Abstract
Low molecular-weight phenolic resin as impregnating resin (IPR, Mn=389) and high molecular-weight one (Mn=962) were mixed and sprayed on sugi (Cryptomeria japonica) particles, and 10mm thick single-layer particleboards (PBs) (SG=0.7) were produced. On the other hand, seraya (Shorea spp.) particles were treated with acetic anhydride to attain at a 16% weight gain by replacing hydroxyl units of wood components with acetyl ones. The acetylated, non-acetylated, and mixed (50:50 weight ratio) particles were pressed into low-density PBs with densities of 0.4 and 0.5g/cm3 using polymeric-type urethane resin adhesive. The specimens of these two kinds of PBs and untreated PBs were subjected to various accelerated aging treatments: a) 6-cycle ASTM D-1037 exposure, b) 6-cycle WCAMA exposure, c) cyclic boil-dry test, d) BS 5669 test, and e) cyclic soak-dry test. Thickness swelling (TS) and internal bond strength (IB) were measured after each step of each cycle. The TS after treatment a) was affected greatly by the addition of IPR or the acetylation treatment. After aging-exposure test a), the TS value of the PBs with only 5% IPR loading or the acetylated PBs was about a half of that of the control boards. The spring back was rarely observed for the treated PBs with 20% IPR loading after cyclic exposure tests of a), b), c), and d). The exposure test affecting most severely TS and IB retention of PBs was test a), followed by tests b), c), and d), in order.
