Effects of Antioxidants on Photodegradation of Wood Flour/Polypropylene Composites during Artificial Weathering

The influence of antioxidants and of their compound systems were evaluated relative to the photodegradation of wood flour/polypropylene (WF/PP) composites using ultraviolet accelerated weathering. Six groups of samples were exposed in an accelerated weathering tester for a total duration of 960 h. The surface color, gloss, and flexural properties of the samples during weathering were tested. In addition, the weathered surfaces were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TG). The results revealed the following: (1) after weathering, all samples showed significant color fading and gloss change; (2) composites containing antioxidants showed less loss of flexural strength, fewer surface cracks, and better thermal stability after weathering than the control composite; (3) the crystallinity of polypropylene increased in weathered samples due to recrystallization of lower molecular weight polypropylene; and (4) antioxidant 168 (AO-168) was beneficial to color stability at the early stage of weathering, while composites containing 0.2% antioxidant 1010 (AO-1010) and 1.0% AO-168 (AO-1) maintained the highest retention ratios of flexural properties during weathering