rubber component which appeared at 215 K. Again, the same observation was observed for the transition temperature peak appeared at 238 K which lies nearer to the 100% NBR component transition temperature peak at 253 K. It is clear from Table 1 that the Tg values calculated theoretically from both Fox’s equation and Gordon–Taylor relation are very close to the obtained experimental values. The DSC transition temperatures of 100% Adiprene CM, 100% NBR, 40% Adiprene CM–60% NBR, and 60% Adiprene CM–40% NBR blends are given in Table 1. It can be seen that each blend displays only one single glass transition temperature (Tg ) which changes its position with blend composition. The presence of one single glass transition temperature in DSC thermograms indicates the miscibility of the two component polymers and hence the good compatibility of the blend [9,17]. Table 2 gives the composition of the Adiprene CM–NR blend system, values of glass transition temperature for component rubbers, the transition temperatures measured experimentally, transition temperatures calculated theoretically according to Fox equation and Gordon–Taylor relation. It is clear from the curves shown in Fig. 5 that the ultrasonic absorption in this blend goes through only
Table 2 Composition of rubber blend, values of glass transition temperatures of component rubbers, transition temperatures measured experimentally, and transition temperatures calculated theoretically Rubber composition (wt.%)
0% Adiprene CM–100% 100% Adiprene CM–0% 40% Adiprene CM–60% 60% Adiprene CM–40%
NR NR NR NR
Transition temperature (K) From references
Experimental ultrasonic
Experimental DSC
Calculated according to Fox’s equation
Calculated according to Gordon–Taylor equation
203.00 [14] 229.00 [9,24,25] – –
199.00 215.00 204.00 210.00
203.07 224.04 209.40 210.32
– – 212.66 217.84
– – 218.12 222.70
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Fig. 5. Variation of attenuation coefficient of Adiprene CM–NR blend with temperature.
one maximum (transition temperature peak) at about 210 K for 60% Adiprene CM–40% NR blend and at about 204 K for 40% Adiprene CM–60% NR blend. This behaviour suggests the occurrence of the same thermal relaxation at some composition. The presence of only one single peak indicates very clearly that this blend system is a compatible blend. Moreover, the transition temperature of the 60% Adiprene CM–40% NR blend (210 K) lies very near to the transition temperature of the 100% Adiprene CM rubber component (215 K) while the transition temperature of the 40% Adiprene CM–60% NR blend (204 K) lies very close to the transition temperature peak of 100% NR rubber component (199 K). These observations indicate very clearly that the ultrasonic method is very successful and can be accepted as a new method for compatibility examination. The transition temperatures determined by DSC measurements, shown in Table 2, are comparable to those calculated theoretically according to Fox equation and Gordon–Taylor
relation. It was reported earlier [19] that the glass transition temperature Tg , which marks the characteristic transition of the amorphous region of the blend from glassy state to a rubbery state, is the most convenient and popular way of investigating the miscibility or immiscibility of pairs of polymers. Fig. 6 shows the relation between ultrasonic absorption and temperature for 100% NBR, 40% Adiprene E–60% NBR blend, 60% Adiprene E–40% NBR blend, and 100% Adiprene E. Only one relaxational temperature peak is observed in each investigated blend composition and its position lies between the transition temperatures corresponding to the two component rubbers. Table 3 gives the composition of the solid blend system, values of glass transition temperature of component rubbers, the transition temperatures measured experimentally, and transition temperatures calculated theoretically according to Fox equation and Gordon–Taylor relation. It is
Table 3 Composition of rubber blend, values of glass transition temperatures of component rubbers, transition temperatures measured experimentally, and transition temperatures calculated theoretically Rubber composition (wt.%)
0% Adiprene E–100% 100% Adiprene E–0% 40% Adiprene E–60% 60% Adiprene E–40%
NBR NBR NBR NBR
Transition temperature (K) From references
Experimental ultrasonic
Experimental DSC
Calculated according to Fox’s equation
Calculated according to Gordon–Taylor equation
241 [14] 216 [26] – –
253 207 237 221
251.98 211.00 246.67 243.84
– – 230.34 225.35
– – 234.94 233.65
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Fig. 6. Variation of attenuation coefficient of Adiprene E–NBR blend with temperature.
