The effect of carbon black and HALS hybrid systems on the UV stability of high-density polyethylene (HDPE)

Abstract

In the present study, attempts were made to study the effect of a hybrid UV stabilizing system on high-density polyethylene (HDPE). For this purpose, high molecular weight PE was used to prepare samples containing different amounts of hindered amine light stabilizer (HALS), carbon black (CB) and HALS/CB systems as UV stabilizers. All samples were exposed to UV irradiation simulating 4 and 8 years of exposure to solar irradiation in central part of Iran (Yazd). FTIR results were used to estimate the carbonyl index (CI) of the samples. It showed that CI increased as UV exposure time increased. However, it was found out that in the samples having both stabilizers (HALS/CB), CI value was much less compared to other samples indicating that the presence of hybrid system would show a synergism effect on UV stabilization of HDPE. The gel content of all samples was measured and it confirmed the same results. The PECH sample (containing HALS and CB) showed the least gel content after equivalent time of 4 and 8 years of exposure (2 and 3.5 wt%, respectively) which was in accordance with CI result. Furthermore, the effect of different UV stabilizing systems on the mechanical properties of HDPE was studied. For this purpose, elastic modulus, elongation-at-break and yield stress of the samples were measured. It was found out that HALS/CB hybrid system preserved the mechanical properties of HDPE much better than the other systems, which was attributed to the synergistic effect of the simultaneous use of HALS and CB.