Excessive moisture content in raw materials during the production of wood-plastic composites (WPCs) can lead to several issues. Firstly, water vaporization during high-temperature plasticization creates bubbles, resulting in surface pitting and internal porosity. Secondly, excessive moisture causes severe melt foaming, disrupting melt homogeneity and causing unstable extrusion processes. In severe cases, this may lead to product cracking and significant mechanical property degradation. Therefore, Yongte's technical team recommends strictly controlling wood powder moisture content below 3%. The specific threshold should be adjusted based on substrate type, product structure, and processing techniques, with the core principle being to prevent moisture vaporization during high-temperature plasticization to avoid product defects.
① The defects of the product are as follows: the moisture in the raw material is vaporized in the high-temperature section of the extruder, which leads to the formation of a large number of bubbles. Consequently, the product surface becomes pockmarked, the interior becomes porous, and the section may delaminate. In serious cases, the product may crack, directly affecting its appearance and structural integrity.
② The production process becomes unstable: moisture in raw materials reduces melt viscosity and disrupts homogeneity, affecting extrusion pressure stability and drawing speed consistency. This leads to dimensional deviations and bending deformations (such as the wall panel bending issue you previously noted) in the final product.
③ Product performance degradation: Internal bubbles and pores in the product significantly reduce its tensile strength, flexural strength, and weather resistance, leading to mechanical property deterioration and decreased aging resistance, thereby directly shortening the product's service life.
④ Increased equipment wear: Hydrolysis between water vapor and the substrate (particularly thermoplastic resins like PE/PP) generates corrosive substances, accelerating corrosion and wear of critical components such as screws and barrels, thereby raising maintenance costs and downtime risks.
① Recommended equipment: Yongte Double-Step Drum Dryer, a continuous drying system with temperature and humidity control. It features simple operation and maintenance, low energy consumption, high output, and is ideal for large-scale production.
② Drying parameters: temperature 100~120℃, drying time adjusted according to the moisture content of wood powder to ensure the moisture content of the output meets the standard.
③ Precautions: After drying, the product must be stored in a sealed container to prevent re-humidification of wood powder. If the workshop has high humidity, drying may be performed prior to material mixing.
In the mixing stage, Yongte uses a high-efficiency thermal mixer to control the mixing temperature at around 105°C. By appropriately extending the mixing time, it helps to remove residual moisture from the wood powder, thereby further reducing the moisture content of the raw materials.
Granulation stage: For PP/PE wood-plastic composites, Yongte employs a high-efficiency parallel twin-screw exhaust granulation extruder. This equipment actively removes residual moisture from the raw material during the plasticizing phase through its exhaust system, further reducing the moisture content.
Extrusion stage: Yongte equips the extruder with a high-efficiency vacuum exhaust system. The vacuum pump is precisely positioned in the plasticizing section of the conical twin-screw extruder. When moisture in the raw material vaporizes due to heat, it can be rapidly extracted by the vacuum pump, effectively preventing adverse effects on product quality caused by water vapor.
