What is the max. Moisture content of wood for making WPC products?

The presence of elevated moisture levels within raw materials utilized in the fabrication of wood-plastic composites (WPCs) can precipitate a multitude of complications. Initially, the evaporation of water vapor at high temperatures during the plasticization phase may induce the formation of bubbles, which in turn can cause surface pitting and internal porosity. Furthermore, an overabundance of moisture can result in pronounced melt foaming, thereby disrupting the uniformity of the melt and leading to unstable extrusion processes. In extreme instances, this disruption may culminate in product cracking and a marked diminishment in mechanical properties. Consequently, Yongte's technical team strongly advocates for the stringent regulation of wood powder moisture content to remain under 3%. The precise limit should be calibrated in accordance with the substrate variety, product architecture, and processing methodologies, with the fundamental objective being to avert moisture vaporization during high-temperature plasticization to circumvent product imperfections.

1. Impact of Excessive Moisture Content

Product Defects and Their Impacts Table

2. Yongte reduces the impact of moisture by optimizing equipment design and production processes.

①　In the mixing phase, Yongte deploys a high-efficiency thermal mixer to sustain the temperature at approximately 105°C. The mixer, through an appropriately elongated mixing duration, facilitates the elimination of residual moisture from the wood powder, thereby further diminishing the moisture content of the raw materials.

②　In the granulation phase, Yongte utilizes a high-efficiency parallel twin-screw exhaust granulation extruder for PP/PE wood-plastic composites. This apparatus effectively eradicates residual moisture from the raw material during the plasticizing phase through its exhaust system, further reducing the moisture content.

③　During the extrusion phase, 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. As 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.

3. Equipment for Reducing Moisture of Wood Powder

①　Recommended Equipment: The Yongte Double-Step Drum Dryer, a continuous drying system equipped with temperature and humidity control mechanisms, is recommended. This system boasts straightforward operation and maintenance procedures, reduced energy consumption, elevated output levels, and is particularly suitable for extensive production activities.

②　Drying Parameters: The system operates at temperatures ranging from 100 to 120 degrees Celsius. The duration of the drying process should be modulated in accordance with the moisture content of the wood powder to guarantee that the resultant product adheres to the prescribed moisture standards.

③　Precautionary Measures: Subsequent to the drying process, it is imperative that the product be preserved within airtight containers to avert the re-absorption of moisture by the wood powder. In scenarios where the workshop environment exhibits elevated humidity levels, it is advisable to conduct the drying procedure prior to the commencement of material blending.