Abstract
BackgroundMechanical 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.ResultsEnzymatic 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.ConclusionsA 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.
Highlights
Mechanical refining is a low-capital and well-established technology used in pulp and paper industry to improve fiber bonding for product strength
Autohydrolysis paired with mechanical refining has been suggested as a cost-effective technology, where the absence of external catalysts creates the possibility to reduce both capital and operational costs, as well as significantly reduce environmental impacts compared to using a mineral catalyst-aided pretreatment [3,4,5]
Our results show that there is a significant difference in carbohydrate conversion between the refined and unrefined samples, especially at the first 48 h
Summary
Mechanical refining is a low-capital and well-established technology used in pulp and paper industry to improve fiber bonding for product strength. 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). Literature reports suggest that mechanical refining can be used to enhance sugar recovery using especially low enzyme dosages [8, 9] and to reduce pretreatment severity and enzyme loadings while still reaching same level of sugar recovery [4, 10]
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