Polychloroprene extrusions

Due to its balance of strength, oil resistance, inflammability, increased resistance to ozone, ageing and weathering, polychloroprene finds widespread industrial use. Typical uses are V-belts, conveyor belts, wire and cable jacketing, footwear, wet suit applications, coated fabrics, inflatables, hoses, extrusions and many other goods. Adhesives are also a strong market area. 

Polychloroprene (Neoprene), 19 828-866 from butadiene, 4 384t calendering and extrusion of, 19 851 commercial conversion of, 19 846-851 compared with EPDM and natural rubber, 19 846t... 

Fast extrusion furnace black with a particle size of 360 A, was used to verify different theoretical concepts of percolation which by definition predicts a rapid change in conductance when volume fraction of conductive particles attains a critical value. Figure 15.38 shows the effect of a carbon black addition to polychloroprene. Up to 30 phr carbon black, the conductivity of poly chloroprene is almost constant and then it increases linearly as concentration of carbon black increases. The following equation applies o = o (P - P Jwhere c is constant, P is concentration of conducting particles, Pc is percolation threshold, and P is exponent which accounts for cluster size."" When data from the Figure 15.38 are replotted as in Figure 15.39 it is evident that the percolation law is valid. 

Synthetic rubbers, EPM/EPDM, nitrile, polychloroprene (neoprene), epichlorohydrin, and polyacrylate have good oil resistance, heat stability, and chemical resistance. Fluoropolymers are used in oil and gas wells 20,000 ft (6096 m) deep. These depths can have pressures of 20,000 Ib/in (137.5 MPa) which cause extrusion failures of down-hole seals by forcing the rubber part out of its retaining gland. TFE/propy-lene jackets protect down-hole assemblies which consist of stainless steel tubes that deliver corrosion-resistant fluid into the well. 

The sol-gel blend or pre-crosslinked grades of polychloroprene such as the T Type polychloroprenes available from DuPont Dow contain a highly cross-linked network, which that acts as an internal processing aid (94,95). The hlend has many of the same characteristics as the sol component, hut different compoimd rheology properties. This composition results in faster extrusion with extrudates having smoother surfaces. Extrudates also retain their shape better with good definition until vulcanized. 

Calendering and Extrusion. Friction compounds are used to build up composite structures of fabric and rubber. The surface of the calendered fabric mnst have good green strength or building tack. Thus calendered stocks are nsnally made from slow-crystallizing polychloroprene types. Polychloroprene... 

Extrusion. Polychloroprene has been employed in a wide variety of extrusion (qv) processes. Intricate cross-sections such as highway compression seals, bulb weather-stripping, and hose represent a few examples. As with calendering, extrusion is very sensitive to nerve. The DuPont Dow neoprene sol/gel blend types are best suited for extrusion applications. Use of low levels of highly structmed furnace carbon blacks, stearic acid, petroleum, paraffin wax, triethanolamine benzoic acid, and calciiun stearate are particularly effective extrusion aids. The screw of the extruder should have a constant diameter root with increasing pitch. Heat history of the compound should be minimized, with only a brief warm-up before extrusion begins. The barrel and screw should be lun cool, 50°C, and the die hot, 95°C (96,119). 

T-types are similar to W-type polychloroprenes but contain a high level of gel, which in this instance offers improvements in processing. They find use where fast, imiform extrusions and calendering is required. 

The monitoring of airborne monomer concentrations around subsequent processing operations may provide one index of the efficiency of such stripping. For example, Nutt has found chloroprene concentrations as high as 20 ppm around polychloroprene latex dipping, whilst 18-45 ppm of methyl acrylate has been found next to dies during the extrusion of Vamac ethylene/acrylic rubber at temperatures between 71 and 93°C. ... 

Mercaptan modified polychloroprenes are preferred because they not only give better insulation values but are more extendable and have better extrusion properties such as speed and smoothness. However, sulphur modified (G) types are sometimes used if high tear strength is needed. 

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