Surface colour change in wood during drying above and below fibre saturation point

A technique has been developed to measure the surface colour change in a single wood sample during drying. This method is useful for studying the development of kiln brown stain. The wood sample is planed carefully in the green state to remove any surface wood that was damaged during cutting. This exposes intact tracheids at the surface rather than the damaged tracheids normally found at the surface of rough-sawn timber. The intact tracheids cause the evaporative front to remain at the surface during drying and therefore colour formation also occurs right at the surface. This means that the colour can be measured using a spectrophotometer at various stages during drying without having to slice the sample. This reduces errors associated comparing matched or unmatched samples. Experiments were carried out to measure the change in colour of wood from green to EMC at different schedules. At the end of each schedule the boards were held at the EMC to determine how the colour changed below fibre saturation point. The results show that the colour of the wood continues to change below fibre saturation point and the nature of the colour change indicates an increase in the complexity of the coloured compounds present

Application of neutron radiography to investigate changes in permeability in bacteria treated pinus radiata timber

The permeability of softwoods can be enhanced by selective bacterial attack of the pit membranes. In this paper, green flat-sawn Pinus radiata sapwood boards were sprinkled for various exposure times with a nutrient solution containing a mixed bacterial population. The timber samples were subsequently dried and the tangential absorption of water was measured using neutron radiography to track the movement of moisture within the wood. There was a significant increase in water absorption after only two days of bacterial exposure, and the quantity of water absorption nearly doubled after a fortnight of bacterial exposure. These measurements showed that dried timber that has had a greater extent of bacterial exposure in the green condition has more void space available to store and conduct water. Scanning electron micrographs showed that bacteria had colonised the pits near the surface of the wood after only two days bacterial exposure. There was also clear evidence of damage to the margo-fibrils and tori of the pit membranes, which was attributed to enzymatic degradation by the bacteria. This study confirms the conclusions drawn by other investigators that bacteria degrade the pits in the green sapwood, so that many of the pathways for moisture flow remain unblocked once the wood is dried

Application of neutron radiography to investigate changes in permeability in bacteria treated pinus radiata timber

The permeability of softwoods can be enhanced by selective bacterial attack of the pit membranes. In this paper, green flat-sawn Pinus radiata sapwood boards were sprinkled for various exposure times with a nutrient solution containing a mixed bacterial population. The timber samples were subsequently dried and the tangential absorption of water was measured using neutron radiography to track the movement of moisture within the wood. There was a significant increase in water absorption after only two days of bacterial exposure, and the quantity of water absorption nearly doubled after a fortnight of bacterial exposure. These measurements showed that dried timber that has had a greater extent of bacterial exposure in the green condition has more void space available to store and conduct water. Scanning electron micrographs showed that bacteria had colonised the pits near the surface of the wood after only two days bacterial exposure. There was also clear evidence of damage to the margo-fibrils and tori of the pit membranes, which was attributed to enzymatic degradation by the bacteria. This study confirms the conclusions drawn by other investigators that bacteria degrade the pits in the green sapwood, so that many of the pathways for moisture flow remain unblocked once the wood is dried

APPLICATION OF NEUTRON RADIOGRAPHY TO INVESTIGATE CHANGES IN PERMEABILITY IN BACTERIA TREATED PINUS RADIATA TIMBER

The permeability of softwoods can be enhanced by selective bacterial attack of the pit membranes. In this paper, green flat-sawn Pinus radiata sapwood boards were sprinkled for various exposure times with a nutrient solution containing a mixed bacterial population. The timber samples were subsequently dried and the tangential absorption of water was measured using neutron radiography to track the movement of moisture within the wood. There was a significant increase in water absorption after only two days of bacterial exposure, and the quantity of water absorption nearly doubled after a fortnight of bacterial exposure. These measurements showed that dried timber that has had a greater extent of bacterial exposure in the green condition has more void space available to store and conduct water. Scanning electron micrographs showed that bacteria had colonised the pits near the surface of the wood after only two days bacterial exposure. There was also clear evidence of damage to the margo-fibrils and tori of the pit membranes, which was attributed to enzymatic degradation by the bacteria. This study confirms the conclusions drawn by other investigators that bacteria degrade the pits in the green sapwood, so that many of the pathways for moisture flow remain unblocked once the wood is drie