Fermentation of kenaf biomass using Lactobacillus rhamnosus for the production of polylactic acid (PLA)

Abstract

An extensive effort is being made by many industries to reduce the usage of petroleum-based products or synthetic fibres, owing to the rising awareness in environmental issues. Realising this phenomenon, research on biodegradable polymers from natural fibres and the production of eco-friendly products are being geared towards replacing these existing petroleum based products. One of these promising polymers is polylactic acid (PLA) since it has good mechanical as well as thermal properties. Therefore, the objective of the study is that PLA is synthesised in-house through the polymerisation of lactic acid obtained from the simple fermentation process of kenaf biomass. Since kenaf biomass has a very complex structure, it needs to be treated first before it can be used in further processes. During the pre-treatment process, kenaf biomass was treated and optimised using the most significant parameters and solvent which can boost up the production of glucose concentration. From the optimisation of the pre-treatment process, the maximum production of glucose concentration occurred when mixing time was set at 60 min and the temperature was 200 oC, producing 3.397 g/L. Next, the fermentation processes were carried out in two operations, which are the shake flask and bioreactor operations. In shake flask operation, the maximum yield of lactic acid is 10.851 g/L and was produced when 2 g of peptone and 2.5 g of yeast extract was used. By using this media composition, the yield of lactic acid was improved using the bioreactor and the maximum production of lactic acid (17.593 g/L) occurred when 0.5 ppm of aeration, 100 rpm of agitation speed and uncontrolled pH was used. Then, the PLA was synthesis using the end product obtained from the fermentation process. Basically, the molecular weights of the produced PLA via ROP and polycondensation methods in this polymerisation were 4196.922 and 411.916 kg/mol respectively. The chemical bonding and thermal properties of the produced PLA were analyzed using FTIR, DSC,and TGA analysis. Beside that and biodegradable tests were also conducted to determine biodegradability properties of the produced PLA. From this study, it found that the PLA produced via ROP method gave a best results compared to PLA produced polymerisation method.