Effects of inorganic fillers on the natural photo-oxidation of high-density polyethylene

This paper will focus on the natural photo-oxidation of HDPE composites, with several inorganic fillers. Fourier transform spectroscopy (FTIR), ultraviolet spectroscopy (UV), scanning electron microscopy (SEM) and pyrolysis gas chromatography-mass spectroscopy (PGC-MS) were used to analyse the structural changes, the reflection and absorbance of ultraviolet light, the surface morphologies and the volatile oxidation products of samples during natural aging. The study shows that some inorganic fillers, e.g., CaCO3 and wollastonite, can stabilize HDPE a little. In HDPEs filled with these fillers lower degrees of degradation were observed. In contrast, other inorganic fillers more or less accelerated the photo-oxidation degradation. Among them, kaolin, diatomite and mica are the most effective fillers to help HDPE degrade. The inorganic fillers also have some effects on the crystallinity of HDPE. After photo-oxidation, the crystallinity changes of HDPE composites in the bulk did not show any rules, while that in the surface region decreased apparently. The surfaces of the composites after exposure became rough and with cracks, but showed different damage patterns. A seriously damaged surface did not definitely correspond to a great oxidation degree. The remaining volatile oxidation products of the photo-oxidised composites were proven to be mostly a series of n-alkanes. A hypothesis was proposed that the relative absorbances to UV light in 290-400 nm by these fillers are the key factors influencing the photo-oxidation.