Determination of surface area and particle size of synthetic latex by adsorption II. Latices containing rosin acid soaps

Abstract

The soap titration method (1) for determination of synthetic latex particle size and specific surface area, applied before to latices containing fatty acid soaps, has been extended to include latices prepared with rosin soaps of various kinds. In this connection it was found that only conductance is a reliable means of following the titration, since surface tension measurements give curves from which it is difficult to ascertain the end point. Effective molecular surface areas have been determined for the sodium and potassium soaps of K-wood rosin, Resin 731, Pexite 42, and Gum 42. The areas for the two soaps of a given rosin acid are identical. Furthermore, the areas remain constant between 25° and 50°C. Free rosin acid in a latex does not interfere with the titration and behaves as if it were not present in the system. Hence it is not necessary to neutralize the free rosin acid prior to the addition of soap. It was also found that fatty acid soaps can displace, at least partially, rosin soaps from the polymer surface. The reverse displacement, i.e., of fatty acid by rosin soaps, does not occur. These observations indicate that fatty acid soaps are adsorbed more strongly by the polymer than are the rosin soaps.