Photo-thermal degradation

Plasma Etching of Poly[A A -(/),/> -Oxydiphenylene) Pyromellitimide] Film and Photo/Thermal Degradation of Etched and Unetched Film... 

The desired thickness of the film for the solar sail application was 2.5 ym, but the thinnest commercially available film of this type was Du Font s Kapton O) with a thickness of <7.5 ym. Hence, a need existed to thin the latter film and to assess the photo-and thermal stability of the resulting, thinned film. This paper describes the use of a radiofrequency (RF) oxygen plasma for etching (thinning) of poly[, N-oxydiphenylene) pyromellitimide] (POP) film, and presents data on the photo/thermal degradation of etched and unetched film in vacuum. Although plasma etching has been applied to many polymers, it has scarcely been used on... 

Photo/thermal Degradation. Samples of etched ( <2.5 pm) and unetched ( X/7.5 pm) POP film were placed in quartz tubes which were continuously evacuated while being heated at temperatures >450 C in a constant temperature block, controlled to 2 C. Other film samples contained in quartz tubes evacuated to <10 Torr were exposed to a Hanovia 450-watt mercury lamp with the etched side facing the lamp. At 14 cm from the lamp, the intensity of the uv radiation incident on the films was equivalent to <5.9 times that of the Sun in the 2000-3500-A range at 1 astronomical unit, i.e., just outside the atmosphere. At that distance from the lamp, the temperature of... 

A is the absorbance at 600 nm and the subscripts o and t refer to a given film before and after heating or irradiation. The gases produced in several photo/thermal degradation runs were collected and analyzed by mass spectrometry. 

Photo/thermal Degradation. Although transmission or ATR IR spectra gave no Indication of a photo- or thermally-induced alteration In the POP microstructure, the uv-lrradlated or heated films showed a definite darkening or blackening. As may be seen from Table II, the rates for photolnduced blackening In etched and... 

The experimental assistance of Mr. Mark L. Rosenberg in the photo/thermal degradation work is gratefully acknowledged. 

The temperature often determines the shape of action or activation spectra where both thermal and photochemical processes produce the same outcome. Both lignocellulose and poly(vinyl chloride), for instance, yellow on exposure to UV radiation as well as on heating. In the case of the latter substrate, even the mechanism of yellowing is the same. It is, therefore, necessary to include adequate controls in the experiments to estimate the relative importance of thermal processes in those exposures that cause combined photo-thermal degradation. Alternatively, additional samples might be exposed behind filters with... 

Two major chain processes occur simultaneously during photo (thermal) degradation of poly(vinyl chloride) ... 

Study of the kinetics of HCl evolution during UV, thermal and photo-thermal degradation shows that the amounts of produced HCl differ significantly depending on the treatment of the poly(vinyl chloride) samples [1792]. 

Kolawole and Olugbemi [156] have published a study of photo and thermal degradation of the two-phase... 

Protection of polymers against thermal and photo-oxidative degradation is achieved with appropriate stabilizers that ensure the desirable polymer properties throughout the entire service life of the polymer. Compatible and polymeric stabilizers usually give the best protection. In order to avoid migration and evaporation, polymeric stabilizers are used. 

Increase the oxidation rate of polymers, e.g. metal ions which increase the hydroperoxide decomposition rate. Photodegradation and thermal degradation are enhanced by transition metal ion containing pro-oxidants, such as iron dithiocarbamate (as opposed to nickel dithiocarba-mate, which acts as a photo-antioxidant). 

What is mechanical degradation Why is it less commonly encountered relative to thermal and photo-oxidative degradation ... 

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