Naphthenic Plasticisers

Applications Identification of polymer additives by TLC-IR is labour intensive and comprises extraction, concentration of extracts, component separation by TLC on silica, drying, removal of spots, preparation of KBr pellets and IR analysis. The method was illustrated with natural rubber formulations, where N-cyclohexyl-2-benzothiazyl sulfenamide, IPPD and 6PPD antioxidants, and a naphthenic plasticiser were readily quantified [765]. An overview of polymer/additive type compounds analysed by transfer TLC-FTIR is given in Table 7.80. 

The carcinogenicity of polycyclic aromatic compound-rich tyre extender oils has lead to the proposal of a legislative ban on their use in Europe. The suitability of naphthenic oils as non-toxic plasticisers in tyre treads is discussed and results are presented of experimental studies of the use of these plasticisers in SBR, EPDM, sulphur-cured EPDM and peroxide-cured EPDM. Despite their low aromatic content, the naphthenic plasticisers are shown to give good results in SBR, probably as a result of the contribution to solvent characteristics of the naphthenic molecular structure. The use of naphthenic oils is expected to increase worldwide as they are said to be one of the best alternatives to aromatic extracts with regard to solvent properties, compatibility, performance and availability. 

Assist the widely dissimilar ingredients used in a rubber compound to coalesce and mix into a homogeneous uniform processable mass. Homogenisers are low-MW polymeric resin blends. The homogenising resin blend contains portions that are compatible with aliphatic, naphthenic and aromatic parts of the elastomers in a blend and higher-MW homologues of the plasticisers. They have a wetting effect. Fatty acid derivatives and phenolic resins are used. 

Facilitate pre-vulcanisation processing, increase softness, extensibility and flexibility of the vulcanised end-product. The rubber processing industry consumes large quantities of materials which have a plasticising function complex mixtures (paraffinic, naphthenic, aromatic) of mineral hydrocarbon additives, used with the large tonnage natural and synthetic hydrocarbon rubbers, are termed process oils. Because of the complexity of these products, precise chemical definition is usually not attempted. If the inclusion of an oil results in cost reduction it is functioning as an extender. The term plasticiser is commonly reserved for synthetic liquids used with the polar synthetic rubber. 

Extending oils for compounds crosslinked with peroxides have to be carefully selected. Synthetic ester plasticisers such as phthalates, sebacates and oleates may be used in combination with crosslinking peroxides without affecting the crosslinking reaction. Some derivatives of alkylated benzenes are also known for their very low consumption of free radicals, which is clearly desirable. Mineral oil with double bonds, tertiary carbon atoms or containing heterocyclic aromatic structure may react with radicals paraffinic mineral oils are more effective than naphthenic types, which usually require extra treatment in order to guarantee optimum results when used in peroxide crosslinked blends. 

Very highly refined naphthenic products are shown to be good plasticisers for EPDM. 7 refs. 

The synthetic rubber industry uses a number of hydrocarbon additives, specifically called process oils (to act as a plasticiser, used below 20 phr) or extenders (used to keep the costs down). There are a wide range of mineral oils used as process oils, produced by blending of crude oil distillates and these may be either paraffinic, naphthenic or aromatic. Process oils containing polycyclic aromatic hydrocarbons, are classified as potential carcinogens (and their use is decreasing considerably). 

The autohesion of rubber compounds is found to marginally decrease with increasing amounts of plasticiser/processing oils such as aromatic, naphthenic or paraffinic [5]. Since plasticiser/processing oil improves the chain mobility of the rubbers this behaviour shows that interdiffusion alone cannot explain all the factors associated with tack or autohesion. But if the modulus is maintained at a constant by the addition of carbon black, oil essentially has no effect on adhesion [9]. 

Volatile plasticisers such as butyl oleate and naphthenic oils should be avoided while rapeseed oil and polyester plasticisers are recommended for permanence. Fine particle size calcium carbonate confers good heat resistance but gives poor weathering performance and low physical properties. Carbon blacks such as FEF or SRF are usually needed. 

Choice of plasticiser is of great importance. Most plasticisers are detrimental to the electrical properties of neoprene, but some ester plasticisers are particularly poor. These must be avoided even in jacket compounds if used without a barrier to prevent migration of plasticiser into the insulation. Naphthenic oils or hydrocarbon resins such as Kenflex A give the highest insulation values. A typical sheathing compound is shown in Table 7. 

Small quantities of plasticiser are used in butyl compounds in order to improve processing, reduce hardness and modulus, increase resilience and reduce cost. Mineral oils are used in most applications, paraffinic and naphthenic oils being particularly appropriate because butyl has a low solubility parameter. Waxes, tars, coumarone-indene resins and certain esters are also widely used, whereas plasticisers containing olefinic unsaturation are avoided because they retard vulcanisation. 

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