A Rapid Determination of the Average Molecular Weight of Rubber in Hevea Latex

Abstract

A method is described for determining viscometrically the molecular weight of rubber in freshly tapped latex. For this purpose the latex is dissolved in a toluene-pyridine mixture. From the intrinsic viscosity of this solution the molecular weight of the rubber can be determined by the Staudinger equation and a known viscosity constant. Molecular weights varying between 238,000 and 480,000 have been found, depending on the kind of clone. Rubber in fresh latex does not have a lower molecular weight than in old preserved latex.

Natural and Synthetic Rubbers

“…Mann (175) admitted the necessity of expanding technical testing facilities at the plantations and of introducing some type of technical system of grading the rubber. Besides the general discussions, the sessions included presentation of several technical papers (37,73,87,95,204), which are referred to in various sections of the present review article. The proceedings of the meeting also include an abridged translation of a French article (134), which was the first to recommend the classification of the rubber into nine grades based on viscosity and rate of cure (283), and which was later presented by Bocquet (40) before a meeting of the International Organization for Standardization in October 1960.…”

Precision associated with determination of dirt content of natural rubber

“…Mechanically and chemically induced bond scissions of rubber in solution lead to the formation of free radicals, which later stabilize by recombining in pairs or on sites along the rubber chains. The presence of oxidation activators reduces the dissolution temperature and also intervenes in the recombination process by reacting rapidly with the free radicals, to give groups that no longer reagglomerate with similar entities 8–10. Progress has been made over the past 50 years to develop standard procedures and improve the repeatability of this measurement, although poor repeatability is still common, even with the use of similar analytical techniques 6, 11.…”