Adhesive-free direct coating of wood and nonwood materials with biomass films produced via reassembling of lignocellulose

Petroleum-derived polymers, which are commonly coated on wood for surface decoration and protection, result in a high load on the carbon balance on Earth and exhibit difficulties related to material recycling. Herein, biomass films were prepared via the disintegration and reassembly of plant cell wall components using formic acid under ultra mild conditions (<50 °C). These films were tightly coated on 30 types of hardwood and softwood offcuts by heat-pressing without synthetic polymers and adhesives. They were also coated on ceramic, glass, plastic, and metal plates. Scanning electron microscopy and water-contact-angle analysis of Eucalyptus globulus and a Japanese cedar film coated above 200 °C revealed a rough surface with fibril bundle structures and an increase in the hydrophobicity from 66° to >90° after film coating. Thermogravimetry–differential thermal analysis coupled with mass spectrometry revealed that heat-pressing caused water evaporation, dehydration, and pyrolytic degradation of the films, along with release of the degraded products, mainly derived from xylan. Pyrolytic degradation induced penetration of the melted film components into the porous structures of the involved wood, affording a tight coating with increased hydrophobicity. Overall, this process enables hydrophobic coatings solely made from woody biomass. (190 words).