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

摘要

This work was focused on the influence of the morphology of composite natural rubber (NR)-based particles on the toughness of polystyrene (PS). Emulsion polymerization processes were used to adjust the microstructure of the latex particles. In order to be suitable for the reinforcement of PS, the NR-based particles were coated with a shell of crosslinked polymethyl methacrylate (PMMA) or PS. Furthermore, PS subinclusions were introduced into the natural core. A continuous extrusion process was adapted for the incorporation of these natural rubber based impact modifiers into thermoplastics. High deformation speeds (impact testing) were necessary in order to evaluate the mechanical properties of PS blends with a series of the prepared structured latexes. PS could only be toughened by core-shell particles. A PMMA shell proved to be advantageous because it is easier to produce by emulsion polymerization than a hydrophobic PS shell. Pre-vulcanized NR-based particles, which do not cavitate easily, were ineffective. Core-shell particles based on NR-containing PS subinclusions toughened PS more effectively. Solid NR particles caused premature craze and polymer fracture, as the rubber particles break down, debond from the matrix and form large voids at the craze/particle interface. Scanning electron microscopy (SEM) of Izod fracture surfaces showed clearly the cavities of debonded solid rubber particles and demonstrated that subinclusions within the rubber core permitted a larger volume of plastic deformation before failure. [References: 45]