Microdomain structure and some related properties of block copolymers. II. Plastic deformation mechanisms of the glassy component in rubber-toughened plastics

Abstract

Abstract The toughening mechanism was investigated by means of mechanical and optical techniques including electron microscopy and polarized light scattering for wide variety of domain morphologies of di-and triblock copolymers and their blends with corresponding homopolymers. Two types of plastic deformation mechanisms of glassy component are emphasized a s the toughening mechanism. One is large plastic deformation of the glassy component, a s bulk, followed by its plastic flow o r fragmentation, depending on the di-or triblock sequence arrangement. The other is development of a microcraze a t the boundary of the rubber particle and its propagation through the glassy matrix. The origins of the two types of plastic deformation mechanisms are postulated a s hydrostatic pressure effects upon the high plasticity of the glassy component due to differences of Poisson's ratios between the glassy and rubbery components and as stress concentration effects of the rubber particle at the glassy phase opposite to the equatorial zone of the rubber particle with respect to the principal stress direction. The nearer the volume fraction of the two components to 50/50, the more efficient is the hydrostatic pressure effects upon inducing high plasticity in the glassy component. On the other hand, the smaller the radius of curvature a t the equatorial zone of the rubber particle, the more concentrated the stress level becomes to generate the microcraze and further microcracks. Thus, there must be an optimum size of the rubber particle to generate the microcrazes in the most efficient rate. The system of alternating lamellar microdomains is sufficient for the generation of high plasticity, hut insufficient for the craze development due to too large radius of curvature to elevate the concentrated stress, if any. The toughening mechanism, in rubber-toughened plastics can be explained generally in terms of these counter balanced factors for the two types of plastic deformation mechanisms of glassy component.