SYNTHESIS OF HIGH IMPACT POLYSTYRENE MODIFIED BY NATURAL RUBBER VIA SUSPENSION POLYMERIZATION

Abstract

Polystyrene (PS) has been well known that it is brittle resulting its low mechanical properties. These drawbacks have limited its industrial applications. The addition of elastomer is one method to improve the mechanical properties called as “High Impact Polystyrene (HIPS)”. Therefore, the aim of this research was to produce green HIPS by using natural rubber (NR) as a modifier and to investigate the significant factors and their interaction on production of green HIPS. The green HIPS was prepared via suspension polymerization by using benzoyl peroxide (BPO) and poly(vinyl alcohol) (PVA) as an initiator and stabilizer, respectively. The studied parameters of the production of HIPS were BPO, NR, and PVA concentrations and agitation rate including reaction time on %Styrene (ST) conversion, green HIPS bead size, tensile and impact strength. The optimum BPO concentration was 0.6 wt% based on ST content that produced fine smooth sheet without cracking. From the 23 factorial design experiment result, it was observed that %ST conversion did not depend on agitation rate while this depended on NR content and PVA concentration. In addition, all studied parameters effected on the mass fraction of green HIPS bead with the size of <1.18 mm. For mechanical properties, it was observed that the significance of reaction parameters on tensile strength and impact strength of green HIPS (most to least significant) was NR content > agitation rate > PVA concentration. The NR content strongly affectd bead size and mechanical properties of green HIPS. The optimum condition that gave the highest tensile (21.2 MPa) and impact strength (13.5 J/m) was 4 wt% NR based on ST monomer, 2.0 % (w/v) PVA based on DI water volume and 400 rpm agitation rate at 90ºC for 6 h. In addition, the incorporation of NR into PS matrix also improved the thermal stability of the synthesized green HIPS.