Degradation photothermal

Volpe et al. studied the photothermal degradation of isoxsuprine on TLC plates irradiated with intense UV light (the heat also emitted from the UV... 

With better understanding of the mechanism of degradation and stabilization, there undoubtedly will be an increased effort to produce polymers with greater photothermal/radiation resistance and also more effective stabilizers to achieve this end. Thus, the study of degradation and stabilization aspects of ethylene-propylene copolymers and their blends (and generally of multiphase polymer blends) appears to be both intellectually stimulating and of practical importance. 

While the MIPs used in this work were inherently stable for at least 1 year, the silver films were prone to atmospheric degradation. Indeed, it was found that the application of the MIPs to the film protected it to some extent, but even when stored in vacuo these substrates were only stable for 5 days. The use of gold substrates is reportedly under investigation. Finally, it must be noted that the equipment used in this work was not a simple off-the-shelf commercial SPR system. These custom-made systems employed either highly sensitive photothermal deflection spectroscopy or a photodiode array to detect the changes in resonance... 

The volatile products of thermal degradation of polypropylene (PP) under vacuum in the temperature range 300-360°C comprise a complex mixture of saturated and unsaturated hydrocarbons. Under u.v. radiation at these temperatures (photothermal degradation), the general pattern of products is similar but the rate is Increased, ehtylene appears as a minor product and the relative amount of methane is very much greater, especially as the temperature Is decreased below 300°C. Energies of activation of the thermal, photothermal and photoreactions are 50.1, 33.9 and 11.7 k cal mole" respectively. 

The experiments described in the first part of this paper thus seek to extend our knowledge of the degradation processes which occur in PP, first, by linking photo and thermal processes through photothermal studies and second, by observing the effect of pre-Irradiation on subsequent thermal degradation. 

Mass spectra of volatile products from photothermal and thermal degradations at 354°C and of photothermal degradation at 200 and 250 C are illustrated in figure 1. They are all typical of a mixture of hydrocarbons with the main peaks separated by 14 units (CH2). They are generally similar, except that as the degradation temperature is decreased, the lines at mass numbers 15 and 16 become relatively much more intense. These two lines, as well as forming part of the breakdown pattern of higher hydrocarbons, are characteristic of methane. Thus it may be concluded that the relative proportions of methane in the volatile products... 

Figure 2. Weight loss of PP after irradiation for 15 hr as a function of temperature. Points represent the difference between extents of thermal and photothermal degradations at these temperatures.

Figure 3. Arrhenius plots for PP degradation. 9, thermal photothermal Y, photo.

Polypropylene. In the thermal and photothermal degradations of PP as prepared as well as In the thermal degradation of the pre-irradiated polymer, the general patterns of volatile products are similar and are qualitatively accounted for In terms of the mechanism of Tsuchlya and Suml ( ), which proposed that the complex mixture of saturated and unsaturated hydrocarbons Is formed in a free radical process in which Inter and Intramolecular transfer play a predominating role. In the photothermal reaction, however, in addition to those products, a very much higher relative concentration of methane and an appreciable amount of... 

Figure 1. Mass spectra of volatile products from photothermal and thermal degradations of PP. A, thermal at 354°C B, photothermal at 354°C C, photothermal at 200°C D, photothermal at 250°C.

Eranqois-Heude A, Richaud E, Desnoux E, Cohn X. Influence of temperature, UV-hght wavelength and intensity on polypropylene photothermal oxidation. Polym Degrad Stab 2014 100 10-20. 

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