The Structure of Hevea Latex and Its Viscosity. II

Abstract This paper deals with the effect of dilution on the viscosity of sulfite or formaldehyde treated and ammoniated latexes, the relationship between viscosity and DRC for ammoniated field latex and concentrate and the influence of the tapping cycle on the viscosity of whole latex and white fraction latex. An explanation is given of the shape of the viscosity curve of water diluted fresh field latex. It is shown that sulfite in increasing concentrations shifts the maximum viscosity of dilution to regions of higher dilutions and at the same time lowers the viscosity value at the maximum. In formaldehyde treated latexes the maximum viscosity in the dilution curve still occurs at 15–20 per cent dilution, but the maximum viscosity value is considerably lower, especially at higher formaldehyde concentrations. Dilution of ammoniated field latex or concentrate yields a viscosity curve typical for a non-Newtonian liquid. The viscosity-DRC relationship for ammoniated field latexes shows wide discrepancies for individual samples and can not be used as a means for determining the DRC. Individual concentrate samples are in much closer agreement. The influence of the occurrence and removal of viscoids on these phenomena is discussed. A description is given of the influence of the tapping cycle on the viscosity of unpreserved fresh latex and the white fraction prepared therefrom, on the viscoid volume and on the DRC and TS of both whole latex and the white fraction. Finally, the possible role of viscoids in latex formation is discussed in connection with some recent investigations concerning their occurrence in sieve tubes and latex vessels in the Hevea tree.