Chemical resistance of polyphenylene sulfide

Adhesives recommended for polyphenylene sulfide include epoxies, and urethanes. Joint strengths in excess of 1000 psi have been reported for abraded and solvent-cleaned surfaces. Somewhat better adhesion has been reported for machined surfaces. The high heat and chemical resistance of polyphenylene sulfide plastics makes them inappropriate for either solvent cementing or heat welding. 

Coatings. The thermal and chemical resistance of polyphenylene sulfide nas led to a wide variety of applications as a coating material. Examples are cookware with heat-resistant, easy-release coatings containing PPS, valves and fittings coated with PPS for protection against corrosive chemicals, and electrical coils coated with PPS as a temperature-resistant insulation. 

This crystalline aromatic nylon, combines the high strength and stiffness of nylon with the thermal stability of polyphenylene sulfide. Molding characteristics are similar to nylon 6/6, with similar or better chemical resistance, but its 24 h water absorption is only 0.2 versus 0.7% for nylon 6/6. A key behavior is high heat resistance. 

Ryton Polyphenylene Sulfide is a new commercial plastic which is characterized by good thermal stability, retention of mechanical properties at elevated temperatures, excellent chemical resistance, a high level of mechanical properties, and an affinity for a variety of fillers. It is produced from sodium sulfide and dichlorobenzene. Its unusual combination of properties suggests applications in a variety of molded parts such as non-lubricated bearings, seals, pistons, impellers, pump vanes, and electronic components. Tough coatings of polyphenylene sulfide can be applied to metals or ceramics by a variety of techniques and are used as protective, corrosion-resistant coatings in the chemical and petroleum industries. Incorporation of small amounts of polytetrafluoroethylene provides excellent non-stick properties in both cookware and industrial applications. 

As regards the general behaviour of polymers, it is widely recognised that crystalline plastics offer better environmental resistance than amorphous plastics. This is as a direct result of the different structural morphology of these two classes of material (see Appendix A). Therefore engineering plastics which are also crystalline e.g. Nylon 66 are at an immediate advantage because they can offer an attractive combination of load-bearing capability and an inherent chemical resistance. In this respect the arrival of crystalline plastics such as PEEK and polyphenylene sulfide (PPS) has set new standards in environmental resistance, albeit at a price. At room temperature there is no known solvent for PPS, and PEEK is only attacked by 98% sulphuric acid. 

The primary resin of interest is epoxy. Carbon-fiber-epoxy composites represent about 90% of CFRP production. The attractions of epoxy resins are that they polymerize without the generation of condensation products that can cause porosity, they exhibit little volumetric shrinkage during cure which reduces internal stresses, and they are resistant to most chemical environments. Other matrix resins of interest for carbon fibers include the thermosetting phenolics, polyimides, and polybismaleimides, as well as high-temperature thermoplastics such as polyether ether ketone (PEEK), polyethersulfone (PES), and polyphenylene sulfide. 

Polyphenylene sulfide also possesses unusual chemical resistance. To demonstrate this resistance, injection-molded tensile bars of cured polymer were exposed to a representative groups of reagents at 200°F for 24 hours. After exposure, the bars were weighed to determine weight gain or loss, and the tensile strength determined. The results of these experiments are given in Table I. 

The term HT-thermoplastics is used for polymers, which in the absence of fillers, have a continuous-use temperature above approx. 200 °C. In contrast, standard plastics, such as PVC, polyethylene or polystyrene, have continuous-use temperatures of the order of 100 °C. In addition to their high temperature stability, HT-thermoplastics, in general, possess good resistance to chemicals and usually also low flammability. Among the most important HT-thermoplastics are polyphenylene sulfides (PPS), polysul-fones (PSU), polyether sulfones (PES), polyether imides (PEI), polyetherether ketones (PEEK) and polyarylates (PAR). 

Polyphenylene sulfide is used in the manufacture of thermoplastic resins, which are marked by high long-term temperature stability (260 °C) and good chemical resistance (Phillips Petroleum, USA Kureha, Japan). 

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