Dimensional instability of cement bonded particleboard: Behaviour of wood chips from various stages of manufacture of CBPB

Abstract

A technique for the dissection and measurement of wood chips used in cement bonded particleboard (CBPB) removed from the unpressed mat and the pressed board has been developed. The prepared chips were subjected to changing relative humidity (RH) conditions. The results illustrated the contribution of wood chips to the performance of CBPB. The trend in change of dissected chips was similar to that of CBPB but to a different degree under both a single and cyclic change in RH. However, the compression, contortion and chemical degradation of, and the inclusion of cement in, wood chips within CBPB resulted in an increase in mass change but decrease in dimensional change of dissected chips which were about 0.7, 3.0 and 1.3 times the change of raw wood chips respectively in mass, length and thickness over period tested. The combined effects of anisotropic characteristic, distribution and orientation of wood chips within CBPB brought about a significantly different ratio between length and thickness change of dissected chips to CBPB, having a ratio of about 2.5 for length and 15 for thickness. The nature of hysteresis loop for dissected chips was also very close to that of CBPB but dissimilar to that of raw wood chips.