What is the difference between nitrile rubber and silicone?

What is the difference between nitrile rubber and silicone?
1. Chemical structure and composition
Nitrile rubber (NBR)
Nitrile rubber is a synthetic rubber mainly composed of butadiene and acrylonitrile. The molecular chain contains carbon-carbon (C-C) double bonds and carbon-nitrogen (C-N) polar bonds. The structural characteristics of its molecular chain make nitrile rubber have good oil resistance, wear resistance and tear resistance. The content of acrylonitrile will affect the performance of nitrile rubber. For example, the higher the acrylonitrile content, the better the oil resistance, but the elasticity will be reduced.
Silicone
Silicone is a high molecular compound containing silicon atoms with silicon-oxygen (Si-O) bonds as the main chain. The main component is polyorganosiloxane, and the bond energy of silicon-oxygen bonds is high, which makes silicone have excellent thermal stability and chemical stability. Silicone molecular chains can also carry different organic groups, such as methyl, vinyl, etc. These groups can affect the physical and chemical properties of silicone, such as flexibility, hardness, etc.
2. Physical properties
Hardness
The hardness range of nitrile rubber is relatively wide, and products of different hardness can be obtained by adjusting the formula. The general hardness (Shore A) is between 40 and 90. For example, the hardness of nitrile rubber used to make oil seals may be around 70 to ensure good sealing performance and wear resistance.
The hardness of silicone can usually be adjusted, but its hardness range is relatively narrow. The hardness (Shore A) of silicone is generally between 30 and 80. For example, the hardness of silicone used to make silicone buttons may be around 40-50, and it feels relatively soft.
Elasticity
Nitrile rubber has good elasticity and strong elastic recovery ability. After being stretched by external force, it can quickly return to its original shape to a certain extent. For example, a sealing ring made of nitrile rubber can quickly rebound when the pressure disappears after being compressed to maintain the sealing effect.
Silicone also has good elasticity and can maintain good elasticity over a wide temperature range. The elasticity of silicone is softer. For example, when silicone products are squeezed, they deform relatively slowly and recover relatively smoothly after the external force disappears.
Tensile strength and tear strength
Nitrile rubber usually has high tensile strength and tear strength. Because of the double bonds in its molecular chain, a relatively strong cross-linked structure can be formed during the vulcanization process, which enables it to withstand greater tensile and shear forces. For example, when nitrile rubber is used to make conveyor belts, it can withstand the tensile force of heavier goods without breaking easily.
Silicone has relatively low tensile strength and tear strength. However, its strength can be improved to a certain extent through special formulas and reinforcing materials. For example, when making silicone molds, some reinforcing materials such as fibers are added to increase the strength of silicone to prevent the mold from tearing during demolding.
Three, chemical properties
Oil resistance
Nitrile rubber has excellent oil resistance. The acrylonitrile group in its molecular chain makes it have good tolerance to non-polar and weakly polar oils. For example, in the oil seal of a car engine, nitrile rubber can be in contact with engine oil for a long time without swelling, softening, etc., thus ensuring good sealing performance.
Silicone has poor oil resistance. Because its molecular structure is mainly composed of silicon-oxygen bonds and organic groups, it is easy to swell when it comes into contact with oils, especially when it comes into contact with non-polar oils, its physical properties will be greatly affected.
Chemical corrosion resistance
Nitrile rubber has a certain tolerance to some chemical substances such as acids and alkalis, but it is relatively weak. For example, in low-concentration acid and alkali solutions, nitrile rubber can maintain a certain stability, but in high-concentration strong acid and strong alkali environments, its performance will be damaged, such as hardening and cracking.
Silicone has excellent chemical corrosion resistance. It has good tolerance to most acids, alkalis and chemical solvents, and can maintain good performance in high-temperature and highly corrosive chemical environments. For example, silicone can be used to make seals in chemical experiments and can withstand the erosion of various chemical reagents.
IV. Processing performance and application areas
Processing performance
The processing of nitrile rubber requires the use of compounding agents such as vulcanizers. The vulcanization process is relatively complex, and parameters such as temperature and time need to be controlled. During the mixing process, care should be taken to prevent scorching. Its processing has high requirements for equipment. For example, it requires equipment such as internal mixers and open mixers for mixing and molding.
Silicone is relatively easy to process. Silicone can be vulcanized by heat or room temperature. Heat-vulcanized silicone requires a certain temperature and pressure during the vulcanization process, while room temperature vulcanized silicone can be vulcanized and molded at room temperature by adding a catalyst. Silicone has good fluidity in the mold and is easy to mold into complex shapes.
Application areas
Nitrile rubber is mainly used in areas that require oil resistance and wear resistance. Such as oil seals, O-rings, oil pipes, etc. in the automotive industry; seals, conveyor belts, rubber rollers, etc. in industrial equipment; and protective products such as oil-resistant gloves.
Silicone is mainly used in areas that require high temperature resistance, chemical corrosion resistance, high elasticity and good insulation. Such as sealing pads, buttons, silicone sleeves for electronic equipment; catheters, artificial organs, etc. in medical equipment; molds, conveyor belts, etc. in food processing.