Development of polypropylene-based ultraviolet-stabilized formulations for harsh environments

This work reports the outdoor weathering performance of ultraviolet (UV)-stabilized polypropylene (PP) products (using PP resins from Saudi Basic Industries Corporation [SABIC]). Different hindered amine light stabilizers (HALS) were used to stabilize PP-film-based formulations that were exposed for 10 months in harsh outdoor weather of Dhahran, Saudi Arabia. Characterization of the exposed PP film products was done in terms of mechanical and Fourier transform infrared (FTIR) spectroscopic properties. HALS are a very effective light stabilizer for polyolefins. They do not act by absorbing UV radiation, but by inhibiting degradation of the polymer, which has started the formation of free radicals. They function by scavenging radicals. HALS has low volatility and high extraction resistance. The effectiveness of HALS is independent of product thickness. Another advantage is that it provides a significant level of stabilization at relatively low concentration. Some important types of high molecular weight HALS are Chimassorb 944 and Tinuvin 622, and a low molecular weight HALS is Tinuvin 770. These HALS, together with other UV stabilizers, are commonly used in polyolefin stabilization. The PP film formulations were divided into five categories based on the type of HALS incorporated. This was done to derive meaningful comparison of the various film formulations. The characterization data are presented for an exposure period of 10 months. The unstabilized PP films were degraded within 2.5 months of the exposure period. The performance in terms of decrease in mechanical properties and FTIR spectroscopic properties was assessed as a result of natural weathering for UV-stabilized samples. Following outdoor weathering trials, the lifetimes of certain formulations were determined. On the basis of the FTIR spectroscopic properties, it was determined that generally, the HALS-stabilized PP film formulations delayed the formation of oxidation products including esters, carbonyls, and trans-vinylenes.