Browsing by Subject "hydroquinone"

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    Analysis of UV induced dehydrochlorinated PVC (With hydroquinone) using direct pyrolysis mass spectrometry (DPMS), TGA, UV/VIS-NIR and FTIR techniques
    (2003) Avcı, Ercan
    Poly(vinyl chloride) (PVC) degrades easily upon heat and light exposure via loss of HCl. The mechanism of this process is well understood, known as the zip mechanism and the dehydrochlorination results in conjugated segments, polyenes. It is also possible to utilize PVC polymer as an in-situ acid donor since the main degradation product is HCl. Addition of hydroquinone (HQ) into PVC matrix sensitizes the photodehydrochlorination of PVC at 312 nm. In this study the effects of photodehydrochlorination on thermal and material properties of PVC were investigated using DPMS and TGA as well as UV-Vis-NIR and FTIR techniques. In addition, the photodegradation of PVC/PVAc blend, copolymer (PVC-coPVAc) and PVAc were similarly investigated. Dehydrochlorination of the polymers resulting from UV-exposure were also investigated for doping of PANI in blends. HCl evolution behavior of the UV dehydrochlorinated PVC exhibits a characteristic property which is different from the unirradiated ones. Both DPMS and TGA results confirms the sensitization of PVC photodehydrochlorination at 312 nm by hydroquinone (HQ) resulting in a temperature onset that is the lowest (140 oC). HQ assistance upon 312 nm UV exposure is not significantly observed in the copolymer. The low temperature onset of UV-induced copolymer is a promising result to produce longer polyene chains, since polymer backbone starts to decompose after ca. 220 oC, using copolymer might be an alternative to PVC.
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    ItemOpen Access
    The mechanism of hydroquinone assisted photodegradation of PVC
    (2002) Balcı, Sinan
    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.