Characterization of biodegradable polylactic acid (PLA) / palm oil based-polyurethane produced by microwave assisted synthesis method [EMBARGOED]

Abstract

Conventional polyurethane (PU) in the current market is majorly non-degradable. Using palm oil polyols as a substitute for petroleum-based polyols could increase PU's biodegradability. The normal way of producing PU is by using conventional heating, which requires a long synthesis time hence, an alternative to the time-saving synthesis method, a microwave-assisted synthesis was introduced in PU synthesis. Polylactic acid (PLA)-diol was one of the polyols used in PU synthesis and was synthesized via microwave-assisted synthesis method, where the optimum reaction conditions were found at 900W microwave power and 1.5 hours reaction time. Fourier transform infrared spectroscopy (FTIR) of samples confirmed the formation of PLA-diol when hydroxyl peak at around 3500 cm-1 was observed. Gel permeation chromatography (GPC) showed that the number average molecular weight of PLA-diol was 624 g/mol, with polydispersity index of 1.82. Microwave-assisted synthesis conditions of PU-isocyanate were optimized at 300W microwave power and a reaction time of 2 hours. FTIR confirmed the successful formation of PU films at the observed peak in between 1745 cm-1 and 1751 cm-1. Three isocyanate groups were tested to determine isocyanate that gave the best PU flexibility, where 1,6-hexamethylene diisocyanate (HDI) showed the highest elongation at break of PU films at 144.5%. Glass transition temperatures and melting temperatures of PU films samples were analysed from differential scanning calorimetry (DSC). X-ray diffraction (XRD) showed the degree of crystallization of the samples where tensile test showcased enhanced mechanical properties of PU samples in which the elongation at break of PU-HDI improved from 144.5% to 164.2%, as the isocyanate contents and polyol contents increased. The biodegradation study showed that the degradation rate of PU increased when isocyanate contents and polyols contents increased. By the end of the research, green and efficient synthesis of PLA-diol and PU were achievable through the microwave-assisted synthesis method. This was proven when PLA-diol synthesis time was shortened from 6 hours to 1.5 hours and PU synthesis time was shortened from 4 hours to 2 hours. On the other hand, incorporating palm-oil polyol and HDI in PU formulation has improved the biodegradability of PU in the end of this research.