Thermostable Insulating Thermoplastic Elastomers from Rubber Polycarbonate Blends

Abstract

Thermoplastic elastomeric blends based on polycarbonate (PC) (30 parts) and elastomers (70 parts) of varying polarity, e.g., ethylene propylene diene rubber (EPDM), chlorinated polyethylene (CPE), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), acrylic rubber (ACM) have been studied and characterized by various methods, e.g., stress-strain measurement, surface energy estimation, thermogravimetric analysis, dynamic mechanical analysis and volume resistivity measurement. The highest tensile strength and best processability are found to be attained with the CPE/PC and HNBR/PC blends. The surface energy mismatch is also low for these systems. EPDM/PC and HNBR/PC offer excellent thermal stability. The amount of carbonaceous residue is found to depend on the elastomer structure present in the blend. The activation energy for degradation lies in the range of 210-320 kJ/mol and the order of reaction in the range of 0.8-1.2. Dynamic mechanical analysis shows existence of two separate glass transition temperatures (T.) classically associated with an immiscible system. The values of elastic modulus display a sharp change in magnitude in the vicinity of glass-rubber transition temperature and follow a linear relationship with frequency. The apparent activation energy for glass rubber transition of the blends lies in the range of 275-296 kJ/mol and that for high temperature relaxation of the polycarbonate phase lies in the range of 563-590 kJ/mole. All the blends show good electrical insulation characteristics. The amount of polycarbonate in the blend exerts a profound influence on the volume resistivity. The level of unsaturation and the polarity of the elastomer phase also affect the resistivity values.