Deterioration of wood-based boards subjected to outdoor exposure in Tsukuba
Various types of wood-based boards were analyzed for deterioration after being exposed to an outdoor environment for 5 years in Tsukuba, Japan. In phenol–formaldehyde resin bonded particleboard (PB(PF)) and aspen oriented strand board (OSB(aspen)), longer exposure caused a greater reduction in the modulus of rupture and internal bond strength, an increase in the coefficients of variation, and a decrease in 95 % lower tolerance limit at the 75 % confidence level (95TL). Nail-head pull-through and lateral nail resistance were also reduced by outdoor exposure, but their coefficients of variation and 95TL were not significantly affected. In contrast, methylene diphenyl diisocyanate bonded medium density fiberboard (MDF(MDI)) only showed a slight deterioration of these properties even after 5-year exposure, and the coefficients of variation and 95TL hardly changed. After 5-year exposure, the retention of shear load in one-plane at relative displacement of 1.0 mm was high in MDF(MDI) and OSB(aspen) at 93.5 and 78.5 %, respectively, but low in PB(PF) at 41.1 %. As with PB(PF), OSB(aspen) also showed a sharp decrease in the modulus of rupture and internal bond strength, but only slightly reduced shear load in one-plane.
配向性ストランドボード(OSB)およびパーティクルボードの強度分布に及ぼす屋外暴露の影響
To study the mechanism of strength degradation of wood-based panels, outdoor exposure tests and strength tests were conducted. Specimens used were commercial oriented strand boards (OSB) and particle boards (PB) which had been exposed in outdoor condition for 1, 3, and 5 years at a field testing site in Forestry and Forest Products Research Institute. To investigate probabilistic properties of modulus of elasticity (MOE), modulus of rupture (MOR), and internal bond strength (IB) of the boards, sixty or seventy-five specimens in one testing condition were tested. Transitions of the distributions for these strength properties were investigated with considering the degradation of adhesion and spring back of elements.The mechanism of strength degradation of the boards is explained with a spot adhesion degradation model. In the case of PB, the degradation of spot adhesion occurs mainly in surface layer after one-year exposure, and decreases the MOEs and MORs of the board. But spring back does not take place, because the amount of degradation is not enough to cause the spring back. After 2 or 3 years, the thickness of the board increases because a number of effective spots which are enough to restrict the spring back, do not remain at the surface layer. After 5 years, the effective spots at the surface layer decrease to tear off a part of particles.Though the rate of the degradation of OSB is lower than that of PB in general, spring back takes place even after one-year exposure because the surface is so rough that some water infiltrates into the board more easily. As the degradation occurs uniformly in the board, relationships between MOEs and MORs do not change. After 5 years, the thickness of the board increases because effective spots enough to restrict the spring back do not remain.
InTlP — a proposed infrared detector material
In1−xTlxP is proposed as a promising material for infrared detectors. A number of key optical and structural properties are studied within local density‐functional theory. In1−xTlxP at x=0.67 and In1−xTlxAs at x=0.15 are estimated to have a gap of 0.1 eV. Their binding energies are larger than that of InSb, and they are found to form stable zinc‐blende alloys for all x. In1−xTlxP nearly lattice matches to InP, and offers the potential to integrate detector array and read‐out circuit.