The Processing of Wood Plastic Composite Materials
Artificial zeolites, the aluminosilicate molecules that capture the powder and absorb odors in the material, can be added to the polymer. The adsorbent traps small organic molecules that produce odors through the large number of crystalline cavities in the powder. Molecular capture adsorbents have been successfully used in polyolefin extruding tubes, injection and extrusion blow molding vessels, isolation packaging materials, extruding packaging and sealing materials. Molecular adsorbed powders can also be used as dehumidifiers to remove moisture from plastics.
1. Extrusion products of different sizes and shapes increase the diversity of wood plastic composite products.
When profiles are not required to have a continuous sheet structure or components with a complex structural design, WPC profiles can be injection molded or molded. Processors sometimes face the problem of how to fully mold wood plastic composite materials during processing. To solve this problem, they need to reduce the amount of wood filler to increase the fluidity of the melt.
Since 200° C is the upper limit for the operating temperature of wood plastic composite materials, some resins, such as PET, whose melting point exceeds 200° C cannot be used in wood plastic composite materials.
Moisture degrades the properties of the composite and also helps to breed microorganisms, so be sure to remove moisture before using wood fillers. Before the processing of wood packing to dry treatment, generally required to deal with the moisture content of less than 1~2%.
Wood plastic composite material processing machinery requires feeding equipment, drying equipment, extrusion equipment and molding equipment, as well as some necessary downstream equipment such as cooling water tanks, traction equipment and cutting equipment.
2. Wood plastic composite material handling
Suitable additives are needed to modify the surface of polymer and wood powder to improve the interface affinity between wood powder and resin.
The dispersion effect of wood powder with high filling amount in the molten thermoplastic is poor, making the melt fluidity poor and extrusion molding difficult.
The plastic substrate also needs to add various additives to improve its processing performance and the service performance of its products.
3. The loading process
Wood powder structure fluffy, not easy to extruder screw feeding, especially wood powder containing more moisture often appear “bridge” and “pole” phenomenon.
The instability of feeding will lead to the phenomenon of extrusion fluctuation, resulting in the reduction of extrusion quality and yield. Interruption of feeding, prolonged stay time of materials in the cylinder, resulting in material burn color, affecting the internal quality and appearance of products.
The forced feeding device and reasonable conveying mode are adopted to ensure the stability of extrusion.
4. Exhaust during processing
The small molecule volatilization substance that contains in wood powder and moisture bring defect to the product extremely easily, and pretreatment cannot remove them completely again. Therefore, the design of the exhaust system of wood plastic composite products extruder should be paid more attention than ordinary plastic extruder.
To a great extent, the better the exhaust effect, the better the extrusion product quality.
5. Configuration design
The screw configuration plays an important role in extrusion of wood plastic composite products. Reasonable screw structure can reduce the friction between screw and wood fiber, produce appropriate shear and dispersion mixing, so that the material system containing a large amount of wood powder can be well uniform plasticizing.
6. Mold design and cooling
In addition to ensuring smooth passage design and reasonable flow distribution, wood plastic composite decks have higher requirements for building pressure capacity and temperature control accuracy.
In order to obtain good fiber orientation and product quality, it is necessary to ensure that the head has enough compression capacity and long shaping section, and even adopt double taper structure in compression section and shaping section.
The thermal conductivity of wood plastic composite products is poor, and its products for the profile, the cooling is more difficult to finalize the design, the use of water cooling to finalize the design. Reasonable design of cooling passage ensures efficient cooling.