Abstract
Physiochemical methods have generally been used to “open-up” biomass substrates/pulps and have been the main method used to fibrillate cellulose. However, recent work has shown that canonical cellulase enzymes such as endoglucanases, in combination with “amorphogenesis inducing” proteins such as lytic polysaccharide monooxygenases (LPMO), swollenin and hemicellulases, are able to increase cellulose accessibility. In the work reported here different combinations of endoglucanase, LPMO and xylanase were applied to Kraft pulps to assess their potential to induce fibrillation at low enzyme loading over a short time period. Although gross fiber properties (fiber length, width and morphology) were relatively unchanged, over a short period of time, the intrinsic physicochemical characteristics of the pulp fibers (e.g. cellulose accessibility/DP/crystallinity/charge) were positively enhanced by the synergistic cooperation of the enzymes. LPMO addition resulted in the oxidative cleavage of the pulps, increasing the negative charge (~100 mmol kg−1) on the cellulose fibers. This improved cellulose nanofibrilliation while stabilizing the nanofibril suspension (zeta potential ζ = ~60 mV), without sacrificing nanocellulose thermostability. The combination of endoglucanase, LPMO and xylanases was shown to facilitate nanofibrillation, potentially reducing the need for mechanical refining while resulting in a pulp with a more uniform nanofibril composition.
Highlights
To improve their profitability, many forest products companies are in the process of diversifying their product portfolios to produce new, higher-value/higher growth products for use in non-traditional pulp markets
The results suggest that enzyme mediated treatments have the potential to reduced refining energy requirements while resulting in more uniform nanofibrils
A fully bleached Kraft pulp (BKP) composed of 77% glucan, 17% xylan and less than 1% lignin was selected as the initial feedstock to assess the potential of individual and combinations of endoglucanase (Novozyme 476), lytic polysaccharide monooxygenase (LPMO) auxiliary activity family 9 (AA9) and endoxylanase to facilitate cellulose nanofibrillation over a range of pH’s
Summary
Many forest products companies are in the process of diversifying their product portfolios to produce new, higher-value/higher growth products for use in non-traditional pulp markets. As well as the potential role that more “classical” cellulases such as endoglucanase and exoglucanase have been shown to play in facilitating refining and fibrillation[12,14,15,16,17,18,19], more recent work has shown how “accessory” enzymes/proteins such as xylanases, swollenin, expansin-like proteins and lytic polysaccharide monooxygenases (LPMO) can boost the hydrolytic performance of cellulase cocktails, primarily by improving accessibility of the enzymes to the cellulosic component[20,21,22,23] These accessory enzymes do not directly hydrolyze cellulose, they have been shown to have high specificity in selectively modifying the carbohydrate network in a relatively fast manner[21,22,24]. The results suggest that enzyme mediated treatments have the potential to reduced refining energy requirements while resulting in more uniform nanofibrils
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