Abstract
Abstract Wood tars from Acacia confusa Merr. and Cryptomeria japonica D. Don. were produced by reduced pressure distillation at 76 mm Hg and 50°C from the bottom layer of crude wood vinegars that had set for over 6 months. The feasibility of using water-soluble, resole-type, wood tar phenol-formaldehyde resins (WT-PF) was investigated. The resins were prepared from phenol (P) and wood tars (WTs) at weight ratios of 100:0, 80:20, 60:40 and 40:60 and F/P molar ratios of 1.5, 1.8 and 2.0 as plywood adhesives. The results demonstrated that WT-PF resins had a higher viscosity, shorter gel times, a higher polydispersity, a lower curing temperature and less heat of curing than conventional PF resins under the same conditions. The shear strength of plywood bonded with WT-PF resins was slightly lower than that of conventional PF resin. However, the WT-PF resin still met the CNS 1349 requirement for the dry test, and phenol substitution levels could be up to 60%, but only 20% for type I and type II plywood. The addition of A. confusa bark powder fillers could significantly improve the bonding strength of WT-PF resins, especially for the warm water soaking and soaking in boiling water tests. The required amounts of fillers added were up to 5% for A. confusa WT-PF resins and up to 3% for C. japonica resins.
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