Toward an understanding of the increase in enzymatic hydrolysis by mechanical refining

• Published in: Biotechnology for biofuels Vol. 11; no. 1; p. 289
• Main Authors: de Assis, Tiago, Huang, Shixin, Driemeier, Carlos Eduardo, Donohoe, Bryon S, Kim, Chaehoon, Kim, Seong H, Gonzalez, Ronalds, Jameel, Hasan, Park, Sunkyu
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 25.10.2018; BioMed Central; BMC
• Subjects: 09 BIOMASS FUELS; Alternative energy sources; Autohydrolysis pretreatment; Bagasse; Biodiesel fuels; Biomass; Biorefineries; Bonding strength; Carbohydrates; Cell walls; Cellulose; cellulose crystallinity; Cellulose fibers; Chemical properties; Conversion; Crystal structure; Crystallinity; Delamination; Digestibility; Disruption; Enzymatic hydrolysis; Enzyme activation; Enzymes; Fiber internal delamination; Fiber morphology; fiber porosity; Hydrolysis; Laboratories; Lignin; Lignocellulose; Measurement techniques; Mechanical refining; Mesoscale phenomena; Microfibrils; Microscopy; Morphology; NMR; Nuclear magnetic resonance; Particle size; Physical properties; Pore size; Porosity; Pulp; Pulp & paper industry; Raw materials; Renewable resources; Size reduction; Substrates; Sugar; Sugarcane; Sugarcane bagasse; Autohydrolysis pretreatment; Fiber morphology; Enzymatic hydrolysis; Fiber internal delamination; Fiber porosity; Cellulose crystallinity; Mechanical refining; Sugarcane bagasse
• ISSN: 1754-6834; 1754-6834
• DOI: 10.1186/s13068-018-1289-3

Mechanical refining is a low-capital and well-established technology used in pulp and paper industry to improve fiber bonding for product strength. Refining can also be applied in a biorefinery context to overcome the recalcitrance of pretreated biomass by opening up the biomass structure and modifying substrate properties (e.g., morphology, particle size, porosity, crystallinity), which increases enzyme accessibility to substrate and improves carbohydrate conversion. Although several characterization methods have been used to identify the changes in substrate properties, there is no systematic approach to evaluate the extent of fiber cell wall disruption and what physical properties can explain the improvement in enzymatic digestibility when pretreated lignocellulosic biomass is mechanically refined. This is because the fiber cell wall is complex across multiple scales, including the molecular scale, nano- and meso-scale (microfibril), and microscale (tissue level). A combination of advanced characterization tools is used in this study to better understand the effect of mechanical refining on the meso-scale microfibril assembly and the relationship between those meso-scale modifications and enzymatic hydrolysis. Enzymatic conversion of autohydrolysis sugarcane bagasse was improved from 69.6 to 77.2% (11% relative increase) after applying mechanical refining and an increase in enzymatic digestibility is observed with an increase in refining intensity. Based on a combination of advanced characterizations employed in this study, it was found that the refining action caused fiber size reduction, internal delamination, and increase in pores and swellability. A higher level of delamination and higher increase in porosity, analyzed by TEM and DSC, were clearly demonstrated, which explain the faster digestibility rate during the first 72 h of enzymatic hydrolysis for disc-refined samples when compared to the PFI-refined samples. In addition, an increased inter-fibrillar distance between cellulose microfibrils at the nano-meso-scale was also revealed by SFG analysis, while no evidence was found for a change in crystalline structure by XRD and solid-state NMR analysis.