Weathering properties of coextruded polypropylene-based composites containing inorganic pigments

Abstract

This study concerns the weathering properties of coextruded polypropylene-based composites containing pigments. Three different pigments were incorporated in the shell layer of the composites: iron oxide, titanium dioxide and zinc oxide. The surface colour, surface gloss and tensile properties were tested. In addition, the weathered surfaces were studied by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The surfaces of the composites containing inorganic pigments were found to have fewer cracks after 500 h of weathering than the surface of the reference composite. The results revealed that the composites containing titanium oxide pigment exhibited better colour stability than the composites made with the other pigments. In spite of its high colour stability in weathering, the tensile properties (strength, Young's modulus and elongation at break) of the composite containing titanium oxide were reduced by weathering. The FTIR analysis revealed that the composite containing zinc oxide had a stabilising effect on polypropylene photo-degradation, which correlates well with the results of mechanical testing, showing that this composite retained its mechanical properties after weathering.