CR (Chloroprene Rubber)

CR – chloroprene rubber is a synthetic rubber based on chloroprene (2-chloro-1,3-butadiene). Its characteristic feature is the high chlorine content in the polymer backbone: it gives CR a combination of weathering resistance, flame retardancy and solid mechanical properties that scarcely any other standard elastomer covers in this breadth.

Properties of CR

Typical of CR elastomers are:

• very good resistance to ozone, UV radiation and weathering
• good ageing resistance – CR remains dimensionally stable and elastic even after a long period of use
• flame-retardant, self-extinguishing owing to the high chlorine content
• good resistance to refrigerants, including ammonia (R717), many HFC and HCFC refrigerants as well as alcohols
• good abrasion and flex-crack resistance
• good resistance to salt water and bases
• satisfactory resistance to dilute acids
• good resistance to mineral oils and greases – for oil-intensive applications, NBR or FKM is the better choice
• limited resistance to aromatic and chlorinated hydrocarbons, fuels and polar solvents

The typical temperature operating range, depending on the compound (https://kremer-tec.de/unternehmen/lexikon-elastomertechnik/glossar-begriff/compound-74.html), is roughly –20 °C (special types briefly down to –40 °C) to +100 °C. Special grades permit briefly higher temperatures up to approximately +120 °C.

A physical peculiarity of CR is storage crystallisation: in the temperature range from around +5 °C to –10 °C, crystalline structures can form within the polymer during prolonged storage – the component becomes hard without any ageing or reduction in quality being present. The effect is reversible: brief warming to around +50 °C restores the original elasticity. With this knowledge, complaints about unexpectedly hard goods can be avoided.

Flame retardancy: what the chlorine content achieves

CR burns within an open flame, but goes out as soon as the flame is removed – this effect is described as self-extinguishing. The cause is the chlorine content in the polymer backbone: it interrupts the combustion reaction as soon as no external ignition source is present any longer. CR thus meets the requirements of many fire-protection specifications and is sought after in safety-critical applications where other elastomers lack the corresponding approval.

Mechanical properties

Compared with many other synthetic rubbers, CR shows above-average characteristic values: tensile strength, tear propagation resistance and abrasion resistance are good, and its flex-crack resistance makes CR particularly suitable for dynamically stressed components and profiles.

The compression set is moderate – for permanently compressed sealing points with high requirements for long-term tightness, the specific compound selection should be checked carefully. In terms of process technology, CR differs from almost all other rubbers: cross-linking is not carried out with sulphur, but as standard with metal oxides – zinc oxide and magnesium oxide.

The ratio of these oxides influences the water absorption of the vulcanisate. For marine and offshore applications with permanent water contact, specially matched cross-linking systems are required in order to maintain dimensional accuracy and electrical insulation capability under water.

Typical applications of CR

The property profile of CR is tailored to applications in which weathering, ageing, refrigerants or fire protection play a central role:

• Refrigeration and air-conditioning technology – seals (https://kremer-tec.de/dichtungen.html), O-rings (https://kremer-tec.de/o-ringe.html) and profiles (https://kremer-tec.de/profile.html) in refrigeration systems and heat pumps, especially with ammonia- or alcohol-based refrigerants
• Fire-protection applications – seals, cable grommets and moulded parts in areas with elevated requirements for flame retardancy
• Construction and façade technology – weather seals, window-sill profiles, expansion-joint profiles with a long outdoor service life
• General mechanical engineering – hoses, grommets, vibration dampers and moulded parts (https://kremer-tec.de/formteile-spritzgussteile.html) with requirements for media and weathering resistance
• Marine and offshore – seals and profiles with good salt-water resistance; for permanent water contact, special compounds with an optimised oxide cross-linking system are required, in order to minimise swelling and a rise in electrical conductance

Disposal

According to the “Regulation on the European Waste Catalogue (AVV)”, the waste product from CR 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: Neoprene®