Can recycled PET be used to produce WPC products?
Customers often request to use recycled PET for making WPC products. However, the application of PET (polyethylene terephthalate) in wood-plastic composites (WPC) is currently limited, primarily due to a fundamental conflict between its physical and chemical properties and the processing requirements of WPC. The following is an analysis of the specific reasons:
1. High-temperature processing leads to carbonization of plant fibers. PET has a high melting point of 250-265°C, while the upper temperature limit for WPC processing typically does not exceed 200°C. When PET is mixed with wood fibers and heated to their melting point, the hemicellulose and lignin in the plant fibers begin to decompose at around 200°C, forming carbonized particles. This carbonization not only destroys the fiber's reinforcing properties but also causes the surface of the finished product to darken and degrade mechanical properties.
2. Poor interfacial compatibility, requiring complex modification. PET's non-polar molecular structure lacks chemical affinity for the hydroxyl groups (polar groups) on the wood fiber surface, resulting in weak interfacial bonding.
3. High melt viscosity and processing difficulties.
PET's melt viscosity is 3-5 times that of PE, resulting in poor fluidity, leading to uneven fiber dispersion, mold filling difficulties, and severe equipment wear.
4. Poor hydrolysis resistance and short outdoor life.
PET is susceptible to hydrolysis in high-temperature and high-humidity environments, breaking ester bonds and causing a decrease in molecular weight and deterioration in mechanical properties. Wood-plastic products are often used outdoors (such as flooring and fencing), where they are exposed to rain and UV rays for a long time, making PET's hydrolysis problem particularly prominent.
In summary, PET's high-temperature sensitivity, poor interfacial compatibility, high melt viscosity, and hydrolysis resistance limitations present significant technical bottlenecks for its application in the WPC industry. Therefore, under current technological conditions, PET is not suitable for the production of WPC products.
