Euglena gracilis biomass based plastics – EG4BIOPLAST

The research program is organized with 4 workpackages, each one being lead by one team :

- WP1 is dedicated to Euglena gracilis’ cultivation and to biomass fractionation : It takes place at GEPEA and is lead by the BAM team « Bioprocesses Applied to Microalgae », where the recruited PhD Student, Visakha WU is located.

The cultivation of Euglena Gracilis is studied both in autotrophic (using only Carbon Dioxide as inorganic carbon source) and mixotrophic conditions (adding organic carbon as a second source) : First at the lab scale on 1 liter photobioreactors, and then at pilot scale using the facilities of the ALGOSOLIS platform allowing the production of paramylon rich euglena biomass batches. Concurrently, an extraction an purification process is develloped at lab scale and then applied to the pilot scale batches to recover the paramylon and coproducts batches necessary for WP3 and WP4, respectively.

- WP2 is dedicated to the design and selection of ionic liquids: It is lead by ICMR, where a young doctor, Katia Bacha, was recruited for the chemical synthesis of the different series of biocompatible ILs. These are first produced in small quantities in order to test their ability to solubilize and plasticize paramylon. Then the selected systems are produced in higher quantities necessary for WP3.

- WP3 is dedicated to thermoplastic paramylon processing and characterization : It is lead by BIA where the recruited postdoc, Flavien Mouillard is located. In interaction with WP1 and WP2, the paramylon and the Ils are characterized and used to formulate the materials for extrusion and thermocompression tests. The structure and properties of the materials obtained are characterized with the objective of drawing Process -structure-properties relationships, in particular for mechanical and bioactive properties.

- WP4 is dedicated coproducts valorization and Life Cycle Analysis : It is lead by the MAPS2 team (Matrix,Food, Process Properties, Structure and Sensorial) of GEPEA, where a postdoc will be located. A first approch will consist in investigating the possible valorization of the coproducts of paramylon’s extraction process as materials, while a second approach will concern the life cycle analysis of the thermoplastic paramylon materials produced in WP3, taking into account the previous steps of euglena biomass production and fractionation in WP1 and of ionic liquids’ synthesis in WP2.

The project's duration is 48 months.

After 24 month, the main results are the following :

- WP1 : Euglena’s cultivation in autotrophic conditions was sucessfully studied and optimized at lab scale before being transposed at pilot scale, allowing the extraction of the paramylon batches necessary for WP3.

- WP2 : A series of ionic liquids were synthesized and characterized, leading to the selection of four systems able to solibilize and plasticize paramylon.

- WP3 : A proof of concept was established using cholinium glycinate and water as a plasticizer of paramylon (see outstanding feature below).

- WP4 as not started yet. However, the necessary data and samples are being collected in WP1,2,3.

So far after 24 month, the most outstanding feature is the publication of an article on the proof of concept of WP3, entitled « Melt processing of paramylon using a water:ionic liquid mixture as plasticizer »

The abstract is the following :

Paramylon is a linear beta-1,3-glucan produced by the microalgae Euglena Gracilis. Due to its native crystalline structure, involving hexagonally packed triple helices, paramylon is neither water soluble nor thermoplastic. While such properties are generally obtained by chemical modification of paramylon, the present work demonstrates that using ionic liquid/water mixtures as solvents or plasticizers may be an alternative: A mixture of water with cholinium glycinate (40:60) allowed: i) obtaining paramylon solutions at 80°C, that form reversible ionogels upon cooling at 20°C, when used as a solvent, and ii) the thermomechanical processing of paramylon below 100°C by extrusion and hot-press into transparent films, when used as a plasticizer. The thermoplastic paramylon obtained consists of an amorphous matrix, self-reinforced by oriented triple helices packed as nanofibers. This results in a storage modulus ranging from 300 to 450 MPa at 25°C, depending on the plasticizer content, and in a tensile strain at break of 27%. For storage times larger than 1 month, a recrystallization of paramylon is observed, with an unidentified crystalline structure different from the native one. Recrystallised samples can be reprocessed into amorphous films by hot pressing.

Microalgae may become a key biomass resource for biobased plastics, with the advantage of their ability to grow on non-arable lands, with a high productivity per unit area. The EG4BIOPLAST proposal focuses on Euglena gracilis, a highly versatile and robust strain that produces up to 80% dry weight of paramylon, a linear B-(1,3)glucan. This storage polysaccharide is not found in terrestrial plants. It accumulates as highly crystalline intracellular granules in Euglena gracilis in either photosynthetic (mineral source of carbon such as C02, with light), heterotrophic (source of organic carbon, such as wastewater or sewage, absence of light) or mixothrophic cultivation conditions.
The interdisciplinary consortium gathers teams specialized in bioprocesses applied to microalgae, biopolymer based materials processing and characterizations, and biobased ionic liquids design. Indeed, these latter will be used as plasticizers of paramylon, allowing to obtain thermoplastic paramylon formulations without chemical modification of the biopolymer, which is currently the only way of making plastics from paramylon.
The research program will first investigate the specific metabolism of euglena in order to develop an optimized culture protocol in solar conditions. Concurrently, biobased ionic liquids (ILs) able to disrupt paramylon’s native crystalline structure in presence of water will be synthesized and screened as paramylon plasticizers. Selected ILs will be used to study the processing of refined or semi-refined paramylon, extracted from euglena gracilis biomass, by extrusion and hot pressing, in order to optimize the structure and properties of the final thermoplastic material. Environmental impacts of the resulting optimized strategy for cultivation, extraction and processing of paramylon will be assessed through a life cycle analysis. Comparison will be made with existing euglena cultivation and paramylon thermoplasticization strategies involving chemical esterification.