Experience in selecting oil resistant rubber
Oil resistant rubber refers to the ability of rubber to resist oil resistant effects such as swelling, hardening, cracking, and deterioration of mechanical properties. Rubber products in contact with oil can penetrate into the interior of the rubber during long-term use, causing swelling; On the other hand, oil substances can extract soluble coordination agents from vulcanized rubber, resulting in a decrease in the volume of vulcanized rubber. In addition, certain additives in synthetic lubricants can chemically interact with rubber, eroding polymer chains; Especially at high temperatures, it can cause cross-linking or degradation of rubber, and severe erosion can lead to the loss of working ability of rubber products.
When we refer to oil resistance, we generally refer to resistance to non polar oils such as fuel oil, mineral oil, and synthetic lubricants. According to the principle of similarity and compatibility, the types of oil resistant rubber that we often come into contact with precisely refer to some polar rubbers: NBR, HNBR, FKM, ACM, AEM, CSM, CR, FMVQ, CO, etc. How to choose a more suitable rubber type based on the different oils that rubber products come into contact with? Below is an introduction to the tolerance of each adhesive to different oils.
1、 Experience in selecting oil resistant rubber
1. Fuel resistance: FKM, FMVQ>CO>NBR>CR, CPE
Fluorine rubber FKM and fluorosilicone rubber FMVQ have the best resistance to fuel oil.
Chlorohydrin rubber has better fuel resistance than nitrile rubber. The fuel resistance of nitrile rubber increases with the increase of acrylonitrile content.
However, chloroprene rubber and chlorinated polyethylene rubber CPE have the worst fuel resistance.
Acid resistance, oxidation and oil burning resistance:
For acidic oxidized fuel, the hydrogen peroxide in acidic oxidized fuel can deteriorate the performance of vulcanized rubber, so the commonly used nitrile rubber and chlorohydrin rubber in fuel systems cannot meet the requirements of long-term use. Ordinary nitrile rubber compound, although it can reduce the permeability of acidic gasoline with increasing acrylonitrile content, cannot work for a long time in acidic gasoline at 125 degrees Celsius.
So it is generally better to choose FKM, FMVQ, or HNBR.
Mineral oil resistance:
Nitrile rubber is a commonly used mineral oil resistant rubber. The mineral oil resistance of nitrile rubber increases with the increase of acrylonitrile content. However, nitrile rubber with high acrylonitrile content has limited heat resistance. When the oil temperature reaches 150 degrees, hydrogenated nitrile rubber, fluororubber FKM, fluorosilicone rubber FMVQ, and acrylic rubber should be used.
When the oil temperature reaches 150 degrees, fluororubber FKM and fluorosilicone rubber FMVQ have the best effect. But the cost is high. To reduce costs, less than 50% acrylic rubber can be incorporated into fluororubber FKM, and the performance of the vulcanized rubber after use can be reduced by no more than 20%.
Acrylate rubber has better mineral oil resistance than nitrile rubber. Ethyl acrylate rubber has better heat and oil resistance than butyl acrylate rubber.
Synthetic hydrogen resistant lubricants:
The oil resistance of nitrile rubber increases with the increase of acrylonitrile content.
Nitrile rubber with high acrylonitrile content, used for synthetic lubricants with high aromatic content resistance.
Nitrile rubber with medium acrylonitrile content, used for synthetic lubricants with low aromatic content resistance.
Nitrile rubber with low acrylonitrile content is used in low expansion synthetic oils such as paraffin oil or where low temperature flexibility is more important than oil resistance.
The use of hydrogenated nitrile rubber can improve heat resistance, ozone resistance, and resistance to additives. Hydrogenated nitrile rubber is suitable for applications with resistance to hot oil between 140 and 150 degrees Celsius. The oil resistance and heat resistance are between nitrile rubber and fluororubber.
Fluorine rubber can withstand 200 degrees synthetic hydrocarbon lubricants for long-term operation. Silicone rubber can withstand 200 degrees synthetic hydrocarbon lubricants for long-term operation. And maintain good flexibility at -60 degrees.
Chlorohydrin rubber can work in synthetic hydrocarbon lubricants at -40 to+120 degrees Celsius for a long time, with low breathability and good ozone resistance. Defects are the corrosion of the mold and the phenomenon of returning to its original state after high-temperature aging.
The resistance of chlorosulfonated polyethylene rubber to synthetic hydrocarbon lubricants increases with the increase of chlorine content. Within the range of -20 to+120 degrees, it expands greatly in naphthenic and aromatic oils.
Silicon-resistant synthetic lubricants:
Generally, silicone oil is not easy to cause rubber expansion, but it can extract the plasticizer from the rubber. Styrene butadiene rubber, ethylene propylene diene monomer rubber, nitrile rubber, hydrogenated nitrile rubber, and fluororubber without plasticizers are all resistant to silicone liquids.
2、 Blending system of oil resistant rubber
To consider the oil resistance of rubber, in addition to the selection of its own rubber type, it is also necessary to pay attention to the selection of materials in the system.
1. Sulfurization system
Overall, increasing the crosslinking density can improve the oil resistance of vulcanizates. In oxidized fuel, nitrile rubber vulcanized with peroxide or semi effective vulcanization system has better oil resistance than sulfur vulcanization.
Nitrile rubber vulcanized with a peroxide curing system has the best stability at 40 degrees, but is not ideal in oxidized fuel at 125 degrees. The nitrile rubber vulcanized with cadmium oxide and sulfur donor system has good long-term thermal aging resistance in 125 degree oxidized fuel.
2. Filling system and plasticizer
Adding carbon black and white carbon black can improve oil resistance, and inorganic fillers can also be selected as nanoscale reinforcing fillers. Fillers with small particle sizes and sheet like structures can also help improve oil resistance.
GreenThinking ® PF81 is a rare broad-spectrum functional filler. Due to its microscopic sheet-like structure and high porosity, it can improve the oil resistance of rubber products and is widely used in oil resistant rubber formulations.
Softeners should be selected that are not easily extracted by oils, preferably using low molecular weight polymers such as low molecular weight polyethylene, oxidized polyethylene, polyester plasticizers, and liquid rubber. Softeners or plasticizers with high polarity and molecular weight are beneficial for oil resistance.
Mainly by adding antioxidants that are not easily extracted.