Particleboards were subjected to outdoor exposure at eight sites in Japan, and the reduction in their strength (modulus of rupture and internal bond strength) was analyzed. The strength decreased with increasing thickness change as the particleboards swelled. Furthermore, the strength decreased with increasing mass loss. The correlation coefficients between thickness change and strength and between mass loss and strength were found to be strong. On the other hand, density reduced with increasing thickness change and mass loss. Since density reduction depended on both thickness change and mass loss, the correlation coefficient between density and strength was found to be the strongest. Therefore, it was concluded that density is a simpler and more useful index than thickness change and mass loss. In addition, score of the first principal component calculated by the principal component analysis of the climate factors, namely, temperature, precipitation, and sunshine duration was also found to be a simple and useful index to simplify these factors. A higher score of first principal component resulted in lower strength after the outdoor exposure test.

The contact time dependence od cross linked polyacrylic pressure-sensitive adhesives (PSA) was investigated. The model adhesives were crosslinked poly(n-butyl acrylate-acrylic acid) (A) and poly(2-ethylhexyl acrylate-acrylic acid) random copolymer (B) with an acrylic acid content of 5 wt% and various crosslinking degrees. Tack was measured by a prove tack test with probe rate of 10 mm/s and various contact times ranging from 3 to 30,000 s. The probe was made of stainless steel (SS). The tack increased with contact time. The order of tack rising with contact time was B > A and decreased with an increase in crosslinking degree. The tack rising order was A > B below the contact time of about 100 s, whereas it was B> A above 100 s. Tack order with the SS probe was A > B with the contact time of 3 s, however, the tack with other polymer probe were either on the same level or B > A. At the shorter contact time, the acrylic acid unit in the A molecule seems to appear a specific interaction with the metal surface. The order of molecular mobility was B > A from pulse nuclear magnetic resonance analysis, so the wettability to adherend surface became B > A at the longer contact time. This is considered to be the reason why the inversion of the tack order of A and B occurred with contact time.