Microstructural and Physical Properties of Thermoplastic Corn Starch/Polystyrene Blend Foams Affected by Different Contents and Combinations of Plasticizers

A comprehensive study was performed on thermoplastic corn starch (TPS)/polystyrene (PS) blend foam to optimize the formulation from the aspects of plasticizer content and the blend ratio. Plasticization of native starch was implemented with various contents of plasticizer [water (W) + glycerol (G)], 21, 23, 25 and 29%, and W/G ratio of 1/2, 2/3, 3/2 and 2/1 using melt extrusion process. The influence of plasticizer loading content and also its combination on the microstructural and physical properties of the blend foam were investigated. The morphological consideration was also carried out by scanning electron microscopy to evaluate the distribution and regularity of the foam cells. The results showed that water had a desirable effect on the cell parameters in W + G = 21 and 29%. In the following, full factorial method in Minitab software was used to optimize the formulation according to the properties. Moreover, the effect of PS content on the moisture absorption and cell structure of TPS/PS blend foam was evaluated. In addition, the blend ratio of 20/80 was obtained as an optimum ratio for the TPS/PS blend foam via evaluating the effect of different contents of PS on the moisture absorption amount and cell structure of the blend foam. The addition of 20% PS to TPS caused to 6 times higher expansion ratio than PS and 60% higher than TPS, while 50% lower moisture absorption than TPS. This combination can be a good alternative candidate for warm food packing applications.