BackgroundLignin is a complex polymer which inhibits the enzymatic conversion of cellulose to glucose in lignocellulose biomass for biofuel production. Cellulase enzymes irreversibly bind to lignin, deactivating the enzyme and lowering the overall activity of the hydrolyzing reaction solution. Within this study, atomic force microscopy (AFM) is used to compare the adhesion forces between cellulase and lignin with the forces between cellulase and cellulose, and to study the moiety groups involved in binding of cellulase to lignin.ResultsTrichoderma reesei, ATCC 26921, a commercial cellulase system, was immobilized onto silicon wafers and used as a substrate to measure forces involved in cellulase non-productive binding to lignin. Attraction forces between cellulase and lignin, and between cellulase and cellulose were compared using kraft lignin- and hydroxypropyl cellulose-coated tips with the immobilized cellulase substrate. The measured adhesion forces between kraft lignin and cellulase were on average 45% higher than forces between hydroxypropyl cellulose and cellulase. Specialized AFM tips with hydrophobic, -OH, and -COOH chemical characteristics were used with immobilized cellulase to represent hydrophobic, H-bonding, and charge-charge interactions, respectively. Forces between hydrophobic tips and cellulase were on average 43% and 13% higher than forces between cellulase with tips exhibiting OH and COOH groups, respectively. A strong attractive force during the AFM tip approach to the immobilized cellulase was observed with the hydrophobic tip.ConclusionsThis work shows that there is a greater overall attraction between kraft lignin and cellulase than between hydroxypropyl cellulose and cellulase, which may have implications during the enzymatic reaction process. Furthermore, hydrophobic interactions appear to be the dominating attraction force in cellulase binding to lignin, while a number of other interactions may establish the irreversible binding.

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Lignocellulosic-biomass-derived transparent nanopaper is an emerging substrate or functional component for next-generation green optoelectronics. The fabrication of such transparent nanopaper typically needs the delignification of lignocellulose; however, delignification not only is environmentally unfriendly but also impairs the nanopaper properties such as water stability and UV-shielding capacity. In this study, we present a green and facile lignin modification method instead of delignification to fabricate transparent nanopaper from agro-industrial waste with the combined intriguing properties of lignin and cellulose. Because lignin modification selectively removes chromophores without affecting the bulk lignocellulosic structures, the as-prepared lignocellulose nanopaper (LNP) achieved a comparable optical transmittance (∼90%) but superior UV-blocking ability and haze (∼46%) compared with previously reported cellulose (or delignified) nanopaper. The well-preserved lignin structures endowed the transparent LNP with a low surface energy and a small mesoporous size and volume. In addition to a high thermal stability, the transparent LNP exhibited excellent water stability, evidenced by an up to 103° initial water contact angle, a low equilibrium water absorption (<60 wt %), and a high wet mechanical strength (nearly 40% tensile strength and 92% toughness retained in the wet state). Furthermore, we fabricated a GaAs solar cell with the transparent LNP as an advanced light-management layer that leads to significantly improved power conversion efficiency, even under damp conditions. This work sheds light on the conversion of agro-industrial waste to nanopaper with desirable performances for optoelectronics and brings us a step closer toward the scalable production and application of LNP.

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