Neoprene Vulcanisates

The unique character of Neoprene vulcanisation is that rubber accelerators as a class are not effective. As a matter of fact several have measurable retarding effects and it has to be understood that mercaptobenzothiazole is an extremely potent retarder in Neoprene vulcanisation. Salicylic acid is a fast accelerator leading many a times to scorching or premature vulcanisation at higher dose levels [3]. 

By comparison, temperatures as high as 150°C are often required for mold-enclosed hard natural mbber compounds, where mold plattens are directly heated by steam or electricity. Synthetic latex mbber compounds, however, can be vulcanised at temperatures higher than those for natural mbber neoprene and acrylonitrile—butadiene can be vulcanised at as high as 135°C. 

FD-MS by itself provides only limited chemical information. Lattimer et al. [92] have also compared the analysis of extracted rubber vulcanisates by means of FD-MS and FAB-MS, using the aforementioned EI/FD/FT/FAB ion source. The systems investigated were neoprene/DOPPD, EPDM/(DOP, PBNA, paraffin wax), neoprene-SBR blend/(DOP, DOPPD, TDBHI). Certain compounds were observed by FD but not by FAB (wax, oil, isocyanurate antioxidant TDBHI). In FAB conditions some polymer additives suppress... 

In an acetone extract from a neoprene/SBR hose compound, Lattimer et al. [92] distinguished dioctylph-thalate (m/z 390), di(r-octyl)diphenylamine (m/z 393), 1,3,5-tris(3,5-di-f-butyl-4-hydroxybenzyl)-isocyanurate m/z 783), hydrocarbon oil and a paraffin wax (numerous molecular ions in the m/z range of 200-500) by means of FD-MS. Since cross-linked rubbers are insoluble, more complex extraction procedures must be carried out (Chapter 2). The method of Dinsmore and Smith [257], or a modification thereof, is normally used. Mass spectrometry (and other analytical techniques) is then used to characterise the various rubber fractions. The mass-spectral identification of numerous antioxidants (hindered phenols and aromatic amines, e.g. phenyl-/ -naphthyl-amine, 6-dodecyl-2,2,4-trimethyl-l,2-dihydroquinoline, butylated bisphenol-A, HPPD, poly-TMDQ, di-(t-octyl)diphenylamine) in rubber extracts by means of direct probe EI-MS with programmed heating, has been reported [252]. The main problem reported consisted of the numerous ions arising from hydrocarbon oil in the recipe. In older work, mass spectrometry has been used to qualitatively identify volatile AOs in sheet samples of SBR and rubber-type vulcanisates after extraction of the polymer with acetone [51,246]. 

In a demonstration of the corrosive effect of fuming nitric acid on rubber tubing, soon after the initial vigorous reaction had subsided, a small explosion followed by ignition occurred. (The sulfur compounds used to compound the rubber were probably involved) [1], Leaded neoprene rubber gloves, (the lead present as red lead, Pb304) used in the nuclear industry, may form explosive compounds in contact with nitric acid. It is hypothesised this could be lead fulminate formation. Since mixtures of lead nitrate with organics, or with sulfur from vulcanisers, would be explosive, this seems unduly complicated [2]... 

The formula is C H Cl, molecular weight is 88.5, degree of polymerisation is 1000-3500 and SG is 1.20-1.25. The vulcanised forms of polychloroprene are known as neoprene . It has good resistance to heat and flames, oils, acids and ozone, which makes it useful for outdoor end-uses such as shelters, covers and industrial protective clothing. 

Butyl rubber like Hypalon, Neoprene or nitrile rubber is a speciality polymer which can be compounded for a soft, deformable elastic vulcanisate similar to the other elastomers, but having certain distinctive characteristics, like low permeability to all gases and resistance to ageing and ozone cracking. Butyl has poor oil resistance and medium low temperature flexibility. 

The rate of diffusion in a given elastomer is found to be related chiefly to the size of the liquid/gases molecule. It is observed that the presence of polar group or methyl group in the polymer molecules reduces the permeability to a given liquid/gas. Therefore butyl, Neoprene and nitrile, along with ebonite, have a low value of permeability when compared with natural soft rubber vulcanisates. 

Most rubbers exhibit a degree of elastic recovery on deformation in the raw state even before vulcanisation, say, like natural and Neoprene rubbers. This nerve5 as it is called is excessive and it must be reduced during the mixing process to a controlled level so that... 

In the presence of light, halogens attack both vulcanised and unvulcanised butyl rubber. Whether vulcanised or unvulcanised the effect of the reaction is to produce rapid deterioration in molecular weight. A strip of butyl vulcanisate suspended in bromine gas degrades rapidly. In a few minutes the specimen becomes fluid enough to drip to the bottom of the vessel. Chlorosulfonated polyethylene is resistant to ozone being better than Neoprene and butyl rubber compounds [18]. 

Details A solid, an accelerator and vulcanising agent for rubber and a plasticiser (for Neoprene). 

Waddell and co-workers [64] applied this technique to Neoprene rubber compound surfaces. The LD-MS of the sulfur-vulcanised natural rubber (NR) Compounds 1 and... 

Solbit is a neoprene, round ribbon which has an electric wire in the centre. It is non-tacky when delivered, but it must be stored at -4°C to prevent any vulcanisation. It is used for bonding and sealing of automotive windshields as shown in Fig. 98 when the electric wire is plugged under 24 V, this heats the rubber which becomes sticky after 30 s the windshield is pressed firmly against the ribbon, and it takes some 4 min to vulcanise the rubber. 

Curve 1. He-vulcanised rubber Curve 2. vulcanised neoprene. 

Neoprene-based adhesive is also found to be effective in bonding vulcanised pieces and a typical formulation is given in Table 5.3. It is used as a 15 - 20% solution in toluene. 

Table 5.3 Neoprene-based adhesive solution for bonding thin vulcanised rubber pieces ...

Polyurethane and CR adhesives are widely used for bonding vulcanised rubber. Urethane adhesives perform better in some respects compared to neoprene adhesives on greasy leather as excessive grease and fatty acid present can affect neoprene adhesives more adversely [35]. Vulcanised SBR can be bonded satisfactorily using neoprene adhesive if the surface is freshly prepared. Urethane adhesives used are of three types ... 

Arruda and Boyce [22] showed that the eight-chain model performed much better than three- and four-chain models in predicting the behaviour of vulcanised mbber in uniaxial and biaxial tension and shear, and also performed excellently in modelling uniaxial and plane strain compression of gum and neoprene mbber. 

The monomer of natural rubber is 2-methyl-l,3-butadiene, which is very similar to the monomer for neoprene. The intermolecular forces between natural rubber polymers are van der Waals forces. A process called vulcanisation was invented to make rubber tyres more resilient and hardwearing. This links rubber polymer chains by covalent bonds across sulfur bridges (Figure 28.22). 

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