Influence of Different Curing Systems on the Physico-Mechanical and Rheological Properties of CSM Rubber

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1 Influence of Different Curing Systems on the Physico-Mechanical and Rheological Properties of CSM Rubber Influence of Different Curing Systems on the Physico-Mechanical and Rheological Properties of CSM Rubber Madhuri Nanda and Deba Kumar Tripathy* Rubber Technology Centre, Indian Institute of Technology, Kharagpur , India Received: 23 July 2009, Accepted: 8 June 2010 SUMMARY Curing systems play a vital role in designing rubber compounds for various industrial applications. Keeping this in view, a comparative study of the effects of four different curing systems such as sulfur, dicumyl peroxide (DCP, metal oxide (PbO and epoxy resin on the curing characteristics, physico-mechanical, and rheological properties of chlorosulfonated polyethylene rubber (CSM has been carried out. The highest values of maximum rheometric torque and scorch safety were observed in the peroxide-cured system, whereas sulfur-cured CSM rubber compounds possessed superior mechanical and rheological properties compared to those of the other cured systems. It is interesting to note that all curing systems exhibited increases in tensile strength, hardness, tear strength and crosslink density after. This may be due to post vulcanization. Unlike uncured CSM compound, in cured CSM compound the loss tangent increased with frequency, which may be due to the insufficient time available for molecular relaxation. Probable crosslinked structures for different curing systems have been proposed based on the observations of attenuated total reflectance Fourier transform infrared spectroscopy. INTRODUCTION Improvement in the properties of polymers can be obtained by chemically modifying the polymer backbone, by introducing structural irregularities or by grafting onto the polymer chain. By chlorosulfonation of polyethylene in solution the structural regularity is destroyed by changing the thermoplastic material into a rubbery material, which is described as CSM rubber according to ASTM D It contains 25% to 43% by weight of chlorine and 1.0% to 1.5% by weight of sulfur as SO 2 Cl units. Depending on chlorine contents, its flexibility also varies. Such chlorinecontaining polymers are commonly used as insulators or sheath materials in nuclear environments because of their well-known radiation resistance 2-4. Compared to unsaturated elastomers they have superior resistance to the *Corresponding author: dkt@rtc.iitkgp.ernet.in Smithers Rapra Technology, 2010 deteriorating effects of ozone, oxygen, weather, heat, chemicals and oil. Polar rubbers interact with their active functional groups via condensation or substitution reactions. The high reactivity of CSM rubber is due to -SO 2 Cl groups, which provides crosslinking sites allowing wide choice of practical curing systems. Two types of curing processes are available for CSM rubber (a Ionic cure (b Covalent cure 5. In ionic curing systems, normally ionic crosslinking occurs which is accelerated by moisture and this is possible only when the acid acceptor is a divalent metal oxide. In the covalent cure system, covalent crosslinking occurs, and most applications for CSM rubber make use of this type of curing 5. The properties and performance of a rubber product depend on many factors including the chemical nature of the rubber, the amount and kinds of ingredients incorporated into the rubber compound, processing and vulcanizing conditions, design of the product and service conditions. Physico-mechanical properties of different curing systems vary due to the difference in their efficiency of crosslinking. In order to obtain a desirable combination of properties and service life a chemical crosslinking system having higher efficiency should be considered. Proper judgment can be obtained from accelerated behaviour, as the crosslinking system has marked influence on the degradation characteristics of elastomers Studies of CSM rubber compounds have not received much attention even though they possess good weather resistance, electrical properties and resistance. Few research works dealing with CSM rubber have been reported in the literature The effect of β irradiation on structural changes of CSM rubber has been studied by Foucault et al. 14. Chailan et al. 15 have investigated the effect of thermal Polymers & Polymer Composites, Vol. 18, No. 8,

