Rubber compounding processing oils

Oil that serves as a temporary or permanent component of a manufactured product. Aromatic process oils have good solvency characteristics their applications include proprietary chemical formulations, ink oils, and extenders in synthetic rubbers. Naphthenic process oils are characterized by low pour points and good solvency properties their applications include rubber compounding, printing inks, textile conditioning, leather tanning. 

In rubber compounding, different oils or plasticizers are proportionally used with the filler loading to achieve cured compound hardness and modulus targets and to improve the uncured processing characteristics. Also, many times the cost of process oil or plasticizer is cheaper than that of the base elastomer, thus reducing the total cost of the compound. 

Naphthenic process oil is used in high volume in general-purpose rubber compounds. Naphthenic oils are usually derived from naphthenic crudes that are more limited in supply than paraffinic crudes. In the world only about 5% of all crude is naphthenic crude. Only certain regions have naphthenic crudes. Pennsylvania was one of these regions, but today much of the naphthenic crudes come from Venezuela. 

In the broadest sense, any compounding ingredient added to rubber to reduce the cost of the compound. The use of the term is now usually limited to certain cheap petroleum rubber processing oils. 

In rubber compounding, the addition of a high proportion (40-50 phr) of a rubber processing oil to an elastomer with the object of improving the processibility of a tough polymer and/or cheapening the compound. 

Petroleum oils are offered to the rubber industry to meet two basic processing and compound requirements to act as a processing additive, or to act as a rubber extender and softener. The classification depends upon the oil volume added to the rubber compound. As processing additives, the oil addition level is usually no more than 5-10 phr for additions in excess of this the oils are regarded as extenders. 

Oils of the three types are offered in a range of viscosities and this will influence their processing character to some extent, although there is little evidence that it will have much influence on the ultimate compound physical properties, at least in natural rubber compounds. The small additions of oil to a compound help with filler dispersion by lubricating the polymer molecular chains and thus increasing their mobility. There will also be some wetting out of the filler particles which enables them to achieve earlier compatibility with the rubber and improve their distribution and dispersion speed. 

Control of the temperature of rubber compound whilst being processed in extruders and injection moulding machines is vital if the product from these processes is to be uniform in quality. Failure to control temperatures in processing equipment can lead to scorching of the compound as it emerges from the extruder die or injection machine nozzle. Most modem items of processing equipment are fitted to a temperature control unit using either oil or water as the circulatory medium. 

Process Oils, Plasticizers. Petroleum-based rubber process oils generally contain a mixture of paraffinic, naphthenic, and aromatic components. These oils vary in composition from grade to grade, but most contain some unsaturated moieties and this unsaturation can compete with the polymer for curatives. Therefore, state of cure can be decreased. This is not easily detected because oil softens the compound which masks the loss of state of cure. 

Carbon black Finely divided carbon made by incomplete combustion or decomposition of natural gas or petroleum-based oils in different types of equipment. According to the process and raw material used, it can be furnace (e.g., HAF), thermal (e.g., MT), or channel carbon black (e.g., EPC), each having different characteristics, such as particle size, structure, and morphology. The addition of different types of carbon blacks to rubber compounds results in different processing behavior and vulcanizate properties. 

Substitute for Conventional Vulcanized Rubbers, For this application, the products are processed by techniques and equipment developed for conventional thermoplastics, ie, injection molding, extrusion, etc. The S—B—S and S—EB—S polymers are preferred (small amounts of S—EP—S are also used). To obtain a satisfactory balance of properties, they must be compounded with oils, fillers, or other polymers compounding reduces costs. Compounding ingredients and their effects on properties are given in Table 8. Oils with high aromatic content should be avoided because they plasticize the polystyrene domains. Polystyrene is often used as an ingredient in S—B—S-based compounds it makes the products harder and improves their processibility. In S—EB—S-based compounds, crystalline polyolefins such as polypropylene and polyethylene are preferred. Some work has been reported on blends of liquid polysiloxanes with S—EB—S block copolymers. The products are primarily intended for medical and pharmaceutical-type applications and hardnesses as low as 5 on the Shore A scale have been reported (53). 

Plasticizers. These materials are added to reduce the hardness of the compound and can reduce the viscosity of the uncured compound to facilitate processes such as mixing and extruding. The most common materials are petroleum-based oils, esters, and fatty acids. Critical properties of these materials are their compatibility with the rubber and their viscosity. Failure to obtain sufficient compatibility will cause the plasticizer to diffuse out of the compound. The oils are classified as aromatic, naphthenic, or paraffinic according to their components. Aromatic oils will be more compatible with styrene-butadiene rubber than paraffinic oils, whereas the inverse will be true for butyl rubber. The aromatic oils are dark colored and thus cannot be used where color is critical, as in the white sidewall of a tire. The naphthenic and paraffinic oils can be colorless and are referred to as nonstaining. 

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