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Interactions Between Elastomers And Oils
The chemical name for rubber is elastomer. Whether rubber gloves or rubber bands, elastomers can be deformed by stretching but bounce back to their original shape and size when released from the deforming force. Natural and synthetic rubbers consist of polymers ̵1; large molecules of mostly carbon and hydrogen atoms together with smaller amounts of nitrogen, chlorine, sulfur or other elements to form large chains. When placed in an oil or other fluid environment, elastomers react with the liquid in varying degrees. Rubber products swell or shrink upon absorbing the liquid, lose their elasticity and eventually can dissolve. Over time, all rubbers are incompatible with oil-based substances.
Natural Rubber Latex
Natural rubber latex is the most reactive of rubbers to oils, fats and greases. These include baby oil, oil-based creams and sun lotions. This rubber swells up rapidly on contact with oil and dissolves. Latex, the milky white sap of the brasiliensis rubber tree, is the raw material that is processed to produce an exceptionally elastic rubber. It doesn̵7;t puncture or breach easily and is ideal for medical gloves, but it triggers an allergic reaction in some wearers.
Chloroprene Rubber
Neoprene, the trade name for chloroprene rubber, offers better protection against oils, greases and oil-based compounds than latex. Neoprene gloves are versatile and resistant to automobile chemicals. However, this is not the case if neoprene has a prolonged exposure to oils. Swedish oil company Nynas demonstrated that neoprene swelled when immersed for one week in various base oils. Base oils are refined crude oil products and account for between 70 percent and 99 percent of a lubricant̵7;s content. They can be either paraffinic, naphthenic or aromatic depending on their molecular structure. Naphthenic oils have a low wax content are are good solvents. Paraffinic oils are stable at high temperatures and are the most widely used oils in motor lubricants. In the Nynas experiment, naphthenic oils caused the maximum swelling in neoprene, while paraffinic oils caused the least amount of swelling. The demonstration showed that while these base oils caused an initial loss of elasticity in neoprene, it would take a long time for them to dissolve neoprene rubber gloves.
Nitrile Butadiene Rubber
Commonly called nitrile or NBR, nitrile butadiene rubber is the most common replacement for natural rubber or neoprene in protective gloves. It is more resistant to cuts and abrasions, resists oils, greases and animals fats than latex and does not contain the latex proteins that cause allergies. Nynas demonstrated that a long immersion in base oils causes an initial loss of elasticity in nitrile. In contrast to neoprene, nitrile shrank when immersed for a week in the oils. Paraffinic oils caused the greatest amount of shrinkage in nitrile, while naphthenic oils caused the least amount of shrinkage. However, nitrile rubber gloves would also take a long time to dissolve in oil.