Microalgae starch-based bioplastics: Screening of ten strains and plasticization of unfractionated microalgae by extrusion

[Display omitted] •Ten microalgae strains were screened for intracellular starch production.•Microalgae was enriched in starch up to 49%w/w in a sulfur-deprived medium.•Starch concentration of 5.07 g/L was achieved in flasks after 35 days.•Direct plasticization of starch-enriched microalgal biomass was performed by twin-screw extrusion. Microalgae were considered in this work as a new resource for developing starch-based bioplastics. Ten green microalgae strains were screened at lab-scale for their ability to produce starch. A long run (800 h) two-stage accumulation strategy was designed with successive cultivation in sulfur-replete, then sulfur-depleted medium in autotrophic conditions. Starch content was assessed on cell lysate by enzymatic digestion of extracted starch into glucose. Chlamydomonas reinhardtii 11-32A strain was selected as it displayed a maximum starch-to-biomass ratio of 49%w/w, 460 h after being switched to a sulfur-deprived medium. Small-scale pilot production (30 L tubular photobioreactor) with C. reinhardtii 11-32A yielded sufficient biomass quantity to investigate its direct plasticization with glycerol in a twin-screw extruder. Microstructural characterization confirmed the ability for starch-enriched microalgae to be homogeneously plasticized, and hence the possibility to use microalgae as a new platform for the development of bioplastics.