Bridging the gap from raw microalgae to bioplastic: conversion of Chlorella vulgaris into thermoplastic starch
Creators: name: Six, Alexandre
name: Fleury, Gatien
name: Compadre, Ana
name: Dimitriades-Lemaire, Alexandra
name: Alvarez-Diaz, Pablo
name: Lancelon-Pin, Christine
name: Putaux, Jean-Luc
name: Dauvillée, David
name: Aragon, Alexandro
name: Sánchez Ballester, Soraya
name: Le Moigne, Nicolas
name: Li-Beisson, Yonghua
name: SASSI, Jean Francois
Publisher: name: Zenodo
Year: 2023

description: Starch, a glucose polymer and major storage molecule in photosynthetic organisms, is extensively used in food industry. However, its low cost and multiple functionalities also make starch highly demanded for non‑food applications, representing nearly half of its market in 2020 [1]. The dual role of starch, serving as both a glucose reservoir and a versatile polymer, has positioned it as a primary feedstock for the bioplastics industry. Indeed, several biobased-biodegradable plastics can be obtained from starch, either through fermentation processes following saccharification (such as polylactic-acid PLA and polyhydroxyalkanoates PHA) or through direct polymer plasticization (thermoplastic starch TPS). Starch resources have therefore emerged as a viable alternative to petroleum‑based materials, further intensifying the demand on amylaceous feedstock. Within this context, Chlorella vulgaris microalgae have been identified as a promising source of starch, with pilot-scale area yields surpassing by almost 2-fold those of traditional crops [2].

Within the framework of EU projects SEALIVE and Nenu2PHAr ([3, 4]), we successively produced a starch‑enriched Chlorella vulgaris at pilot scale, achieved sustainable starch extraction and converted this microalgal starch into thermoplastic starch. A 360L culture of Chlorella vulgaris was produced in greenhouse under natural light, with starch-enrichment reaching 42%wt after nutrient deprivation. This biomass was mechanically disrupted using a high-pressure homogenizer (HPH) until 95% of the cells were broken. A single centrifugation step separated starch granules from the biomass broth, resulting in starch purity of 85%wt in the recovered starch pellet. Raw starch was subsequently washed using successive water rinses until complete whitening. Interestingly, the non-starch fractions were enriched in lipids and proteins, making them appropriate for additional valorization in a biorefinery scheme with multiple product outputs. At the end of the process, 179 gDW of pure starch was obtained from a microalgae biomass containing initially 181 gDW of extractable starch. The starch granules were found to be smaller than plant starch, whereas crystallinity, phase transitions as well as amylose/amylopectin ratio were similar, making algal starch suitable for bioplastics formulation. Finally, the extracted microalgal starch was successfully plasticized with water and glycerol into thermoplastic starch in a twin-screw microcompounder, and then shaped into injection-moulded specimens.

 

KEYWORDS

microalgae, Chlorella vulgaris, starch, bioplastics, extraction, purification, down-stream process, green process, biorefinery, thermoplastic starch.