Polystyrene weathering stability

Copolymers of polystyrene with acrylonitrile (SAN), a-methylstyrene (SMS), acryl-styrene-acrylester (ASA), or acrylonitrile-ethylene-propylene styrene (AES) exhibit better weathering stability than homo-polystyrenes, Table 5.3. All polymerized styrenes will yellow under long-term weathering conditions, however, and their... 

The first move in this direction was to improve the weatherability of impact-resistant polystyrene. Because polybutadiene, the most widely used rubber in impact-resistant polystyrene, is unsaturated, it is sensitive to photooxidation, and impact-resistant polystyrene is therefore not suitable for outdoor applications. A saturated rubber might be able to help here. In the ABS sector this has been successfully tried out with acrylate rubber (77) and EPDM (78, 79), and the latter has also been used in impact-resistant polystyrene (80, 81) This development has elicited satisfactory responses only in certain areas and more work still has to be done. For instance, attempts have been made to improve resistance to weathering by using silicone rubber (82 ). This approach is effective, but economic factors still stand in its way. Further impetus may also be expected from stabilizer research. Hindered secondary amines (83), to which considerable attention has recently been paid, are a first step in this direction. 

In terms of weatherabilityf polystyrene does not exhibit ultraviolet stability and is not considered we ather-re sis tan t as a clear material. Continuous, long-term exposure results in discoloration and reduction of strength. Improvement in weatherability can be obtained by the addition of ultraviolet absorbers, or by incorporating pigments. The best pigmenting results are obtained with finely dispersed carbon black. 

Polypbenylsulfone Polystyrene Polysuifone Excellent thermal stability, resists creep, inherent high color Excellent processibility, poor UV resistance, brittle Excellent thermai/hydrolytic stability, poor weatherability/impact strength... 

Atactic polystyrene (aPS) is clear, transparent and easily fabricated, and has reasonable mechanical and thermal properties but is slightly brittle and softens near 100 °C. It is readily attacked by a large variety of solvents, including dry-cleaning agents. Its stability to outdoor weathering is poor it turns yellow and... 

In the current study, samples of impact polystyrene that contained a combination of light stabilizers LS I and LS II and samples that contained no light stabilizers were weathered outdoors in Florida and were monitored for changes in physical appearance and for changes in the chemical structure of the surface by use of a multiple internal reflectance IR spectrophotometer. Also, samples of a thermoplastic polyurethane that was stabilized with just LS I and samples that contained no light stabilizers were weathered and monitored in the same way as the impact polystyrene. We hope to establish at what point... 

In contrast to polyamides in polystyrene phenolic antioxidants are not able to reduce the decrease in tensile strength during UV irradiation [141]. UVAs as well as HALS stabilizers are effective in polystyrene (PS). The best protection can be reached by using combinations of a UVA and a HALS. According to Gugumus [133,134] the synergism between UVA and HALS is distinct when the time until a AYI = 5 is taken as failure criterion (see Table 17.12). However, when as criterion the yellowness index after 1600 h in a Weather-Ometer is taken, the synergism between a UVA and a HALS is much smaller (see Fig. 17.14). 

Polystyrene (PS) is prepared by the polymerization of styrene (CeHs—CH=CH2), also known as vinylbenzene. Commercial PS is mostly of the atactic variety and is therefore amorphous. The polymer, on decomposition, unzips and forms the monomer with some benzene and toluene. Its major defects are poor stability to weather exposure, turning yellow and crazing in sunlight. In spite of these drawbacks and its brittleness it has found wide use as molded containers, Uds, bottles, electronic cabinets. As a foamed plastic it is used in packaging and insulation. The thermal conductivity of the expanded PS foam is about 0.03 Wm K The foam can absorb aromatic hydrocarbons usually found in the exhaust of automobiles and buses, causing the foam to disintegrate after long periods of normal exposure to a polluted environment. 

Non-stabilized polystyrene is one of the plastics that exhibit relatively low resistance to weathering influences, especially to solar radiation. While their light stability is satisfactory for normal applications, stabilization against harmful UV radiation... 

SAN is more resistant than polystyrene thanks to its acrylonitrile content (commonly 38%). After one to two years of outdoor weathering, the level of mechanical properties decreases in non-stabilized SAN test specimens yellowing and surface roughening occur simultaneously. UV-stabilization delays these property changes. Figure 5.39 [661]. 

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