Effect of calcium and zinc carboxylates on the thermal stabilisation of PVC |
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Authors: | MK Naqvi PA Unnikrishnan YN Sharma IS Bhardwaj |
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Institution: | 1. Research Centre, Indian Petrochemical Corporation Ltd, P.O. Jawahar Nagar, Vadodara-391 346, Gujarat India;2. Department of Applied Chemistry, University of Cochin, Cochin-22, India |
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Abstract: | Metal carboxylate stabilisers are believed to replace labile chlorines in PVC with more stable ester linkages resulting in an increase in the stability of the polymer. In the present work, effects of combinations of stearates, palmitates and laurates respectively of zinc and calcium, in various proportions, on the thermal stability of PVC were studied. Combinations of palmitates and stearates having more than 75 mol% of calcium salt were found to increase the stability of the polymer. The combinations of the three carboxylates showed the following order of stabilising: palmitate > stearate > laurate. This effect is explained in terms of a critical chain length of the n-alkyl group of the carboxylate anion which is most effective in the stabilising process. Highly crystalline, low molecular weight polyethylenes are used as plasticisers for PVC. They were found to have a stabilising effect explained in terms of a dilution effect by the non-polar polyethylenes on the polar interactions in PVC; compatibility of polyethylenes with PVC is the limiting factor in this stabilisation. |
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