Water Resistance, Biodegradation and Thermal Stability of Thermoplastic Starch Reinforced with Unvulcanized Natural Rubber, Epoxidized Natural Rubber and Dissolving Pulp

Biodegradable thermoplastic starch (TPS) has been expected to be sustainable alternative to petrochemical-based polymers due to its biodegradability with proper and controlled costs. However, brittleness and biodegradation rate of TPS are insuf- ficient for usage as a single material. The present work aims to improve TPS properties by incorporating with unvulcanized natural rubber (NR), epoxidized NR with 25 and 50 mol% epoxide (ENR25 and ENR50) and 0–15 phr of dissolving pulp (Fiber) using combined techniques of internal mixer and compression molding at 180 °C. The results based on mechanical properties, water resistance, biodegradation and thermal stability of TPS were studied. It was found that the tensile proper- ties, following ASTM D638 Type I, increased after the addition of ENR25 relative to the NR and ENR50 cases. In addition, the combination of 10 wt% ENR50 and 15 phr fiber to the TPS showed high potential on improvement of tensile properties of the composites relating polarity effects. This blending ratios also enhanced the thermal stability of the composites, relat- ing the thermogravimetric analyzer (TGA), whereas the solubility and disintegration in terms of the dimensions and shape of the TPS after water and soil exposure were reduced monitoring through weight loss investigation. This means that the incorporation of ENR50 and fiber at 10 wt% and 15 phr, respectively, to the TPS properly showed a synergistic effect on increasing of TPS properties by increasing flexibility and retarding biodegradation rate after soil exposure for 60 days. This environmentally friendly materials could be use as seed tray, slow released fertilizer for agriculture applications.