Raw Materials for Particleboard

The raw materials for making particleboard include two main categories: wood or wood fiber materials, adhesives, and additives. The former accounts for over 90% of the dry weight of the board. Wood raw materials are mostly obtained from inter-forest logging, small-diameter timber (usually less than 8 cm in diameter), logging residues, and wood processing residues. These are processed into flakes, strips, needles, granules, wood chips, sawdust, etc., and are called wood chips. In addition, non-wood materials such as plant stems and seed husks can also be made into boards, often named after the material used, such as hemp stalk (particleboard) or bagasse (particleboard). Adhesives commonly used are urea-formaldehyde resin and phenolic resin. The former has a lighter color and lower curing temperature, providing good bonding to particleboard made from various plant materials such as wheat straw and rice husks, with a hot-pressing temperature of 195–210℃. It is widely used in production, but has the disadvantage of releasing free formaldehyde, polluting the environment. The morphology of wood shavings is a decisive factor in the quality of particleboard; therefore, producing qualified shavings is the first step. Wood shavings, residues from wood processing, can be reprocessed and used as the core layer of particleboard. Surface shavings are mainly made from high-grade residues from logging or processing (wood ends, board edges, etc.). The length, thickness, and width dimensions of shavings vary depending on the production method and whether they are used for the core or surface layer. Processing equipment for shavings includes chippers, re-crushers, sanders, and fiber separators; cutting methods include cutting, shearing, and crushing. To obtain high-quality shavings, processes such as initial crushing, sanding, re-crushing, and screening are required.

 

The initial moisture content of the processed shavings is approximately 40-60%, with the core layer requiring a moisture content of 2-4% and the surface layer 5-9% to meet processing requirements. Therefore, a dryer is used to dry the shavings with varying initial moisture contents to achieve a uniform final moisture content. The dried shavings are then mixed with liquid adhesives and additives. Typically, 8-12 grams of adhesive are applied per square meter of wood shavings surface area. The adhesive is sprayed from a nozzle into particles with a diameter of 8-35 micrometers, forming an extremely thin and uniform continuous adhesive layer on the shavings surface. The adhesive-coated shavings are then laid into a slab, typically 10-20 times the thickness of the finished product. Pre-pressing and hot-pressing processes are then performed. The pre-pressing pressure is 0.2-2 MPa, using a flatbed press or roller press.