Modeling Photodegradation in Transparent Polymers

Abstract

A model for photodegradation of transparent thermoplastics has been developed and tested using data from polystyrene samples. The proportionality between incident energy and amount of degradation is calculated at each wavelength to yield the "wavelength sensitivity spectrum" for degradation of the polymer. The formal derivation of the wavelength sensitivity spectrum is described. The model was tested by exposing polystyrene samples containing several different stabilizers at various loadings to two different sources of xenon arc ultraviolet radiation. The degradation rates predicted by the model correlated well with the experimentally observed rates over all the different conditions. The model systematically underestimates the absolute degradation. Measurement of stabilizer concentration as a function of depth into the molded test specimens showed that the stabilizer was distributed uniformly before exposure to the light source. After exposure, the stabilizer was largely depleted from the surface layer, but the concentration was unchanged in the bulk of the specimens.

Photo-induced Structural Changes in Polyolefin-nanoclay Composite

“…It is known that photooxidation of polyolefins by exposure to solar radiations (weathering) is a complex process involving macromolecular mobility, diffusion-controlled reactions, reactions caused by free radicals resulting into chain scission as well as cross-linking and formation of hydroxyl/hydroperoxy and carbonyl groups 10,16 . These factors make the structure of the exposed sample highly strained.…”

“…Coupled with solar radiations, the humidity, rains, and elevated temperatures during the day can influence the destructive effect of solar radiation, by accelerating the rate of secondary reactions. These, in turn, alter the reaction process that follows the primary photochemical step of bond breaking by increasing the rate of oxygen and water permeation into the material 7,9,10 19 . The steeper initial part of the curve indicates stiffness of the material that sets in after the solar exposure.…”

“…Photodegradability of polyolefins has been studied for reducing the problem of waste disposal and to understand its mechanism [4][5][6][7][8][9][10] . In general, it is found that pure polyolefins, specially polyethylene, are transparent down to < 200 nm wavelength and therefore, can be called indefinitely stable to sunlight having wavelengths >290 nm [9][10] . However, for practical purposes, on exposure to solar radiation these polymers are found to degrade to varying extents.…”

Photophysics

“…A study on modeling UV stabilization 11 is an example of one such effort already in progress. The model used to evaluate the protective effect of stabilizers is based on Beer's law and wavelength sensitivity: [2.17] where:…”

A novel facility for ageing materials with narrow-band ultraviolet radiation exposure

“…[5][6][7][8][9][10][11][12] Stability of materials under UV radiation is tested in various ways. It is not possible to make generalized assumptions, such as, all UV radiation would have similar effect despite the wavelength, or that the most energetic photons would cause the highest damage.…”