Evolution of structure in the softening/melting regime of miscible polymermixing

Structure development in the softening/melting processing regime is investi gated using the model miscible blend poly(styrene-co-acrylonitrile) (SAN)/p oly(methyl methacrylate) (PMMA). Feed materials of four different particle sizes are compounded to study their effects upon structure development. Fou rier-transform infrared spectroscopy is used to help determine the normaliz ed sample variance, a quantitative measure of mixing. The normalized sample variance is determined both as a function of sample size and as a function of feed particle size in an effort to assess the characteristic size scale (s) present in the blend at short mixing times. Results of these experiment s indicate that the distribution of size scales in the softening regime is at least bimodal. Optical examination of pigmented mixtures reveals that th is multimodality is due to the operation of the Scott/Macosko sheeting mech anism of morphology development, which was previously shown to be active in immiscible blends. This is contrary to the currently accepted laminar mixi ng model, which postulates the formation of a striated mixture while ignori ng the softening/melting regime.