Binderless films from lignin-rich residues of enzymatic saccharification

Abstract

The goal of this study was to examine the conversion of lignin-rich residues from (hard)wood cellulosic sugar production into films without adding binders. Enzymatic hydrolysis was conducted on alkaline pretreated aspen wood to attain saccharification (liberation of monomeric sugars). Non-converted lignin-rich residues in the solid waste stream were fibrillated and formed into films with the aid of micro/nanofibrillated wood (non-saccharified). The films were hotpressed to activate the adhesive characteristic of the lignin in situ. Results showed that hotpressing drastically improved water resistance and wet strength. These effects, not attributable to densification alone, are judged to have arisen from heat-induced hydrolytically stable bonding and hydrophobization. The fully biobased films, even at highly moist (98% RH) conditions, are comparable in strength and stiffness, and tested significantly more biodegradable compared to polystyrene polymer. Overall, this study offers a simple route for converting wood saccharification residues without pre-refining for lignin, thereby favoring cost efficiency of a coproduction strategy in the cellulosic sugar production.