Effects of natural weathering on the properties of recycled polypropylene composites reinforced with rubberwood flour

• Composites based virgin PP had smaller loss of MOR and MOE than based recycled PP.
• Composites with 1 wt% UV stabilizer had smaller loss of MOR and MOE than without.
• Increase of rubberwood flour content in composites increased loss of MOR and MOE.

The effects of natural weathering on the physical and mechanical properties of polypropylene (PP)/rubberwood flour (RWF) composites were investigated for various compositions, with different grades of plastic (virgin and recycled) and varied contents of wood flour and ultraviolet (UV) stabilizer. Composite panels were manufactured using a twin-screw extruder. Weathering sharply changed lightness (L*) and discoloration, and slightly reduced flexural strength (MOR) and modulus (MOE) of the PP/RWF composites up to 120 days and then clearly decreased after 180 days. Virgin PP had smaller relative changes of lightness and smaller relative loss of hardness, MOR, and MOE than recycled PP (rPP), both in composites and as unfilled plastic. Increasing RWF content from 25 to 45 wt% in composites increased the change of L* and loss of MOR, MOE, and maximum strain. Addition of 1 wt% UV stabilizer reduced change of L* and loss of hardness, MOR, MOE, and maximum strain, compared to composites without UV stabilizer.