Closed-loop circularity of mixed biomass waste: cellulose extraction and conversion into cellulose acetate bioplastic for use as growing substrates in plant cultivation

Abstract

Abstract Currently, composting remains the primary method of processing mixed biomass waste, despite being a plentiful and renewable resource, the heterogeneous nature and widespread distribution of the mixed biomass waste have led to its underutilization. Similar situation in space, 80% of space-grown crop results in biomass waste, and the current waste disposal method of storing wastes and returning them to Earth or burning them up in the atmosphere is not suitable for long-duration human space exploration missions. In addition, Rockwool has been currently utilized as the growing substrate for space plant cultivation, which is not sustainable and depends on space logistics. Therefore, this study investigated a novel circular approach of converting mixed biomass waste into bioplastics and using it as a growing substrate to support plant growth, then the plant residue was converted into bioplastics again. Mixed garden waste was collected and treated with alkaline hydrogen peroxide (AHP) to extract cellulose. The cellulose content of the AHP-treated biomass increased by 75%, while the hemicellulose and lignin contents decreased by 46% and 58%, respectively. The cellulose extraction performance of AHP was assessed by FTIR and SEM. A solvent-free acetylation method using anhydride and iodine was used to convert the extracted cellulose into cellulose acetate (CA). A degree of substitution of 2.5 was measured using a titration technique. Triethyl citrate (TEC) was used to plasticize the synthesized CA by dissolving them both in acetone. The plasticization and 3D printability of plasticized CA were assessed with DSC and rheological tests. Porous structures were produced using the plasticized CA and a self-constructed granule-based material extrusion printer. Plant garden peas were able to grow on these porous structures. After the harvesting, the plant residues were reprocessed into CA, showing a circular approach to the mixed biomass waste valorisation.