Poly chemical resistance

Nitrile mbber finds broad application in industry because of its excellent resistance to oil and chemicals, its good flexibility at low temperatures, high abrasion and heat resistance (up to 120°C), and good mechanical properties. Nitrile mbber consists of butadiene—acrylonitrile copolymers with an acrylonitrile content ranging from 15 to 45% (see Elastomers, SYNTHETIC, NITRILE RUBBER). In addition to the traditional applications of nitrile mbber for hoses, gaskets, seals, and oil well equipment, new applications have emerged with the development of nitrile mbber blends with poly(vinyl chloride) (PVC). These blends combine the chemical resistance and low temperature flexibility characteristics of nitrile mbber with the stability and ozone resistance of PVC. This has greatly expanded the use of nitrile mbber in outdoor applications for hoses, belts, and cable jackets, where ozone resistance is necessary. 

The chemical resistance and excellent light stabiUty of poly(methyl methacrylate) compared to two other transparent plastics is illustrated in Table 5 (25). Methacrylates readily depolymerize with high conversion, ie, 95%, at >300° C (1,26). Methyl methacrylate monomer can be obtained in high yield from mixed polymer materials, ie, scrap. 

Poly(vinyl chloride). PVC is one of the most important and versatile commodity polymers (Table 4). It is inherently flame retardant and chemically resistant and has found numerous and varied appHcations, principally because of its low price and capacity for being modified. Without modification, processibiUty, heat stabiUty, impact strength, and appearance all are poor. Thermal stabilizers, lubricants, plasticizers, impact modifiers, and other additives transform PVC into a very versatile polymer (257,258). 

CPA. Copolymer alloy membranes (CPAs) are made by alloying high molecular weight polymeries, plasticizers, special stabilizers, biocides, and antioxidants with poly(vinyl chloride) (PVC). The membrane is typically reinforced with polyester and comes in finished thicknesses of 0.75—1.5 mm and widths of 1.5—1.8 m. The primary installation method is mechanically fastened, but some fully adhered systems are also possible. The CPA membranes can exhibit long-term flexibiHty by alleviating migration of the polymeric plasticizers, and are chemically resistant and compatible with many oils and greases, animal fats, asphalt, and coal-tar pitch. The physical characteristics of a CPA membrane have been described (15). 

The excellent chemical resistance and physical properties of PVA resins have resulted in broad industrial use. The polymer is an excellent adhesive and possesses solvent-, oil-, and grease-resistant properties matched by few other polymers. Poly(vinyl alcohol) films exhibit high tensile strength, abrasion resistance, and oxygen barrier properties which, under dry conditions, are superior to those of any other known polymer. The polymer s low surface tension provides for excellent emulsification and protective coUoid properties. 

The most chemical-resistant plastic commercially available today is tetrafluoroethylene or TFE (Teflon). This thermoplastic is practically unaffected by all alkahes and acids except fluorine and chlorine gas at elevated temperatures and molten metals. It retains its properties up to 260°C (500°F). Chlorotrifluoroethylene or CTFE (Kel-F, Plaskon) also possesses excellent corrosion resistance to almost all acids and alkalies up to 180°C (350°F). A Teflon derivative has been developed from the copolymerization of tetrafluoroethylene and hexafluoropropylene. This resin, FEP, has similar properties to TFE except that it is not recommended for continuous exposures at temperatures above 200°C (400°F). Also, FEP can be extruded on conventional extrusion equipment, while TFE parts must be made by comphcated powder-metallurgy techniques. Another version is poly-vinylidene fluoride, or PVF2 (Kynar), which has excellent resistance to alkahes and acids to 150°C (300°F). It can be extruded. A more recent development is a copolymer of CTFE and ethylene (Halar). This material has excellent resistance to strong inorganic acids, bases, and salts up to 150°C. It also can be extruded. 

Compared with the phenolics and polyesters the resins have better heat resistance, better chemical resistance, particularly to alkalis, greater hardness and better water resistance. In these respects they are similar to, and often slightly superior to, the epoxide resins. Unlike the epoxides they have a poor adhesion to wood and metal, this being somewhat improved by incorporating plasticisers such as poly(vinyl acetate) and poly(vinyl formal) but with a consequent reduction in chemical resistance. The cured resins are black in colour. 

For very difficult to adhere bag substrates, such as poly-coated bags, or where extreme chemical resistance is needed, polyamide hot melts are used. These adhesives are very lightly formulated if at all. They provide soft adhesives with outstanding heat and chemical resistance, but at roughly double the price. 

The high degree of crystallization and the thermal stability of the bond between the benzene ring and sulfur are the two properties responsible for the polymer s high melting point, thermal stability, inherent flame retardance, and good chemical resistance. There are no known solvents of poly(phenylene sulfide) that can function below 205°C. 

One of the first fictional fluoropolymers was poly-1,2,2-trifluorostyrene. On one hand, it has much better oxidation and chemical resistance in comparison with common hydrocarbon polymers and, on the other hand, a wide range of functional groups can be attached to the aromatic ring. A sulfonated polymer was successfully used as a membrane for fuel cells by General Electric Co.3... 

Poly(benzimidazole)s possess excellent thermal stability, flame resistance, and outstanding chemical resistance. The solubility of hexafluoroisopropyli-dene-unit-containing poly(benzimidazole)s is remarkably improved.24 They are readily soluble in strong acids such as formic acid, concentrated sulfuric acid, and methanesulfonic acid and in aprotic polar solvents such as DMAc and NMP. The polymer from tetramine (23) is soluble even in m-cresol and pyridine. 

Aromatic poly(benzothiazole)s are thermally and thermooxidatively stable and have outstanding chemical resistance and third-order nonlinear optical susceptibility. Aromatic poly(benzothiazole)s can be spun into highly-oriented ultrahigh strength and ultrahigh modulus fibers. However, this type of polymer is insoluble in most organic solvents. Therefore, hexafluoroisopropylidene units are introduced in the polymer backbone to obtain soluble or processable aromatic poly(benzothiazole)s. 

Poly(organosiloxane)s have a number of outstanding properties such as thermal and oxidative stability, water and chemical resistance, electric insulating capacity, selective permeability to gases, and biocompatibility. 

The selective separation of water from aqueous solutions of isopropanol or the dehydration of isopropanol can be carried out with different membranes, which contain polar groups, either in the backbone or as pendent moieties. For the dehydration of such a mixture, poly(vinyl alcohol) (PVA) and PVA-based membranes have been used extensively. PVA is the primary material from which the commercial membranes are fabricated and has been studied intensively for pervaporation because of its excellent film forming, high hydrophilicity due to -OH groups as pendant moieties, and chemical-resistant properties. On the contrary, PVA has poor stability at higher water concentrations, and hence selectivity decreases remarkably. 

Poly(ether ether ketone) (PEEK) is an aromatic, high performance, semicrystalline polymer with extremely good thermal stability, chemical resistance, and electrical and mechanical properties. This polymer shows little solubility in organic solvents due to the crystallinity. One of the first ways to characterize PEEK was by sulfonating the polymer. By adding sulfonic acid groups to the backbone, the crystallinity decreased and solubility increased.Commercially available Victrex appears to be one of the more interesting poly(arylene ether) s used for postmodification. 

Poly(phenylene sulfide) 260 Good dimensional stability and chemical resistance... 

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