2 Madhuri Nanda and Deba Kumar Tripathy degradation on the viscoelastic and dielectric properties of metal oxide cured CSM compounds. Recently physical and electrical properties of sulfur cured carbon black filled CSM rubber compound has been reported by Tripathy et al. 16,17. No further study on the effect of curing systems on CSM rubber has been reported so far. In the present study an attempt has been made to explore the details of physico-mechanical and dynamic rheological behaviour of CSM rubber cured by four different curing systems with a view to select the most suitable curing system for industrial use. The influence of curing system on heat properties of CSM rubber has also been studied. Surface analysis has been studied using attenuated total reflectance Fourier transform infrared (ATR-FTIR spectroscopy. EXPERIMENTAL Materials Details of the compositions of the mixes are given in Table 1. CSM rubber [(Hypalon-40, 35% chlorine content, Mooney viscosity ML 1+4 at 100 C = 56] manufactured by DuPont Dow Elastomers was used. Magnesium oxide used was of analytical grade with specific gravity 3.8, and was supplied by E. Merck Limited, Bombay, India. Sulfur of chemically-pure grade with a specific gravity of 1.9, was supplied by M/S Nice chemicals Pvt Cochin, India. Curatives such as dibenzothiazyl disulfide (MBTS, diphenylguanidine (DPG and dipentamethylenethiuram tetrasulfide (Tetrone-A were supplied by M/S ICI limited, Hoogly, India. Triallyl cyanurate used in a stabilized form (40% was manufactured by Degussa, Germany. Dicumyl peroxide (DCP with a purity of 40% was procured from M/S ICI limited, Hoogly, India. Lead monoxide (PbO was supplied by Loba Chemie Pvt Ltd, Mumbai. Toluene was of analytical grade with BP C, which was procured from Ranbaxy Chemicals, New Delhi, India. Epoxy resin, grade Araldite LY553, was obtained from Cibatul Limited, Bombay. Stearic acid of chemically-pure grade was procured locally. Sample Preparation Mixing was carried out in a laboratory size two roll mixing mill (325 mm 150 mm at a friction ratio of 1: 1.25 according to ASTM D3182 with careful control of temperature, nip gap, mixing time and uniform cutting operation. The curing characteristics of the compounds were determined with a Monsanto Rheometer (R 100 according to ASTM D2084 and ASTM D5289 procedures. Moulding was done Table 1. Compositions of unfilled CSM vulcanizates in phr (parts per hundred rubber Mix No / Curing System Epoxy (G 1 Metal oxide (G 2 Peroxide (G 3 Sulfur (G 4 CSM MgO Stearic acid MBTS DPG TETRONE A TAC DCP Epoxy Resin PbO Sulfur in an electrically heated hydraulic press having 300 mm 300 mm platens at 160 C (Peroxide and 150 C (Epoxy, metal oxide, and sulfur at a pressure of 4.0 MPa. Vulcanization was done to optimum cure (90% of the maximum cure using different moulding conditions determined from torque data obtained from Monsanto Rheometer. The test specimens were punched out from moulded sheets. TESTING PROCEDURE Physical Test Methods The cure characteristics of the compounds were determined with the help of an oscillating disc rheometer with an arc of oscillation of 3. The chemistry of peroxide vulcanization explains that an oxygenoxygen bond present in peroxide undergoes homolytic cleavage at high temperature. The rheometric characteristics of CSM compound for the peroxide system and for other three curing systems were studied at 160 and 150 C respectively. Tensile Strength, modulus and elongation at break were determined by a Hounsfield 1145 universal testing machine according to ASTM D at 25 C using dumb-bell shaped specimens. Tear strength was also determined using Hounsfield 1145 according to ASTM method D 624 using a die C specimen. Shore-A hardness of the vulcanizates was determined according to ASTM D Compression set was determined by compressing the specimen to 25% of its original thickness for 22 hours at 70 C. The specimen was removed and allowed 30 min recovery, and then the permanent set was measured as a percentage of the original thickness according to ASTM D Moulded sheets were heat-aged at 100 C for 72 hours in an electrically heated air oven for the study. Chemical Test Methods The resistance to solvent was determined by a swelling test. The 418 Polymers & Polymer Composites, Vol. 18, No. 8, 2010

