MECHANICAL AND THERMOOXIDATIVE PROPERTIES OF BLENDS OF POLY(VINYL CHLORIDE) WITH EPOXIDIZED NATURAL-RUBBER AND ACRYLONITRILE-BUTADIENE RUBBER IN THE PRESENCE OF AN ANTIOXIDANT AND A BASE

Being polar and compatible with poly(vinyl chloride), epoxidized natur al rubber (ENR) is similar in behaviour to acrylonitrile butadiene rub ber (NBR). To assess the extent of this similarity, the mechanical pro perties of 50/50 blends of PVC with these two rubbers were compared. T heir response to thermo-oxidative ageing in the presence of an antioxi dant and a base was also investigated by ageing the blends al 100 degr ees C for 7 days. Studies involving mechanical properties and FTIR wer e used to evaluate the extent of thermal degradation. The results reve aled that blends of ENR show mechanical properties which are as good a s, and in some instances better than, those of the NBR blends. However , the ENR blends with PVC are very prone to oxidative ageing. This mig ht be attributed to the susceptibility of the oxirane group to ring-op ening reactions, particularly in the presence of PVC, which yields HCl as it degrades. The amine-type antioxidant 2,2,4-trimethyl-1,2-dihydr oquinoline (TMQ) improved the oxidative stability of both blends. This was more significant in the ENR blend, which in some cases attained s tability comparable with that of NBR. The addition of a base, calcium stearate [Ca(St)(2)], did not show any influence in the PVC/ENR blend, even though it was expected to curb acid-catalysed degradation. Ca(St )(2), however, improved the oxidative stability of the PVC/NBR blend. The combination of optimum amounts of TMQ and Ca(St)(2), effectively i mproved the tensile strength of both unaged blends, without appreciabl e adverse effect on elongation at break. This combination also imparte d stability better than that of TMQ alone.