Although wood plastic composite material
has many advantages, but due to the composite resin and wood powder, on the one hand, the toughness, impact strength and bending strength mechanical properties such as relative not fill plastic will have fallen, on the other hand, the opposite is true of natural lumber, around twice the density is wood, cannot serve as an ideal substitute for wood, so its application is limited by some.
The Expansion of Raw Materials in WPC Products
Adding foaming agent to the raw material of WPC for foaming extrusion, the foamed WPC has a good cellular structure, which can passivate the crack tip and effectively prevent the crack expansion, thus significantly improving the impact resistance and toughness of the material. The product density is close to the wood, while the mechanical strength is higher than wood, which makes it can be used as a good substitute for wood, and the product cost is reduced, which further widens the application range of WPC.
Material formulation design is one of the key steps of PVC wood-plastic composite microcellular foaming. The melt viscosity and stiffness of PVC are increased by adding wood fibre, making it difficult to obtain high porosity. On the other hand, wood powder has strong water absorption and strong polarity, while PVC resin is non-polar and hydrophobic, so the compatibility between the two is poor and the bonding force of the interface is very small. Appropriate additives should be added to improve the interface affinity between wood powder and PVC resin. At the same time also need to add a variety of additives to improve its processing performance and the use of finished products.
Stabilizer in Wood Plastic Composite Decking Products
An ideal stable system should be a reasonable combination of several stabilizers. One of the keys to control the processing technology of WPC is to prevent the thermal degradation of plastics and wood powder during mixing and moulding. The wood powder has poor thermal stability, and cellulose and lignin in it are easy to decompose. When oxygen exists at 190℃ or so, it will start to smoke and change colour. At the same time, due to the close processing temperature and decomposition temperature of PVC, sufficient heat stabilizer must be added in the processing to improve its degradation temperature. In the production of PVC WPC composite microporous foaming materials, the use of composite lead stabilizer, organic tin stabilizer, calcium and zinc stabilizer.
Plasticizer in Wood Plastic Composite material
PVC resin melt flow viscosity is relatively high, and wood powder complex often needs to add plasticizer to improve its processing performance. Add plasticizer can lower processing temperature, molecular structure of plasticizer contained two polar and nonpolar groups, under the high-temperature shearing action, it can into the polymer molecular chain, through the polar group attracted to each other to form uniform and stable system, and its long nonpolar molecule is weakened into the polymer molecules attracted to each other, so as to make the process easier.
Lubricants and lubricants are important influencing factors for extrusion of PVC wood-plastic composite
foamed materials. Suitable lubricants are needed to improve the fluidity and surface quality of extrusion products, and lubricants are good dispersants for pigments in composites. Lubricant has a certain influence on the service life of mould, barrel, screw, surface finish and low-temperature impact performance. Lubricant is divided into the internal lubricant and external lubricant according to function.
Colourant in Wood Plastic Composite Decking Products
Through the reasonable selection and collocation of colorant, we can produce the imitation of black walnut, red walnut, cherry wood and other wood plastic composite foamed materials, so colorant in the wood plastic composite foamed materials production also has a more extensive application, it can make the products have a wood uniform and stable colour.
The Foaming Agent in Wood Plastic Composite material
Generally speaking, the ideal material is that the bubble size in WPC is small and the bubble density is large. The foaming rate is high or low depending on the application and function. Commonly used blowing agent AC blowing agent, CO2, N2 and so on. Foaming agent dosage should be controlled reasonably, too little foaming effect is not good, too much will lead to material decomposition and discolouration, not only can not reduce the density through foaming, improve the impact resistance and toughness of the material, but will make the material brittle, affect the quality of inside and outside.
There are many factors affecting the extrusion of WPC microcellular foamed products, including wood plastic composite material
, formula and process. In the actual production process, formula and temperature, speed, pressure and other process conditions should be reasonably controlled according to the technological characteristics of the equipment, so as to produce qualified products.