High-pressure vulcanisation

Network structure and reaction mechanisms in high pressure vulcanisation (HPV) and peroxide vulcanisation of BR was studied by 13C solid-state NMR [43]. Different samples of polybutadiene (51% trans, 38% cis, and 11 % vinyl) were peroxide cured with dicumyl peroxide on a silica carrier and by the HPV conditions of 250 °C and 293 MPa. The 13C NMR spectra from peroxide and HPV cures were compared to a control samples heated to 250 °C for 6 minutes under atmospheric pressure. Although no new isolated strong peaks were detected in either the peroxide or HPV vulcanisations, small increases in both spectra were observed at 29.5, 36.0, 46.5, and 48.0 ppm. These peaks compare favourably with calculated shifts from structures that arise from main chain radical addition to the pendent vinyl groups. These assignments are further reinforced by the observation that the vinyl carbon concentration is substantially reduced during vulcanisation in both peroxide and HPV curing. Two peaks at 39.5 and 42.5 ppm appear only in the peroxide spectrum. Cis-trans isomerisation was absent in both cures. 

Rubbers are also being extruded, in a not essentially different way from plastics. Cooling of the extrusion cylinder is necessary to prevent premature vulcanisation as a result of the heat developed by internal friction. The extruder is fed by ribbons, obtained from milled sheets. End products are hoses, profiles, and cable mantles. On-line vulcanisation can be achieved by passing the extrudate through a steam channel, while the rate of extrusion is adjusted to the rate of curing. For this purpose high-rate vulcanisation recipes have been developed. Steam temperatures of about 200 °C are being applied (15 bars pressure). Treads for motorcar tyres are also extruded they are wrapped round the pre-formed carcass and then formed and vulcanised in a press. 

Silicone rubber compounds can be molded, extruded and calendered. The vulcanisation of rubber compounds occurs in two stages 1) in a press or steam boiler at high pressure and 120-150 °C 2) by thermostatic control at atmospheric pressure and 200-250 °C. 

Meuzelaar et al. [453] have reported experiments with non-vulcanised styrene-butadiene rubber (SBR) in the presence of various catalysts and co-processing runs of coal and lower grade postconsumer polymers (coloured PE and PS, waste rubber tyres, commingled plastic mixture) in a high pressure TG-GC-MS system at a hydrogen pressure of 900 psi. This system is essentially designed for applied rather than analytical TG-GC-MS work. 

Conference Communications.Conference Proceedings. Paris, 12th-14th June 1990, p.347-9. 012 BEHAVIOUR OF RUBBER VULCANISATES UNDER HIGH PRESSURE GAS CONDITIONS (INCLUDING EXPLOSIVE DECOMPRESSION) Seregely ZI... 

Apphed to a high polymer which undergoes a chemical change when it is subjected to heat, after which its shape cannot be changed by the application of further heat and pressure. Although vulcanisation of rubber is a thermosetting process the term is usually applied to plastics . See Thermoplastic. 

Braiding hoses with wires to resist high burst pressures or for external protection is common, using a braiding machine. The wires used, usually of steel, will be either zinc- or brass-coated to achieve adhesion during vulcanisation. The gauge of the wire and its tensile properties will be matched to the expected service demands for the hose. 

The main properties of some rubber compounds and vulcanised rubbers, as well as their applications, are given in Table 20. As seen from the table, silicone elastomer-based rubbers are designed for prolonged use in a wide range of temperatures from -50 to +250 °C, some from -70 to + 350 °C (for a short period of time). These rubbers are efficient in air, ozone and in an electric field rubbers based on IRP-1339 and IRP-1401 compounds are also efficient in case of limited air supply. They function well in high humidity and under the influence of oxidants, hot water, vapour and low pressure. They are stable in weak-acid and weak-alkali media and are nontoxic. 

Pfeffer deposited a copper ferrocyanide membrane in the walls of a porous clay pot. This was filled with the solution to be investigated, attached to a mercury manometer, and immersed in water. Some water entered the pot and the pressure increased, reaching a maximum value, called the osmotic pressure. The pressures were high, more than 3 atm. for a solution of 1 5 per cent, of potassium nitrate. Ladenburg and R. H. Adie confirmed Pfeffer s main results, and Raoult obtained a pressure of 50 atm. with ether and methyl alcohol and a vulcanised rubber membrane. Measurements with aqueous solutions, at pressures higher than those reached by Pfeffer, were made by H. N. Morse and collaborators and the Earl of Berkeley and E. G. J. Hartley. ... 

BR is a raw material (a raw rubber) which has two main markets the rubber goods industry and the plastics producers. The former blend it with other types of rubber and mix it with reinforcing fillers, oil and vulcanising chemicals to produce rubber compoimds. The rubber compound is then shaped and vulcanised under heat and pressure to produce the finished rubber article. The latter incorporate a small amount (5 to 8 %) during their polymerisation processes to enhance the impact strength of the finished plastic. The most widely produced material is high impact polystyrene, HIPS. 

However, under the conditions of mixing, rubber is usually a soft solid and it does not diffuse spontaneously into the void of agglomerates. Even if rubber were assumed to be a high-viscosity fluid, it would not flow into and fill the void under the pressure generated by the rotor blade and within the incorporation time of only 1.5 - 5.0 minutes [38]. The density measurements were made with vulcanised specimens. The amount of the penetrated rubber might have increased during vulcanisation. Significant increases of the bound rubber as a result of vulcanisation were detected with the NMR by Wardell and McBrierty [39]. 

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