Blends containing core–shell impact modifiers. Part 5 – Ductile–brittle transition temperatures in impact and slow bending

Abstract

Dart drop, Charpy impact and single edge notched bending fracture tests were conducted over a range of temperatures on blends of polycarbonate (PC), poly(methyl methacrylate) (PMMA), poly(styrene-co-acrylonitrile) (PSAN), and poly(vinyl chloride) (PVC) with two core–shell impact modifiers, which were based, respectively, on polybutadiene and poly(butyl acrylate-co-styrene). The T _g values of the two rubbers were −75 and −8°C, respectively. The transition from fully brittle to partially or fully ductile behaviour occurred at various temperatures T _BD depending upon a number of factors, which included the T _g of the rubber phase, the choice of thermoplastic matrix, and the type of test. In disc specimens subjected to dart drop impact, ductility was observed at lower temperatures than in sharply-notched specimens tested in slow three-point bending. It is concluded that the T _g of the rubber phase generally marks a lower limit for ductility in rubbertoughened blends, but that other factors can shift the brittle–ductile transition to higher temperatures.