Drying of wood flour

Drying of wood flour

Time:2020-12-11

Because wood flour contains a lot of moisture, it is necessary to fully dry the wood flour before molding to remove moisture and volatile components. If the drying is insufficient, smoke will appear during the molding process, the product will have bubbles, and the color of the product will become dark and dull, which will also affect the mechanical properties of the product. Wood flour has different chemical composition due to different varieties and production areas, but its main components are usually cellulose, hemicellulose and lignin, as well as resins, other organic compounds and water and other extracts (5%~10%). Wood fiber contains a lot of hydrophilic hydroxyl groups, which are easy to absorb water, and the maximum water content can reach 14%~15%. When such a high water content is compounded with resin, except for part of the water being heated and evaporated, most of it is still Residues in the composite system can cause problems such as fuming, foaming, scorching, and even explosion in the barrel, making it impossible to mold, or bringing serious adverse consequences to the performance of the molding and final product. In order to ensure smooth molding and processing and product quality, wood flour must be dried before use to reduce the moisture content of wood flour to below 4%, preferably to 1%. Generally, when wood flour is dried and heated, the water evaporates first , Then the easily decomposable part of lignin is thermally decomposed, cellulose is oxidized and decomposed after further heating, and finally lignin is decomposed.
For the drying of wood flour, temperature conditions are the most important. If the drying temperature is higher than 200℃, or even higher than 260℃, the decomposition reaction will be fast, the termination of the decomposition reaction will be difficult, and there will even be a fire hazard; in the presence of oxygen, wood flour will violently smoke at about 200℃, reducing the weight by 5% ~10%, the color becomes darker and black; wood flour is heated in oxygen, usually at 260~290℃, it will catch fire. In order to ensure safety, it is best to heat and dry in an inactive gas (such as nitrogen). If the temperature is lower than 160℃, the dehydration and devolatilization of wood flour will be slow, so the drying time should be extended. Therefore, the drying temperature is best selected below 200°C. The drying and heating time can generally be adjusted according to the moisture content of the wood flour or the reduction of the wood flour composition by 3%, preferably 5% to 15%, so that the molding process can be carried out smoothly. The general drying treatment temperature in the laboratory is 80~100℃, and the time is 18~24h. The drying and heating device can adopt a constant temperature oven, an air dryer, a vacuum oven, a drum dryer, a high-speed mixer, or a screw conveyor. Continuous drying equipment. Generally, the unit output of intermittent drying equipment can reach 450kg/h.

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