3 Influence of Different Curing Systems on the Physico-Mechanical and Rheological Properties of CSM Rubber volume fraction of rubber (V r in the vulcanizate was determined by equilibrium swelling in toluene, using the method reported by Ellis and Welding 18. The relationship used for calculating V r is represented by equation (1: 1 ( D FTρ V r = r ( D FTρ 1 1 r + A 0 ρ s (1 where T is the weight of the test specimen, F is the weight fraction of the insoluble components in the sample, D is the de-swollen weight of the test specimen, A 0 is the weight of absorbed solvent, corrected for swelling increment, ρ r is the density of the rubber and ρ s is the density of the solvent. The number of effective network chains per unit volume of rubber is denoted as υ, which was calculated using Flory Rehner equation (equation (2 19,20 υ = 1 ln 1 V 2 ( r + V r +µv r V s V 1/3 r V r / 2 (2 Where υ is the number of effective network chains per unit volume of rubber, V s is the molar volume of the solvent and μ is the polymersolvent interaction parameter (Flory- Huggins s interaction parameter, which was found to be FTIR ATR Measurements Fourier-transform infrared spectra (FTIR were recorded on a Nexus 870 spectrometer with an attenuated total reflection (ATR attachment. A minimum of 32 scans were signalaveraged at a resolution of 4 cm -1. For FTIR-ATR measurements, the spectrometer was equipped with a DTGS detector. The internal reflection element (IRE chosen was a 45 degree ZnSe crystal. Rheological Measurements For measurement of dynamic viscoelastic properties, Rubber Process Analyzer (RPA2000, Alpha Technologies, Akron, USA was used. The RPA was a parallel plate rheometer, capable of measuring the complex modulus of rubber compounds under dynamic shear deformation. It helped in measuring the rheological, rheometric, and dynamic viscoelastic properties of the polymers over a wide range of conditions. The frequency sweep test was performed, in which the oscillating frequency change was programmed in steps from 0.13 to 30 Hz at a constant strain amplitude of 2.9% and under constant temperature conditions (110 C. RESULTS AND DISCUSSION Curing Characteristics The cure characteristics of the samples obtained from the Monsanto Rheographs are summarized in Table 2. The highest value of maximum rheometric torque (M H was shown by the peroxide system, whereas the lowest value was shown by the metal oxide system. This is due to high crosslink density of peroxide cured CSM compounds 22. Among all the systems, the peroxide one showed the highest scorch safety. The highest value of minimum rheometric torque (M L was shown by the sulfur system, whereas the lowest value was shown by the peroxide system. The effect of different curing systems on the optimum curing time (T 90 and cure rate of CSM compounds was found to be marginal. Physico-Mechanical Properties The physico-mechanical properties of CSM vulcanizates cured by four different curing systems both before and after are presented in Table 3. Depending on the vulcanization system, different crosslink structures are obtained. In sulfur and epoxy cured CSM rubber C-S-C crosslinks are formed, while peroxide yields C-C crosslinks. In the metal oxide system, ionic crosslinks are formed. The free mobility of the chain segments of the macromolecules depends on their relative distance, and therefore on the length of the crosslinks. Therefore, the type of crosslink structure influences the property spectrum of the vulcanizate From this table, it can be observed that the tensile strength for sulfur-cured vulcanizates has been found to be higher than those of the other three systems. This may be due to the formation of sulfidic crosslinks in the CSM vulcanizates. In the metal oxide and epoxy cure systems, comparable tensile strength was observed. An intermediate value of tensile strength was observed for the peroxide cure system. Sulfur-cured CSM vulcanizates showed higher modulus values. The DCP cured systems have rigid C-C linkages, which can be broken easily under an applied stress, whereas in sulfur cured systems, flexible C-S and S-S linkages exist and they require more stress to break the bonds. However higher tear strength was observed in the metal oxide cure system, which may be due to the ionic crosslinked structure. Table 2. Rheometric characteristics of unfilled CSM vulcanizates Mix no Initial viscosity d N-m Minimum torque (M L, d N-m Maximum torque (M H, d N-m Scorch time (min Optimum cure time (T 90, min Cure rate (min -1 G G G G Polymers & Polymer Composites, Vol. 18, No. 8,

