Elastomer additives characteristics

Chart I. Chemical structures and characteristics of dicyanate monomers, elastomer additives, and PES additives. 

Polyester (PE) elastomer combines characteristics of thermoplastics and elastomers. They have excellent resistance to ozone and good resistance to general weathering. However, the polyester rubbers do not have satisfactory resistance to sunlight-induced aging unless they are formulated with appropriate additives. 

Grade Selection Criteria Melt flow characteristics for injection moulding, extrusion and blow moulding. Filler/reinforcement additions, elastomer additions, food contact approvals, electrical properties. ... 

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. 

Elastomeric Modified Adhesives. The major characteristic of the resins discussed above is that after cure, or after polymerization, they are extremely brittie. Thus, the utility of unmodified common resins as stmctural adhesives would be very limited. Eor highly cross-linked resin systems to be usehil stmctural adhesives, they have to be modified to ensure fracture resistance. Modification can be effected by the addition of an elastomer which is soluble within the cross-linked resin. Modification of a cross-linked resin in this fashion generally decreases the glass-transition temperature but increases the resin dexibiUty, and thus increases the fracture resistance of the cured adhesive. Recendy, stmctural adhesives have been modified by elastomers which are soluble within the uncured stmctural adhesive, but then phase separate during the cure to form a two-phase system. The matrix properties are mosdy retained the glass-transition temperature is only moderately affected by the presence of the elastomer, yet the fracture resistance is substantially improved. 

Plasticizers (qv) are usually present at lower concentrations compared to general-purpose mbber-based compounds, because of their volatility at typical ACM service temperatures and/or their partial extractabiflty by the aggressive fluids where acryflc elastomers are employed. Other additives are therefore required to improve processibiflty. These processiag aids act as lubricating agents and enhance the release characteristics of the acryflc compound and/or reduce compound viscosity. 

Extruded Articles. In extmded article compounding, the most important parameters are scorch safety and flow characteristics (53). The bisphenol cure system again offers the best scorch resistance of the available fluorocarbon elastomer cure systems. Good flow characteristics can be achieved through proper selection of gum viscosities. Also, the addition of process aids to the formulation can enhance the flow characteristics. Typical formulations for extmsion grade fluorocarbon elastomers are given iu Table 7. 

Vulcanisation can be effected by diamines, polyamines and lead compounds such as lead oxides and basic lead phosphite. The homopolymer vulcanisate is similar to butyl rubber in such characteristics as low air permeability, low resilience, excellent ozone resistance, good heat resistance and good weathering resistance. In addition the polyepichlorohydrins have good flame resistance. The copolymers have more resilience and lower brittle points but air impermeability and oil resistance are not so good. The inclusion of allyl glycidyl ether in the polymerisation recipe produces a sulphur-curable elastomer primarily of interest because of its better resistance to sour gas than conventional epichlorhydrin rubbers. 

In addition, any chemical aging (Section 23.5.3) could affect these mechanisms for instance, if an elastomer surface is degraded by contact with hostile chemicals, access to the interior may be facilitated and its permeation characteristics would change accordingly. 

H. Ismail, Effect of palm oil fatty acid additive (POEA) on curing characteristics and vulcanizate properties of silica filled natural mbber compounds. Journal of Elastomers and Plastics, 32, 33, 2000. 

Finally, oligomers in reactive processing to produce foamed plastics and elastomers for various industrial purposes. These materials have many of the valuable properties of conventional polymers, with the addition of low density and high heat, electrical, and sound insulation characteristics.23... 

Seals, o-rings, and valve membranes must be manufactured out of polymers that are resistant to thermal sterilization and to the bases and acids used in the biopharmaceutical industry. When in contact with the product, the elastomers employed must additionally present the following safety characteristics the rates of release of polymer components must be low and remain below well-established threshold levels the components released must be innocuous to human health, according to rules previously established. 

Methylphenyldimethoxysilane is used as a stabiliser (antistructuring additive) in the production of rubber compounds based on silicone elastomers and highly active fillers. Introducing up to 10% (weight) of methylphenyldimethoxysilane into a rubber mixture improves the physicochemical properties of vulcanised rubbers and helps to preserve the technological characteristics of the compounds in storage. 

The metathesis polymerisation of dicyclopentadiene, an inexpensive monomer (commercially available cyclopentadiene dimer produced by a Diels-Alder addition reaction containing ca 95 % endo and ca 5 % exo form), leads to a polymer that may be transformed into a technically useful elastomer [144-146, 179] and thermosetting resin [180,181]. The polymerisation has characteristics that make it readily adaptable to the reaction injection moulding ( rim ) process [182], The main feature of this process comes from the fact that the polymerisation is carried out directly in the mould of the desired final product. The active metathesis catalyst is formed when two separate reactants, a precatalyst (tungsten-based) component and an activator (aluminium-based) component, are combined. Monomer streams containing one respective component are mixed directly just before entering the mould, and the polymerisation into a partly crosslinked material takes place directly in this mould (Figure 6.5) [147,168,183-186],... 

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