Polychloroprene ageing

Of the dihydric phenols, catechol exhibited a significant synergistic accelerating effect on joint use with TMTD in curing systems for polychloroprene. Ageing... 

Chloroprene Elastomers. Polychloroprene is a polymer of 2-chloro-l,3-butadiene. The elastomer is largely composed of the trans isomer. There are two basic polymer types the W-type and the G-type. G-types are made by using a sulfur-modified process W-types use no sulfur modification. As a result, G-types possess excellent processing and dynamic properties, and tend to be used in V-belts. However, they have poorer aging properties than W-types. The W-types tend to be used in appHcations requiring better aging, such as roUs and mechanical goods (see Elastomers, SYNTHETIC-POLYCm.OROPRENE). 

Neoprenes. Of the synthetic latices, a type that can be processed similarly to natural mbber latex and is adaptable to dipped product manufacture, is neoprene (polychloroprene). Neoprene latices exhibit poor initial wet gel strength, particularly in coagulant dipped work, but the end products can be made with high gum tensile strength, oil and aUphatic solvent resistance, good aging properties, and flame resistance. There are several types of neoprene latex, available at moderately high (ca 50 wt %) and medium soHds content. Differences in composition between the types include the polymer s microstmcture, eg, gel or sol, the type of stablizer, and the total soHds content (Table 22). 

Two propylene oxide elastomers have been commercialized, PO—AGE and ECH—PO—AGE. These polymers show excellent low temperature flexibihty and low gas permeabihty. After compounding, PO—AGE copolymer is highly resiUent, and shows excellent flex life and flexibiUty at extremely low temperatures (ca —65°C). It is slightly better than natural mbber in these characteristics. Resistance to oil, fuels, and solvents is moderate to poor. Wear resistance is also poor. Unlike natural mbber, PO—AGE is ozone resistant and resistant to aging at high temperatures. The properties of compounded ECH—PO—AGE he somewhere between those of ECH—EO copolymer and PO—AGE copolymer (22). As the ECH content of the terpolymer increases, fuel resistance increases while low temperature flexibihty decreases. Heat resistance is similar to ECH—EO fuel resistance is similar to polychloroprene. The uncured mbber is soluble in aromatic solvents and ketones. 

During World War II, several new synthetic elastomers were produced and new types of adhesives (mainly styrene-butadiene and acrylonitrile copolymers) were manufactured to produce adequate performance in joints produced with new difficult-to-bond substrates. Furthermore, formulations to work under extreme environmental conditions (high temperature, resistance to chemicals, improved resistance to ageing) were obtained using polychloroprene (Neoprene) adhesives. Most of those adhesives need vulcanization to perform properly. 

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... 

Mercaptan-inodified polychloroprenes provide lighter colour to solutions and are more resistant to discolouration than sulphur-modified polychloroprenes. Also mercaptan-modified polychloroprenes exhibit better ageing, and improved thermal and solution stability. 

Neoprene GN (1942). It is a general-purpose sulphur-modified polychloroprene used in the shoe industry. This polychloroprene has two limitations the viscosity decreases on ageing and a black discolouration appears during storage. 

Acid acceptor. This is the main function of metal oxides in CR adhesive formulations. Upon age, small amounts of hydrochloric acid are released which may cause discolouration and substrate degradation. Magnesium oxide (4 phr) and zinc oxide (5 phr) act synergistically in the stabilization of solvent-borne polychloroprene adhesives against dehydrochlorination. 

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. 

Heat, See also High temperature entries Hot entries Temperature entries Therm- entries effect on rubber aging, 27 785 in ethylene oxidation, 70 650 exponents of dimensions, 8 585t external resistance to, 25 312-316 in industrial hygiene, 74 221 wood reaction to, 26 348-351 Heat aging, of polychloroprene polymers, 79 844-845... 

In 1931 Du Pont introduced the first synthetic elastomer, polychloroprene (Neoprene , Duprene ), and Thiokol Corporation introduced a polysulfide rubber called Thiokol . Polychloroprene, although veiy expensive compared to polyisoprene, has superior age resistance and chemical inertness. It is also nonflammable. 

In addition, some rubbers, for example natural rubber and polychloroprene, stiffen at low temperatures by partial crystallisation. This is a gradual process continuing over many days or weeks and is most rapid at a particular temperature characteristic of each polymer, for example -25°C for natural rubber. Hence, tests intended to measure the effect of crystallisation must detect changes in stiffness or recovery after periods of ageing at a low temperature. 

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). 

The analysis of rubbers containing large amounts of carbon black by IR spectroscopy is difficult, particularly studies of their chemical evolution upon ageing. The use of a horizontal ATR accessory equipped with a germanium crystal is described. Horizontal ATR(Ge)/FTIR analysis of both thermal- and photooxidations of EPDM, polychloroprene and NBR were first validated by conventional transmission spectroscopy in the absence of carbon black. Horizontal ATR(Ge) was then used with fully formulated rubbers with the aim of studying their long-term behaviour. The effects of temp., UV exposure, carbon black or stress as well as the oxidation profile across the materials on... 

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