| The objective of research is to set up a new technology for the deresination of larch wood which is modified by the method of microwave-cell-explosion. The principle of the deresination technology is that when the green lumber of larch wood, which is of high percent moisture content (about 30-60%), is placed in the high intensive microwave field, the water molecule in the wood will be polarized and rapidly rotate, and frictionating with each other, generating heat and steaming. The vapor pressure in the cell will be increased rapidly, and the weaker part of the wood cell such as pit membrane will be broken, the new fluid entryway is formed, the permeability of larch wood will be improved. The microwave modified larch wood was de-oiled and deresinated by a steaming device using saturated water vapour with normal atmospheric pressure as working medium. In this case the preheating procedure is not required, and the saturated steam can penetrate into the test wood quickly. In the condition of high temperature and high humidity, the turpentine oil will boil together with water, and it will be removed from the test wood accompanying with the water vapour. Without the dissolving of the turpentine oil, the solid state rosin can not seep out from the wood.The penetration test showed that the permeability of tested wood was improved obviously by proper microwave treatment. It is helpful to improve the permeability of the wood to prolong the time of microwave irradiation properly. The longer the time of microwave irradiation, the better the permeability of the test wood improved. The extraction test showed that there is little difference between the extraction ratio of resin from the microwave-modified wood by petroleum ether, by cool water and by boiled water, while the steaming treatment can obviously decrease the content of resin in wood, and the treatment of wood by microwave combined with steaming decreased the resin content more than the only steaming treatment;and the best extraction of the resin was observed when further prolonged the steaming time. The wood color test showed that the effect of microwave and steaming treatment is not obvious in short time. There is little influence of the microwave irradiation time on the wood color, but more change appeared when prolonged the time of steaming treatment. In 8 hour steaming treatment, there was a little change in the wood color. There was little change in the bending strength, Young's modulus and dynamic ductility of the test wood treated by microwave irradiation and steaming appropriately. The moisture absorption degree of the wood treated by microwave irradiation and steaming was decreased, but the dimensional stability was not improved obviously. From the scanning electron microscope analysis, the weaker part of the wood cell such as pit membrane was broken by proper microwave irradiation;the amorphous substance that covered on the pit membrane was eliminated or decoated by the steamingtreatment. According to the result of DMA, the storage modulus of the tested wood treated by microwave and steaming decreased obviously compared to the control. According to the result of FTIR, the absorption peak of the hemicellulose became weaker. The results of the vacuum-pressure-treatment of larch wood by fire retardant solution and the CONE test showed that the larch wood treatment by fire retardant wood (FRW) was easier and the effect of fire retardant treatment was obvious.To summarize the results mentioned above, by properly controlling the power of the microwave and the time of irradiation, when the larch wood of proper moisture content is treated with high-intensity microwave, its permeability can be improved obviously. And then the treatment of steaming in normal atmosphere pressure can effectively deresinate larch wood. Using this method to deresinate, the influence on the color and mechanical property of wood is insignificant, and the liquid penetration is improved, consequently put the protective treatment such as fire retardant into effect. |
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