The raw materials for making particleboard include wood or lignocellulosic materials, adhesives and additives. The former accounts for more than 90% of the dry weight of the board. Wood raw materials are mostly taken from forest cuttings, small diameter materials (usually below 8 cm in diameter), harvesting residues and wood processing residues. It is processed into flakes, strips, needles, and granules, wood chips, wood chips, sawdust, etc., and is called scrap. In addition, non-wood materials such as plant stems and seed shells can also be made into sheets, which are often named after the materials used, such as hemp (planing) boards, bagasse (shavings) boards, and the like. Urea-formaldehyde resin glue and phenolic resin glue are used for the adhesive. The former has a light fat color and a low curing temperature, and has good gluing effect on various plant materials such as wheat straw, rice husk and the like, and the hot pressing temperature is 195 to 210 °C. It is widely used in production, but it has the disadvantage of releasing free formaldehyde to pollute the environment.
The shaving pattern is the decisive factor in the quality of the particle board, so first of all to produce qualified shavings. The shavings of the remainder of the wood processing can be used as a core layer for the particle board. Surface shavings are mainly processed by high-grade residues (wood truncated, edged, etc.) in harvesting or processing. The length, thickness and width of the shavings vary depending on the production method and the core layer or surface layer used for the production. The processing equipment for preparing shavings includes a chipper, a crusher, a sander and a fiber separator, and the cutting methods include cutting, cutting and crushing. In order to obtain high-quality shavings, it is necessary to undergo primary crushing, grinding, crushing and sieving.
The processed wood shavings have an initial moisture content of approximately 40 to 60%, a water content of 2 to 4% in accordance with the process requirements, and a surface layer of 5 to 9%. Therefore, the shavings with different initial moisture contents are dried by a dryer to achieve a uniform final moisture content. The dried shavings are then mixed with liquid glue and additives. Usually 8 to 12 grams of sizing is applied to the surface area per square meter of shavings. The compound is ejected from the nozzle to form particles having a diameter of 8 to 35 microns, forming a very thin and uniform continuous layer of glue on the surface of the shavings. The sized rubber shavings are then laid into slabs, and the thickness is generally 10 to 20 times the thickness of the finished product. Preloading and hot pressing are possible. The pre-pressing pressure is 0.2 to 2 MPa, and is carried out using a plate press or a roll press.
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