continuous expansion of the output and application range of plastic-wood
composite materials, problems such as poor toughness and creep are
gradually exposed. At present, there are many
researches on strengthening and toughening of plastic-wood composites.
The main methods include adding reinforcements (rigid particles,
reinforcing fibers), improving the toughness of plastic substrates
(plastic modification treatment), and using compatibilizers to improve
biomass fibers and polymerization. Interfacial compatibility between objects, etc. Reinforcing
fibers have been widely used in polymer composites, and they are also
effective in strengthening and toughening plastic wood. The fibers
commonly used in composite materials can be divided into two categories:
organic and inorganic fibers. Organic fibers can be classified into
natural ones. Cellulose fibers and synthetic fibers, which can be further divided into metal fibers and non-metal fibers. Different
types of fibers can be selected for different reinforcement purposes,
such as increasing modulus, strength or toughness.
Glass fiber reinforced plastic wood composite
Glass fiber has the characteristics of high tensile strength, high modulus of elasticity and wear resistance. It is the first fiber used to reinforce resin composite composites. There are many researches on glass fiber reinforced plastic wood composites. The glass fiber is used to reinforce the plastic wood by first granulation and hot pressing.
The powder/high density polyethylene (HDPE) composite material, namely glass fiber, wood powder and plastic, interacts to form a stable three-dimensional structure. This three-dimensional structure exists as a strong skeleton in the plastic matrix, preventing the generation of cracks. And expansion, thereby improving the mechanical strength and impact resistance of the composite; the results also show that the mechanical properties of the wood-plastic composites increase first and then decrease with the increase of glass fiber content. The mechanical strength of glass fiber reinforced plastic-wood composites has a "critical value" of fiber content. When the fiber content is less than "critical", the fiber is too small, and the reinforcing effect is not obvious; if the fiber content is too much, fiber agglomeration will occur, resulting in fiber agglomeration. The mechanical properties of the material decrease. However, the "critical value" is not a fixed value and will vary depending on factors such as the length of the fiber, the type and content of the plastic substrate, the processing technology (processing temperature, molding method, etc.).
Mineral fiber reinforced plastic wood composite
Mineral fibers are used as reinforcing materials in basalt fiber and mineral wool. Basalt fiber and glass fiber have similar properties. It is a new type of inorganic high-performance fiber which is made by rapidly extruding basalt rock composed of oxides such as silica, alumina, calcium oxide, iron oxide and titanium dioxide. With high strength and high modulus, it also has excellent properties such as high temperature resistance, high compressive strength and high shear strength. It is suitable for use in various environments and is widely used in composite materials.
Plastic-wood composite materials have been developed at a high speed for more than 20 years with their unique environmental advantages. After experiencing the bottleneck period at this stage, the next step is bound to develop towards high efficiency, high performance and high quality. It is an effective method to increase the strength of wood-plastic composites by adding reinforcing fibers, especially to improve the impact resistance of wood-plastic composites. It is of great significance for expanding the application of plastic-wood composites. However, fiber-reinforced plastic-wood composites are still in the research stage, and there is still a long way to go before industrialization. The following aspects need to be solved:
1) Further increase production efficiency. As far as ordinary plastic-wood composite materials are concerned, the current extrusion production efficiency in China is generally low, and the extrusion speed is less than 1 m·min-1 on average. Improving production efficiency can be started from the stability of raw materials, optimization of formula, improvement of equipment and improvement of process level. The most important one is the improvement of extrusion equipment and process, achieving high-efficiency plasticization, low-temperature extrusion and precise determination. And effective cooling is the key to improving the efficiency of extrusion production. For fiber-reinforced high-performance, high-quality plastic wood products, to achieve rapid industrialization, the improvement of production efficiency is imperative.
2) Develop special equipment for fiber reinforced plastic wood composite materials. The fiber is easy to "bridge" when feeding, and it is not easy to disperse evenly in the matrix, and it is easy to agglomerate, and excessively intense dispersion shearing will cause most of the fiber to break, especially for softer flexible fibers. It is obvious. To solve these technical problems, it is necessary to improve and improve the existing equipment. For example, in the mixing equipment, it is possible to consider a special screw for the melt distribution of the wood-plastic composite material with high viscosity characteristics, which not only achieves the effect of fiber dispersion but also does not affect the fiber. Produces excessive shear.
3) Develop continuous fiber reinforced plastic wood composite technology. Continuous fibers have been widely used in reinforced polymer composites, and there are many molding methods available, such as pultrusion, injection molding, winding, and immersion hot pressing. The reinforcing effect is obviously better than short cutting. fiber. Plastic wood composites have been studied less in continuous fiber reinforcement, and no mature reinforcement technology has been formed. The difficulty lies in the low fluidity of the plastic-wood composite melt and the limitations of molding processing.
4) Develop a market for high performance plastic wood composite materials. Most of the wood-plastic composite materials currently presented to the public are decorative materials with low added value and low performance, such as outdoor decking, pavilions, fences, exterior wall hanging boards, indoor hanging sheds and interior wall decorative boards, etc. High-value-added car seats, interiors, and wood-wood composites that require high strength or impact resistance, such as doors, windows, and furniture. The development of these market areas will increase the demand for high-performance plastic-wood composite materials, which will lead to the industrial development of fiber-reinforced plastic-wood composite materials.
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