| Wooden structural engineering materials which can be used as load bearing structure of the support beams or engineering planks are obtained from woods through the bonding technology. Because the applications of wooden structural engineering materials are very extensive in indoor and outdoor,wooden structural adhesives should have the advantage of high bonding strength, excellent water resistance, flame retardance, environment protection and so on. As the size is large, wooden structural engineering materials are not suitable for hot forming process. Then the adhesives should be cured at lower temperature. Therefore, it has great significance to carry out the studies of manufacturing technology of the environmental friendly high-strength adhesives.Resorcinol-Phenol-Formaldehyde (RPF)resin adhesive is formed by phenol, formaldehyde and resorcinol through polycondensation in alkaline condition. It not only has the advantage of excellent mechanical properties and water resistance,but also can be cured at lower temperature than ordinary phenolic resin. So it can be widely used in agglutination of large wood constructions in outdoor. However, the current synthesis of RPF resin adhesive has the following problems. On the one hand, the content of free formaldehyde is too high,which is easy to cause environmental pollution. On the other hand, the content of resorcinol is much high, which increases the cost of production.Based on the influence of water resistance, curing properties and many other factors of RPF resin adhesive, the influence of curing agents and curing process on the water resistance and shear strength of RPF resin were investigated. Meanwhile, the fraction section structure and curing properties were analyzed by Scanning Electron Microscope (SEM),Differential Scanning Calorimeter (DSC), Fourier Transform Infrared Spectroscopy (FTIR). The research showed that:1.The content of resorcinol, pressing temperature and curing agents had a great influence on the water resistance of RPF resin adhesive.2.Based on the analysis of single factor test and orthogonal test, the results indicated that the optimal conditions for bonding process were as follows:R/P mole ratio of 1:4, pressing temperature of 80 ℃, pressing time of 1 h, the pressure of 1 MPa. Under this condition, the dry shear strength was 14.8 MPa and the wet shear strength was 8.2 MPa.3.The adding type of curing agents had a great effect on the performance of the RPF resin adhesive. The results indicated that when replacing a part of paraformaldeh-yde with nano-magnesium hydroxide as curing agents, the RPF resin adhesive could still have the advantage of excellent water resistance and bonding strength.Meanwhile, the content of free formaldehyde would be gradually reduced, which was good for the environmental protection.4.The analysis of the DSC and FTIR indicated that hydroxymethyl would be gradually consumed, aromatic ring structure would be changed, and the structure of carbonyl C= O would be generated in the progress of curing reaction.5. When used in the bonding process of pine, the dry shear strength of RPF resin adhesive was more than 10 MPa, and broken rate of pine specimen was from 90% to 100%. It was indicated that the strength of the RPF resin adhesive was higher than the strength of the pine itself. When selecting 10% paraformaldehyde and 5% nanomagne-sium hydroxide as curing agents, the pine specimen had excellent water resistance. |
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