clear from Table 3 that the Tg value theoretically calculated from both Fox’s equation and Gordon–Taylor’s relation for 40% Adiprene E–60% NBR and 60% Adiprene E–40% NBR blends, are very close to the experimental values. The presence of only one single transition temperature in Fig. 6 confirms the ultrasonic analysis indicating that this blend is a compatible blend. The Tg values obtained from DSC measurements are very close to those obtained from ultrasonic methods. It can be seen from Figs. 7 and 8 that the transition temperature peaks for 40% Adiprene E–60% NR blend appears as two transition temperature peaks at 201 and 204 K. The first transition temperature peak appeared at 201 K may be due to the relaxation of NR domain, while the second transition temperature peak at 204 K may be due to the relaxation of Adiprene E domain. The first transition peak lies very near to 100% NR transition temperature, while the second transition temperature peak lies very near to 100%
Adiprene E transition temperature peak. For the blend composition; 60% Adiprene E–40% NR, there is also two transition temperature peaks appeared at 202 and 205 K. The first transition temperature peak appeared at 202 K lies very near to 100% NR transition temperature, while the second transition temperature peak appeared at 205 K lies nearer to the transition temperature peak of 100% Adiprene E. However, the presence of two temperature peaks in the ultrasonic attenuation–temperature diagrams gives an evidence of phase separation and therefore the formation of two phases. The phase separation and consequently the formation of two phases are mainly due to the very poor intermolecular mixing between the two parent component rubbers of this blend system. Moreover, blends of incompatible rubbers that segregate into distinct phases exhibit glass transitions which may be shifted to those of the unblended components. Table 4 gives the composition of the blend system, values of glass transition temperature for component rubbers, the
Table 4 Composition of rubber blend, values of glass transition temperatures of component rubbers, transition temperatures measured experimentally Rubber composition (wt.%)
0% Adiprene E–100% 100% Adiprene E–0% 40% Adiprene E–60% 60% Adiprene E–40%
NR NR NR NR
Transition temperature (K) Polymer handbook
Experimental ultrasonic
Experimental DSC
203.00 [14] 216.00 [26] – –
199.00 215.00 201, 204 202, 205
203.07 211.00 212.83 211.72
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Fig. 7. Variation of attenuation coefficient of 40% Adiprene E–60% NR blend with temperature.
Fig. 8. Variation of attenuation coefficient of 60% Adiprene E–40% NR blend with temperature.
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Fig. 9. Scanning electron micrographs of (500×) for: (A) 100% NR; (B) 100% Adiprene E; (C) 40% Adiprene E–60% NR blend; (D) 60% Adiprene E–40% NR blend.
transition temperatures measured experimentally by ultrasonic technique and DSC. It can be observed from Table 4 that there is only one transition temperature peak measured experimentally by DSC technique, which lies at 212.83 K for 40% Adiprene E–60% NR blend. Moreover, only one transition temperature peak appeared at 211.72 K for the blend system 60% Adiprene E–40% NR. Although the use of Tg in determining polymer compatibility is based on the judgement that the observation of two transition temperature peaks between those of pure components is taken as evidence of incompatibility [20,21], there are certain circumstances under which the transition temperature criterion may be inapplicable or even misleading. The application of the single transition criterion requires that the transition temperature of the parent components to be sufficiently displaced from each other so that the resolution is possible. The limits of resolution of transition temperatures less than about 20 K apart between the two parent components is very poor [22]. The closeness of blend components transi-
tion temperatures may be even a more severe problem for detecting by DSC technique [23]. The electron microscopy analysis of Adiprene E–NR blend system shown in Fig. 9 may confirm qualitatively the behaviour shown by ultrasonic measurements. The micrographs show dark and bright regions for 100% NR, large and elongated lines forming some sort of large opaque domains for 100% Adiprene E, some aggregates of dark and transparent domains for both blends 60% Adiprene E–40% NR and 40% Adiprene E–60% NR. The last two micrographs depict two homopolymeric constituents and can be roughly classified into two groups.
