Modification of beech veneers with N-methylol melamine compounds for the production of plywood: Natural weathering

Abstract

Beech (Fagus sylvatica L.) veneers were treated with two formulations based on N-methylol-melamine (NMM): (1) NMM solution (NMM-1, 10% solid content), (2) fatty acid modified NMM dispersions containing paraffin (with an aluminium salt as catalyst, mNMM-2, 5% solid content). Five veneers were glued with a phenol formaldehyde adhesive to produce plywood. The plywood specimens were weathered outdoors over a period of 18 months according to EN 927-3 (2006). The moisture content of the treated plywood was clearly reduced during the exposure as compared to panels from water treated veneers (controls). As a consequence, the treated plywood displayed higher form stability and less cracks and delamination than the control plywood. Coated, NMM-treated plywood panels displayed remarkable lower degrees of discoloration than the coated controls. These differences between the treated, coated and the coated control panels were not so clearly observed in the case of uncoated panels. The treatment with NMM compounds additionally led to reduced surface colonisation by staining fungi on the indirectly weathered reverse sides of the plywood panels. © Springer-Verlag 2011.