TOUGHENING OF POLYSTYRENE BY NATURAL RUBBER-BASED COMPOSITE-PARTICLES.1. IMPACT REINFORCEMENT BY PMMA AND PS GRAFTED CORE-SHELL PARTICLES

This work was focused on the influence of the morphology of composite natural rubber (NR)-based particles on the toughness of polystyrene (P S). Emulsion polymerization processes were used to adjust the microstr ucture of the latex particles. In order to be suitable for the reinfor cement of PS, the NR-based particles were coated with a shell of cross linked polymethyl methacrylate (PMMA) or PS. Furthermore, PS subinclus ions were introduced into the natural core. A continuous extrusion pro cess was adapted for the incorporation of these natural rubber based i mpact modifiers into thermoplastics. High deformation speeds (impact t esting) were necessary in order to evaluate the mechanical properties of PS blends with a series of the prepared structured latexes. PS coul d only be toughened by core-shell particles. A PMMA shell proved to be advantageous because it is easier to produce by emulsion polymerizati on than a hydrophobic PS shell. Pre-vulcanized NR-based particles, whi ch do not cavitate easily, were ineffective. Core-shell particles base d on NR-containing PS subinclusions toughened PS more effectively. Sol id NR particles caused premature craze and polymer fracture, as the ru bber particles break down, debond from the matrix and form large voids at the craze/particle interface. Scanning electron microscopy (SEM) o f Izod fracture surfaces showed clearly the cavities of debonded solid rubber particles and demonstrated that subinclusions within the rubbe r core permitted a larger volume of plastic deformation before failure .