Industrial Kiln Drying and its Effect on Microstructure, Impregnation and Properties of Scots Pine Timber Impregnated for Above Ground Use. Part 2. Effect of Drying on Microstructure and Some Mechanical Properties of Scots Pine Wood

Summary

Scots pine (Pinus sylvestris L.) planks were dried in industrial progressive, conventional batch and high temperature kilns. The timber was further impregnated in an industrial autoclave with three preservatives used for above ground use. Samples dried by the three test methods and control samples were thereafter processed for scanning electron microscopy observations. Small clear specimens were sawn for determination of impact bending strength, modulus of elasticity and rupture (MOE and MOR) and hardness. The high temperature dried wood (at 115 °C) was characterised by partially damaged apertures in some bordered pits and nano- (10–20 nm) and micro checks (1–2 μm) in the warty and S3 layers of the cell walls. It is probable that certain modifications in the structure of the wood polymer complex also occurred due to hemicellulose thermal degradation. The above-mentioned structural changes facilitated the penetration of the preservative during impregnation and its evacuation during the final stage of vacuum. The industrial progressive and conventional batch kiln drying had no visible effect on the microstructure of Scots pine wood. There was no critical reduction of the impact bending strength, hardness and MOE of the dried untreated wood regardless of the drying method. MOR was significantly decreased after the conventional kiln drying, but not following high temperature drying. Impregnation with Tanalith E and conventional batch kiln drying aggravated the MOE and MOR of the high temperature dried wood, but both MOE and MOR did not differ significantly from those of progressive and conventional batch kiln dried samples.