Properties and manufacturing of a new starch plastic

Abstract

Abstract Environmental awareness has strongly stimulated the introduction of biodegradable materials based on renewable resources of natural origin. This paper describes the properties and manufacturing of such a bioplastic. In a counter‐rotating twin screw extruder, starch and polystyrene were mixed. To enhance material properties such as tensile strength and impact strength, two routes were followed. First, the starch was altered by grafting polystyrene onto the starch backbone using a counter rotating twin screw extruder. The newly formed material was blended with polystyrene in difierent ratios. Tensile strengths of 10 to 35 MPa were obtained while notched impact strengths varied from 0.5 J m −1 to 1.5 J m −1 . Soaking the material for a certain time in water end measuring the tensile strength of the wet material revealed that the tensile strength remained more the less the same for blends containing more than 30 wt% PS. Second, polystyrene grafted starch was used as a compatibilizer. A homogenous blend could bobtained (according to scanning electronic microscopy pictures) by adding the compatibilizer to a starch, polystyrene, and water mixture. Again, tensile and impact strengths were measured for different ratios of the polymers used. The tensile strength and the impact strength were of the same magnitude as they were with the blended material. X‐ray diffraction and DSC measurements revealed a highly ordered system. When the fraction of polystyrene was above 60 wt% of the blend, the amylose part of the starch crystallized.