Adhesive/fibre interaction in medium density fibreboard

Summary Qualitative and quantitative Jamin-Lebedeff interference microscopy was used in combination with embedding and thin sectioning to study the interaction between phenol-formaldehyde or urea-formaldehyde resins, and the fibre surface of medium density fibreboard from a wide range of commercial sources. Interference microscopy was used to measure the refractive indices of both resins to enable positive identification of resin within the board. Contact angle between resin and fibre surface was measured to provide an estimate of the degree of wetting of the fibre. Phenol-formaldehyde resin showed significantly lower contact angles and therefore better fibre wetting when compared with urea-formaldehyde. Phenol-formaldehyde tended to form a thin layer on the fibre surface while urea-formaldehyde tended to form large compressed droplets or patches of resin between the fibres. It is suggested that by improving the wetting properties of urea-formaldehyde resin, significant improvements in internal bond strength may be achieved.The authors gratefully acknowledge the assistance of Fletcher Wood Panels (NZ) Ltd, Canterbury Timber Products (NZ) Ltd and ICI (NZ) Ltd in providing materials and financial support. The authors acknowledge the assistance of Dr J. M. Uprichard, Dr R. Franich, Mr J. McLaughlan (FRI) and Dr R. Naylor (A. C. Hatrick (NZ) Ltd) in the preparation of this report