Spectroscopic investigation of polyvinyl chloride photodegradation in blends with basic traps

Abstract

Polyvinyl chloride degrades via loss of HCI when it is exposed to heat, energetic particles or photons. The mechanism is known as the zip mechanism and results in conjugated segments, polyenes. Degradation also leads to loss of mechanical properties of PVC. However, from another point of view, PVC is a Bronsted acid source, with controllable emission. Furthermore, the polyenes are small segments of polyacetylene, which itself is a very interesting one-dimensional system. Understanding the building blocks clearly helps to envisage larger systems. This study has two main goals. The first goal is benefiting from the radiation induced in-situ created HCI by incorporating basic traps into the polymer matrix and inducing optical or electrical conductivity changes. The second goal is to tune the wavelength of photodegradation by introducing sensitisers into the polymer matrix to affect the chain length of the polyenes. For the first part of the study, pH indicators, and basic forms of conducting polymers were blended with PVC and the films were irradiated with UV radiation. Optical changes were monitored with UV-Vis-NIR Spectroscopy. Similar to several other dyes tried, Bromcresol Green, and Methyl Violet changed their optical properties when they were exposed to UV radiation in the PVC matrix. However, Methyl Violet, being resistant to UV radiation, proved to be a suitable component for possible dosimetric and lithographic applications. Basic forms of polyaniline and poly-2-chloro aniline were blended with PVC, and upon irradiation of the blend, they were converted to conducting salt forms as a result of doping with in-situ created HCI. The structural changes were monitored with UV-Vis-NIR spectrophotometry as well as FTIR spectroscopy. PVC/2-CI PAN I blends gave better results compared to PVC/PANI blends. For the second part of the study, hydroquinone, anthraquinone, and anthracene were introduced into the PVC matrix. The samples were irradiated with monochromatic UV radiation at the absorption maxima of these sensitisers. It was established that the nature of polyene formation is dependent on the wavelength of irradiation as well as the amount of energy transferred to the PVC chains.