Bioprocessing for production and applications of bioplastics from algae

Considering critical pollutions caused by the persistent accumulation of conventional plastics in the nature environment, researchers and industries have put in intensive efforts for the development and innovation of fabrication of bio-based and biodegradable plastics. Algae emerged as a promising feedstock for biobased plastics production due to its multiple advantages of abundance, biocompatibility, biodegradability, rapid growth rate, the ability of resource recovery from waste streams, and environmental-friendly. Researchers have employed different cultivation strategies, including nutrient deprivation, increased salinity, limitation of gas exchange, utilization of wastewater as nutrient source as well as the addition of xylose, propionate and acetate for polyhydroxyalkanoates (PHAs) production from microalgae and cyanobacteria. Genetic engineering has been performed by inserting PHA-accumulating enzymes-expressing genes and PHA synthesis pathway from Ralstonia eutropha into cyanobacteria and microalgae for high PHA accumulation. Three types of polysaccharides, including alginate, carrageenan and agar among various types of seaweed polysaccharides are the most potential for the production of biofilms for applications of food, cosmetics, pharmaceutical and medical industries. The physicochemical properties of alginate depend on the ratio of guluronic acid and mannuronic acid where higher guluronic acid content gave better moisture barriers, while higher content of mannuronic acid produces a flexible product. For carrageenan, κ-carrageenan form strong and rigid, but brittle gel, while ι-carrageenan gave softer, flexible, elastic and cohesive gel. For agar, the gelling properties of agarose provide agar with its continuous film-forming ability. However, the development of biofilms derived from macroalgae is still in its infancy stage compared with other bio-based films. Hence, more efforts should be poured in to exploit their full potential for commercial-scale applications. On the other hand, protein-rich microalgae such as Chlorella, Spirulina, Nannochloropsis and microalgal consortium emerged as the promising precursors for the fabrication of bioplastics and biocomposites. Furthermore, different types of additives, such as plasticizer, compatibilizer, nanoparticles and other functional compounds can be incorporated for biopolymer products with enhanced mechanical strength, thermal stability, barrier, and material properties. Natural additives have been introduced to provide antioxidant and antimicrobial properties in food applications as well. Compatibilizers enhanced the interaction between the blend of hydrophilic algae biomass and hydrophobic polymers. Technologies, such as film casting, compression molding, extrusion, injection molding, and electrospinning, were employed in the fabrication of algae-based plastic materials.