Chemical structure and bonding performance of CTBN-toughened phenol formaldehyde resin
Phenolic(PF)resin has high bonding strength,high water(wet)weathering resistance,and better flame-retardant properties,which is widely used as an adhesive for outdoor wood-based panels.The cured PF resin shows a high degree of polymerization of three-dimensional network structure,high brittleness,lack of toughness,the adhesive layer in the external forces.Especially the impact load is easy to produce cracks and rapid expansion,resulting in adhesive layer cracking or even failure.Toughening and modification of the PF resin can improve the impact resistance of wood-based panels and their products on the basis of retaining its inherent excellent bonding properties,which can further broaden the application scenarios of the products.This study investigated the introduction of terminated carboxylated nitrile butadiene rubber(CTBN)with toughening modification(5％-25％application)for trial production of poplar plywood.Analyses by Fourier transform infrared spectroscopy,X-ray diffraction,and solid-state NMR showed that the flexible chain segments of CTBN were not only efficiently embedded in the curing body of the PF resin,but also grafted to the hydroxymethyl group of the PF resin through the reactive end group(—COOH).The nanoindentation test results showed that the hardness and Young's modulus of the PF resin cured body showed a decreasing trend with the increase of CTBN addition,and the modified PF resin cured body had lower hardness and Young's modulus compared to the unmodified PF resin cured body,which indicated that the modified PF resin cured body had good toughness.The results of the bonding strength showed that the addition of CTBN had a significant effect on the bonding strength of plywood.When CTBN was added by 15％,the dry bonding strength was 2.03 MPa,which was 110.5％higher than that of pure PF plywood,and when CTBN was added by 5％,the wet bonding strength was 1.50 MPa,which was 48.33％higher than that of pure PF plywood.Overall,the optimal addition amount of CTBN was 5％,and the plywood could be used in a wider range of application scenarios.The failure modes of the specimen glued interface were mainly cohesive damage and mixed damage.The digital scattering results proved that the addition of CTBN made the strain distribution at the interface between liquid adhesive and wood veneer more uniform,which was more conducive to stress transfer and less likely to produce stress concentration phenomenon.The findings in this study confirmed the theoretical and technical feasibility of CTBN for toughening PF resins and improving wood bonding properties.
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维普
