Microstructure of thermally modified radiata pine wood

Abstract

The thermal modification of wood is a potential alternative method for improving wood dimensional stability and increasing the resistance of wood to decay. However, during thermal modification, morphological changes occur within the microstructure of the cell, and these confer different properties to the wood. This study investigated the effects of the thermal modification process on the microstructure of radiata pine juvenile wood. Therefore, anatomical measurements were performed via optical microscopy in selected earlywood and latewood samples after each treatment, and the results were compared to untreated wood samples. In this study, two temperatures (190 °C and 210 °C) were considered for the thermal modification process. The results showed that the level of temperature of modification affected to microstructure of cell wall. The cell wall thickness decreased as treatment temperature increased, whereas the average lumen diameter increased slightly as temperature increased. Thermally modified radiata pine showed signs of damage (cracks, broken cells and deformations in the wood cell wall). The proportion of destroyed area increased as temperature increased, and significant differences were evident for the thermal treatment at 210 °C.

The behavior of thermally modified wood after exposure in maritime/industrial and urban environments

“…7 f). Cracks, broken cells, and deformations in the wood cell wall are also reported in recent studies in Pinus radiata [ 58 ], Pinus taeda, Eucalyptus grandis [ 59 ], and Pinus oocarpa [ 40 ]. According to the same authors, these alterations of the wood's cellular structures, namely hemicellulose, cellulose, and lignin, are probably caused by the chemical changes during thermal modification.…”

The Impact of Earlywood and Latewood on the Compressive Stress of Thermally Modified Douglas Fir

“…Specifically, some wood cells were entirely compressed (Figure 5 solid arrows) but there were also tracheids with a nearly intact morphology (Figure 5 dashed arrows). Most probably, the high thermal modification temperature degraded the wood cell walls [17], although not to the same extent everywhere, resulting in large differences in local stiffness and local damage. During the compression test, the strain most probably accumulated in low-stiffness regions consisting of such low-stiffness cell walls.…”

“…It is clear that the effects of the thermal modification on earlywood and latewood are not the same, which further complicates the effect of earlywood and latewood on the overall mechanical performance of the thermally modified wood [16]. The cell wall thickness decreases and cell lumen size increases with increasing thermal modification temperature [17]. Using a thermo-gravimetric analysis, it was found that earlywood is more susceptible to thermal degradation than latewood [18,19].…”

The impact of earlywood and latewood on the compressive strength of Douglas fir

“…The wood blocks, measuring 30 mm×50 mm×150mm, located around the 18th annual ring counting from the pith, were cut from Douglas r (Pseudotsuga menziessi). The density of the wood blocks was approximately 0.53 g/cm 3 , after conditioning at 65% RH and 20°C. Defects, such as knots and cracks, were avoided by visual selection.…”