Effect of temperature and time for the production of polylactic acid without initiator catalyst from lactide synthesized from ZnO powder catalyst

Abstract

Polylactic acid (PLA) is a biodegradable polymer that most importance at the present due primarily to its properties as biological degradation and biocompatibility derived from renewable resources. This study investigated the role of zinc oxide powder and tin(II) 2-ethylhexanoate as the catalysts for lactide and PLA synthesis, respectively. Polylactic acid was obtained by four stages: dehydration, oligomerization, depolymerization and ring opening polymerization. The catalyst was added and water was removed at the first stage then the reactions are carried out at different temperatures and reaction time on the other stages. The ratio of lactic acid and zinc oxide powder was 1000:3 for lactide synthesis, the ratio of lactide product and tin(II) 2-ethylhexanoate was 1000:4 for PLA synthesis without any initiator. The PLA products were analysed for the yield, some chemical and physical properties such as functional group, decomposition temperature, melting temperature of synthesized PLA. It is found that at reaction temperature of 160°C and reaction time for 5 h gave the highest yield PLA of 64.5% with its decomposition temperature of 311°C and melting point temperature at 152°C. There are two main mechanisms, polymerization and depolymerisation occurring in reaction and each mechanism plays a major role with respect to the reaction condition. At higher reaction temperature and longer time, the rate of depolymerisation is higher than that of polymerization leading to the lower of decomposition and melting temperature of synthesized PLA.