Vulcanised natural rubber

Figure 11.15. Typical chemical groupings in a sulphur-vulcanised natural rubber network, (a) Monosulphide cross-link (b) disulphide cross-link (c) polysulphide cross-link (j = 3-6) (d) parallel vicinal cross-link (n = 1-6) attached to adjacent main-chain atoms and which have the same influence as a single cross-link (e) cross-links attached to common or adjacent carbon atom (f) intra-chain cyclic monosulphide (g) intra-chain cyclic disulphide (h) pendent sulphide group terminated by moiety X derived from accelerator (i) conjugated diene (j) conjugated triene (k) extra-network material (1) carbon-carbon cross-links (probably absent)...

Oil resistance demands polar (non-hydrocarbon) polymers, particularly in the hard phase. If the soft phase is non-polar but the haid phase polar, then swelling but not dissolution will occur (rather akin to that occurring with vulcanised natural rubber or SBR). If, however, the hard phase is not resistant to a particular solvent or oil, then the useful physical properties of a thermoplastic elastomer will be lost. As with all plastics and rubbers, the chemical resistant will depend on the chemical groups present, as discussed in Section 5.4. 

Carbon blacks are the most widely used fillers for elastomers, especially vulcanised natural rubber. They cause an improvement in stiffness, they increase the tensile strength, and they can also enhance the wear resistance. Other particulate fillers of an inorganic nature, such as metal oxides, carbonates, and silicates, generally do not prove to be nearly so effective as carbon black. This filler, which comes in various grades, is prepared by heat treatment of some sort of organic material, and comes in very small particle sizes, i.e. from 15 to 100 nm. These particles retain some chemical reactivity, and function in part by chemical reaction with the rubber molecules. They thus contribute to the crosslinking of the final material. 

Vulcanised butyl rubber is very similar to vulcanised natural rubber in various physical characteristics but has better resistance to oxidation and has low permeability to gases. Hence, it is widely used in tubes for cycles, scooters, motor cars, etc. It is also used as rubber in many other applications. 

Figure 2.1 Stress versus strain for a typical elastomer of vulcanised natural rubber. The straight line shows that a simple Hooke s law response would be observed up to 40% strains...

Carbon Black Filled Vulcanised Natural Rubbers... 

Figure 15.15 Natural abundance 2H MAS spectra observed in a series of vulcanised natural rubbers with various vulcaniser (sulfur 1 or 3 wt%) and/or filler (carbon black 0 or 40 wt%) contents. The spinning speed is 0.5 kHz. The number of scans is about 300000. Spectra are simulated with two components (a mobile and a rigid one) with various residual quadrupolar interactions...

The inner sides of the walls are coated with vulcanised natural rubber or P.V.C. In an electrolyzer of the described size the bottom measures 660 sq.dm and is not coated. It is electrically connected to the main cathode bus-bar, located on the insulators under the cell. Older models had walls and the bottom made of concrete and the current was led in by iron disks, inserted into... 

In appearance, HR resembles natural crepe rubber, since it is an aliphatic, hydrocarbon polymer the density being the minimum (0.91) attainable for elastic materials of this type. In HR, the original unsaturation is very small, and even this low unsaturation is greatly reduced and may even be entirely eliminated during the compounding and curing process. The fact that once vulcanised it is extremely resistant to chemical attack is understandable because it becomes, after vulcanisation, not only a nonthermoplastic strong elastic material, but also essentially a chemically saturated product as well. This means that whilst physically vulcanised HR resembles soft vulcanised natural rubber, chemically it may be considered most similar to ebonite almost devoid of any unsaturation. 

This equation shows that the ratio of the birefringence to the true stress should be independent of stress. The expression on the RHS of equation (11.13) is known as the stress-optical coefficient. A test of equation (11.13) can be made by plotting An against cr, when a straight line should be obtained. Such plots for a vulcanised natural rubber at various temperatures are shown in fig. 11.5. The hysteresis shown in the curves for the lower temperatures is interpreted as being due to stress crystallisation, with the crystallites produced being oriented in the stretching direction and... 

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... 

MBT in vulcanisates semiquantitatively. The accelerator zinc-A-dimethyldithiocarbamate (ZDMC) cannot be detected by PyGC-MS analysis at 550 C in the unfragmented state because of its low thermal stability [502]. However, ZDMC in vulcanised natural rubber (NR) could unambiguously be identified by DI-MS on the basis of the peak spectrum of the molecular mass trace m/z 304 (Pig. 2.37). 

Rubber surfaces were characterised directly by ToF LMMS, LD-FTMS and TD-FTMS [201, 202]. The surface chemistry of the antiozonant N-(l,3-dimethylbutyl)-lV -phenyl-p-phenylenediamine (HPPD) in vulcanised natural rubber compounds was explored by ToF LMMS in order to investigate the mechanism of rubber-surface ozone ageing... 

CRYSTALLISATION QUARTER LIVES (/j/J AT -26°C OF VULCANISED NATURAL RUBBER AND SYNTHETIC POLYISOPRENE... 

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