Reassembly of wood to plastic- and paper-like films via ultra-mild dissolution in formic acid

Abstract

Wood is the most abundant lignocellulosic biomass and has the potential to be a resource to mitigate environmental impacts. Here, we present the dissolution of wood sawdust and chips in formic acid at 50 °C under ultra-mild conditions without using ball milling and added catalysts. We found that depressurization and occasional light pressurization of wood sawdust or chips during stirring in a formic acid solution significantly accelerated solubilization accompanied by the formylation of wood components. Multi-dimensional NMR analyses revealed formylation of lignin, hemicellulose and cellulose. Substituents of formyl groups broke the hydrogen bond networks among cell wall components, resulting in the disintegration and solubilization of wood. Casting the solution from the total dissolved solution of Eucalyptus globulus on a release film and natural evaporation gave a plastic-like film with tensile strength (61 MPa), Young's modulus (3097 MPa), and glass transition temperature (T_g = 177 °C) values comparable to those of acryl resin, and a paper-like sheet formed from Japanese cedar. These two types of films from wood were also compared among the films produced from agricultural waste. Thus, the three plant cell wall components in wood sawdust and chips were directly disintegrated through formylation under ultra-mild conditions and reassembled to the films just by casting.