The Structure and Viscosity of Hevea Latex. I.

Abstract

Fresh Hevea latex is characterized by the presence of viscoids of greatly varying size (5–200 microns). When the viscosity of such a latex is determined with a viscometer of the rotary type the values found cover a wide range, having no clear relation to the initial DRC of the latex. Also, with the aid of a rotary viscometer, the structural viscosity of fresh or any other type of latex can be clearly demonstrated. When fresh Hevea latex is treated with ammonia in increasing amounts there is a sharp and regular drop in viscosity up to 0.05 per cent NH₃. This runs parallel with a gradual and finally complete disintegration of the viscoids. Treatment with sodium sulfite in increasing concentrations up to 0.30 per cent yields a more slowly decreasing viscosity with end values approximately twice as high as with ammonia. Microscopic investigation shows a slow and only partial breakdown of the viscoids in the same area. Formaldehyde gave irregular results, but, in general, did not decrease or increase the initial viscosity considerably, neither could any influence be established on the size and shape of the viscoids. The viscosity of fresh Hevea latex is profoundly influenced by addition of distilled water giving a considerable increase up to 20 per cent and a sharp drop afterwards. Latex diluted with 20 per cent of water was microscopically found to be in a stage of pre-coagulation, with the immobilized rubber particles embedded in the viscoid complexes. It is concluded that the viscoids play a dominant role in viscosity phenomena of Hevea latex.