Investigation of Some Properties of Calabrian Pine (Pinus brutia) Wood Heat-Treated in Accordance with ISPM 15 Standard and Used in Pallet Manufacturing

Abstract

Wooden pallets have become extensively used for logistic purposes worldwide. Because of its delicate structure and a food source for creatures, it is important to sterilize it during international trade of commercial goods which are used for stacking elements. In this context, the ISPM 15 standard must apply to those pallets before the topic of international transportation. Regarding this issue, heat treated Calabrian pine woods which were subjected to wooden pallet manufacturing, according to the ISPM 15 standard, were evaluated in terms of physical and optical properties, especially the changes in color values and Shore D hardness properties. However, heat-treated wood samples show, each stimulus value varies independently of the others, and no consistent trend emerged. The heat-treated wood samples show higher variation directionally and tangent surfaces usually show higher changes (darkening) rather than radial surfaces. It was found to be ΔX(t1-r1): 11.47% for X stimuli, ΔY(t1-r1): 12.20% for Y stimuli and ΔZ(t1-r1): 18.15% for Z stimuli, in that order. It is worth noting that Y and Z stimulus values are higher than X stimuli for control samples, while heat treatments impact all color properties and are higher than radial surfaces at similar conditions. It was determined that the lightness (L*) of the wood samples decreased on both surfaces following heat treatment. It decreased on the tangential surface by 2.04 units, while that on the radial surface decreased by 6.61 units. Regarding a* (red-green) color parameter, calculations showed that tangential surfaces shifted toward red (+a*), while radial surfaces shifted toward green (-a*). A combined evaluation of all three color parameters revealed that the radial surface color distribution of control samples was more homogeneous and varied within narrow limits, whereas tangential surfaces exhibited greater heterogeneity and wider ranges of variation. The heat treatment increased hardness values for both surfaces. The greatest increase was measured on the tangential surface, reaching 21.72 (Shore D units), a 126.3% rise compared to the control, followed by the radial surface, which showed a 9.33% increase. Regarding gloss properties, the surface gloss values of the wood were found to be very low (matte surface, <5 GU); however, while the heat treatment was observed to increase gloss on tangential surfaces, a decrease was noted on radial surfaces.