Rubber – an overview of properties
There are 2 types of rubber Natural and Synthetic. Natural rubber is an elastic hydrocarbon polymer known as an elastomer that was originally derived from latex which is a milky colloidal suspension, found in the sap of some plants. Polyisoprene is the chemical of the purified form of natural rubber which can also be produced synthetically. Both natural rubber and synthetic rubber are used extensively in many applications and products. Depending on the use for which the rubber is intended, will influence which rubber type is used. Therefore below we give a broad overview of the properties of a number of different types.
This guide is only intended as a first step in selection – mainly to eliminate materials which are obviously unsuitable. Factors such as oxidation resistance and oil resistance and the properties of vulcanized rubber can be significantly influenced in the compounding. The base polymer, is mixed with fillers, anti-degradants, accelerators crosslinking agents and so on. To ensure that you have the correct compound for the intended job it is always advisable to test the compound to ensure it is fit for purpose. The latest ISO recommendations are used as the base for the abbreviations used. Depending on the final compound mix of any of the rubbers below the temperature ranges shown below will vary , and are given as a rough guide only. All the information given below is given in good faith, but Augesco International Ltd can accept no responsibility for the information. Full test should be made before any material is selected for use.
NATURAL RUBBER , abbreviation NR
It has a long fatigue life and high strength even without reinforcing fillers. This along with the outstanding strength of natural rubber has maintained its position as the preferred material in many engineering applications. It can be used to approximately 100C, other than for thin sections. It is able you retain its flexibility down to -60C if appropriately compounded. It has good creep and stress relaxation resistance . The main disadvantage is its poor oil resistance and its lack of resistance to oxygen and ozone, however these disadvantages may be overcome by chemical protection. Alternatively one of the following compounds maybe better suited
NITRILE RUBBER, abbreviation NBR
Nitrile rubber provides an economic material with a high resistance to aliphatic hydrocarbon oils and fuels. The higher the acrylonitrile (ACN) content, the higher the oil resistance but this reduces the low temperature flexibility. It has high resilience and high wear resistance but only moderate strength. It has limited weathering resistance, and poor aromatic oil resistance. The temperature ranges up to 100C, or with special compounding up to 120C and down to about -30C, but special grades can operate at lower temperatures.
STYRENE BUTADIENE RUBBER, abbreviation SBR
This a general purpose synthetic rubber. With suitable fillers it is a strong rubber although not approaching natural rubber. It has similar chemical and physical properties to natural rubber, with generally better abrasion resistance but poorer fatigue resistance
POLYCHLOROPRENE, abbreviation CR
Second only to natural rubber for its good balance of mechanical properties and fatigue resistance, it is however superior to Natural rubber for chemical oil and heat resistance. It has ozone resistance. It is unsuitable in contact with fuels however it is suitable for use with mineral oils and greases and dilute acids and alkalis. Generally it has a poorer set and creep than natural rubber. Without appropriate compounding it is less resistant than natural rubber to low temperature .
ETHYLENE PROPYLENE RUBBER, abbreviation EPDM
This material is widely used in sports surfaces and children playgrounds, due to the excellent resistance to atmospheric ageing, oxygen and ozone up to about 150C, up to 180C in steam for peroxide cures. With good resistance to most water-based chemicals and to vegetable-based hydraulic oils. But with poor resistance to mineral oils and di-ester based lubricants. Probably the most water resistant rubber available, and so used widely on flat roof installations.
BUTYL RUBBER, abbreviation IIR
Whilst not suitable for use in contact with mineral oils it is highly impermeable to gases, which makes it an idea material for the use in pneumatic inner tubes, and other high pressure applications. It has good ozone, weathering, heat, and chemical resistance.
SILICONE (and FLUOROSILICONE) RUBBER, abbreviations are FMQ,PMQ,VMQ or MQ
Whilst they do not have very good physical properties, the properties they do have are retained to high temperatures, typically the range is -60C to 200C and above. As such many are used in cookware . The FMQ range have better oil and water resistance than the others,due to their ability to be used in room temperature vulcanizing they are widely used in the building industry in sealants for joints. The above range is most generally used but other polymers are available for specific applications.