Mechanical and Thermo-oxidative Properties of Blends of Poly(vinyl chloride) with Epoxidized Natural Rubber and Acrylonitrile Butadiene Rubber in the Presence of an Antioxidant and a Base

Abstract

Being polar and compatible with poly(vinyl chloride), epoxidized natural rubber (ENR) is similar in behaviour to acrylonitrile butadiene rubber (NBR). To assess the extent of this similarity, the mechanical properties of 50/50 blends of PVC with these two rubbers were compared. Their response to thermo-oxidative ageing in the presence of an antioxidant and a base was also investigated by ageing the blends at 100°C for 7 days. Studies involving mechanical properties and FTIR were used to evaluate the extent of thermal degradation. The results revealed that blends of ENR show mechanical properties which are as good as, and in some instances better than, those of the NBR blends. However, the ENR blends with PVC are very prone to oxidative ageing. This might be attributed to the susceptibility of the oxirane group to ring-opening reactions, particularly in the presence of PVC, which yields HCI as it degrades. The amine-type antioxidant 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ) improved the oxidative stability of both blends. This was more significant in the ENR blend, which in some cases attained stability 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 improved the tensile strength of both unaged blends, without appreciable adverse effect on elongation at break. This combination also imparted stability better than that of TMQ alone.