On wood plastic composites

Briefly speaking, wood plastic composites 12

1. Characteristics of wood plastic composites

good processability. Wood plastic composites contain polyester and fiber, so they have similar processability with wood. They can be sawed, nailed and planed. The production of woodworking high-speed trains also greatly increases the demand for polyurethane adhesives, which can be completed with tools, and the nail holding force is significantly better than other synthetic materials

good strength properties wood plastic composites contain polyester, so they have good elastic modulus. In addition, because it contains wood fibers and is cured by resin, it has the same physical and mechanical properties as hardwood, such as compression resistance and impact resistance, and its durability is significantly better than ordinary wood materials

excellent water and corrosion resistance wood plastic materials and their products can resist strong acid and alkali, water and corrosion, and do not reproduce bacteria, are not easy to be eaten by insects, and do not grow fungi

excellent adjustable performance by adding different additives, polyester can undergo polymerization, foaming, curing, modification and other changes, thus changing the density, strength and other characteristics of wood plastic materials, meeting the special requirements of anti-aging, anti-static, flame retardant and so on

there are a wide range of raw materials. In addition to using a certain amount of additives, more than 95% of the raw materials of wood plastic materials are polyester and wood fiber, which have a wide range of sources and relatively stable supply channels

II. Application of wood plastic composites

packaging products such as pallets and packaging boxes. Wood plastic materials are mainly used in the packaging industry, such as pallets (also known as pallets in Southeast Asia), packaging boxes, container containers, etc., and the consumption is quite large. Just take pallets as an example, the consumption of pallets in North America is as high as more than 200 million. According to the statistics of Japan Pallet Association (JRP), the consumption of pallets in Japan is about 6million per year. The Pallet Professional Committee of China Federation of logistics and purchasing predicts that the average use of wooden pallets in China may exceed 20million per year in recent years

wood plastic materials for storage products such as planking and beam laying are suitable for shelf planking, sleepers, beam laying, floors, etc. used in the storage industry because of their moisture resistance and moth resistance. In China, although the application of wood plastic materials in the storage industry has just begun, in the first half of 2002, the amount of wood plastic storage planks used in the pharmaceutical and grain storage industries reached more than 80000 square meters, and the amount of wood plastic sleepers used in the military field reached 200000 meters

arbors, chairs, flower pots, garbage cans and other urban construction supplies made of wood plastic materials, such as arbors, chairs and so on, are waterproof, moisture-proof and corrosion-resistant, and have long service life and low price. They are widely used in North America. More than 70% of gardens and roadside seats in Vancouver, Canada, are made of wood plastic materials

building materials and supplies such as houses, floors and building templates in recent years, there are more and more houses, outdoor floors, sunshine houses, docks, guardrails and other products made of wood plastic composites in North America. The annual output value of processing and manufacturing such products is as high as hundreds of millions of dollars

with the continuous improvement of people's understanding of wood plastic materials, the technical level of wood plastic composites continues to improve, and the application field of products has also expanded in recent years. The product research and development of automobile interior decoration, composite pipes, railway sleepers, carriage box plates, cable protective tubes and well covers are also stepping from the demonstration stage to the application test stage. It is believed that the application field of wood plastic products will be further expanded in the near future

III. current situation and development trend of wood plastic composite technology in foreign countries

although wood plastic composite technology was proposed earlier, it has only been more than ten years since it was really studied and applied abroad. Relatively speaking, some European and American countries have relatively more applications, and dozens of enterprises and research institutions are engaged in production and R & D, including the famous Onyx company, dury Inc, Tim Tech Inc and David standard manufacturer

at present, the use of wood plastic composites in North America has taken on a considerable scale, and its application field has also developed from relatively simple low value-added products to relatively complex high value-added products such as houses, buildings, pipes, etc. the technology of wood plastic composites is also becoming more and more mature due to the development of the market, especially in the aspects of mixing, molding, temperature control, speed, cutting, formula, etc. bending tests are carried out on another machine; Two testing machines can also be used for fastener testing, sample supply and management; Or a Rockwell hardness tester and a tensile testing machine have been greatly innovated and improved to make them more suitable for the current situation of raw material sources, effectively improve the strength and reduce the cost. Take a Canadian American joint venture company located in Toronto as an example. By the end of 1999, it had 43 production lines of various wood plastics, and plans to invest another 66 production lines for new products with high added value. The total investment is about 35.64 million US dollars, and the annual output value is close to 500 million US dollars

with the continuous development of wood plastic material technology, its development trend may include the following aspects:

first, the selection of raw materials is developing in a wide range. After cleaning the recycled single component waste plastics (PE, PP, PVC, ABS, etc.), the wood plastic products can be processed and manufactured by adding specific modifiers

the second is the development of special equipment. The processing mode has developed from single screw extrusion to other traditional plastic processing, and from water-cooled molding to air-cooled molding

the third is the development of processing technology. Introduce foaming technology, and develop from high foaming to low foaming and micro foaming

fourth, the products have developed from low added value (such as wood plastic pallet and storage floor) to high-end direction (such as interior decoration materials)

fifth, from single extruded profiles to composite coextrusion and package coextrusion

IV. processing technology of wood plastic composites

the technical feature of wood plastic materials is to mix two kinds of different materials with great differences, that is, wood materials are combined into one

wood powder (or fiber powder of crops) can withstand high temperature and high pressure in high-speed flight. As an organic filler for plastics, it has many advantages that other inorganic fillers cannot compare, such as wide source, low value, low density, good insulation and so on. However, it has not been widely used like inorganic fillers, mainly because of poor compatibility with matrix resin and poor dispersion effect in molten thermoplastic, resulting in difficulties in fluidity and extrusion processing. Because the wood flour is mainly cellulose, which contains a large number of hydroxyl groups, which form intermolecular hydrogen bonds or intramolecular hydrogen bonds, so that the wood flour has water absorption, the moisture absorption rate can reach 8%-12%, and the polarity is very strong. Most of the thermoplastics are non-polar and have flowing water, so the compatibility between them is poor, and the adhesive force of the interface is very small. It is necessary to use additives to modify the surface of plastics and wood flour to improve the affinity of the interface between them. The modified wood flour has reinforcing property, which can well transfer the stress between filler and plastic, so as to enhance the strength of fumata material

extrusion molding, hot pressing molding and injection molding are the main molding methods for processing wood plastic composites. Due to the short processing cycle and high efficiency of extrusion molding, extrusion molding method is a commonly used process route

from the perspective of the technological characteristics of wood plastic composites, there are mainly the following categories:

from the perspective of raw material use, one is that the plastic raw materials used are pure plastic or commercial grade plastic; The other is the use of single component waste plastics with certain characteristics

from the perspective of processing technology, one is the two-step molding method, that is, plastic and wood powder are granulated before molding; The other is one-step molding method, that is, plastic and wood powder are mixed and directly processed

in terms of molding mechanism, one is physical molding, that is, using hot-melt adhesives to bond plastic and wood flour together in the molding process. The other is physicochemical molding. By adding additives, the raw material mixture and relatively low molecular weight additives can be transformed into polymer state under the control of pressure and temperature, resulting in inaccurate data. The internal structure of the material made by this process is completely the molecular structure regenerated after fusion. Therefore, the bending, compression and impact strength of wood plastic products produced by other processes can be achieved