Initial mechanisms of dispersion of core-shell impact modifiers in a polymer matrix

Core-shell impact modifiers are effective toughening agents for many thermo plastics. In order to achieve optimum performance, agglomerates of these pa rticles must be dispersed and the individual submicron particles well distr ibuted within the polymer matrix. The focus of this paper is a description of the initial mechanisms of dispersion during compounding of core-shell im pact modifiers into polymer matrices. Model experiments were conducted with acrylic-based modifiers in a poly(methyl methacrylate) matrix by using a b atch intensive mixer. Based on the observed morphologies at numerous mixing times, a qualitative description of the mechanism is developed. Significan t structural changes occur in all three of the classical processing regimes : solids conveying, melting, and melt flow. Differences in the form of modi fier addition, pellet or powder, are explored. The degree of fill of the mi xer is found to have a critical effect on the dispersion mechanism.