Radiation vulcanisation

The mechanism of radiation vulcanisation of NR with 2-ethyl hexyl acrylate (EHA) was examined by 13C NMR [46]. All peaks in spectrum due to the acrylate decrease in intensities and broaden with increasing radiation dose. Using the solid-state CP technique, all peaks corresponding to EHA and NR were observed. The olefin peak at 129 ppm in the acrylate was absent, however, indicating that all the EHA had polymerised. 

As the length and frequency of branches increase, they may ultimately reach from chain to chain. If all the chains are coimected together, a cross-linked or network polymer is formed. Cross-links may be built in during the polymerisation reaction by incorporation of sufficient tri- or higher functional monomers, or may be created chemically or by radiation between previously formed linear or branched molecules (curing or vulcanisation). Eor example, a Hquid epoxy (Table 1) oligomer (low molecular weight polymer) with a 6-8 is cured to a cross-linked soHd by reaction of the hydroxyl and... 

Hot air, steam, and hot water vulcanisation is widely used in the latex industry, and fluid-bed heat transfer and electronic microwave curing has also been used. Cross-linking by electron radiation has been experimentally used, but has not yet been developed commercially. 

Vulcanisation of elastomers by heat produced by high frequency radiation, approximately 12.5 cm wavelength, 2450 MHz. 

These are unstable forms of elements which decay by the emission of radiation. A radioactive isotope of an element behaves chemically in the same way as the non-radioactive form, but its radiation may be detected and measured by a suitable instrument. In the rubber industry radioactive isotopes are used in beta ray thickness gauges, in studying the precise role of sulphur in vulcanisation, in the speedy determination of tread wear in tyres, etc. See Beta Rays. 

Due to the absence of double bonds in the main chain, these materials can only be crosslinked by the action of peroxides or radiation. It is recommended that metal oxides are added to act as acid acceptors during vulcanisation, the oxides of magnesium and lead being used zinc oxide is not used as it decreases the stability of the polymer. 

Hot air tunnels are often used for vulcanisation of cable covered with rubbers such as silicone. These systems may also incorporate infrared radiation as a means of boosting heat transfer to the product. 

There is wide variety of vulcanisation agents and methods available for crosslinking rubber materials including peroxide, radiation, urethane, amine-boranes, and sulfur compounds [20]. Because of its superior mechanical and elastic properties, ease in use, and low cost, sulfur vulcanisation is the most widely used. Although vulcanisation with sulfur alone is not practical compared to the accelerated sulfur vulcanisation in terms of the slower cure rate and inferior physical properties of the end products, many fundamental aspects can be learned from such a simply formulated vulcanisation system. The use of sulfur alone to cure NR is typically inefficient, i.e., requiring 45-55 sulfur atoms per crosslink [21], and tends to produce a large portion of intramolecular (cyclic) crosslinks. However, such ineffective crosslink structures are of interest in the understanding of complex nature of vulcanisation reactions. 

The vulcanisation of rubber sheet by radiation—instead of using sulphur in the manufacture of tyres— is being used commercially by several tyre companies. 

Chemical links/(the setting up of chemical links) between different molecular chains. A high amount of crosslinking can convert a thermoplastic into a thermoset, and this can be accomplished by chemical reaction, vulcanisation, degradation and radiation. 

The vulcanised carborane-siloxane rubber [530] has an unusual degree of thermal stability it does not show any persistent changes after 100 h at 250 °C in the open air. Hot-hardened rubbers are used mainly in electrical engineering and the aircraft industry. Those intended for medical applications may be vulcanised under radiation without a catalyst. 

As it was in case of HNBR vulcanisates the commercially modified MMT had negative effect on the ageing of the samples. The resistant against LTV radiation and atmospheric ageing of the vulcanisates containing montmorillonite modified with ionic liquids was higher in comparision to vulcanisate filled with ammonium salts modified MMT. 

The application of ionic liquids influenced on the cross-linking density of the vulcanizates, rheometric and mechanical properties of HNBR. We did not observed the influence of modification on curing time of EPR vulcanisates. The application of montmorillonites did not lead to a significant improvement in mechanical properties of EPR rubber. The ageing studies (thermal, atmospheric and under UV radiations) showed that the modification of montmorilonite with ammonium salts had strong effect on ageing properties of vulcanisates. 

It is explained that acrylic coagents can improve processability and vulcanisation of elastomers used in automotive applications, and that Saret coagents from Sartomer Co. of the USA provide scorch-retarding properties along with improved radiator hose properties for all curing situations. This article describes tests comparing several coagents in ethylene propylene diene monomer radiator hose formulations. Results are presented and discussed. 

COMPARISON BETWEEN PROPERTIES OF RADIATION CURED SBR VULCANISATE AND SULPHUR CURED ONE... 

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