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

Abstract

Rotary cut beech (Fagus sylvatica L.) veneers were treated with two formulations based on N-methylolmelamine (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 treated veneers were bonded with phenol formaldehyde (PF) adhesive to produce plywood in two different processes. The plywood treated with NMM-1 displayed increased shear strength in comparison to the controls, whereas the treatments with mNMM-2 diminished the shear strength of the plywood to different extents. Treatment with NMM-1 also enhanced other mechanical properties of the plywood as compared to water-treated control plywood such as Brinell hardness, modulus of elasticity and bending strength. The plywood treated with mNMM-2 showed only slight changes of these mechanical properties compared to the control plywood. The plywood specimens were subjected to cyclic water submersion and oven-drying. The treatment with mNMM-2 caused greater reduction in water uptake and thickness swelling than NMM-1; the degree of delamination depended on the process. The plywood treated with NMM-1 exhibited lower equilibrium moisture content than that treated with mNMM-2. The formaldehyde emission of NMM-1-treated plywood was much higher than that of the control and the mNMM-2-treated plywood. © The Author(s) 2011. This article is published with open access at Springerlink.com.