The Coagulation of Latices by Polar-Nonpolar Liquids

(1) Diluted latices—Abiarana gutta-percha latex was specially investigated—may be coagulated by shaking them with organic liquids, not miscible with water in all proportions, provided that the liquids form a second liquid phase and that their molecules have a polar-nonpolar structure (butyl alcohol, isobutyric acid, cyclohexanol, etc.). Nonpolar liquids (petroleum ether, chloroform, etc.) do not coagulate diluted latices on shaking under these conditions. (2) This coagulating action can be explained by assuming that the latex particles are strongly accumulated at the interfaces of polar-nonpolar liquids and water; this is not the case with nonpolar liquids. (3) Small concentrations of some polar-nonpolar substances of small molecular weight, soluble in water, can also coagulate Abiarana gutta-percha latex if they form unstable foams; this was observed with propanol and isopropanol. If the foam formed under these conditions is stable, as with small concentrations of dissolved butanol and isobutanol, no coagulation takes place. This behavior can be explained as in (2), the air bubbles behaving like the second liquid phase. (4) Jelutong latex is known to contain an excess of resins, compared with the amount of rubber. A method of coagulating this latex quickly and separating the resins from the rubber consists in shaking the latex for some seconds with certain polar-nonpolar liquids, forming a second liquid phase, such as isobutyl or isoamyl alcohol. A lump of rubber is accumulated at the interface of the two liquids; the resins are contained in the organic phase.