Abstract
Knowledge of mass distribution of particle sizes in latex is very important to the latex technologist. Therefore, it is desirable to have available a simple method for the determination of mass distribution of particle sizes. This paper presents a method, based on fractional creaming of latex with sodium alginate, which can be used in any laboratory without special equipment. The method is particularly advantageous for analyzing latexes of very wide particle size distributions. When analyzed with an electron microscope, these latexes require counting a very large number of particles. McGavack found that partial creaming of normal hevea latex with ammonium alginate gives concentrates of larger average particle size than the original latex. He found that the average particle size in the cream approaches that of the original latex as the amount of creaming agent is increased. In a previous paper from this laboratory, Schmidt and Kelsey demonstrated that the phenomenon of fractionation according to particle size with increasing amounts of creaming agent is applicable in a wide variety of anionic latex systems and in colloidal silica. Their results indicated also the existence of a quantitative relationship, independent of the nature of the dispersed particles, between the concentration of creaming agent and size of creamed particles. Maron confirmed fractionation with respect to particle size as a consequence of partial creaming with alginate. He showed that the mass average particle sizes of fractions, determined optically, cumulate to that of the original latex. Although the previous paper by Schmidt and Kelsey implied the basic concept of a method of determining particle size distribution by fractional creaming, it was not exploited at that time. In order to adapt the fractional creaming phenomenon to a quantitative method for particle size determination, we required a more precise knowledge of the relation between creaming agent concentration and size of particles creamed. It was proposed to establish this relationship with the aid of the electron microscope. Various factors influencing the creaming of latex, such as polymer concentration, electrolyte, soap content, and variability of the creaming agent, had to be considered in standardizing the creaming procedure.
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