Elastomers polymeric degradation

Chloroprene is available commercially on a restricted basis in the United States as crude P-chloroprene with a minimum purity of 95% (Lewis, 1993 DuPont Dow Elastomers, 1997). The principal impurities are dichlorobutene and solvents, with smaller amounts of 1-chlorobutadiene (a-chloroprene), chlorobutenes and dimers of both chloroprene and butadiene. Due to its reactivity, chloroprene is stored at 0°C or below under nitrogen and contains significant quantities of inhibitors, such as phenothiazine, tert-butylcatechol, picric acid and the ammonium salt of A -nitroso-N-phenylhydroxy lamine, to prevent degradation and polymerization (Stewart, 1993). Generally within six weeks of manufacture, crude chloroprene is distilled to produce polymerization grade, which is used within approximately 24 h of distillation. 

Although the technological basis of all fluorine-containing plastics and most elastomers continues to be the free radical polymerization of fluoroolefins, which themselves are based on the vastly greater fluorocarbon refrigerant industry, important advances have been made in the past two decades These include primarily the production of polymers that are more resistant to degradation by heat, oxidation, bases, and solvents, as well as polymers that are more easily processable, that is, able to be converted mto their final forms for use, whether by thermoplastic or thermoset processes [1,2,3,4]... 

The mechanical degradation and production of macroradicals can also be performed by mastication of polymers brought into a rubbery state by admixture with monomer several monomer-polymer systems were examined (10, 11). This technique was for instance studied for the cold mastication of natural rubber or butadiene copolymers in the presence of a vinyl monomer (13, 31, 52). The polymerization of methyl methacrylate or styrene during the mastication of natural rubber has yielded copolymers which remain soluble up to complete polymerization vinyl acetate, which could not produce graft copolymers by the chain transfer technique, failed also in this mastication procedure. Block and graft copolymers were also prepared by cross-addition of the macroradicals generated by the cold milling and mastication of mixtures of various elastomers and polymers, such as natural rubber/polymethyl methacrylate (74), natural rubber/butadiene-styrene rubbers (76) and even phenol-formaldehyde resin/nitrile rubber (125). 

Bart and co-workers [25] and others [34, 101, 163] have reviewed the application of TG-MS for the study of polymeric materials, thermoplastics, thermosets and elastomers. This thermoanalytical technique is used for the structural characterisation of homopolymers, copolymers, polymeric blends and composites and finds application in the detection of monomeric residuals, solvents, additives, (toxic) degradation products, etc. Information is... 

Chapter 14 provides the basic principles of polymer science, and addresses the importance of this subject. This chapter aims to give a broad and imified description of the subject matter—describing the polymerization reactions, structures, properties, and applications of commercially important polymers, including those used as plastics, fibers, and elastomers. This chapter focuses on synthetic polymers because of the great commercial importance of these materials. The chemical reactions by which polymer molecules are synthesized are addressed along with the process conditions that can be used to carry them out. This chapter also discusses topics on degradation, stability, and environmental issues associated with the use of polymers. 

Materials Compatibility Einally, any lubricant is required to be compatible with non-metallic components used in the engine, such as plastics, resins and elastomers. In particular, polymeric materials used in seals and plastics need to retain their integrity when in contact with the lubricant. ACEA and most OEMs have material compatibility tests to ensure that the lubricant will not cause undue degradation in key physical parameters of the polymer. These parameters include tensile strength, hardness, volume and crack formation. Any such loss of polymer integrity could be manifest as oil seal leaks or in more extreme cases as a blown gasket. Current engine test examples for American, European and selected OEM specifications are shown in Table 9.5. 

Three methods that were used to measure the chemical changes associated with oxidative degradation of polymeric materials are presented. The first method is based on the nuclear activation of lsO in an elastomer that was thermally aged in an, 802 atmosphere. Second, the alcohol groups in a thermally aged elastomer were derivatized with trifluoroacetic anhydride and their concentration measured via 19F NMR spectroscopy. Finally, a respirometer was used to directly measure the oxidative rates of a polyurethane foam as a function of aging temperature. The measurement of the oxidation rates enabled acceleration factors for oxidative degradation of these materials to be calculated. 

Acrylic-styrene-acrylonitrile terpolymers, ASA, are produced by simultaneous polymerization of styrene and acrylonitrile monomers in the presence of an acrylic rubber (polybutylacrylate). Thus, the material has a two-phase strucmre similar to ABS. However the elastomer phase in ASA is saturated and thus significantly more resistant to oxidative degradation. ASA is used in applications requiring good weatherability, mostly with PVC. The blends are primarily extruded for exterior trims and window profiles applications. 

The growing concern over the toxicity of residual ethylene oxide after sterilization of polymers for use in the field of medicine has led to the rapid growth of the field of radiation sterilization. The medical industry consumes a massive volume of polymeric material in both equipment and implants. As a consequence there is much interest in the effects of radiation on the physical properties and stability of irradiated polymers. The standard dose for radiation sterilization is 25 kGy, which is sufficient to alter the properties of many polymers, being for example close to or above the gel dose of many elastomers. There is also interest in the reaction of oxygen with long-lived radical species formed during irradiation. A common polymer used in medical equipment, poly(propylcne) is susceptible to oxidative degradation, and must be blended with appropriate stabilizers before radiation sterilization. 

This technique is highly useful to study the behavior of the polymeric materials like, thermoplastics, thermosetting polymers and elastomers. Thermogravimetric analysis can be used to analyze the effect of the nanoparticle incorporation on thermal degradation temperature of the composite system. 

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