Upscaling and process development for wood modification with N-methylol compounds using superheated steam: Fid-Bau Portal

Upscaling and process development for wood modification with N-methylol compounds using superheated steam

Schaffert, S. / Krause, A. / Militz, H.

For nearly 20 years, investigations have been done in order to modify wood using N-methylol compounds (Nicholas and Williams 1987) especially with the well-known DMDHEU (dimethylol-dihydroxyethyleneurea). Publications show improved properties (most notably, the durability against fungal attack and the dimensional stability) of small samples treated with these textile resins (Militz 1993, van der Zee et al. 1998). The modification is based on vacuum-pressure impregnation and curing at temperatures >100 deg. The treatment of small wood blocks appears to be unproblematic, but with bigger dimensions, non-uniform distribution, crack initiation and discoloration of wood pieces may occur. A method has been developed for the modification of wood in large dimensions on an industrial scale. Different process conditions affect the quality of the treated wood markedly. With appropriate conditions, the target property profile of the modification (enhanced durability, improved swelling and shrinking behaviour and increased hardness) can be obtained, while avoiding negative impacts. Some properties are strongly linked to the changing curing conditions, like the enhancement of durability against fungal attack and the release of formaldehyde, while other characteristics like chemical distribution are more or less independent of process parameters. The work provides the basis for the optimisation of the curing process to produce tailor-made properties of the modified wood for different uses.