THERMOSTABLE INSULATING THERMOPLASTIC ELASTOMERS FROM RUBBER POLYCARBONATE BLENDS

Thermoplastic elastomeric blends based on polycarbonate (PC) (30 parts ) and elastomers (70 parts) of varying polarity, e.g, ethylene propyle ne diene rubber (EPDM), chlorinated polyethylene (CPE), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), acrylic rubber (ACM) have been studied and characterized by various methods, ag., stress-strain measurement, surface energy estimation, thermogravimetric analysis, dy namic mechanical analysis and volume resistivity measurement. The high est tensile strength and best processability are found to be attained with the CPE/PC and HNBR/PC blends. The surface energy mismatch is als o low for these systems. EPDM/PC and HNBR/PC offer excellent thermal s tability. The amount of carbonaceous residue is found to depend on the elastomer structure present in the blend. The activation energy for d egradation lies in the range of 210-320 kJ/mol and the order of reacti on in the range of 0.8-1.2. Dynamic mechanical analysis shows existenc e of two separate glass transition temperatures (T-g) classically asso ciated with an immiscible system. The values of elastic modulus displa y a sharp change in magnitude in the vicinity of glass-rubber transiti on temperature and follow a linear relationship with frequency. The ap parent activation energy for glass rubber transition of the blends lie s in the range of 275-296 kJ/mol and that for high temperature relaxat ion of the polycarbonate phase lies in the range of 563-590 kJ/mole. A ll the blends show good electrical insulation characteristics. The amo unt of polycarbonate in the blend exerts a profound influence on the v olume resistivity. The level of unsaturation and the polarity of the e lastomer phase also affect the resistivity values.