Usability of maleic anhydride as wood modification agent for the production of medium density fibreboards (MDF)

This study focuses on the development of up-scaling of modifications with maleic anhydride (MA) for the production of medium density fibreboards (MDF). In order to assess the effect of MA modification on the wood itself, preliminary investigations were carried out on spruce veneer strips treated with 10 (wt v⁻¹) MA in dimethylsulfoxide (DMSO) prior to fibre modification and board manufacture. The veneers were cured at 150 °C and showed cell wall bulking and anti-swell efficiency (ASE) of 2.3 ± 0.2 and 22 ± 3 % (mean value ± std), respectively, due to MA-treatment. Fibres treated with MA in DMSO and cured at 160 °C were pressed to MDF by using polymeric diphenyl-methane-diisocyanate (PMDI) as adhesive. These boards showed a modulus of rupture and modulus of elasticity reduced by 50 and 20 % compared to those of control boards. Internal bond strength (IBS) and IBS after cook test of MA-treated MDF were approximately twofold and threefold higher than those of control boards. MA-treatment induced a minor reduction in water thickness swelling, but not in water uptake of the MA-treated MDF. The results indicate that MA-modifications cause severe degradation of the cell wall and do not result in considerable hydrophobation of solid wood and MDF, but improve bonding with PMDI.