Characterization of thermoplastic sago starch/novolak and thermoplastic sago starch/novolak/polyvinyl alcohol

Abstract

In this study, novolak type phenolic resin was blended into glycerol plasticized thermoplastic sago starch (TPS) via twin screw extrusion, in order to improve the thermal resistance and water absorption of the latter. The compression molded blends were characterized in terms of their physical, chemical, morphological, thermal and moisture absorption properties. Density and differential scanning calorimetry implied that the blends were miscible in all compositions. The interaction accountable for the miscibility was identified as hydrogen bonding between the hydroxyl groups of the TPS and novolak through Fourier transform infra-red spectroscopy. However, scanning electron microscopy and x-ray diffraction showed that the blends were immiscible when the novolak content reached 60 wt%. Results from water absorption and thermogravimetry analysis also showed that addition of novolak improved the thermal resistance and moisture sensitivity of the TPS, especially the latter. In view of the brittle nature of the blends, the study was extended by adding 60 wt% of polyvinyl alcohol to the blends. Flexural properties of the ternary blends were greatly improved.