THE MODE OF ACTION OF METAL STEARATE STABILIZERS IN POLY(VINYL CHLORIDE) .4. THE APPLICATION OF FLUORESCENCE SPECTROSCOPY TO CHARACTERIZE CHROMOPHORIC SPECIES

Fluorescence emission spectroscopy has been used to monitor the develo pment of polyenes in poly(vinyl chloride) [PVC] which has been stabili sed with mixtures of pre-heated (180 degrees C) calcium stearate (CaSt (2)) and zinc stearate (ZnSt(2)). Treatment with NaBH4 has been used t o distinguish polyenes attached to carbonylic groups. Emission from ex citations at 245 and 360 nm enabled the development of short polyene s equences and carbonylic polyenes to be followed. CaSt(2) when pre-heat ed and added to ZnSt, and PVC produced high amounts of carbonylic poly enes and lead to secondary reactions yielding large amounts of black m aterial attributed to the action of the prodegradant ZnCl2 formed. Pre -heated ZnSt(2) produced small quantities of longer polyene sequences as shown by a slight yellowing of the PVC, and a pre-heated mixture of the soaps led to small quantities of carbonylic groups and an initial yellow discoloration. For the pre-heated mixture of soaps and pre-hea ted ZnSt(2) the formation of a complex is suggested which interacts wi th the PVC chain from the beginning of degradation; the nature of the interaction being ionic and determining the specific mechanism of the stabilisation. (C) 1997 Published by Elsevier Science Limited.