S. Kole’s research while affiliated with Indian Institute of Technology Kharagpur and other places

Polychloroprene and polyacrylamide form a self-crosslinking blend during mixing and moulding in the temperature range 140 to 190°C and mis inter-crosslinking is revealed by a torque rise in the rheometric studies. The nature of the stress-strain curves of the blend indicates the generation of a bonded structure where one soft matrix is bonded with a rigid phase and the bonding fails after a critical loading. The results of hysteresis measurements are in agreement with a bonded structure. The SEM study shows that the majority of the polyacrylamide particles are covered with a layer of rubber matrix. It also shows the distribution of particles and the extent of breakdown of the particles in various blends. The SEM observations are also in line with interfacial bonding and help in understanding the physical properties of various blends based on the extent of inter-crosslinking reaction. Thermogravimetric analysis of aqueous solutions, cast film, and dry powdered of polyacrylamide confirms the role of moisture in polyacrylamide degradation. It also confirms that although polychloroprene imparts some water resistance to the polyacrylamide component, it still remains degradable by water.

Dielectric measurements in the frequency (1 - 10(5) Hz) and temperature (25 - 200 degrees C) domains have been carried out for silicone, EPDM, and their 50/50 (by weight) blend before and after ageing in water, steam and air. Low values of permittivity and loss tangent for EPDM reflect its non-polar and loss-free nature. Thermal depolarisation is also observed with EPDM and the air-aged specimen shows little rising trend due to dipole orientation. Silicone is found to be polarised in two steps. Changes in dielectric properties and DC resistivity on hydrothermal weathering and air ageing confirms that charge carriers contribute in the low-temperature step and polar silanol groups contribute in the high-temperature region. The properties of the 50:50 blend are very much sensitive to the medium of ageing. Hydrothermal ageing improves the quality of the dielectric of silicone due to removal of charge carriers and the suppression of silicone hydrolysis by EPDM. Ageing of the blend in air increases the polarisation to a very high level owing to the charge carriers, the additional interface and the dipoles formed during ageing. Activation energies suggest that the low temperature polarisation step is associated with charge carrier mobility and orientation of pendent groups.

The contact angles and surface energies have been determined for silicone rubber functionalized with amide group and EPDM rubber modified with sulfonic acid and maleic anhydride. The functionalization of the polymers decreases the equilibrium contact angles of water and formamide with an increase in the surface energy. The changes in the surface properties are due to the changes in the concentration of the polar groups as measured by IR spectroscopy. The lap shear measurement on joints of silicone and EPDM rubber indicates an increased strength on modification. © 1996 John Wiley & Sons, Inc.

Surface energy of EPDM, silicone rubber, and their 50 : 50 (by weight) blend during aging was determined by contact angle measurement using water and formamide as the probe liquids. The surface energy increases initially with aging time. The results are explained on the basis of the polar component of the surface energy. Blending offers a good degree of protection toward aging of EPDM rubber. The generation of polar groups during aging is confirmed by IR and ESCA investigations. © 1995 John Wiley & Sons, Inc.

Acrylamide-grafted silicone (AM-g-Si) and maleic anhydride modified EPDM (MA-g-EP) were blended in a weight ratio of 50:50 at 35, 70 and 150°C and moulded at the blending temperature in order to understand the effect of interaction on the physical properties. I.r. spectra confirm the chemical bonding between the two rubbers. The tensile strength, the modulus and the swelling resistance increase with the extent of interaction. Ageing studies at 175°C for various times and dynamic thermogravimetry further reveal improved retention of physical properties and thermal stability of the interactive blends. The chemical interaction increases the storage modulus in the rubbery zone.

The grafting reactions in blends of vinyl methyl silicone rubber, Si, with polypropylene, PP, and polyethylene, PE, prepared by melt mixing in an internal mixer at 180°C and 100 rpm rotor speed were studied. FTIR analysis of the blends prepared at various mixing times indicated the reactive nature of Si-PP system and supported a grafting reaction, whereas Si-PE system was found to be inert. Wide angle X-ray analysis and differential scanning calorimetry studies further corroborated these observations. A mechanism, accounting for the Si-PP grafting reaction was suggested.

Hydrothermal weathering of the peroxide vulcanized specimens of silicone rubber, EPDM rubber, and their 50 : 50 blend carried out for various durations at different temperatures reveals that silicone is very susceptible to degradation. For example, the modulus, the strength, and the elongation at break consistently fall with aging period. For 72 h of aging at 210°C, it practically loses its rubberiness (elongation < 50%); while EPDM and the 50 : 50 blend maintain more than 100% elongation at break during the times and temperatures. While hydrolytic chain scission is the main degradation mechanism for silicone, EPDM undergoes a predominantly crosslinking reaction. The kinetics study reveals that the better retention of properties of the blends over silicone is due to an increase in the activation energy of degradation in the presence of EPDM rubber, and this protection effect is higher in liquid-phase weathering than in steam-phase weathering. © 1994 John Wiley & Sons, Inc.

Polychloroprene and polyacrylamide form a self-crosslinking blend during mixing and moulding in the temperature range 140 to 190°C and mis inter-crosslinking is revealed by a torque rise in the rheometric studies. The nature of the stress-strain curves of the blend indicates the generation of a bonded structure where one soft matrix is bonded with a rigid phase and the bonding fails after a critical loading. The results of hysteresis measurements are in agreement with a bonded structure. The SEM study shows that the majority of the polyacrylamide particles are covered with a layer of rubber matrix. It also shows the distribution of particles and the extent of breakdown of the particles in various blends. The SEM observations are also in line with interfacial bonding and help in understanding the physical properties of various blends based on the extent of inter-crosslinking reaction. Thermogravimetric analysis of aqueous solutions, cast film, and dry powdered of polyacrylamide confirms the role of moisture in polyacrylamide degradation. It also confirms that although polychloroprene imparts some water resistance to the polyacrylamide component, it still remains degradable by water.

Silicone rubber was functionalized with acrylamide (AM) to effect interaction with sulfonated EPDM. I.r. spectroscopic studies confirm the dipole-dipole interactions between this graft copolymer (AM-g-silicone) and sulfonated EPDM (S-EPDM) through the splitting of the carbonyl stretching and NH stretching peaks. Physical property measurements show that the functionalized blend has a higher tensile strength, modulus and swelling resistance and lower elongation at break. The thermal stability and ageing behaviour of the new blends are improved owing to an increase in the activation energy of degradation. Finally, dynamic measurements show that the transition temperatures are all increased by 8–10°C and the storage modulus in the temperature range 25–125°C is higher, owing to strong interspecies interactions between the components in the functionalized blends.

The silicone-EPDM system has been studied with blend ratios (silicons:EPDM) of 5050, 4060 and 3070. The first set of blends was prepared by roll-mixing of the elastomers and curative whereas in the second set, DCP-cured powder of EPDM, prepared in a Brabender plasticorder, was mixed with silicone rubber and DCP in a roll mill. A comparison of blends show that the second set exhibits inferior properties as compared to the first set. Specimens were also aged at 150 and 175 C for various periods. The physical properties of the aged specimens show a reversal in trend, i.e. the second set of specimens shows better physical properties on ageing. The strengthening of the silicone phase by use of a different curative (Perkadox 14/40) in the 5050 blend of the second set shows a beneficial action on ageing. Morphology studies with SEM confirm the two-phase structure for both sets of blends. In both cases phase separation occurs with ageing, but the continuous phase for the second set of blends maintains its continuity for a higher period than the corresponding specimens of the first set.