Polychloroprene rubber applications

Neoprene, or polychloroprene rubber (CR) was one of the very first synthetic rubbers produced. It was a material of choice for exterior applications such as profiles used in vehicles, building seals, and cables. Many more marketable products have benefited from this plastic. Except for SBR and IR, neoprene (CR) elastomers are perhaps the most rubberlike of all materials, particularly with regard to its dynamic response (Table 2.6). CRs are a family of elastomers with a property profile that approaches that of NRs (natural rubbers) but has better resistance to oils, ozone, oxidation, and flame. CRs age better and do not soften up on exposure to heat, although their high-temperature tensile strength may be lower than that of NRs. They are suitable for service at 250C (480F). 

Paraffinic Natural rubber Polyisoprene Butyl SBR Polychloroprene Textile application Caulking Sealants... 

Further information on rubber-based adhesives is to be found in specialized articles Natural Rubber-Based Adhesives, Nitrile Rubber Adhesives, Polychloroprene Rubber Adhesives Applications and Properties and Polychloroprene Rubber Adhesives Modifiers and Additives. 

It is interesting to compare the properties of NBR adhesives with those of another polar rubber Polychloroprene rubber adhesives applications and properties. 

Most Rubber-based adhesives may be cured by a sulphur-based vulcanizing system (see Rubber-based adhesives compounding), however, as mentioned in Polychloroprene rubber adhesives applications and properties, CR adhesives are cross-linked by various reactions involving the labile chlorine atoms in the repeat unit. This is reflected in the additives used, as discussed below. ... 

During the World War II, several new synthetic elastomers were prodnced, and new types of adhesives (mainly styrene-butadiene and acrylonitrile copolymers (see Nitrile rubber adhesives)) were manufactured to produce adequate performance in joints produced with new difficult-to-bond substrates. Furthermore, formulations to work under extreme enviromnental conditions (high temperature, resistance to chemicals, improved resistance to ageing) were obtained using polychloroprene (Neoprene) adhesives (see Polychloroprene rubber adhesives applications and properties and Polychloroprene rubber adhesives modifiers and additives). Most of those adhesives need vnlcanization in order to perform properly. 

Several elastomers can be used in rubber-based adhesives. The elastomer provides the backbone of the adhesive, so the main performance of the adhesive is provided by the rubber properties. However, several specific properties for application are imparted by adding other ingredients in the formulations. The most common elastomers used in rubber-based adhesives are natural rubber (NR), butyl rubber (BR) and polyisobutylenes, styrene-butadiene rubber (SBR), nitrile rubber (NBR) and polychloroprene rubber Neoprene) (CR). 

Polychloroprene rubber (CR) is the most popular and versatile of the elastomers used in adhesives see Polychloroprene rubber adhesives applications and properties and Polychloroprene rubber adhesives modifiers and additives. 

The elastomeric sheetings made out of butyl and polychloroprene rubbers were first introduced as barriers against water migration. In the early 1960s, EPDM rubbers were commercially available. Considering the superiority of EPDM-based membrane over other elastomers, its application to construction industry as moisture barrier was first introduced in the United States about 30 years ago. 

Polychloroprene rubbers find use in such applications as cable-sheaths, hose and weather strips. Latices are used in the production of dipped goods, such as gloves and balloons, foams, adhesives and corrosion-resistant coatings. 

The early commercial synthetic rubbers created were the polysulphide rubbers now known as Thiokols these rubbers had good oil resistance, unlike natural rubber, but with a very serious drawback which prevented their widespread acceptance, namely their smell. Processing of these materials in factory-size batches proved to be very obnoxious. Acrylonitrile-butadiene copol3nners (nitrile rubbers) were developed by Bayer and were to find eventually worldwide acceptance in many applications requiring oil resistance. In the mid 1930s polychloroprene rubbers became a commercial proposition after early experimental work at Du Pont. These rubbers, intermediate in properties between nitrile and natural rubber, soon found wide acceptance. 

Many rubbers and elastomers are comprised of long hydrocarbon segments, and thus can accept petroleum oils and other predominately hydrocarbon products for use as plasticizer or extenders. These products are available at a significantly lower cost than the synthetic ester plasticizers. Phthalates and adipates of linear alcohols are used to enhance low temperature properties of certain rubber applications, which cannot be met using the hydrocarbon extenders. Polar elastomers such as nitrile rubber and polychloroprene have low compatibility with hydrocarbons and require more polar products such as phthalates or adipates. 

The polychloroprene latex determines the initial tack and open time, the bond-strength development and hot bond strength, the application properties, and the adhesive s viscosity. Because most latices have low viscosities by compounding, most of the water-borne polychloroprene rubber adhesives are sprayable. Thickeners such as fumed silicas can be added to increase viscosity and thixotropy. 

The applications of polysulphide rubbers are due to their excellent oil and water resistance and their impermeability to gases. Because of other factors, including their unpleasant odour, particularly during processing, they are much less used than the two major oil-resistant synthetic rubbers, the polychloroprenes and the nitrile rubbers. 

Structural applications of rubber base adhesives were also obtained using rubber-thermosetting resin blends, which provided high strength and low creep. The most common formulations contain phenolic resins and polychloroprene or nitrile rubber, and always need vulcanization. 

During World War II, polychloroprene was chosen as a replacement for natural rubber because of its availability. Two copolymers of chloroprene and sulphur which contain thiuram disulphide were available (Neoprene GN and CG). One of the first successful applications of these polychloroprene adhesives was for temporary and permanent sole attachment in the shoe industry. However, these polychloroprene cements show a decrease in viscosity on ageing and a black discolouration appears during storage in steel drums. Discolouration was produced by trace amounts of hydrochloric acid produced by oxidation of polychloroprene... 

Butyl phenolic resin is a typical tackifier for solvent-borne polychloroprene adhesives. For these adhesives, rosin esters and coumarone-indene resins can also be used. For nitrile rubber adhesives, hydrogenated rosins and coumarone-indene resins can be used. For particular applications of both polychloroprene and nitrile rubber adhesives, chlorinated rubber can be added. Styrene-butadiene rubber adhesives use rosins, coumarone-indene, pinene-based resins and other aromatic resins. 

Fig. 25. Evolution of the tack of polychloroprene-aromatic hydrocarbon resin blends as a function of the resin content. Tack was obtained as the immediate T-peel strength of joints produced with 0.6 mm thick styrene-butadiene rubber strips placed in contact without application of pressure. Peeling rate = 10 cm/min.

The use of plasticisers, with other than PVC applications, is extensive. Many polar rubber sealants or caulking materials are plasticised in order to make them more pliable, e.g., polysulfides, polychloroprene (Neoprene ), nitrile rubber. Esters, similar to those employed with PVC, are used to render cellulose diacetate ("Acetate") overhead projection sheets more flexible. 

The chlorine atom also confers an increased level of resistance to oils, so that the oil resistance of polychloroprene is roughly intermediate between natural rubber and nitrile rubber, and is often sufficient for many applications. Polychloroprene is also self-extinguishing in flame tests. 

Ethylenethiourea has a wide variety of uses in addition to vulcanization, a principal application since 1948. The curing process converts most of the ETU to other compounds, but traces of it are still found in the rubbers. Neoprene (polychloroprene) is found largely in automotive parts, wire and cable insulation, construction and adhesives. Consumer products containing neoprenes include container seals (e.g., aerosol dispensers) and shoes. It is also an intermediate in the manufacture of antioxidants, dyes, fungicides, insecticides, pharmaceuticals, synthetic resins, and a constituent of plating baths. 

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