Toughened Plastics: Toughening Phenomenon and its Mechanism in Polymer Blends Consisting of Ductile Polymer and Brittle Polymer

Abstract

A polymer blend of ductile polymer with brittle polymer, e. g., polycarbonate (PC) with poly (styrene-co-acrylonitrile) (AS), is a new way to design toughened plastics. Both the stiffness and the toughness of ductile polymer can be improved by inclusion of the brittle polymer particles. In order to find out new combinations similar to PC/AS, we investigated mechanical properties of various blends consisting of ductile and brittle polymers. Among them, new 6 combinations were found to be the toughened blends. The toughening seems to be a rather general phenomenon for some class of brittle/ductile combinations. Morphological studies by SEM and TEM revealed the cold drawing mechanism of brittle polymer particles, by which the impact energy is absorbed to improve the toughness. Analysis of stress concentration on the dispersed particles was undertaken by using the modified Eshelby theory. The cold drawing of brittle polymer particles can be well described in the framework of Mises' condition for yielding. These suggest a potential for semi-quantitative prediction of the development of toughening by means of material constants, such as Young's moduli, Poisson's ratio, and brittle-to-ductile transition pressure (or Mises' k).