Polylactic Acid/Microalgal Biopolymer Synthesis: a Complete Process Including the Optimization of Microalgae and Biopolymer Characterization

Abstract

This study aims to investigate and enhance PLA/microalgal biopolymer properties and minimize microalgal production costs using a statistical design of experiments optimization methodology. The Box-Behnken design, which is a response surface-based methodology, was used for media optimization, resulting in a lower cost of microalgal cultivation and a lower yield compared with BG-11 with an average biomass weight and cell count of 226 mg l-1 and 1.704 cells ml-1 compared with 451 mg l-1 and 4 x 106 cells ml-1 obtained with BG-11, costing only US$ 0.017 l-1 for the utilized media. Furthermore, this cheap media composition demonstrated high substrate uptake up to 1200 mg l-1 for the first time for Chlorella vulgaris. Following the successful growth of microalgae, the biomass was harvested by centrifugation use of synthesized magnetic particles with a harvesting efficiency of 92.9% for further biopolymer production in which the polylactic acid was used in the solvent-casting method. This methodology was applied for the first time with a two-step annealing process at 105 degrees C with a comparative approach including a no-annealing process. The process results demonstrated improved tensile strength with a maximum value of 15.646 MPa, and to our knowledge, this is the highest obtained by utilizing Chlorella vulgaris with PLA in the solvent casting method. Finally, the biodegradation profiles in seawater were briefly examined, showing a weight reduction of up to 0.9-3.5 mg after 20 days.