4 Madhuri Nanda and Deba Kumar Tripathy Table 3. Physico-mechanical properties of unfilled CSM vulcanizates Properties Epoxy (G 1 Metal oxide (G 2 DCP (G 3 Sulfur (G 4 Before After Before After Before After Before Tensile strength, MPa M100%, MPa M200%, MPa M300%, MPa Elongation at break (% Tear strength (N/mm Hardness IRHD Compression set 22 hrs at 100 C,% Crosslink density(υ 10 3, mol/cc After The crosslinking systems that lead to covalent bonds, such as sulfur and dicumyl peroxide systems exhibited better compression set response. The best set properties were achieved with the organic peroxide system, which forms strong C C links between the polymeric chains. The crosslinking efficiency of CSM vulcanizates is measured in terms of their crosslink density. A higher crosslink density value was observed for the peroxide and epoxy curing systems. In the peroxide curing system, triallyl cyanurate was used as a coagent, which improved the cure rate, giving higher crosslink density. Intermediate values of crosslink density were observed in the case of the sulfur curing system. In metal oxide cured CSM vulcanizates, the crosslink density value was comparatively low, which may be due to an ionic crosslink network being formed between the polymeric chains. Fourier Transform Infrared/ Attenuated Total Reflectance (FTIR ATR Spectroscopy Infrared spectra of the compounds were obtained for both CSM rubber and vulcanized compounds. Special attention was paid to the spectral region of the -SO 2 Cl groups to establish the existence of variations between the raw and the crosslinked states. The assignments of the principal bands for raw rubber are presented in Table 4. Similar findings have also been reported 26. Figure 1 represents the FTIR-ATR spectra of CSM rubber (spectrum a and epoxy cured CSM vulcanizate (spectrum b. IR analysis provided a confirmation of the assumption that such specific bonds were formed. It appeared that the characteristic band of C-SO 2 Cl (at 1366 cm -1 in the spectrum of pure CSM was less intense in the spectrum of the vulcanizate. The absorption bands at 829 and 1246 cm -1 may be due to the C-O-C stretching vibrations of the epoxy ring. The band at 1654 cm -1 is due to the C=C stretching frequency which is observed as a result of decomposition of the SO 2 Cl group present in pure CSM rubber. The band at 1183 cm -1 is due to C-S-C stretching vibrations, which further supports the formation of a crosslinked network in CSM vulcanizates as shown in Scheme 1 1. Additionally, the vulcanizate spectrum revealed the presence of a broad yet weak band at 3386 cm -1 which may be attributed to the stretching vibrations of OH (H- bonded groups, obtained due to ring opening of the epoxy resin (Scheme 1. Figure 2 represents the FTIR-ATR spectra of CSM rubber (spectrum a CSM rubber having no unsaturation sites possesses excellent resistance to heat, weather, ozone and chemicals. Changing the curing systems had a marginal effect on the behaviour of CSM vulcanizates. Increases in the tensile strength and tear strength after were observed in all systems, which may be due to post-vulcanization. Elongation at break decreased after for all samples. Heat studies also showed marginal effects on the hardness and crosslink density. Table 4. Assignment of infrared bands of chlorosulfonated polyethylene Wavenumber (cm -1 Group Assignment 2928 CH3-, -CH2-, >CH- υ(c-h 2855 CH3-, -CH2-, >CH- υ(c-h CH2 δ(c-h SO2Cl υ(so 2 asym CH2- γ(ch SO2Cl υ(so 2 Sym 1016 Unknown Unknown 723 -CH2- γ γ (CH CHCl- υ(c-cl 420 Polymers & Polymer Composites, Vol. 18, No. 8, 2010

