Is neoprene an EPDM



Chloroprene rubber, also polychloroprene or chlorobutadiene rubber, better known in German-speaking countries as Neopren®, is a polymer based on 2-chloro-1,3-butadiene (chloroprene) and special rubber (elastomer) for various technical applications. The abbreviation according to ISO 1043 (1975) for chloroprene rubber is CR. Neoprene® is a brand name of the DuPont company. Other manufacturers sell similar products (e.g. Baypren® from Lanxess).

Structural formula

Cl Cl Cl Cl | | | | ...- CH2-CH = C-CH2-CH2-CH = C-CH2-CH2-CH = C-CH2-CH2-CH = C-CH2-...

The double bonds are both in trans- as well as in cis-To find a position. The relationship trans / cis is about 9: 1. The vinylic bonded chlorine atoms are very inert and contribute to the stability and resistance of polychloroprene. Installation in the 1,2 and 3,4 positions also occurs to a very small extent. The resulting structures are called 1,2- or 3,4-units in the literature and occur in the polymer chain in the order of one percent, depending on the polymerization temperature.

Cl | ...- C-CH2-... (1,2 structural unit) | C = CH2 ...- CH2-CH -... (3,4 structural unit) | Cl-C = CH2

Due to the much more reactive chlorine atom, the 1,2-unit is of crucial importance for the crosslinking (vulcanization) of the polymer.

history

In 1930 Arnold Collins, in the team of Wallace Hume Carothers, among others. For the first time polychloroprene polymerized under economically favorable conditions in the emulsion process. In 1932, the American company DuPont brought the polymer onto the market under the name Duprene, later in 1938 as Neoprene. In the following decades there were various improvements in terms of the manufacturing process and polymer properties:

  • Copolymers with sulfur (Neoprene GN) for improved processability 1939 (DuPont)
  • Mercaptan-regulated M-grades in the 1950s (DuPont) for improved heat resistance and solubility
  • Xanthogen disulphide-modified XD grades (Bayer AG) in the 1980s for improved properties of the vulcanizates and reduced tendency to crystallize.

Manufacturing

Chloroprene rubber is produced on an industrial scale using the emulsion polymerization process.

Due to the regular structure and high proportion of 1,4-trans linkages of the monomer during the polymerization, polychloroprene tends to crystallize more or less, which leads to hardening of the material some time after processing. This is desirable for adhesives, but less so for rubber articles (vulcanizates). By suitable choice of the polymerization temperature, of co-monomers and the use of regulators to adjust the molecular weight, the tendency towards crystallization can be influenced accordingly in the desired direction.

Properties and uses

When dissolved in organic solvents, polychloroprene is also suitable for various adhesives due to its good resistance. Vulcanizates, d. H. Rubber items with a corresponding compound structure are characterized by chemical resistance, good resistance to aging, weathering, ozone attack and flame retardancy.

  • Good resistance to swelling in mineral oils with a high aniline point, fats, many refrigerants and water (with a special mixture structure)
  • Medium resistance to swelling in mineral oils, low molecular weight aliphatic hydrocarbons (gasoline, isooctane).
  • Strongly swelling in aromatics, e.g. benzene, toluene, chlorinated hydrocarbons, esters, ethers, ketones.
  • Thermal application range approx. −45 ° C to +100 ° C depending on the mixture composition (briefly up to 130 ° C).

Hoses, cable sheathing, extruded profiles, seals and drive belts based on chloroprene rubber can be found particularly in the automotive industry thanks to their favorable combinations of properties.

A known application, e.g. B. as a material for diving suits, is the foamed vulcanizate. By using chemical blowing agents, which release gases below the vulcanization temperature, a pressure-resistant foam or foam or sponge rubber with excellent insulation properties can be obtained.

The worldwide consumption of chloroprene rubber including adhesives is estimated at over 300,000 tons.

vulcanization

Unlike most other unsaturated elastomers, chloroprene rubber cannot be vulcanized with sulfur. Metal oxides such as zinc oxide (ZnO) and magnesium oxide (MgO) are usually used to vulcanize polychloroprene. For reasons of environmental protection to a limited extent, lead oxide can be used for improved water resistance. A typical vulcanization accelerator is ethylene thiourea (also ETU = E.thylene Thio Urea) who acts as a sulfur donor (sulfur donor) applies. The chemical structures that arise during the vulcanization of polychloroprene by means of ZnO and MgO in the presence of ETU are exclusively due to the reaction of allylically bound chlorine, which is only present in a few percent in the polymer chain. Diallyl ether, diallyl thioether and C-C linkages from addition reactions through elimination of diene structures formed were proven to be network nodes. The majority of the vinylic bonded chlorine atoms do not react under the vulcanization conditions (approx. 160 ° C). For this reason, the crosslinking density of polychloroprene cannot be increased by adding more vulcanizing agents.

Polychloroprene can be blended with various other polymers: in a mixture with natural rubber (NR) or polybutadiene (BR) to reduce costs and improve low-temperature flexibility, with styrene-butadiene rubber (SBR) to reduce costs and reduce the tendency to crystallization, and with acrylonitrile-butadiene rubber (NBR) or ethylene propylene rubber (EPDM) to improve oil resistance.

foamed neoprene

Many small gas bubbles are evenly distributed in the foamed neoprene, which gives it excellent thermal insulation properties. This use is best known for the production of cold protection suits for water sports (diving suits, surf suits), but also bottle coolers, sports bandages and protective covers of all kinds, sound insulation bearings for flights of stairs or other supports

For the use of sportswear, neoprene is produced in different thicknesses according to the desired thermal insulation. Thicker material insulates better, but is also less stretchy and has a higher buoyancy.

Usually is Neoprene Laminated on both sides with textile fabric (nylon or Lycra), which closes the surface and is less prone to damage. Smooth skin neoprene is only laminated on one side and has a closed, smooth rubber surface on one side. This material is suitable for waterproofing strips within the Neoprene-Dress. In addition to the laminated suit versions, there are also uncovered ones. They are particularly elastic and, because of their tight fit, also water and heat insulating. The advantage is particularly in the flexibility, which allows great freedom of movement. A disadvantage is their sensitivity to mechanical influences.

In the production of Neoprene-Clothing, the material is glued together butt.

literature

  • R. Musch, E. Rohde and H. Casselmann, Kautsch. Rubber, plastic 49 (1996) 340
  • R. Musch, Hagg, The Polymeric Materials Encyclopedia, CRC Press, Inc. 1996

Category: Plastic