Kinetics of Photo-Induced Chemiluminescence Decay from Polymers

Abstract

Previous studies showed that the decay of photo-induced chemiluminescence (PICL) in polymers does not obey classical first or second order kinetics. This study demonstrates that plotting PICL second-order decay from three fibrous polymers (polypropylene, polyamide 6 and wool keratin) in a modified form gives excellent linear plots. The existence of a significantly less reactive fraction of macroperoxy radicals in heterogeneous polymers can explain the deviation from classical behaviour and this fraction can be quantified from the gradient of the modified plots. This unreactive fraction could be due to either dispersive or diffusive effects in a disordered heterogeneous polymer medium. Both dispersive and diffusive models give very good fits to the PICL decay profiles using three fitting parameters.

Photoprotection by Silk Cocoons

“…This peak was also found in the absence of the sample and is due to irradiation of the metal components in sample cavity as explained by Millington and George. 19 Peak 2 in Figure 8 is the chemiluminescence peak and is obtained in the presence of oxygen. The intensity of peak 2 corresponds to the free radicals generated upon exposure to UV-A.…”

“…The cocoons were cut very carefully into small pieces and 0.1 g of sample was compressed into pellet using 5 mm die and a 5 tonne load in the Spectropress. Each specimen was placed in an aluminum pan located directly on top of a heating element in the instrument and then irradiated with UV light (320–400 nm) at a fixed temperature of 40 °C. , A high intensity medium pressure mercury lamp (Lumatec SUV-DC, Lumatec GmbH, Deisenhofen, Germany) produced a selected wavelength of light with spectral intensity of 365 nm and this light entered the Lumipol instrument via a flexible light pipe and then irradiated the sample through a 45° quartz prism which was placed above the sample cavity. After the sample irradiation, the light pipe was withdrawn in order to allow measurements of weak chemiluminescence that the sample emits.…”

“…18 In addition to reflectance spectroscopy, we have used photoinduced chemiluminescence (PICL) to measure the number of free radicals produced when silk materials were exposed to UV radiation. 19 2. EXPERIMENTAL SECTION 2.1.…”

“…It is a useful technique to analyze the diffusely reflected light from the phase boundaries of solid materials such as fibers, biomaterials, and polymers and has been used to study the UV absorbance of protein materials . In addition to reflectance spectroscopy, we have used photoinduced chemiluminescence (PICL) to measure the number of free radicals produced when silk materials were exposed to UV radiation …”

The effect of dyes on photo-induced chemiluminescence emission from polymers

“…We have also shown that the experimental PICL decay profiles from several different polymers (polypropylene, polyamide 6 and wool keratin) can be fitted to the expected second order kinetics if one assumes the presence of a significantly less reactive fraction of macro-peroxy radicals in the heterogeneous materials [16].…”