The Concentration of Latex by Creaming

Abstract

Abstract Latex consists of a suspension of microscopic particles of rubber, bearing an adsorbed layer of protein, in an aqueous serum containing principally l-methyl inositol, so-called rubber resins, and saline substances. The rubber particles are in continuous oscillatory motion, which may be seen under the microscope. Brownian movement is due to the bombardment of the suspended particles by the molecules of the dispersion medium, and it can be demonstrated that the smaller particles are in more violent oscillatory movement than the larger particles. The rubber particles in latex are sufficiently small to remain in suspension in the aqueous serum for an indefinite period, but if latex is left to stand, a concentration gradient will develop throughout its bulk, leading to the formation of an upper concentrated layer of closely packed rubber globules in a manner analogous to the formation of cream on milk. This behavior is shown by all types of latex, field, preserved, and concentrated, but the effect is stated to be much greater with preserved latex than with field latex (Bishop and Fullerton, Latex Preservation and Shipment Planting Manual, No. 4, Rubber Research Institute of Malaya, July, 1932). The same authors give figures (Table I) which show the magnitude of this effect for freshly ammoniated latices which had remained undisturbed for a period of two months. It will be observed that creaming occurred to a considerable extent in all samples, accompanied by a diminution in the ammonia contents of the surface layers.