5 Influence of Different Curing Systems on the Physico-Mechanical and Rheological Properties of CSM Rubber and metal oxide (PbO cured CSM vulcanizate (spectrum b. In the case of ionomeric CSM, the peak at 1606 cm -1 with a shoulder at 1581 cm -1 is probably due to the asymmetric COO - stretching of magnesium stearate. The band at 1016 cm -1 with a shoulder at 1040 cm -1 is believed to be due to the symmetric stretching of sulfonate groups present as lead sulfonate as shown in Scheme 2 1. The characteristic band of C-SO 2 Cl (at 1366 cm -1 in the spectrum of pure CSM was found to be less intense in the spectrum of the CSM vulcanizate, which further supports the hydrolysis of the sulfochloride group present in the polymer (Scheme 2. due to N-CH 2 stretching vibrations that arise from TAC domains associated with crosslinks 27 (Scheme 3. Figure 4 represents the FTIR-ATR spectra of CSM rubber (spectrum a and sulfur cured CSM vulcanizate (spectrum b. The band at 1657 cm -1 is due to the C=C stretching frequency, which is obtained as a result of decomposition of the SO 2 Cl group present in the pure CSM rubber. The band at 1183 cm -1 is due to C-S-C stretching vibrations, which further supports the formation of crosslinked network in CSM vulcanizates as shown in Scheme 4 1. Figure 1. FTIR ATR spectra of raw CSM rubber and epoxy cured CSM vulcanizate Figure 3 represents the FTIR-ATR spectra of CSM rubber (spectrum a and DCP cured CSM vulcanizate (spectrum b. Bands at 1695 cm -1 may be due to N (C=O N from crosslinking associated with TAC domains. The band at 1611 cm -1 can be attributed to the quadrant stretching of TAC present as a part of the CSM crosslinked domain. Formation of cumyl alcohol through dissociation of DCP during curing reactions can also account for the broad yet weak band at 3400 cm -1 (Scheme 3. The band at 1099 cm -1 is Scheme 1. Probable network structure of chlorosulfonated polyethylene crosslinked by epoxy system Polymers & Polymer Composites, Vol. 18, No. 8,

6 Madhuri Nanda and Deba Kumar Tripathy Figure 2. FTIR ATR spectra of raw CSM rubber and metal oxide cured CSM vulcanizate Figure 3. FTIR ATR spectra of raw CSM rubber and DCP cured CSM vulcanizate Scheme 2. Probable network structure of chlorosulfonated polyethylene crosslinked by metal oxide system 422 Polymers & Polymer Composites, Vol. 18, No. 8, 2010

7 Influence of Different Curing Systems on the Physico-Mechanical and Rheological Properties of CSM Rubber Scheme 3. Probable network structure of chlorosulfonated polyethylene crosslinked by DCP system The characteristic band of C-SO 2 Cl (at 1366 cm -1 in the spectrum of the vulcanizate was found to be less intensive. This drop in intensity of the sulfochloride group (SO 2 Cl absorption clearly indicated the participation in the crosslinking of CSM rubber by different vulcanizing systems. Rheological Properties Frequency Sweep Figure 5 reveals the processibility of uncured compound via complex viscosity (η* as a function of frequency. All samples show shear thinning effect, i.e. a decrease in η* with increasing frequency. Compounds obtained from sulfur cure formulation were more viscous than those of the other systems. Figure 6 shows the elastic modulus (G as a function of frequency for the uncured compound. It is apparent from the figure that the different curing systems had a Polymers & Polymer Composites, Vol. 18, No. 8,

8 Madhuri Nanda and Deba Kumar Tripathy Scheme 4. Probable network structure of chlorosulfonated polyethylene crosslinked by sulfur cure system remarkable effect on the rheological behaviour even at high frequency. Storage modulus increased with frequency; however, the rate of increase decreased with increase in the test frequency, which may be due to the insufficient time available for molecular relaxation. In other words, the higher the test frequency, the higher the elasticity. At low frequency, the influence of different curing systems on storage modulus was more pronounced. Sulfur-cured CSM compounds showed the highest storage modulus. Figure 7 shows the loss tangent (tan δ as a function of frequency for the uncured compound, which decreased sharply at lower frequency, while at higher frequency the rate of decrease was slow, so that the curves are nearly parallel to the horizontal axis. In the entire range of frequency studied, tan δ for the epoxy curing system was higher than those of the other three curing systems. This may be due to the predominantly viscous response of epoxy cure CSM compound with relatively low molecular entanglement. Figure 4. FTIR ATR spectra of raw CSM rubber and sulfur cured CSM vulcanizate Figure 5. Complex viscosity as a function of frequency in uncured CSM compounds Cured Compounds Figure 8 shows the complex viscosity (n* as a function of frequency of cured compounds. It is clearly observed from the plot that the viscosity of cured compounds increased for all curing systems compared to those of uncured compounds. This is due to the formation of three dimensional crosslinked networks in the CSM vulcanizates. All samples show a very strong shear-thinning effect. Figure 9 shows the plots of the storage modulus 424 Polymers & Polymer Composites, Vol. 18, No. 8, 2010

