In this study, the effect of accelerated freeze-thaw cycling on the stability of co-extruded polypropylene-based wood-plastic composites containing fire retardants was examined. Five fire retardants, namely melamine, aluminum trihydrate, graphite, zinc borate and TiO₂ were incorporated into the shell layer. The results showed that the tensile strength and modulus of all composites declined by around 11–18 % and 5–21 %, respectively. Fourier transform infrared spectroscopy analysis revealed that melamine and zinc borate leached partly from the surface during weathering. Significant changes in the surface morphology of the weathered composites were observed with a scan electron microscope.

Keywords: wood-plastic composites, fire retardants, freeze-thaw cycling.