The influence of wood surface treatments with different biomolecules on dry and wet strength of linear friction welded joints

The moisture resistance of friction-welded wood joints can be improved by applying bio-based bonding additives. Several biomolecules including tannic acid, organosolv lignin from hardwood, kraft softwood, and derivates thereof, were investigated regarding their applicability as additives in the friction welding process. Welding with showed significantly increased stability after 24 h water immersion. An average wet bond strength 1.5 MPa compared to 0.38 untreated spruce was obtained. Modification through succinylation, acetylation or depolymerisation led no further improvement stability. Depolymerised resulted an even higher delamination rate samples during immersion than samples. Structural analysis variations FTIR-ATR, GPC 31P NMR combination thermal TGA DSC impact various structural chemical features on behaviour intermolecular interactions applied lignin.