Plasticity and Elasticity of Rubber

Abstract

Abstract PLASTICITY determinations of raw and masticated rubber have in recent years attracted a great deal of the rubber chemists' attention, as the publications of Marzetti, Williams, De Vries, Griffiths and others have proved. In various laboratories, plasticity measurements have even become routine tests for raw and masticated rubber. There are, generally speaking, two methods of determining the plasticity of rubber, viz.: (1) The extrusion method, in which the masticated dough is extruded through an orifice (Marzetti), and the extruded portion weighed. This method can be used only for masticated rubber and rubber mixings. (2) The compression method, in which a piece of raw or masticated rubber is compressed and the decrease in thickness is measured. The latter method has been used in the past by many investigators for plasticity measurements of various substances, e.g., by Speedy, who as long ago as 1920 carried out plasticity determinations on gutta-percha, balata, and various bitumens with the Widney resiliometer, an apparatus based on the compression principle. Williams was the first to apply this method, in 1924, to the determination of the plasticity of rubber, and since then De Vries especially has made use of this method in his extensive investigations of the plasticity of raw rubber.