Influence of the internal air temperature on properties of wood-plastic composites processed by rotational molding

Abstract

In the processing of wood-plastic composites (WPC) by rotational molding, thermal decomposition of wood can occur due to the high temperatures of the process. However, it can be avoided by controlling the peak internal air temperature (PIAT). In this perspective, the main purpose of this work is to determine how the PIAT and the properties of the rotomolded WPC are related to each other. To achieve this, several materials were processed using different oven temperatures and heating times. As a consequence, the PIAT reached a specific value during the process in each case. Then, characterization tests were carried out to determine mechanical and physical properties of the obtained materials. Finally, using the test results, a relationship between the PIAT and those properties was defined. The rotomolded WPC were made of 85% of recycled high-density polyethylene (HDPER) and 15% of capirona wood particles (CWP), but materials made of 100% of HDPER were also processed. Results show that a PIAT of 208 °C is required for a rotomolded WPC to be fully densified. Under this condition, it has optimal properties and it does not undergo thermal degradation. As for the material made of 100% of HDPER, a PIAT of 233 °C is necessary to reach such state. In addition, using the second derivative of the internal air temperature profiles, the beginning and end of the six phases of the rotational molding process were identified, too.