THE EFFECT OF DI-2-ETHYLHEXYL PHTHALATE ON THE THERMOOXIDATIVE AGING OF POLY(VINYL CHLORIDE) EPOXIDIZED NATURAL-RUBBER BLENDS/

The effect of di-2-ethylhexyl phthalate (DOP) plasticizer on the degra dation behaviour of 50/50 poly(vinyl chloride)/epoxidized natural rubb er (PVC/ENR) blend was studied by long-term exposure to ambient condit ions (27-30 degrees C) in the laboratory. While the unplasticized blen d showed obvious changes in physical properties such as hardening, los s of elasticity and embrittlement, the plasticized blend retained its properties. Thermo-oxidative ageing studies were carried out by evalua ting the mechanical properties before and after ageing in an air oven at 80 degrees C for 168 h. The relatively rapid degradation of PVC/ENR blend has been attributed to the high concentration of epoxy groups a nd the occurrence of ring-opening reactions to form ether crosslinks. It was found that the plasticizer confers adequate stabilization upon the addition of a certain threshold amount. The optimum amount of plas ticizer required to adequately stabilize the blend is 20 phr. Above th is there is a tendency for plasticizer migration to occur. The use of an antioxidant in conjunction with the plasticizer further stabilizes the blend. The general trend is of decrease in mechanical and physical properties with increase in DOP concentration. In addition, ease of p rocessing also increases as indicated by the torque maxima and minima obtained from the Brabender plastograms.