At present, countries around the world to a variety of waste plastic pollution to carry out a full range of treatment, and has achieved certain results, including the use of wood powder or plant fiber filling, by special equipment extrusion, pressing or injection molding, can be used in some occasions to replace wood products plastic wood products are particularly practical. The result is a practical new technology that has been developed abroad in recent years with significant economic benefits and can be widely used in packaging, construction and other industries. The products can be made into plates, profiles, sheets, pipes, etc. and have the processing advantages of wood.

The development and research of wood powder and waste plastic composites can not only provide the opportunity to make full use of natural resources, but also reduce the environmental pollution caused by waste plastics, therefore, this plastic wood composite material is a green environmental protection material that saves energy and protects the environment. Its application range is also wide, mainly in building materials, automotive industry, packaging and transportation of goods, decorative materials and daily life utensils, etc. There is a broad development prospect. As an organic filler for plastics, wood powder has many excellent properties that are incomparable to other inorganic fillers: wide range of sources, low price, low density, good insulation, and low wear and tear on processing equipment. However, it is not as widely used as inorganic fillers, mainly because of poor compatibility with the base resin, poor dispersion in the molten thermoplastic, poor fluidity and difficulties in extrusion processing.

With the continuous development of plastic wood technology and the increasing demand for environmental protection, plastic wood technology has transitioned from single-component waste plastics and wood flour mixed together to multi-component waste plastics and wood flour mixed together to produce plastic wood products, so that the compatibility between multi-component waste plastics becomes very important.

As the main component of wood flour is cellulose, which contains a large number of hydroxyl groups, these hydroxyl groups form inter-molecular hydrogen bonds or intra-molecular hydrogen bonds, making the wood flour absorbent, with moisture absorption rates of up to 8-12%, and very polar; while most thermoplastics are non-polar and hydrophobic, so the compatibility between the two is poor, and the bonding force at the interface is very small. The use of appropriate additives to modify the polymer-wood powder surface can improve the interfacial affinity between wood powder and resin, and the modified wood powder filler has a reinforcing nature, which can well transfer the stress between the filler and resin, thus achieving the effect of enhancing the strength of the composite material. Therefore, in order to get good performance and meet the conditions of plastic wood composite materials, the first thing to solve is the problem of material compatibility, the compatibility problem mainly relies on the addition of various additives to solve.

1. Coupling agent method

Coupling agents can improve the compatibility between inorganic fillers, inorganic fibres and the matrix resin, and also improve the interfacial condition between the wood powder and the polymer. Silane coupling agents and titanate coupling agents are two of the most widely used coupling agents. Experiments have shown that both coupling agents can improve the compatibility of fillers with resins. US patent US 518802 describes the relevant treatment methods. US 5480602 also describes the application of polyimide ester coupling agents.

 2. Compatibiliser method

The addition of compatibilisers is the simplest and very effective method. Suitable compatibilisers have been reported to include grafted vegetable fibres such as maleic anhydride or maleic anhydride modified polyolefin resins, acrylate copolymers, and ethylene acrylic copolymers. Most of these compatibilisers contain carboxyl or anhydride groups, which are capable of esterifying with the hydroxyl groups in the wood flour, thus reducing the polarity and hygroscopicity of the wood flour and making it very compatible with the resin.