Abstract : A brief summary of the origin and status of wood-plastic composites (wpc) is presented, and the progress made in performance improvement and process equipment at home and abroad are described. Analyzed the current status of the field and the future development direction, and prospected the future application fields and market prospects of wood-plastic composite materials
1 The origin of wood and plastic (15753708086)
Promote the industrialization of wood-plastic composite material probably originated in the 1980s, mainly in the birthplace of the United States. Wood-plastic composite (wpc) is a new type of material that is made of wood fiber or vegetable fiber as the main component and is pretreated to be combined with thermoplastic resin or other materials. . Compared with wood, it has good co-directionality, weather resistance and dimensional stability. The product is not afraid of insects, does not decay, is not easy to absorb water and deformation, has good mechanical properties and is more durable. Compared with plastics, it has better hygienic properties, and the surface is easy to decorate. It can be printed, painted, sprayed, covered, etc., and its environmental performance is also good. [1]
2 The status of China's wood and plastic
Research and development of wood-plastic composite materials in China starting in the mid-1990s, industrialization of composite materials research and development more than a decade later than foreign WPC. However, the amount of sawdust produced by wood processing in China is very large. Other natural fibers, such as rice bran, reach 10 million tons, and the amount of waste plastics produced in the city reaches 2.4-2.8 million tons . [2] In particular, it is worth mentioning that wood-plastic composite materials not only can be used as raw materials for processing waste plastics and waste wood, but also can be recycled and reused. This is of great significance for reducing environmental pollution and protecting forest resources. Development provides an inherent advantage. After years of unremitting efforts by many wood-plastics people, the young wood-plastics manufacturing industry has become one of the few industries in China's manufacturing industry that can enjoy equal rights with European and American developed countries' manufacturers.
3 classification of wood products
Wood plastic products are divided into ordinary wood-plastic composite materials, micro-foam wood-plastic composite materials.
Since ordinary WPC plant fibers are compressed during processing resulting in product density is too large in recent times traditional wood density, to transport, construction and processing bring some difficulties. And because the fibers themselves hydrophilic, hydrophobic plastic, so that the binding force between them is small, leading to mechanical tensile and flexural strength than the product of unfilled plastic smaller. The addition of plant fibers reduces the toughness of the plastic itself, and the impact strength decreases accordingly.
Compared with ordinary wood-plastic materials, the micro-foamed wood-plastic composite material can passivate the crack tip due to the presence of a good cell structure inside the material, and prevent crack propagation; thus, it can effectively overcome the large brittleness and ductility of the general wood-plastic composite materials. and low impact stress disadvantages and reduces the density of the material, not only to save raw materials, and the septum, sound insulation performance is good. In the building materials, automotive interiors, aerospace, logistics, gardens, interior decoration and other aspects have been widely used . [3]
4 wood plastic formula
4.1 Content and Trends of Formula Research
The research contents of wood-plastic composite materials at home and abroad mainly include types of wood flour, surface modification of plastics, dosage of wood flour, amount of filler, type and amount of foaming agent, processing aids, and process parameters. Foaming degree, cell structure and distribution, as well as the final impact on the mechanics and other properties of the product, such as tensile strength, bending strength, impact strength, weatherability and flame retardancy. For the current domestic market, the research direction of the formula is to reduce the cost at the premise of ensuring product performance. The main means is to increase the amount of filler CACO3 and wood flour.
4.2 Achievements
Through wood-plastic profile formulation test, wood-plastic door panel formulation test, wood-plastic building template formulation test. The process parameters such as extruder temperature, extrusion pressure and screw rotation speed, the amount and type of foaming agent, and the amount of wood flour added to the foam were investigated; different additives ( ACR , CPE , lubricants, etc.) The effect of processing performance and use performance of wood-plastic composite materials; through the addition of low-cost fillers and recycled materials, to reduce the cost of wood and plastic.
5 wood processing equipment
At present, the main molding methods of wood-plastic composites are continuous extrusion molding and injection molding. Because of its advantages such as short processing cycle, large output, high efficiency, and simple molding process, the continuous extrusion method has wider application in industrial production than other processing methods ( molding and injection molding ) .
The equipment currently used for the extrusion of wood-plastic composites is mainly single- and twin-screw extruders. [4]
Single-screw, because the single-screw extruder is mainly based on friction to make the components mixed evenly, the plastic refining capacity is not strong, wood powder filled polymer makes the melt viscosity becomes larger, the fluidity becomes worse, extrusion is difficult, the material is The residence time in the barrel is long, it is easy to scorch, and at the same time, the exhaust effect is poor, which limits its application in the production of wood-plastic composite materials.
The use of a single screw to produce WPC requires mixing and granulating of the material before extrusion. Due to the weak single-screw material transport and plasticizing ability, the single screw extrusion of wood and plastic currently uses single-screw plasticizing and mixing is not effective. The characteristics used to produce wood-plastic profiles with patterns.
Twin-screw, compared with single-screw extruder, twin-screw extruder is mainly based on the positive displacement principle of conveying materials, there is no pressure reflux, exhaust and plasticizing effect is better, the material mixing is more uniform, wood powder in the barrel The residence time is short, it is not easy to scorch, and the WPC can be produced using powder , so the wood-plastic composite processing equipment is mainly a twin-screw extruder.
My company from 2009 began developing the production of wood-plastic twin-screw device, after four years of continuous improvement optimization, now we have a mature wood double cone (51/105, 65/132, 80/156, 92/188) full Series extruders have reached the domestic advanced level. In order to adapt to the increasingly fierce competition in the wood-plastic industry, improve the competitiveness of products, and adapt to the needs of low-cost formulas, the twin-screw extruders produced by our company have also been optimized and improved on the screw structure, increasing the strength in the homogenization section. The mixing unit and the method of changing the width and groove of the screw section of the feeding section have improved the plasticizing ability of the screw, thereby realizing the normal production of highly filled, high-foaming, and low-cost composite materials.