The effects of preservatives used for glue-line treatment on the curing of phenol-formaldehyde resin (PF) were studied by dynamic mechanical analysis and differential scanning calorimetry. Storage modulus, G 0 , loss modulus, G 00 , and loss tangent, tan d, of PF with and without preservatives were recorded as a function of time under isothermal heating. The time required for G 0 , G 00 , and tan d to reach steady values increased with addition of preservative. The G 0 , G 00 , and tan d curves of PF containing benzyl alcohol (used in the preservative as a diluent) were almost identical to those of PF containing preservative. However, the addition of antitermite and anti-fungal compounds alone had no effect on the curing process. There were no differences in total reaction enthalpy or dependence of activation energy on degree of conversion between pure PF and mixtures. Our results indicate that benzyl alcohol in preservatives plasticizes the curing system for PF.
Cross-laminated timber (CLT) laminates layers of laminae side by side, with the fiber direction of each layer orthogonal to each other. Therefore, any error in the thickness of the laminae may cause gaps in the glue lines, leading to adhesion failure. In this study, a three-layer CLT with a thin lamina inserted in the inner layer was manufactured, and the gap-filling performance of adhesives and the allowable error for lamina thickness were investigated. The outer layer of CLT was arranged with 30.0 mm-thick laminae, and the inner layer alternated between 30.0 mm-thick lamina and thin laminae (29.9, 29.7, and 29.5 mm). One-component polyurethane adhesives (PUR), emulsion polymer-isocyanate (EPI) adhesives, and phenol-resorcinol-formaldehyde resin (PRF) were used. The glue line thickened when the lamina thinned down in PUR and EPI. By contrast, the glue line thickness at the lamina thickness of 29.5 mm in PRF was almost the same as the glue line thickness without gaps. Delamination tests and block shear test showed that the PUR had a low delamination even at 29.5 mm thickness and a high wood failure rate (WF, > 95%), indicating good adhesion. For EPI, the lamina thicknesses of 29.7 and 29.5 mm showed an increase in delamination and a decrease in WF. For the PRF, an increase in delamination and a decrease in WF were observed at a lamina thickness of 29.5 mm. These results indicated that good adhesive properties can be obtained with a lamina thickness error of 0.1 mm for EPI and 0.3 mm for PRF.
Naoyuki FURUTA � To reuse waste concrete form plywood (hereafter, waste plywood) as core of plywood, the author investigated various properties of waste plywood. A significant positive correlation between the density and shear strength was evident in the cyclic boiling test in the case of new plywood, but the correlation was low in the case of waste plywood. The EB0 (MOE parallel to grain) of waste plywood was lower than that of new plywood, but EB90 (MOE perpendicular to grain) was equal to that of new plywood. Therefore ,there was no deterioration of bending� properties of waste plywood in crossband and core veneer.
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