9 Influence of Different Curing Systems on the Physico-Mechanical and Rheological Properties of CSM Rubber G versus frequency for different curing systems of the CSM vulcanizates. It is clearly observed from Figure 9 that storage modulus exhibits nearly frequency-independence, supporting the crosslinking of polymeric phase in the polymer matrix. Due to network formation between the polymeric chains in CSM vulcanizates there is no molecular slippage taking place within this range of frequency. Storage modulus increased after curing for all cure system, which may be due to increase in elastomeric phase in CSM vulcanizates. The frequency dependence loss tangent for CSM vulcanizates is displayed in Figure 10. Unlike the uncured compound loss tangent increased with increase in frequency for all curing systems. This was attributed to the fact that, at higher frequencies, the polymer chain did not have sufficient time for molecular relaxation. Sulfurcured CSM vulcanizate showed higher loss tangent values compared to those of other curing systems. This may be due to high elastic modulus value of sulfur-cured vulcanizate. Figure 6. Elastic modulus as a function of frequency in uncured CSM compounds Figure 7. Damping factor (tan δ as a function of frequency in uncured CSM compounds CONCLUSIONS The effect of different curing systems on curing characteristics, physicomechanical and rheological properties of CSM vulcanizates was investigated. From rheometric studies of CSM compounds it was observed that the peroxide system exhibited the maximum rheometric torque and maximum scorch safety while the metal oxide system showed minimum rheometric torque. It was evident that the sulfur-cured system showed higher tensile strength and hardness values, whereas the metal oxide system showed higher tear strength. Increase in tensile strength, tear strength, and decrease in elongation at break were observed after for all curing systems studied. This may be due post-vulcanization. Better physical properties supported by good resistance make CSM vulcanizates Figure 8. Complex viscosity as a function of frequency in cured CSM compounds Polymers & Polymer Composites, Vol. 18, No. 8,

10 Madhuri Nanda and Deba Kumar Tripathy Figure 9. Elastic modulus as a function of frequency in cured CSM compounds physico-mechanical and rheological studies, both peroxide and sulfur system exhibited better properties than the epoxy and metal oxide systems. The present investigation also revealed that the negative effect of metal oxide as a curing system due to its toxic nature can be successfully overcome by sulfur and peroxide curing systems in the case of CSM rubber. REFERENCES Figure 10. Damping factor (tan δ as a function of frequency in cured CSM compounds suitable for industrial applications such as conveyor belt linings or cable and conductor insulators. -SO 2 Cl groups participated in a different way during the crosslinking process, which depended on the crosslink agent used. A probable crosslink structure has been proposed for all curing systems, which has been supported by ATR studies. Higher viscosity values have been observed for the sulfur cure system in frequency-dependent viscosity plot for both uncured and cured CSM compound. The viscosity increase was accompanied by an increase in the storage modulus (G. In the case of the cured compounds, the frequency independence nature of storage modulus has been observed. This can be explained on the basis of formation of three dimensional crosslinked network structures in CSM vulcanizates. Unlike the uncured CSM compounds, in the cured CSM compound the loss tangent increased with frequency. This was attributed to the insufficient time available for molecular relaxation. Based on the 1. Brydson J.A., Rubber Chemistry, Applied science, London ( Gillen K.T. and Clough R.L., Radiation-thermal degradation of PE and PVC: Mechanism of synergism and