| Structural glulam bonded by cold type of adhesives on the grain direction is a kind of engineering wood. Acted as one of the modern timber structural forms, it has been regarded as the fundamental material in bearing construction of bonding wood. Meanwhile, it is so widely applied in the architectural structure including wood construction residence, large-span spatial structure, wooden bridge, tower and so on that plays an essential role in timber-framed buildings. According the above architectural structure, the adhesives used in structural glulam should be cold curing.Functions of high bonding strength, water-resistant, hot-resistant etc. on formaldehyde resin adhesive are excellent, curing temperature has limited its application. Resorcinol-phenol-formaldehyde (RPF) resin, which is obtained by modifying phenolic resin with resorcinol, effectively decreases curing temperature.The influence of resin solid content, viscosity and shear strength was investigated by F/P mole ratio, R/P mole ratio, condensation pH value, pre-reaction temperature, co-reaction temperature and co-reaction time in the preparation procedure of modified phenolic resin. Orthogonal test was employed to optimize the conditions. The results indicated that the optimal process conditions were as follows: F/P mole ratio of1.5:1, R/P mole ratio of1:4, condensation pH value of10, pre-reaction temperature of80℃, co-reaction temperature of60℃, co-reaction time of2hours. RPF has the fast-curing characteristic at low temperature and viscosity of305.5mPas, pH value of9.52, solid content of62.09%, free formaldehyde of0.47%. Its dry shear strength is12.9MPa and wet shear strength is7.9MPa.The curing process, structure and fractured surface on RPF resin were analyzed by technology tools of TG-DSC, FTIR, and SEM.The study has shown that RPF resin adhesive under the optimal synthesis process has fast-curing characteristic at low temperature, its shear strength meet the national standard GB/T50708-2012. |
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