CSM (chlorosulfonated polyethylene)

CSM – chlorosulfonated polyethylene – is produced by the chemical treatment of polyethylene: chlorine and sulphonyl chloride groups are deliberately incorporated into the polymer chain. It is precisely this modification that is the key to the property profile of CSM: the chlorine in the backbone gives the material flame retardancy and chemical resistance, while the sulphonyl chloride groups serve as cross-linking sites during vulcanisation – typically with metal oxides such as magnesium oxide or lead oxide.

In the past, lead oxide was frequently used for the highest water resistance, although today, owing to strict environmental and health guidelines (such as REACH), it is mostly replaced by safe alternatives in modern compounds.

The result is an elastomer with an unusually broad resistance to aggressive environmental conditions, which is used particularly where other synthetic rubbers reach their limits.

Properties of CSM

Typical of CSM elastomers are:

• very good resistance to ozone, UV radiation and weathering – CSM is one of the most weather-stable elastomers of all
• very good oxidation resistance, including towards concentrated oxidising acids such as nitric acid and chromic acid
• good resistance to dilute acids, alkalis and many inorganic chemicals
• good ageing resistance at elevated temperatures
• good flame retardancy owing to the chlorine content in the polymer backbone – similarly to CR , CSM is self-extinguishing
• moderate resistance to aliphatic hydrocarbons
• limited resistance to aromatic and chlorinated solvents, fuels and esters

The typical temperature operating range, depending on the compound, is roughly –30 °C to +120 °C. The mechanical properties – tensile strength, tear propagation resistance, abrasion resistance – are at a good level.

One weak point of CSM compared with EPDM is the compression set: the recovery capability, in particular at higher temperatures, is considerably poorer than that of EPDM. For permanently compressed sealing points – such as static flange seals above +80 °C – CSM is therefore only suitable to a limited extent. Anyone relying primarily on chemical resistance in such applications should check the compression-set values of the specific compound carefully and, where appropriate, consider EPDM as an alternative.

Owing to its dense polymer structure, CSM also exhibits a lower gas permeability than many standard elastomers – considerably lower than EPDM or silicone, although not at the level of IIR. For gas-carrying diaphragms and special seals in the process industry, where EPDM is not sufficient as a barrier material and butyl rubber reaches its chemical limits, CSM is a technically sensible compromise.

Classification: CSM and Hypalon®

The trade name Hypalon® goes back to DuPont and was for decades the most familiar brand name for CSM. Following the discontinuation of Hypalon production in 2010, other manufacturers today supply chemically comparable CSM types.

In practice, the name Hypalon® continues to be frequently used as a generic designation, but refers to the material type CSM as a whole. The specific properties depend – as with all elastomers – on the particular compound. The manufacturer's technical data sheets are authoritative in material selection.

Typical applications of CSM

The property profile makes CSM the first choice in applications where chemical aggressiveness, weathering resistance and fire protection come together:

• Cable sheathing and insulation – especially in areas with elevated requirements for flame retardancy and UV resistance
• Acid-resistant hoses – for handling oxidising acids and inorganic chemicals
• Container linings and tanks – protection against chemical media that would attack other elastomers
• Seals and diaphragms in the chemical and process industry
• Protective equipment and coatings in chemically stressed environments
• Rubber-to-metal bonded parts – CSM adheres very well to metal cores and fabric reinforcements, forming a chemically robust bond that remains permanently stable even under aggressive environmental conditions.
• Roof waterproofing membranes and outdoor applications – wherever long-term stability under UV and weathering is required
• Coloured outdoor applications and architectural profiles – CSM is one of the few high-performance rubbers that remains permanently weather-stable even in light colours (white, grey, coloured).

Other elastomers require carbon black as a fillerfor UV and ozone resistance and are thereby restricted to dark shades. Its outstanding colour stability makes CSM the first choice for coloured roofing membranes, hose outer layers and architectural exposed profiles in outdoor areas.

Key data and resistances of CSM at a glance

Disposal

According to the “Regulation on the European Waste Catalogue (AVV)”, the waste product from CSM can be classified according to Chapter 7 “Wastes from organic chemical processes” and the waste code 07 02 99. This waste code stands for waste classified as non-hazardous.

They can therefore be disposed of in normal household quantities with normal household waste. Please use the container provided by your public waste disposal authority for residual waste as the appropriate disposal container.

Synonyms: Chlorosulfonyl polyethylene rubber, Chlorosulfonated polyethylene