Chloroprene rubber (CR)

Chloroprene rubber is a material that combines many favorable properties. These include, for example, good static and dynamic mechanical properties, decent heat, weather and ozone resistance, and average oil resistance.

In this respect, chloroprene rubber was one of the most important synthetic rubbers for a long time. Nowadays, chloroprene is being replaced in many applications by rubbers that have better values in terms of specific, targeted properties.

Chloroprene compounds are also known to many under the name Neoprene®, under which they are marketed by DuPont.

Due to its interesting property profile and its still widespread use, we would like to take a closer look at the material chloroprene in the following blog post, explain why the name chloroprene is not entirely correct chemically, and describe its mechanical characteristics as well as its thermal and chemical resistance in detail.

In the first half of the 20th century, the demand for rubber increased sharply, especially due to developments in the automotive sector, which promoted research into synthetic rubbers in particular. At this time, the U.S. company DuPont discovered the polymerization of 2-chloro-1,3-butadiene (chloroprene) and was thus able to develop a new elastomer. Further developments led to the production of polychloroprene in 1935, which has since been marketed by DuDont under the brand name Neopren®.

Chloroprene rubber (CR) is thus an umbrella term for rubber compounds that have chloroprene (2-chloro-1,3-butadiene) as their monomer base. For the sake of simplicity, chloroprene rubber (or corresponding compounds) is therefore often referred to as chloroprene for short, which is therefore not entirely correct from a chemical point of view.

Chloroprene rubber can be crosslinked with the aid of sulfur compounds and, above all, with metal oxides (magnesium oxide or zinc oxide) or peroxides. 

Mechanical properties of chloroprene rubber (CR)

Rubber parts made of chloroprene rubber are generally characterized by very good mechanical values. The tear resistance is generally quite high and is only slightly below the enormous tear resistance of natural rubber. In terms of tear strength, the values are even comparable with natural rubber. If chloroprene compounds are modified with sulfur, the tear strength increases even further. Positive effects can then also be expected in dynamic applications. The integration of flexible sulfur groups into the polymer chain leads to an improvement in dynamic properties. Either way, however, the dynamic properties of chloroprene rubber are very decent.

The compression set of chloroprene is highly dependent on the crosslinking system and the particular compound structure. It is without a doubt possible to create chloroprene compounds that achieve good compression set values.

Chloroprene rubber features good adhesion to metallic substrates, making it well suited for finished parts where a rubber-to-metal bond is required.

Chloroprene rubber compounds can be adjusted to hardnesses between 20 Shore A and 90 Shore A.

Thermal properties of chloroprene rubber

Overall, the temperature resistance of chloroprene can be described as good.

The heat resistance of finished parts made of chloroprene rubber compares favorably with articles made of other diene rubbers. In continuous use (over 1,000 hours), the heat resistance is around 100 degrees Celsuis or 215 degrees Fahrenheit. Molded parts made of chloroprene can also be exposed to temperatures of up to 120 degrees Celsuis or 250 degrees Fahrenheit for short periods. It should be noted that the hardness of the finished parts can increase significantly at higher temperatures in conjunction with atmospheric oxygen.

For applications with higher heat resistance requirements, other elastomers should be used.

The cold resistance of chloroprene is around -40 degrees Celsuis (-40 degrees Fahrenheit). Cold flexibility can be improved somewhat by using synthetic plasticizers.

Chemical resistance of chloroprene rubber (CR)

A particular strength of chloroprene rubber is its high flame retardancy. Although rubber molded parts made of chloroprene burn when exposed to a direct flame, they also extinguish as soon as the flame is removed. Chloroprene rubber is thus considered a self-extinguishing rubber. However, due to its halogen content, finished parts made of chloroprene rubber are not very suitable for use in electrical insulation. However, its good flame retardancy allows it to be processed into or used as cable sheathing or cable conduit.

The ozone, weathering and aging resistance of chloroprene is also good and, for example, better than that of NBR, but somewhat weaker than that of EPDM or silicone rubber. However, molded parts made of chloroprene are superior to other elastomers, especially under dynamic stress.

There is good resistance to water. The same applies to acids and alkalis.

Chloroprene rubber generally exhibits moderate oil resistance. It is good, for example, against silicone oils and greases as well as paraffinic mineral oils with low VAI / high aniline point such as ASTM oil 1. By contrast, resistance is average with ASTM oil 2, i.e. naphthenic mineral oils with high VAI / low aniline point.

With hydrocarbons, the resistance of chloroprene is average if they are low molecular weight aliphatic. On the other hand, there is no resistance to aromatic and chlorinated hydrocarbons such as benzene and trichlorehtylene.

Insufficient resistance, leading to severe swelling of rubber parts made of chloroprene, exists to typical solvents such as acetone or ethyl acetate, as well as esters and ketones.

Applications of chloroprene rubber

Nowadays, rubber parts made of chloroprene are mainly used where high flame resistance as well as good weathering and aging resistance are required.

The general property profile of chloroprene rubber leads to its use in the technical sector, for example, as hoses, belts, roller coverings, cable sheathing or conveyor belts. Chloroprene seals are also produced for various applications in industry, construction or motor vehicles.

The good dynamic properties as well as a decent chemical resistance also allow the use of chloroprene for the production of diaphragms.

Chloroprene is also used in sportswear and diving gear, where it is particularly known under the trade name Neopren®. 

In some areas, such as profile seals for windows, chloroprene rubber has been replaced by EPDM.

Chloroprene rubber is used to a large extent in the manufacture of technical rubber parts, but due to its pronounced tendency to crystallize it is also used as a base for glues, adhesives and insulating materials.

Overview of chloroprene rubber properties

In conclusion, here is a recap of the properties of chloroprene rubber.

Remember, this is only a general guide and not to be used for your ultimate selection of materials. The individual properties of blends can be positively and negatively influenced by targeted formulation and as such may be different from the information presented here.

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For more details about properties or chemical resistance, or if you have a query about a particular application, please do not hesitate to contact us.  

If you have a question about this blog post or would like us to discuss a particular aspect of elastomers in an upcoming blog, please email us on info@hepako.de   

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