Factors affecting the oil resistance of rubber


The oil resistance of rubber refers to the characterization of the oil resistance of vulcanizate under the condition of long-term contact with the oil medium. Generally speaking, the rubber soaked in oil will have two changes: the oil of small molecules will continuously migrate and At the same time, the compounding agents in the rubber (including plasticizer, antioxidants, and other substances) will also be continuously extracted and diffused into the oil, resulting in the shrinkage of the rubber volume; When the oil absorption of rubber is greater than the extraction of compounding agent, the volume of rubber increases macroscopically; On the contrary, the volume becomes smaller. The longer the immersion time, the greater the degree of swelling or extraction . When the rubber is completely saturated with oil, the volume will remain unchanged, and it can be considered that it has reached equilibrium; The str The ucture of rubber will change with the extraction of various additives.

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The oil resistance of rubber is usually expressed by the physical property change, volume, and mass change rate of vulcanized rubber after soaking in oil. According to the volume expansion rate of different rubber in ASTM No.3 oil, the oil resistance of rubber is divided into ten grades.

According to the theory of “similarity and compatibility”, the greater the absolute value of the solubility parameter difference between oil and rubber, the harder the rubber will swell and the better the tolerance to the oil. In short, polar rubber products can be used in non-polar mineral oil. The oil resistance of rubber can be expressed by the volume change rate after oil immersion. If the volume change rate in oil is too large, it indicates that the oil resistance of rubber is poor and oil leakage and other accidents are easy to occur; The smaller volume indicates that the extraction of the mixture is more serious, which will seriously pollute the sealed medium 7; Zhang Fengling [18 et al. Found by studying the effects of two aviation hydraulic oils (YH-10 and yh-15) on the properties of nitrile rubber: the increase of additive content in hydraulic oil will have a great impact on the service performance of nitrile rubber seals. Therefore, the chemical composition in the additive w ill damage the molecular structure of rubber, which is an important reason for the damage of product properties after oil immersion.

The most important factor affecting the oil resistance of rubber is the nature of rubber itself. The structure of rubber largely determines the medium environment it can adapt to. General oils are usually nonpolar, so rubbers with polar side groups connected to the macromolecular main chain ( such as FKM, HNBR, Co, ACM, NBR, etc.) usually have strong oil resistance. Among all oil-resistant rubbers, fluorine atom-containing rubbers (fluoro rubber sheet, fluorosilicone rubber sheet, and fluorometer rubber sheet) have good resistance to both ordinary fuel and peroxide mixed fuel. However, due to the high price, they are rarely used except in some extreme environments. Among the general rubber, nitrile rubber has the best oil resistance, and with the increase of acrylonitrile content, the oil resistance of NBR gradually improves, which is the largest oil-resistant rubber material at present.

Vulcanization is an important technological process of rubber. The type and degree of a crosslinking bond will greatly affect the service performance of rubber products. For oil-resistant rubber materials, properly increasing the degree of crosslinking can effectively reduce the volume expansion of products after oil immersion. Through the study of HNBR sealant, Zhou Yang found that the greater the cross-linking degree of HNBR, the smaller the compression set of the sealant. This is because, with the increase in crosslinking degree, the number of crosslinking points increases and the network structure becomes more and more perfect. The crosslinking points formed by the chemical reaction are equivalent to fixing the molecular chain at a certain position, which greatly weakens its movement ability. When the oil is immersed in the rubber, the molecular chain is difficult to fully extend, which also limits the further diffusion of the oil; For sealing products, the greater the crosslinking degree of the rubber, the stress borne by each molecular chain will be relatively reduced, and the possibility of permanent deformation caused by sliding of rubber molecular chain under the action of compressive stress will be greatly reduced; Therefore, the swelling degree and compression set are effectively reduced, which is conducive to maintaining the sealing performance. Weng Guowen and others found through the research on the diesel resistance of NBR that the curing system of dpi / s can effectively improve the performance retention of NBR hot diesel after aging. Compared with pure sulfur or peroxide vulcanization system, DCP / s NBR has the advantages of a small compression set and good cold resistance.

Carbon black is an important rubber reinforcing agent. By filling different kinds and amounts of carbon black, rubber materials with different performances can be obtained, and the production cost can be reduced. In oil-resistant rubber products, filling carbon black can effectively reduce the swelling degree of rubber, because the swelling is mainly caused by oil entering the rubber molecules. Filling carbon black can effectively reduce the rubber content of rubber and help to improve the swelling resistance. In the selection of plasticizers, oil-resistant rubber materials should use high molecular weight plasticizers that are not easy to be extracted by oil. Generally speaking, plasticizers with large molecular weight and polarity are of great help to improve oil resistance. Due to the harsh service environment and high service temperature of oil-resistant materials, the antioxidant should also be hot oil, which has good stability and is not easy to be extracted or processed by oil. The selection of reactive antioxidants in oil-resistant formula needs to be considered. Zhang Jian B0 et al. Studied the effect of a reinforcement plasticizing system on the oil and low-temperature resistance of NBR. It was found that the oil-resistant NBR material with good cold resistance can be obtained by using the reinforcing system of high abrasion-resistant carbon black and spray carbon black and using sebacic acid two octyl resin as a plasticizer.Click here to find more:  Suconvey Rubber