Effects of UV weathering on surface properties of polypropylene composites reinforced with wood flour, lignin, and cellulose

- The addition of lignin, cellulose and wood flour accelerated the surface photodegradation process of PP.
- Cellulose-based composites exhibited better color stability, but showed a lot deterioration in its flexural properties after weathering.
- Composites containing lignin showed less loss of flexural properties, less cracks, and better hydrophobicity on weathered surface than other types of composites.
- The stabilization and antioxidation effects of lignin were proved.

In this study, the influence of accelerated weathering on polypropylene composites reinforced with wood flour (WF), lignin, and cellulose at different loading levels were evaluated. Six groups of samples were exposed in a QUV accelerated weathering tester for a total of 960 h. The surface color, surface gloss, contact angle and flexural properties of the samples were tested. Besides, the weathered surface was characterized by SEM and ATR-FTIR. The results revealed that (1) the discoloration of composites was accelerated by the presence of lignin, especially at high content; (2) composites containing lignin showed less loss of flexural strength and modulus, less cracks, and better hydrophobicity on weathered surface than other groups, confirming its functions of stabilization and antioxidation; (3) cellulose-based composites exhibited better color stability but more significant deterioration in flexural properties after weathering compared to other composites, suggesting that such kind of composites could not be used as load-bearing structure in outdoor applications.