Case Studies On Synthesis Of PLLA Bioplastic Starting From Food And Agricultural Wastes

C. M. Narayanan


Polylaevo Lactic Acid (PLLA) is an excellent biopolymer that is biodegradable and has characteristics exactly similar to polystyrene. However, at present, the market price of this biopolymer is significantly higher than polystyrene and other synthetic plastics. The major hindrances to the large scale manufacture of this polymer are the lack of availability of a cheap raw material and the overall economy of synthesis of lactic acid from the same. In this paper, the solutions to the above two bottlenecks are discussed based on the successful industrial projects handled by the author. The two recommended raw materials for the synthesis of PLLA are (1) cheese whey and (2) molasses. Both are discharged as waste effluents by industries, the former by dairy farms and milk processing units and the latter by sugar manufacturing units. In the case of cheese whey, it has to be first freed from proteins by ultrafiltration. A novel design of tubular ultrafiltration module developed by the author, that employs variable area tubes, provides much higher permeation rate and enhanced solute rejection. The protein concentrate obtained is of food grade and thus forms a valuable byproduct of the process. The cheese whey permeate/molasses is fermented to produce lactic acid in a continuous fluidized bed biofilm reactor, the former using a culture of Lactobacillus helveticus and the latter Enterococcus faecalis. The performance of the bioreactor has been simulated mathematically and a multi-parameter CAD (software) package has been developed. The package has been tested and verified using elaborate experimental data (collected both on laboratory scale as well as on pilot plant scale). Direct industrial adaptation of the developed CAD software can be thus recommended with confidence. Based on the above innovations, lactic acid can be economically synthesized on commercial scale starting from low cost natural materials and this would make industrial production of a biodegradable plastic such as PLLA substantially cost effective.

Keywords: Bioplastics, PLLA, cheese whey, molasses, ultrafiltration, diverging-converging tubes, fluidized bed biofilm reactor, lactic acid synthesis, CAD software

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