UV Stabilising Synergies between Carbon Black and Hindered Light Stabilisers in Linear Low Density Polyethylene Films

摘要

The combined effects of selected carbon black pigments and hindered light stabilisers (HALS) on the UV stabilities of linear low density polyethylene film have been studied under UVA and UVB fluorescent radiation sources. While the presence of HALS do not change the chemistry of film photodegradation, whether they are low or high molecular variants, their presence significantly extends film lifetime relative to the sum of the effects of carbon black and HALS individually. These lifetime extensions may be defined in terms of a synergy factor defined with respect to film time to lose a specific percentage of a tensile property, namely t_(20), the time to lose 20% of initial elongation-at-break, or the carbonyl index associated with this condition. It is proposed that possible causes of this synergy are a result of the UV screening effect of the carbon black particles which provide lower concentrations of polymer radicals for the HALS component to interact with and/or an accompanying thermal stabilising effect by the latter as a consequence of the higher polymer local temperature during irradiation of pigmented films.