Biocomposite adhesion without added resin: understanding the chemistry of the direct conversion of wood into adhesives

Abstract

In this work we revealed how the controlled degradation of wood surfaces with infrared light from a CO₂ pulsed laser facilitated adhesion between two biobased substrates without the use of additional resins. Laser modification physically and chemically altered the natural biopolymer organization of lignocellulosic materials enabling adhesion when subsequently hot pressed using typical industrial equipment. Surface analysis of the modified material revealed that laser modification changed the native wood morphology as it appeared to coalesce, while the hemicelluloses were depolymerized and vaporized, and the surface was enriched with cellulose II and lignin. The latter two materials made up over 90% of the solid surface. The lignin itself was partially depolymerized resulting in enrichment of cinnamyl alcohol end groups, which are structures arising from homolytic cleavage of the β-O-4 linkages. An adhesion mechanism related to heat induced coupling in the presence of structural polysaccharides was discussed. Laser modification of wood followed by hot pressing provided a bio-based alternative for petroleum and natural gas derived wood adhesives and provides a path towards utilizing cellulose and lignin directly as structural adhesives.