Differential response of heartwood and sapwood to heat treatment. Part 1: strength properties

Abstract

Abstract The transition from sapwood to heartwood is characterised by several changes including increasing acidity. On the basis of the strong correlation, which has been established between strength reduction and wood acidity during heat treatment, the differences in the response of heartwood and sapwood strength properties were investigated. Heartwood and sapwood samples obtained from one board of Scots pine (Pinus sylvestris) were heat-treated and their strength properties compared. There was 15.8% and 3.3% reduction in modulus of elasticity in the heartwood and sapwood respectively while the loss in modulus of rupture is 32.9% and 15.6% in the heartwood and sapwood respectively. The lower reductions in the strength properties in the sapwood compared to the heartwood indicate that the former is less amenable to heat treatment than the latter. This is probably due to the higher acidity of the former, which could have resulted in higher degree of degradation, higher cellulose crystallinity and consequently higher strength reduction. Therefore the effects of heat treatment on wood especially the strength properties depends on the proportions of heartwood and sapwood.