4. Conclusion The present investigations indicate clearly that the compatibility of rubber blends can be studied successfully in solids by ultrasonic techniques. It may be concluded that the
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simple measurement of ultrasonic velocity, ultrasonic absorption, and glass transition temperature by ultrasonic technique provide clue to the compatibility of blends which is in general obtained by sophisticated techniques of the DSC and scanning electron microscopy. References [1] M. Shen, H. Kawai, Am. Chem. Eng. J. 24 (1978) 1. [2] S. Krause, in: D.R. Paul, S. Newmann (Eds.), Polymer–Polymer Compatibility in Polymer Blends, Vol. 1, Academic Press, New York, 1978. [3] Y.P. Singh, R.P. Singh, Eur. Polym. J. 19 (1983) 529. [4] Y.P. Singh, S. Das, S. Maiti, R.P. Singh, J. Pure Appl. Ultrasonic 3 (1981) 1. [5] D.J. Hourston, I.D. Hughes, Polymer 19 (1978) 1181. [6] M.A. Sidkey, A.M. Abd El-Fattah, A.A. Yehia, N.S. Abd El-All, J. Appl. Polym. Sci. 43 (1991) 1441. [7] N.S. Abd El-All, A.A. Yehia, S.H. El-Sabbagh, J. Pure Appl. Ultrasonic 16 (1994) 103. [8] M.A. Sidkey, N.S. Abd El-Aal, A.M. Eid, The Specific Conference on Rheology and Polymer Processing (PCR), September 26–30, 1994, Kyoto, Japan, p. 345.
[9] B. Zerjal, Z. Jelcic, T. Malavasic, Eur. Polym. J. 32 (1996) 1351. [10] S. Shaw, R.P. Singh, Eur. Polym. J. 23 (1987) 547. [11] M.A. Sidkey, A.M. Abd El-Fattah, Z. Abdel Aziz, A.Z. Mohamed, N.S. Abd El-Aal, J. Pure Appl. Ultrasonic 15 (1993) 1. [12] A.H. Al-Salah, Polym. Bull. 40 (1998) 477. [13] D.J. Hourston, I.D. Hughes, Polymer 18 (1977) 1175. [14] J.E. Brandrup, Polymer Hand Book, Wiley/Interscience, New York, 1960. [15] T.G. Fox, Bull. Am. Phys. Soc. 1 (1956) 123. [16] M. Gordon, J.S. Taylor, J. Appl. Chem. 2 (1952) 493. [17] M. Song, A. Hammiche, H.M. Pollock, D.J. Hourston, M. Reading, Polymer 36 (1995) 3313. [18] Y.P. Singh, R.P. Singh, Eur. Polym. J. 20 (1984) 201. [19] R.P. Singh, J. Acoust. Soc. Ind. 21 (1993) 159. [20] N.S. Abd El-All, Ph.D. Thesis, Ain Shams University, Cairo, Egypt, 1992. [21] S. Zheng, J. Huang, Y. Li, Q. Guo, J. Polym. Sci. B 35 (1997) 1383. [22] S. Krause, N. Roman, J. Polym. Sci. A 3 (1965) 1631. [23] V.R. Landi, Rubber Chem. Technol. 45 (1972) 222. [24] M.M. Pohl, R. Dany, R. Mix, J. Gahde, G. Hinrichsen, Polymer 37 (1996) 2173. [25] A. Ferry, P. Jacobson, J.D. Van Heumen, J.R. Stevens, Polymer 37 (1996) 737. [26] C.J. Spaans, J.H. De Groot, F.G. Dekens, A.J. Pennings, Polym. Bull. 41 (1998) 131.