Study On Interfacial Interaction And Mechanical Property Of Wood/isocyanate

In the recent decades, the research of the wood adhesives was focused on the adhesive mechanism of the isocyanate adhesives for wood. In this paper, the interfacial physical reactions of the wood- isocyanate adhesives and wood adhesion performance affected by surface characters of wood and a series of isocyanate content adhesives were studied in detail by inverse gas chromatography, IGC, X-ray photoelectron spectroscopy, XPS, combining with the test of the mechanics performance.The surface dispersive free energy of the ashtree, birch and poplar and adhesives were determined by IGC, the values of wood were 47.13,36.90 and 36.20 mJ·m^-2 (328.15K), respectively. The difference of them is not bigger, and they all belong to high energy surface; their capabilities of accepting electrons are bigger than that of donor electrons and they all show acidic character. The Lewis acidic number, K_a of ashtree, birch and poplar were 0.53,0.29 and 0.67,respectively. The Lewis basic number, K_b were 0.21,0.12 and 0.24,respectively. They all belong to amphoteric materials. It was found by studying the isocyanate (isocyanate content 5.3, 7.0,13.0 and 19.6% )and phenol formaldehyde resin adhesives using IGC that they were all basic different from the wood characteristic. The Lewis acidic number, K_a of adhesives were 0.29,0.38,0.12 and 0.18, respectively. The Lewis basic number, K_b were 0.34,0.76,0.33 and 0.65, respectively. The more isocyanate group containing the more basic the surface of adhesive is. That proved theoretically the surface acid-base reactions of the said adhesives to wood.In the microcosmic interface analysis, pervasion of isocyanate adhesive in wood was studied by XPS. The adhesive content of different deepness in birch plywood was calculated quantitatively.The mechanics test of poplar/isocyanate adhesives plywood shows that with the increment of surface basic property of adhesives, the shear strength of plywood increased also.Based on the acid and base theory, the polyethylene(PE), which surface character of both K_a and K_b are zero was choose to simulated wood structure. The mechanics data of solid and porous PE/adhesive plywood were obtained.The results showed that the shear stress increase with roughness of the PE board surface. The riveted joint effect act on adhesive strength was proved. The data obtained by mechanics test link the adhesive strength of interface and macro mechanics performance together. In adhesive strength test, the relationship of real wood/adhesive shear stress data with isocyanate group content and surface character of a series of adhesives were studied. Adhesive strength increased with increment of basic property and content of isocyanate group in adhesives. For simulated wood (PE) structure, the contribution of dispersive and riveted joint effect was separated from the whole adhesive strength. The individual interface adhesive strength of simulated wood according to change inner structure was calculated also. Results showed that the greater amount of sealed and ventilate pore in wood, the stronger the adhesive strength of plywood. The superposition of two factors gives more obvious influence to adhesive strength.