Enhancement of the properties of high impact polystyrene scrap by an inpact modifier

Abstract

Two kinds of HIPS scrap, i.e., commercial scrap and post-fabrication industrial scrap which has been compounded and thermoformed were ground. Each of the ground scraps was then repeatedly injected and ground for five times. For pure HIPS scrap, the mechanical properties, namely, the tensile properties and the elongation at break were found to decrease slightly. Deterioration in the Izod impact strength was rather significant. Color change which is one major concern was evident in the recycled scraps. The yellowness was found to increase progressively with more passes of recycling. A study on the properties of the HIPS scraps modified by and impact modifier was conducted. Two kinds of SBS block copolymers were used separately as an impact modifier. Within the range of SBS block copolymer of 0 to 10 % w/w, the impact strength was found to increase significantly. The enhancement in the impact strength is believed to be imparted by the butadiene rubber phase in the SBS block copolymer. Other properties such as the tensile properties and the hardness became lower while the elongation at break increased with the amount of SBS block copolymer. However, each of the SBS block copolymers was found to depict an opposite effect on the melt flow rate and the Vicat softening point. The oil content in one of the SBS block copolymers is believed to be the major contributor for the different effect. The SEM fractography evidently confirms the miscibility between the HIPS and the SBS block copolymer.