New environmentally friendly material wood plastic composite material (below)

Third, foreign wood composite materials technology status and development trend

Although the technology of wood-plastic composites was proposed earlier, the history of real research and application abroad has only been more than ten years. Relatively speaking, some European countries and the United States have relatively more applications, and dozens of companies and research institutions are engaged in production and research and development. The famous companies are ONYX, DURY INC, Tim Tech INC and DAVID STANDARD.

At present, the use of wood-plastic composites in North America has reached a considerable scale, and its application areas have also evolved from relatively simple low-value-added products to relatively complex high value-added products such as houses, buildings, pipes, etc. Plastic composite materials technology has also matured due to the development of the market, especially in the mixing, molding, temperature control, speed, cutting, formula, etc., has undergone substantial innovation and improvement, making it more suitable for the current status of raw materials, and effective Increased strength and reduced costs. Take a Canadian-United States joint venture company located in Toronto as an example. By the end of 1999, it had owned 43 types of wood-plastic production lines and planned to invest 66 additional production lines for new products with high added value, with a total investment of approximately US$35.64 million. . The annual output value is close to 500 million U.S. dollars.

With the continuous development of wood-plastic materials technology, its development trend may have the following aspects:

The first is the selection of raw materials to develop in a wide range of directions. After the recovered single-component waste plastics (PE, PP, PVC, ABS, etc.) are cleaned, special modifiers can be added to process the wood-plastic products.

The second is the development of special equipment. The processing method is developed from the single screw extrusion to other traditional plastics processing direction, from the water cooling forming to the air cooling forming development.

The third is the development of processing technology. The introduction of foaming technology, from high foam to low foam, micro-foaming direction.

Fourth, the products are developed from low value-added (such as wood-plastic trays, storage floors) to high-end (such as interior decoration materials).

The fifth is the development of a single extrusion profile in the direction of composite coextrusion and co-extrusion.

Fourth, wood plastic composite processing technology

The technical feature of wood-plastic materials is that two different materials with different majorities are mixed together, that is, wood and plastic are combined into one.

Wood powder (or fiber powder of crops) is an organic filler of plastics, and has excellent properties that are not comparable to many other inorganic fillers such as wide sources, low prices, low density, and good insulation properties. However, it is not widely used as an inorganic filler. The main reasons are: First, the compatibility with the matrix resin is poor, and the second is that the dispersion effect is poor in the molten thermoplastic, resulting in poor fluidity and difficulty in extrusion molding. Since the main ingredient in wood flour is cellulose, containing a large number of hydroxyl groups, these hydroxyl groups form intermolecular hydrogen bonds or intramolecular hydrogen bonds, making wood flour absorbent, moisture absorption rate of up to 8% to 12%, and very strong polarity . Most thermoplastics are non-polar and hydrophobic, so the compatibility between the two is poor and the bonding strength at the interface is small. It is necessary to improve the affinity of the interface between the plastic and wood flour surfaces by using additives to modify the surface. The modified wood flour has a reinforcing property and can transfer the stress between the filler and the plastic well, thereby achieving the effect of enhancing the strength of the composite material.

Extrusion molding, hot press molding and injection molding are the main molding methods for processing wood-plastic composite materials. Due to the short cycle time and high efficiency of extrusion molding, the extrusion molding method is a relatively common process route.

From the characteristics of wood-plastic composite technology, there are mainly the following categories:

From the use of raw materials, one type of plastic raw materials used is pure plastic or commercial grade plastic; the other is the use of single-component waste plastics with certain characteristics.

From the point of view of the processing technology, one type is the two-step forming method, that is, plastic and wood flour are granulated and then processed by molding; the other one is a one-step molding method in which the plastic and the wood powder are directly mixed and processed.

From the aspect of the molding mechanism, one type is physical molding, that is, using a hot-melt adhesive to bind plastic and wood flour together during molding. The other type is physicochemical molding. By adding additives, under the control of pressure and temperature, the raw material mixture is converted into a polymeric reticular fiber material together with relatively low molecular additives. The material formed by this process has an internal structure that is completely regenerated after fusion. Therefore, it can achieve the unmatched bending, compression and impact strength of wood-plastic products produced by other processes.