Decrease in the mechanical resistance of blue stained and "orange stained" Pinus radiata wood
M C Rose, L Reyes, J Alvarez, A Andaur, C Beltran, D Rivera
It is recognised that sapwood attacked by Ceratocystis pilifera increases its permeability to pressure preservative treatments. Since hiphae not only utilise pits, but also the cell wall for crossing from one cell to another, the mechanical resistance of the stained wood might be affected. The orange colour very commonly present in Pinus radiata logs heartwood under water sprinklers, has not received enough attention and among others, its effect on the mechanical properties of timber is not known. Lumber with no visible bluestain, 50% stained and totally stained was commercially obtained, then it was dried to 12% moisture content and cut for testing its bending strength according to the Chilean standard NCh 987. The following mechanical tests were carried out on "orange stained" heartwood samples taken from the central part (without pith) of Pinus radiata logs. Static bending, compression parallel to the fibre, traction perpendicular to the fibre and shear parallel to the fibre were measured according to the Chilean standards NCh 987, 973, 975 and 976 respectively on orange stained and sound wood samples. Bending strength of 50% bluestained wood samples was 29% lower than that of sound wood samples. The bending strength fluctuation of 50% to 100% bluestained wood samples was 29% lower than that of sound wood samples. In orange stained wood samples the mechanical test results did not show significant difference in the 4 measured and standardised properties between orange stained and sound samples. Considering non-standardised data the bending MOE and the traction MOR were lower in orange stained wood. The evenly fully developed orange colour of the samples did not mean deterioration of the cell walls and this was confirmed under microscopic observations of microtomed material. A few hiphae were found and coloured matter was more often observed in parenchymatic cells.