Production process of bioplastic from thermoplastic starch and polyethylene

Abstract

Plastics have been used widely for packaging materials. However, plastic wastes can pollute environment because of its persistency to be biodegraded by microorganisms. Efforts have been conducted to develop environmental friendly plastic from renewable resources. Problems encountered in the manufacture of bioplastic are poor physical-mechanical properties and incompatibility between hydrophilic/polar and hydrophobic/non-polar materials. The modification of raw materials and use of compatibilizer can be applied to improve the compatibility between the two material blends. The purpose of this study is to develop a process of manufacturing bioplastic by modifying the raw material characteristics and the use of compatibilizer. This study consisted of three steps, namely preparation of thermoplastic starch, preparation of maleic anhydride (MA) grafted with LLDPE/HDPE (LLDPE-g-MA/HDPE-g-MA) and manufacturing process of bioplastic. Thermoplastic was prepared by mixing distilled water and glycerol with tapioca, and then allowed to aging for 8 days to a mixture of distilled water and glycerol can be absorbed completely into raw materials (tapioca). Grafting of maleic anhydride with LLDPE/HDPE (LLDPE-g-MA and HDPE-g-MA) was carried out in a twin screw extruder. There were three levels of maleic anhidride concentration namely 2.5%, 5%, 7.5% (w/w) and dicumyl peroxide 0.1% (w/w polymer) used in this experiment. After mixing LLDPE-g-MA and HDPE-g-MA compatibilizer with thermoplastic starch (TPS), the resulting mixtures were then extrudered with LLDPE/HDPE. Four ratios between LLDPE/HDPE and TPS were investigated namely 0:100; 20:80; 40:60; and 60:40. The plastic properties observed included melt flow rate, density, thermal, mechanical, barrier, and degradation properties. The results showed that increasing thermoplastic starch content decreased melt flow rate, melting temperature, mechanical, oxygen transmition rate properties and increased density, water vapor transmition rate and its biodegradability. The presence of LLDPE-g-MA/HDPE-g-MA compatibilizer resulted in better physical and mechanical properties of bioplastic. The compatibilizer improved surface adhesion and decreased surface tension between TPS and LLDPE/HDPE matrix. The best formulation for wrapping applications was the LLDPE-TPS with 40% of TPS and 5% MA with 6,96% of grafting degree, whereas that for plastic bag applications was HDPE-TPS with 30% of TPS and 7,5% MA with 3,21% of grafting degree. Stability tests of bioplastic TPS-LLDPE and TPS-HDPE for packaging applications at room and low temperature showed no significant changes in the mechanical properties, permeability, and morphology, and therefore the product has the ability to maintain mechanical properties at low temperature.