dose rate effects, Radiation Physics and Chemistry, 18 ( Clough R.L., Radiation-resistant polymers, in Encyclopedia of Polymer Science and Engineering (eds.: Kroschwitz J. Wiley, New York, ( Chaianya S.S., Mahendra J.P., Manish R.D. and Madhav V.P., Highenergy radiation-resistant elastomeric vulcanizates. I. Chlorosulfonated polyethylene, Journal of Applied Polymer Science, 51 ( Morton M., Rubber Technology. Van Nostrand Reinhold, NewYork, ( Bevilacqua E.M., Thermal Stability of Polymers, Marcel Dekker, New York ( Capps R., Effect of cure systems and reinforcing fillers on dynamic mechanical properties of chlorobutyl elastomers for potential vibrationcontrol applications, Rubber Chemistry and Technology, 59 ( Shelton J.R., Stabilization fundamentals in thermal autoxidation of polymers, in Stabilization and Degradation of Polymers, (eds.: Allara D.L., Hawkins W.L. Wiley- Interscience, New York, ( Saha Deuri A. and Bhowmick A.K., Ageing of rocket insulator compound based on EPDM, Polymer Degradation and Stability, 16 ( Polymers & Polymer Composites, Vol. 18, No. 8, 2010

11 Influence of Different Curing Systems on the Physico-Mechanical and Rheological Properties of CSM Rubber 10. Saha Deuri A., and Bhowmick A.K., Influence of ageing on strength properties and morphology of fracture surface of hydroxy terminated polybutadiene rubber, Materials Chemistry and Physics, 18 ( Owczarek M. and Zaborski M., Chlorosulfonated polyethylene crosslinked with aminosilanes, Kautschuk Gummi Kunststoffe, 58 ( Nersasian A., King K.F. and Johnson P.R., Novel curing systems for chlorosulfonated polyethylene, Journal of Applied Polymer Science, 8 ( Maynard J.T. and Johnson P.R., Ionic crosslinking of chlorosulfonated polyethylenes, Journal of Applied Polymer Science, 7 ( Foucault F., Esnouf S., Le Moel A., Irradiation/temperature synergy effects on degradation and ageing of chlorosulfonated polyethylene, Nuclear Instruments and Methods in Physics Research B, 185 ( Chailan J.F., Boiteux G., Chauchard J., Pinel B. and Seytre G., Effects of thermal degradation on the viscoelastic and dielectric properties of chlorosulphonated polyethylene (CSPE compounds, Polymer Degradation and Stability, 48 ( Nanda M. and Tripathy D.K., Physico-mechanical and electrical properties of conductive carbon black reinforced chlorosulfonated polyethylene vulcanizates, express Polymer Letter, 2 ( Nanda M., Chaudhary R.N.P. and Tripathy D.K., Dielectric relaxation of conductive carbon black reinforced chlorosulfonated polyethylene vulcanizates, Polymer Composite (on line published. 18. Ellis B. and Welding G.N., Estimation, from swelling, of the structural contribution of chemical reactions to the vulcanization of natural rubber Part I. General method, Rubber Chemistry and Technology, 37 ( Flory P.J., Principles of Polymer Chemistry, Cornell University Press, Ithaca, NY ( Flory P.J. and Rehener J., Statistical mechanics of cross-linked polymer networks Π. Swelling, Journal of Chemical Physics, 11 ( Braton A.F.M., Handbook of Solubility Parameters and Other Cohesion Parameters. CRC Press, BocaRaton, USA. ( Abdel-Aziz M.M., Mofti S. and Basfar A.A., Influence of different curing systems on the physicomechanical properties and stability of SBR and NR rubbers, Radiation Physics and Chemistry, 63 ( Sacrini E., Fontanelli R. and Fontana A., New organic peroxides and their use in elastomer curing, Kautschuk Gummi Kunststoffe, 37 ( Brazier D.W. and Schwarz N.N., The cure of elastomers by dicumyl peroxide as observed in differential scanning calorimetry, Thermochimica Acta, 39 ( Capla M. and Barsig E., Simultaneous degradation and crosslinking effect of dicumyl peroxide on ethylene propylene copolymers, European Polymer Journal, 16 ( Roychoudhury A. and De P.P., Studies on chemical interactions between Chlorosulfonated polyethylene and Carboxylated nitrile rubber, Journal of Applied Polymer Science, 63 ( Mitra S., Ghanbari-Siahkali A., Kingshott P., Rehmeier H.K., Abildgaard H. and Almdal K., Chemical degradation of crosslinked ethylene-propylene-diene rubber in an acidic environment. Part II. Effect of peroxide crosslinking in the presence of a coagent, Polymer Degradation and Stability, 91 ( Polymers & Polymer Composites, Vol. 18, No. 8,

12 Madhuri Nanda and Deba Kumar Tripathy 428 Polymers & Polymer Composites, Vol. 18, No. 8, 2010