Study On Interfacial Interaction And Mechanical Property Of Wood/isocyanate

In the recent decades, the research of the adhesives for wood was focused on the adhesive mechanism of the isocyanate adhesives for wood. In this paper, the interfacial physical reactions of the wood- isocyanate adhesives were studied in detail by inverse gas chromatography, IGC, X-ray photoelectron spectroscopy, XPS, and scanning electron microscopy, SEM, combining with the test of the mechanics performance.The surface dispersive free energy of the ashtree and poplar was determined by IGC, the values of them were 36.32 and 37.98mJ. m^-2 (323.15K), 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 are all of stronger acidic. It was found by studing the isocyanate and phenol formaldehyde resin adhesives using IGC that they were all basic different from the wood characteristic, that proved theoretically the surface acid-base reactions of the said adhesives to wood. The surface dispersive free energy of the phenol formaldehyde resin was 34.38 mJ·m^-2, that was bigger slightly than 31.80 mJ·m^-2 of the isocyanurate, but the basic constant of the isocyanurate was nearly twice of the phenol formaldehyde resin, the overall surface free energy of the isocyanurate was bigger than that of phenol formaldehyde resin.In the microcosmic interface analysis, the porous wood was replaced by cellulose membrane, which was unknit and compact for convenient to study the interface. It was found that molecules diffused in the interface of the isocyanate adhesives and the cellulose membrane by XPS, and the hydrogen bonds interactions existed in the interface. It was observed that isocyanate adhesives had a better compatibility with the cellulose membrane than phenol formaldehyde resin adhesive; and even using the same isocyanate adhesives, there was difference of the interface compatibility due to the cured temperature.In order to study the macroscopical mechanics performance of the said systems, the shear strength was tested for cellulose membrane-adhesives bondings. It was found that the cleavage pattern was interface peel off at lower cured temperature, in the contrariwise, adhesive layer cleavage at high cured temperature, that was consistent with the results of the microcosmic interface analysis. The adhesive strength of the binders decreased evidently with the increasing of the content of the isocyanurate at high cured temperature.