SearchPublisher and Institutes
You are here: Home :: Area NEM :: Agricultural science
Mari de Meijer, Holger Militz
Sorption Behaviour and Dimensional Changes of Wood-Coating Composites
The moisture related properties of wood-coating composites have been studied to evaluate the influence of coating penetration on the protection of wood against moisture. Pine sapwood samples were vacuum-impregnated with 7 pigmented and unpigmented coatings, both water and solvent borne. The retention and void filling of the coating have been determined. After drying, the samples were exposed to relative humidities between 33 and 98 % and to liquid water and equilibrium moisture content and dimensional changes were measured. The rate of swelling and moisture sorption has been measured, the latter was also used to calculate diffusion coefficients. The sorption isotherms were analysed by the Hailwood-Horrobin equation. In order to obtain additional information on the hygroscopicity of coatings, similar measurement were made on free coating films.
The void filling of wood with coating material has the strongest impact on the uptake of liquid water. A limited reduction was observed for the equilibrium moisture content, the diffusion coefficient during adsorption and the rate of dimensional change. No influence on the equilibrium swelling have been found but the shrinkage during desorption was however often slightly increased for the wood-coating composites.
The limited impact of the penetrated coating on moisture related properties can to a large extent be explained by the low void filling after drying (20–60%) and the relatively high moisture sorption and swelling of the coating film itself. In general, it can be concluded that the moisture protection of penetrated coating material is low in comparison to coating applied as a film on the surface of wood.
Holzforschung, Walter de Gruyter
Print ISSN: 0018-3830
Volume: 53, 09/1999
Pages: 553 - 560