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Malcolm, A. M. (1939) An investigation of the cold vulcanisation of rubber by the Peachey Process. Masters thesis, Northern Polytechnic.
It has been shown that for uniform vulcanisation by the Peachey Process, exposures of from 2-3 hours to each gas are necessary.
After successive vulcanisations by the Peachey Process, an apparent limit to the combination of sulphur is reached. This is not a chemical but a physical effect, due to the lowering of the sorptive capacity of the rubber by water and sulphur. By a modification of the procedure, ebonite has been obtained.
A mechanism which explains these experimental observations has been postulated for the Peachey Process.
It has been shown that when rubber is exposed to hydro gen sulphide and sulphur dioxide, the gases are adsorbed upon the surface of the rubber, and not dissolved in it.
Isotherms for the adsorption of hydrogen sulphide and sulphur dioxide at different temperatures have been measured, and heats of adsorption calculated from them. The isotherms for hydrogen sulphide obey the classical sorption isotherm, but those of sulphur dioxide show a deviation due to swelling of the rubber by the vapour. The adsorption of sulphur dioxide is depressed by the presence of an accelerator in the rubber.
Adsorption isotherms have been measured for carbon tetrachloride, benzene and ethyl alcohol, and heats of ad sorption calculated from them which agree with the latent heats of vaporisation. The isotherms are reproducible, indicating the presence of long-range structural forces in the rubber even when it is swollen with 200% of its weight of carbon tetrachloride. The isotherm for carbon tetrachloride at low pressures obeys the Langmuir equation.
The sorption isotherms for different temperatures of the rubber when plotted against partial pressures of the vapour are found to be coincident.
The effect of mastication or vulcanisation of the rubber is to lower its sorptive capacity. The presence of water vapour in the rubber lowers its sorptive capacity.
The application of theories of sorption to the case of rubber had led to the belief that vapours are sorbed on to rubber in multimolecular layers.
Heats of adsorption on rubber have been measured for hydrogen sulphide and sulphur dioxide, and agree with the calculated values.
A determination has been made of the heat of vulcanisation of rubber by the Peachey Process, which indicates that the reaction is exothermic and proportional to the amount of combination of sulphur.
It has been shown that sulphur dioxide can combine with rubber to form products resembling vulcanised rubber. These are resistant to acids and ozone and to swelling in rubber solvents.
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