| Thermal modification is a kind of environmental friendly wood improvement process that is facing a surge of interest. After thermal treatment, the chemical compositions of wood change, therefore reducing the water absorption of wood, as well as improving its dimensional stability and biological durability. However, there are also some basic deficiencies of thermally modified wood, such as the poor long-term water repellency, the worse mechanical properties and the poor mold and termite resistance, which limit the application of thermal modificaiton. Because of the shortage of thermal modification, this study prepared several kinds of paraffin wax based water repellent, which was suitable for combining with thermal modification. The water repellency, dimensional stability, mechanical properties, biological resistance and thermal stability of combined treated wood were determined. Several methods, such as Fourier transform infrared spectroscopy (FTIR), scanning electron microscope with energy dispersive X-ray analysis (SEM-EDXA), X-ray diffractometer (XRD) and low field nuclear magnetic resonance (LF-NMR) were used to investigate the modification mechanism. The main results of this study are summarized below.(1) By selecting the emulsion formulation and preparation process, the paraffin wax emulsion with the average particle size of 200nm and well stability were prepared. The permeability of this emulsion in southern pine (Pinus spp.) was good, while the permeability in Scots pine (Pinus sylvestris) was poor. The wood with combined treatment of paraffin wax emulsion impregnation and thermal modification exhibited good water repellency, dimensional stability, and low corrosiveness to metals. The results comfirmed that the synergistic effect between two modification method was mainly dur to the redistribution of the paraffin wax, which filled the newly formed cracks caused by high temperature.(2) Through the orthogonal experiment, the silane/wax compound emulsion was prepared, and then was used to combine with thermal modification. Compared to the modified wood prepared by the method in part (1), the samples with the combined treatment of silane/wax compound emulsion impregnation and thermal modification obtained much higher water repellency and dimensional stability. This could be explained by following reasons:the silane in compound emulsion could penetrate into the wood cell wall and react with the hydroxyl groups in wood. Moreover, with the preimprgnation of compound emulsion, the surface hardness and thermal stability of thermally modified wood increased.(3) Borate pretreatment could increase the bending mechanical properties of thermally modified wood by inhibiting the degradation of hemicellulose during thermal modification. By combination of borate/wax emulsion combined system impregnation and thermal modification, the modified wood had much higher mechanical properties, mold resistance and termite resistance than the solely thermally modified wood. Moreover, this combined treatment could improve the anti-leaching property, water repellency and dimensional stability of borate treated wood.(4) The organo-montmorillonite (OMMT) could be introduced into wood cell wall by both two-step impregnation method and OMMT/wax compound emulsion impregnation, and thus improving the properties of modified wood. By combination of OMMT/wax compound emulsion impregnation and thermal modification, the water repellency, dimensional stability, compression strength, bending strength, surface hardness and thermal stability increased significantly. First thermal modification and then OMMT/wax compound emulsion impregnation was the optimum treating process of this work. |
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