Polychloroprene CR

Over 600 million pounds of polychloroprene is produced in the world annually. This represents about 2.5% of all synthetic rubber production. 

Chloroprene monomer Is unstable, highly reactive, and must be stored in refrigeration. Transportation of monomer is limited and most monomer plants are located near the polymer plants 

Today more butadiene is produced from butene (another C4) through steam cracking of naphtha gas oil from ethylene/propylene production. Through extractive distillation of this C4 cracker stream, the butadiene is obtained. Commonly the yield achieved for BD is dependent on the quality of the feedstocks used for ethylene production. Usually the heavier the feedstock is, the greater the BD production. Reportedly, the hght feedstock only yields about one-fifth the yield of butadiene compared to the heavy feedstock. 

One major problem with the availability of polychloroprene in the recent past has been the availability of butadiene monomer. Because of the gradual switchover from naphtha feedstocks from petroleum to ethane feedstocks from natural gas in the production of ethylene for the plastics industry, there are fewer C4 streams available for butadiene production. Ethylene plants are gaining significant economic savings by making this feedstock conversion from naphtha to ethane. This has resulted in significant shortages of butadiene to the rubber industry. However, there is optimism now that butadiene will be more available than before because 

Polychloroprene is dependent on chloroprene (2-chloro-l,3-butadiene), which is mostly produced from the chlorination of butadiene. 

Neoprene is the generic name for polychloroprene rubber. It has been produced commercially since 1931 and had rapid and wide acceptance because it is much superior to natural rubber for heat and oil resistance. Heat resistance is far better than NR, BR or SBR. but less than EPDM. When heated in the absence of air, neoprene withstands degradation better than other elastomers which are normally considered more heat resistant, and retains its properties fifteen times longer than in the presence of air. Compression set at higher temperature is better than natural rubber and 100°C is typically the test temperature rather than 70°C. Abrasion resistance is not as good as natural rubber but generally better than most heat resistant and oil resistant rubbers. This is also true for tear strength and flex resistance. 

The resilience of gum neoprene vulcanizates is little lower than natural rubber but it decreases with increased filler incorporation. Therefore, the resilience of most practical neoprene compounds is higher than that of natural rubber with comparable volume loading. Because of the presence of chlorine in the neoprene molecule, products made from neoprene resist combustion to a greater degree than products made from non-halogen bearing rubbers. This means neoprene can be compounded to meet the flammability requirements of the Mine Safety and Health Administration (MSHA) USA or similar requirements as might be stipulated by any other countries, 

These same types of compounds are also more resistant to many acids at high temperatures than natural rubber can handle. Neoprene should not be used in parts which are bonded to metal for hydrochloric acid service because acid migration can cause failures. For hydrochloric acid service ebonite lined mild steel equipment is the correct selection. Ebonites form rubber hydrochloride film in contact with natural rubber and this film is the protective layer against corrosion. 

The cost of neoprene is very high when compared to NR, BR, or SBR and even other heat resistant and ozone resistant rubbers such as EPDM. So when EPDM can be used for such conditions for ozone and heat and not flame resistance, it should be the preferred rubber in place of CR. 

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Polychloroprene CR Satisfactory resistance organics fair poor with oxidative chemicals and hydrocarbon solvents Fair 0 to 100... 

Elastomer types used successfully in these areas are natural rubber (NR), polychloroprene (CR), and nitrile rubber (NBR), and hydrogenated nitrile rubber (HNBR), where oil resistance is also required. 

These steps are typical for most of the synthetic elastomers. The use of sulfur for vulcanization is common for the production of most elastomers. Magnesium and zinc oxides are often used for the cross-linking of polychloroprene (CR). Saturated materials such as EPM and fluoroelastomers are cross-linked using typical organic cross-linking agents such as peroxides. 

Lead stabilisers have been used in a variety of PVC as well as other polymers for many years. In some halogenated polymers, such as chlorinated PE (CPE), chlorosulphonated polyethylene (CSM), polychloroprene (CR) and epichlorohydrin (ECO), dibasic lead phthalate and dibasic lead phosphite are used to scavenge HC1 arising from crosslinking as well as from degradation. In some of these cases, the metal may participate in crosslink formation. With lead-based stabilisers, the result is typically a product with greater water and chemical resistance than if a light metal, with more soluble halide salts, were used instead. In other cases, lead stabilisers may be used solely for function in metal oxide... 

Oxidation Mechanism of CR. A chlorine substituent on the double bond Introduces considerable complexity In the degradation of trans-l,4-polychloroprene (CR). CR Is more resistant to oxidation than BR and IR, but Is subject to dehydrochlorlnatlon (32. 33, 34). 

Contact adhesives can also be processed in the form of aqueous dispersions, whereby the longer time required for evaporation of the water must be taken into account. These contact adhesives are also more sensitive to moisture. Typical examples of contact adhesives are solutions of polychloroprene (CR) (e.g., Baypren firom Bayer AG, Neoprene from DuPont). The solvents are xylene, benzine, cyclohexanone, ethyl acetate, or methylene chloride. CR is characterized by a pro-notmced crystallization behavior with a crystallite melting temperature of 53 C. The crystallinity is controlled in accordance with the specific formula in each case (adhesive contains Zn and Mg oxides that result in partial crosslinkage of chlorine to carbon with double bonds). The adhesive strength and heat resistance increase with the degree of crystallinity, UV stability and flexibility are very high. 

Styrene-Butadiene Random Copolymer, 25% (wt) Styrene (SBR) Styrene-Butadiene Block Copolymer, about 25% Styrene (YSBR) Cis-1,4- Polyisoprene (Natural Rubber NR, Also Made Synthetically IR) Cis-1,4 Polybutadiene (BR) Polychloroprene (CR), Neoprene Butadiene-Acrylonitrile Random Copolymer, Variable % Acrylonitrile (NBR) Reclaimed Rubber (Whole Tires) (Mainly NR and SBR)... 

Chloroprene rubber, polychloroprene (CR). A syniheXic rubber produced by polymerization of chloroprene (2-chlorobutadiene, CH2=CCl—CH = CH 2). High weather and chemical resistance, better oil resistance than that of natural rubber products. Some applications building sheets, belts, cable insulations, technical rubber goods, contact adhesives. Trade names Baypren (FRG), Neoprene (USA). 

It is proposed that this is due to attack of carbonyl oxides, in their biradical form, on the rubber double bonds. Typical diene rubbers (polyisoprene and polybutadiene) have rate constants several orders of magnitude greater than polymers having a saturated backbone (polyolefins). Other unsaturated elastomers having high reaction rates with ozone include styrene-butadiene (SBR) and acrylonitrile-butadiene (NBR) rubbers. As an example, Polychloroprene (CR) is less reactive than other diene rubbers, and it is therefore inherently more resistant to attack by ozone. 

Adhesion Properties of N330 and Attrited N330 Filled Polychloroprene (CR)... 

Polychloroprene (CR) has much more chlorine than the chlorobutyl rubber examined by Lawson and good adhesion to untreated CR wonld be expected provided there was no weak layer was on the surface. If such layers exist a suitable solvent treatment or abrasion should result in good adhesion. Cyclisation has been recommended as a pre-treatment [50, 51]. Lawson noted a large uptake of chlorine, nitrogen and oxygen on treatment of polychloroprene with TCICA, indicating addition across the carbon-carbon donble bond. 

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