Wood-plastic composite board raw material selection
1. Selection of wood
The wood raw materials of WPC can be sawdust, wood powder, wood fiber. Wood powder is made by drying and grinding sawdust, divided into different grades according to particle size, from coarse mesh to superfine mesh, with a moisture content of less than 100%. Wood fibers can utilize recycled wood pulp fibers. Waste wood can also be used as raw material for wood-plastic panels. Waste wood mainly includes post-industrial wood waste in lumber factories. Wood waste produced by secondary processing refers to wood residues and consumer wood waste produced during the industrial production process of furniture, doors and windows. When choosing waste wood as raw materials for production, it is necessary to formulate specification standards and select raw materials according to the standards and specification parameters. In some developed countries, consumer waste wood has been excluded as a source of raw materials for the production of wood-plastic panels, mainly relying on the above-mentioned materials. The cleanliness of waste wood is very important as a raw material for production. If a small amount of glue, paint and veneer materials are not exceeded, it is generally within the acceptable range. The Washington Cleaning Center in the United States has developed standards for the degree of corrosion, metal and plastic content, and dirt content of waste wood.
2. Selection of plastic parts
Choice of plastic The choice and treatment of plastic depends on several factors, while wood degrades in high temperature state, plastic can still be handled and used at ℃. The polymers used in wood-plastic panels are mainly polyethylene, polypropylene and polystyrene. Any plastic that can be melted and processed below the degradation point of wood is suitable for the production of wood-plastic panels. Taking into account the further improvement of performance and cost control and other reasons, recyclable resins and raw materials will also be used. According to the current wood-plastic panel production technology, the different applications of wood-plastic panels determine the choice of different plastics. For example, the wood-plastic panels for outdoor applications mainly choose polyethylene as raw material.
HDPE: High-density polyethylene. Usually used to produce milk bottles. This translucent material is more valuable in the market.
LDPE: Low-density polyethylene. It has a wide range of uses and is usually used as a packaging film. A foreign company uses a piece of low-density polyethylene waste film to produce wood-plastic board trestles every year.
PVC: polyvinyl chloride. Consumable polyvinyl chloride is usually used as daily packaging materials and edible oil packaging. Due to the small amount of use, it cannot be used on a large scale to produce wood-plastic boards.
PP: Polypropylene. One of the most widely used general-purpose plastics in life and industry, it is widely used in automobile interior decoration and furniture. Although polypropylene is the main raw material for wood-plastic panels, the production of wood-plastic panels using raw polypropylene plastics is far greater than recycled polypropylene. The processing technology of plastics determines that small and uniform particles will be more beneficial for material feeding, bending and further processing. The current recycling methods for polymer plastics are mainly done mechanically. Waste plastics are decomposed into small particles and pellets, and reused in the production of new products. The cleaning of recycled plastics is a very important link. Some waste plastics with high recycling costs and not suitable for further processing tend to be buried.
3. Application of additives
Application of Additives As an essential element in the production process of wood-plastic panels, additives have different effects on the quality and application of the panels. These additives include cements, stabilizers, pigments, lubricants, fungicides and foaming agents. The following table lists the application of different additives in the production process.
The organic bond of wood flour and plastic makes the material hard, but much more brittle than plastic without the mix. Compared with solid wood products of the same specification, wood-plastic panels have lower strength, hardness and bending strength due to the use of foaming agents. However, the low water absorption of wood-plastic panels offsets these shortcomings, and instead makes wood-plastic panels more corrosion-resistant. The ability to absorb UV rays further reduces the damage the panels suffer from sun exposure.