IMPROVING STIFFNESS OF LIGNOCELLULOSICS THROUGH CELL WALL MODIFICATION WITH CHITOSAN-MELAMINE CO-POLYMERS*

Chemical modification with chitin- and chitosan-hexamethyl methylol melamine (HMMM) co-polymers was investigated for improving the stiffness of lignocellulosic materials. Chitin and chitosan were converted by chemical means to low molecular weight oligosaccharides with molecular weight profiles suitable for penetration of lignocellulosic cell walls. The oligomers were reacted under controlled conditions with hexamethyl methylol melamine (HMMM) to produce aqueous formulations of oligosaccharide bonded to HMMM, the “pre-polymers”. The chitosan oligomers reacted with HMMM to produce, on condensation polymerisation, a water-insoluble polymer in high yield (69%), whereas the chitin oligomer HMMM condensation reaction gave poor co-polymer yields (28‐34%). The yield of co-polymer from the condensation polymerisation reaction was critical to the success of the cell wall modification in improving stiffness. Pinus radiata D. Don veneers were treated with chitin and chitosan oligomer HMMM formulations to average dry weight percentage gains of 69% and 57% respectively. No improvement in veneer stiffness was obtained with the chitin oligomer HMMM treatment, whereas the chitosan oligomer HMMM treatment resulted in an average veneer stiffness enhancement of 20%. There was a linear relationship between the level of stiffness improvement and the degree of co-polymerisation of the oligomers with HMMM. A threshold of greater than approx. 30% co-polymer yield was necessary before any improvement in veneer stiffness was observed. Polysaccharides with a β-(1→4) configuration, such as chitosan, therefore offer potential for lignocellulosic stiffness property modification.