Coagulant dipping of natural rubber latex

Shukri, Bin Abdul Wahab (1982) Coagulant dipping of natural rubber latex. Doctoral thesis, Polytechnic of North London.


A detailed study has been made of' the coagulant dipping of natural rubber latex using calcium, chloride as the coagulant. The primary object of the investigation was to deepen understanding of the kinetics and the mechanisms of deposition.

Results are given for the effect of variables such as solids content, latex viscosity, added fatty-acid soaps, amount of calcium on the former, added non-ionic surfactants and latex pH upon the thickness-time relationship in the coagulant dipping process. All, except the initial amount of calcium on the former, were found to have little effect upon the wet thickness-time relationship. The relationship between the wet deposit thickness and the square root of the dwell time was found to be linear.

An investigation has also been made into the fate of the calcium ions during the dipping process. It was found that the deposition of rubber on the former involves reaction between the cations of the coagulant and the adsorbed anions which stabilise the latex. Fatty-acid anions and other unknown anions were found to react with the calcium ions.

The process was found to be diffusion-controlled. The diffusion coefficient of calcium ions in the latex gel was calculated to be approximately 1.4 x -10-6cm2. sec-1. However, the assumptions made in deriving this value are such that it should be viewed with suspicion until confirmed by further experimentation and analysis.

It postulated that the mechanisms of deposition involve dehydration of the latex particles, neutralisation of the fatty-acid anions adsorbed on the latex particles and there is some evidence for compression of the double layers.

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