Polystyrene , outdoor exposure

Polystyrene. Polystyrene [9003-53-6] is a thermoplastic prepared by the polymerization of styrene, primarily the suspension or bulk processes. Polystyrene is a linear polymer that is atactic, amorphous, inert to acids and alkahes, but attacked by aromatic solvents and chlorinated hydrocarbons such as dry cleaning fluids. It is clear but yellows and crazes on outdoor exposure when attacked by uv light. It is britde and does not accept plasticizers, though mbber can be compounded with it to raise the impact strength, ie, high impact polystyrene (HIPS). Its principal use in building products is as a foamed plastic (see Eoamed plastics). The foams are used for interior trim, door and window frames, cabinetry, and, in the low density expanded form, for insulation (see Styrene plastics). 

Under irradiation with polychromatic light at X > 300 nm and 60 °C, representative of outdoor exposures, polystyrene (PS) homopolymer, copolymers and blends do not directly absorb the incident radiation. It is well known that the photooxidation of these polymers results from light absorption by chromopho-ric impurities [1,2]. Photooxidation generates modifications of the chemical structure of the material, which results in the formation of oxidized groups, the development of discoloration and the loss of the initial mechanical properties. 

Degradable Polystyrenes. The Ecolyte "Fast" polystyrene foam has a higher concentration of photosensitive vinyl ketone comonomer than the Ecolyte "Slow" foam and as a result has a shorter irradiation time to embrittlement as listed in Table I. The "Fast" foam was brittle after one month outdoor exposure or 275 hr xenon arc irradiation. The outdoor exposure was facilitated by wind and rain erosion. Turning the sample over after 35 hr xenon irradiation lowered the embrittlement time to a remarkably short period of 70 hr considering the thickness and opacity of the foam. Similarly the "Slow" foam had its xenon embrittlement time reduced from 21+00 hr to only 600 hr by turning the foam over after each 2l+ hr irradiation period. To obtain a better idea of the rate of... 

After 9 months of outdoor exposure in Florida (Figure 5), and even after 12 months (Figure 6), the SEM photomicrographs of the IPS (impact polystyrene) show minimal surface deterioration for the samples that contain 0.5% LS I and 0.5% LS II, while the samples that contain no light stabilizers show extreme surface erosion and the presence of mildew. 

GP-PS is a clear, rigid polymer that is relatively chemically inert. Polystyrene, as produced, has outstanding flow characteristics and consequently is very easy to process. Its excellent optical properties, including high relractive index, make it usefiil in optical applications. However, GP-PS has a number of limitations, including its brittleness, low heat-deflection temperature (Table 15.1), poor UV resistance, and susceptibility to attack by a variety of solvents. Polystyrene is sensitive to foodstuffs with high fat or oil content it erazes and turns yellow during outdoor exposure. 

In order to improve the surface gloss and appearance, thin layers of polystyrene or chromium have been applied to rubber-toughened plastics like ABS. However, these surface layers are brittle. Outdoor exposure to ultraviolet radiation (Chapter 10) can also convert the surface layer of a plastic into a brittle state. The effects of such layers are the most marked when the product is bent, with the brittle layer being in tension. The tensile failure strain of the surface layer is smaller than that of the substrate, so it fails first. A series of sharp cracks forms perpendicular to the surface tensile stress each relieves the surface stress over a limited length. The cracks start at the outer surface, and accelerate rapidly through the surface layer. If the substrate is tough, the cracks can be arrested, but if it has a... 

Keywords Reciprocity UV intensity Weathering Acceleration Correlation ORWET Polystyrene Irradiance Temperature Ultra-Accelerated Weathering System UA EMMA Exposure Exhapolation ASTM G90 Color Outdoor Static Dynamic Hypervolume... 

The Sedona paper described a simple experiment exposing polystyrene standard reference materials (SRMs) to outdoor accelerated weathering conditions under concentrated solar irradiances at four different levels out to the same level of radiant energy. The exposure temperatures were held constant across different irradiance intensities via linked exposure devices. The data from the Sedona paper showed significant deviations from strict reciprocity predictions for the polystyrene SRMs in the experiment as shown in Fig. 11.2. The data indicated that the assumption of strict reciprocity was not a valid assumption for the data shown. 

Many polymeric materials serve in applications that require exposure to outdoor conditions. Any resultant degradation is termed weathering, which may be a combination of several different processes. Under these conditions, deterioration is primarily a result of oxidation, which is initiated by ultraviolet radiation from the sun. Some polymers, such as nylon and cellulose, are also susceptible to water absorption, which produces a reduction in their hardness and stiffness. Resistance to weathering among the various polymers is quite diverse. The fluorocarbons are virtually inert under these conditions some materials, however, including poly(vinyl chloride) and polystyrene, are susceptible to weathering. 

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