EFFECT OF PROCESSING ON THE THERMAL AND PHOTOOXIDATIVE BEHAVIOR OF 2-HYDROXYBENZOPHENONE STABILIZERS IN POLYOLEFIN FILMS - INFLUENCE OF 2,2,6,6-TETRAMETHYLPIPERIDINE SUBSTITUTION

The effect of processing history has been examined on the thermal and photostabilising action of two types of 2-hydroxybenzophenone light st abilisers in polypropylene (PP) and Philips grade high density polyeth ylene (HDPE). Both differ in terms of the nature of the 4-substitution , one with a butoxy-4-amino-2,2,6,6-tetramethylpiperidinyl group and t he other with an n-octoxy group. Using infrared absorption spectroscop y (FTIR), hydroperoxide analysis and differential scanning calorimetry , the former stabiliser is shown to exhibit both effective thermal (ov en ageing and melt) and light stabilisation in the two polyolefins. Ca rbonyl growths are consistent with initial hydroperoxide concentration s in the polymers as well as the polymer type and its processing histo ry. In both polymers, processing history reduces the stability of the stabilisers and their stabilising effectiveness in the polymers due to the formation of increased levels of hydroperoxides. The hindered pip eridine stabiliser exhibits strong autoretardation on both thermal and photoageing, illustrating its behaviour as an effective photothermal anti-oxidant, the effect being dependent upon the processing history o f the polymer. This is in marked contrast to the 4-n-octoxy stabiliser which exhibits no thermal antioxidant behaviour. Differences in the b ehaviour of the two types of stabiliser and the complex interplay of p rocessing history are discussed.