Preparation of polystyrene - starch composite by melt extrusion method and evaluation of its mechanical, thermal biodegradation properties

Conventional plastics has a large impact in increasing the environment’s pollution. That’s why the interest has turned towards novel partially and completely biodegradable polymers. In this work, composites of polystyrene and starch with glycerol as plasticizer and compatibilizer were prepared in different ratios of starch and glycerol by melt mixing in twin screw extruder. To study the biodegradation properties, samples were buried in soil for 12 weeks and their weight changes were measured during two-week periods. Besides, the structure of prepared composites was studied using SEM analysis. To evaluate the impact strength and thermal properties of composites, we used Izod impact strength test, MFI (Melt Flow Index) and Vicat softening temperature tests. To examine the interaction between composite elements, thermal stability and degradation process, the samples were subjected to analysis using TGA. Biodegradation results and SEM analysis showed that the rate of biodegradation not only starch present in composites but also depends on the quality of starch particles dispersion. Notched Izod test showed the independence of samples impact strength to starch present. Due to the reduction of stress accumulation points, homogeneous dispersion of starch in the matrix leads to increase impact strength in unnotched Izod test. MFI test showed that addition of starch and glycerol leads to respectively increase and decrease in composites’ viscosity. Study of starch/glycerol ratio in obtained results showed that in an optimal amount of plasticizer, interaction between the composite components is in conditions that the best mode of starch particles dispersion is achieved in polystyrene matrix.