Process and Performance of WPC extrusion

Wood, namely wood-plastic composites (WoodPlasticComposites, WPC), is the use of waste plastics instead of the commonly used resin adhesive, and wood flour, rice husk, straw and other agricultural plant fiber as raw material produced a new type of environmental modification material, widely used in construction, furniture, packaging, garden, transportation and other industries.
As an important branch of composite materials in the field of research WPC is highly valued, including several aspects, such as: physical mechanical properties of WPC, wood and plastic interface compatibility and preparation process control.
At present, its industrial production molding method used are: extrusion molding, injection molding and thermoforming. Since extrusion molding cycle is short, high efficiency, simple molding process, it is compared with other processing methods in industrial production has wider application.
WPC extrusion technology
A molded extrusion molding, also known as extrusion molding or extrusion molding, compression is by means of the screw, so that the heat melted plastic in a pressure driven, forced through a die and a continuous profile having a constant cross-section of method.
Almost all extrusion molding of thermoplastics. Production products are pipe, sheet metal, plastic and cable coverings and other materials, composite materials, is a high efficiency, versatile, adaptable molding method. For the production of wood-plastic composites, extrusion process with stable product quality, low cost, relatively small investment, etc., so rapid development.
Extrusion production of wood-plastic composite materials are the main equipment screw extruders, including single screw extruder, parallel twin-screw extruders and conical twin-screw extruder.
It features a single-screw extruder is at a higher pressure head molten material and stable, but low mixing efficiency, it is generally used for less demanding mixing efficiency profile extrusion, granulation. Single-screw extruder structure is relatively simple, the price is not high.
Twin-screw extruder, especially engaging with the characteristic twin-screw extruder is shear, high mixing efficiency, but not as good as the melt pressure control stationary single screw extruder, a twin-screw extruder, it is mainly used for mixing efficiency requirements of the occasion, such as fiber and plastic composite melt. Twin-screw extruder complex structure, the price is usually quite single-screw extruder screw diameter of multiple machines.
Of course, if the twin-screw extruder with a single screw extruder series combination, and with the auxiliary composition profiles profile extrusion lines, it is able to give full play to their respective advantages. Not only reduces energy consumption, but also helps reduce thermal degradation of the material.
The conical twin-screw extruder, in recent years much attention. Its ability to mix the material stronger than the single-screw extruder, and extrusion pressure is large than the twin-screw extruder, can be used to direct extrusion profiles. Not only that, there are the characteristics of the material compression ratio, which is the raw material for the lower bulk density of wood-plastic composite extrusion process, the equipment is outstanding advantages. However, there are advantages must be missing, in terms of mixing efficiency, conical twin screw extruder is far less than the parallel twin-screw extruder.
Performance comparison of different resin-based WPC
Due to the application of WPC wood fiber filler generally can withstand the maximum processing temperature of 200 ℃, therefore, WPC usually PE, PP, PVC and other relatively low processing temperature of the thermoplastic resin, different matrix resin, which performance quite different.
PE stiffness, tensile strength is small. Compared with other polymers, PE anti-flexure, water resistance, chemical resistance and low temperature flexibility and excellent performance, processing performance, low prices. Wherein, HDPE tensile strength, surface hardness and rigidity than LDPE high, with the continuous improvement of living standards, people on the wood-plastic composite material properties, texture requirements are also improved, therefore, currently HDPE resin matrix WPC accounted for the majority, generally used for outdoor component.
PP melt viscosity is small, not very temperature sensitive, good processing performance. Compared with HDPE, which has pulled high strength, surface hardness, tensile yield strength and stiffness, but easy to crack at low temperatures. PP-based WPC weather resistance than PE based plastic products, so that its scope of application subject to certain restrictions.
PVC has a rigid, high-strength, low cost, etc., has good adhesion and coloring, but its cold resistance, aging resistance and thermal stability is poor, poor processing performance, these shortcomings can be improved by adding additives such as plasticizers, stabilizers, lubricants, impact resistance aids the ACR. PVC high melt strength, can be used for the preparation of plastic foam composites currently. PVC-based WPC materials are mainly used in interior decoration.
[Conclusion] There is now editor of the ecological problems and resource crisis more and more attention, so people in the study of WPC also set off a new upsurge. After the emergence of wood-plastic composite materials, natural resources have been fully utilized, reducing environmental pollution problems caused by waste plastic waste and waste wood products and furniture caused. Although China started relatively late in this regard, but the development speed is very fast, industrialized production and processing technology has gradually matured.