Co-Coagulated Compounds

Co-coagulation is the method by which large quantities of fillers can be incorporated in dispersion polymerized polytetrafluoroethylene. The addition of fillers takes place prior to coagulation of the resin from its dispersion state. In the process of co-coagu-lation, the additives are added to the polytetrafluoroethylene dispersion and mixed. This dispersion is coagulated and the compound is recovered. The smaller the filler particles, the smaller the points of stress rise in the compound will be. Significantly larger quantities of filler can be compounded in PTFE by this technique. 

Coagulation is quite rapid and is completed in less than three minutes. Clear liquid on top indicates complete coagulation while the appearance of a milky layer is a sign of incomplete coagulation. Agitation of the dispersion should continue until coagulation is completed. Afterwards, minimal shear should be applied to the compound to avoid separation of the polymer and the fillers. 

Co-coagulated compounds can also be molded into thick sections. In this case, the surfactant should be removed by heating the material for 4 hours at 300°C. The lumps formed during this step can be broken by chilling and pulverizing. 

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