INFRARED SPECTRAL CHANGES IN PVC AND PLASTICIZED PVC DURING GELATION AND FUSION

The behaviour of PVC and PVC plastisols has been studied during their thermal treatment using an in situ FTIR technique. The plasticizer int roduces certain modifications in the spectrum of the resin which are m ore marked in the case of the more compatible plasticizers. The A(1427 )/A(1435) and A(637)/A(616) ratios of the intensities of the crystalli ne and amorphous bands of the resins, decrease in the plastisols when increasing the compatibility of the plasticizer. On the other hand, wh en the plastisol undergoes the gelation process, a great decrease of t hese ratios is observed, showing that the increase in temperature prod uces a decrease in the amount of the crystalline phase in the resin wi th respect to the amorphous phase. This behaviour has also been observ ed when the resin is heated without plasticizer, and is a reversible p rocess. The CO band corresponding to the plasticizer shows a different behaviour to the resin bands. When the temperature increases, a shift to lower wavenumbers is observed. This displacement is irreversible ( the band does not recover its original location after cooling) and the process occurs in a relative narrow temperature interval. This temper ature range, where the carbonyl band suffers these changes, is in good agreement with the gelation temperature as measured by other techniqu es. (C) 1997 Elsevier Science Ltd.