Polyhydroxybutyrate production from dark-fermentative effluent and composite grafting with bagasse derived α-cellulose in a biorefinery approach

Abstract

The study evaluated the preparation of a biocomposite using waste-derived polyhydroxybutyrate (PHB) and bagasse cellulose (α-cellulose) in a biorefinery approach. PHB was produced using dark fermentation effluent rich in volatile fatty acids (VFA) derived from vegetable waste and α-cellulose was extracted from sugarcane bagasse (SCB). Nutrient limitation induced microbial PHB accumulation, wherein maximum production of 0.28 ± 0.06 g PHB/g DCW (28%) was observed. Confocal examination showed the deposition of PHB granules in the cell cytoplasm and NMR spectrum exhibited a structural correlation. α-Cellulose (0.22 ± 0.02 g α-cellulose/g SCB) was extracted through SCB pretreatment. Thereafter, grafting α-cellulose with PHB offered intermolecular bonding, which resulted in enhanced thermal stability of the biocomposite than corresponding pristine PHB. FE-SEM morphological examination of biocomposite depicted that α-cellulose functioned as a filler to PHB. XRD profiles showed significant decrement in PHB crystallinity, signifying the functional role of α-cellulose as an effective reinforcing agent. Additionally, ether functional group of α-cellulose and ester group of PHB also appeared in XPS analysis of the composite, thus authorizing the effective blending of α-cellulose and PHB. Utilization of bagasse-derived cellulose for strengthening biologically produced PHB expands its applications, while simultaneously addressing the plastic pollution issues. Additional value from this process was further achieved by incorporating the concept of biorefinery, wherein acidogenic fermentation effluents were used for the production of PHA, which enabled the re-entry of products (VFA) to the production cycle, thus achieving circularity.