Process and Performance of WPC extrusion
Wood, namely wood-plastic composites (WoodPlasticComposites, WPC), mainly using waste instead of the commonly used plastic resin adhesive, and wood flour, rice husk, straw and other agricultural plant fiber as raw material produced a new type of modified environmental protection material, widely used in construction, furniture, packaging, gardens, transportation and other industries.
As an important branch of composite materials in the field of research WPC is highly valued, including aspects such as: the mechanical properties of WPC physical, wood and plastic interface compatibility and preparation process control.
At present, its industrial production molding method used are: extrusion, 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 a wider application.
WPC extrusion technology
An extrusion molding, also known as extrusion molding or extrusion molding, compression is the use 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 Methods.
Extrusion molding almost all thermoplastics. Production of products are pipe, sheet metal, wire wrap and plastic and other materials, composite materials, is a high efficiency, versatile, and adaptable molding method. For the production of wood-plastic composite materials, extrusion process has a stable product quality, low cost, a relatively small investment, etc., so the development of faster.
Production of wood composite extrusion major equipment are screw extruders, including single screw extruder, parallel twin-screw extruders and conical twin-screw extruder.
Features 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 the shear force, high mixing efficiency, but not as good as a single smooth melt pressure control 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, price is generally quite single-screw extruder having a screw diameter 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 is stronger than the single-screw extruder, and extrusion pressure is large than the twin-screw extruder, can be used for direct extrusion profiles. Not only that, there are the characteristics of the material compression ratio, which is the raw material for the low bulk density of wood-plastic composites extrusion process, it is to highlight the advantages of equipment. 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 general can withstand a maximum working 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 with anti-flex, water resistance, chemical resistance and low temperature flexibility and excellent performance, processing performance, low prices. Which, HDPE tensile strength, surface hardness and rigidity than LDPE high, with the continuous improvement of people's living standards, people WPC performance, texture requirements are also improved, so, currently HDPE resin matrix WPC accounted for the majority, are generally used for outdoor component.
PP melt viscosity is small, temperature-sensitive small, 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 weathering 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 it's cold, anti-aging and thermal stability is poor, poor processing performance, these shortcomings can be improved by adding additives such as plasticizers, stabilizers, lubricants, ACR impact additives. PVC high melt strength, can be used for the preparation of plastic foam composites, currently. PVC-based WPC is mainly used in interior decoration materials.