The mechanism of hydroquinone assisted photodegradation of PVC

Abstract

Pure poly(vinyl chloride) (PVC) degrades upon exposure of UV radiation (λ <300 nm) by the loss of HCl and formation of long conjugated structures known as polyenes. The mechanism of this process is fully understood and known as the zip mechanism, firstly involving the elimination of chlorine radical from the PVC backbone and then the formation of HCl. Addition of chromophores (light absorbing units) into the matrix of the PVC increases the wavelength absorption of the matrix. One of these compounds is Hydroquinone (HQ), which sensitizes the photodehydrochlorination of PVC at 312 nm. The purpose of this thesis is to shed light into the mechanism of HQ assisted photodehydrochlorination of PVC at 312 nm. Accordingly, the effect of (i) the minimum concentration of HQ, (ii) the temperature of the medium on the rate of PVC photodegradation, (iii) the viscosity of the PVC, (iv) the flux of the irradiation, and (v) the hydroquinone-benzoquinone composition on the rate of PVC photodegradation are investigated. Various sensitizers and quenchers are also used to compare the HQ’s sensitisation ability and to investigate the effect of the triplet-state of HQ in the mechanism of the HQ sensitized PVC photodegradation. UV-Visible, IR, and XPS spectroscopic techniques are used to determine the effect of the mentioned parameters.V In the light of all the findings, a mechanism of the HQ assisted (sensitized) photodegradation is proposed to involve mostly formation of a triplet state of HQ followed by effective transfer of this energy to the PVC matrix for dehydrochlorination.