Influence of drying and curing parameters on phenol-formaldehyde impregnated wood veneers

Abstract

The purpose of this experimental research study was to obtain new understanding on adhesion and mechanical characteristics of impregnated spruce veneer samples wherein a low molecular weight phenol formaldehyde (PF) resin simultaneously acts both as impregnant and as adhesive. Impregnated veneer specimens were pre-dried by varying drying temperature and duration in order to obtain samples with different intermediate states of condensation. After bond formation, tensile shear strength and corresponding wood failure amount were determined. In the second part of this study, press parameters (i.e., pressing temperature and pressing time) were varied to obtain knowledge about the curing behaviour of pre-dried PF-impregnated veneer specimens. Tensile shear strength of the adhesive bond, tensile strength, the corresponding modulus of elasticity and hardness of the substrate material were determined in addition.As a result, clear effects of the various investigated parameters could be observed. While drying temperatures mainly affected the tensile shear strength, excessive pressing temperatures and times showed an impact on both, the tensile shear strength and (negatively) on the mechanical properties of the wood substrate.