ABSTRACT
The term processability refers to the relative ease with which neat or compounded polymers can be handled in production operations and equipment. The most frequently applied production operations are mixing, milling, extrusion, molding, and curing. The end-user manufacturer is concerned with the processing quality or processability of the polymer-based article and is sensitive to factors that may affect the material’s behavior and variability during the various manufacturing stages. In the rubber industry, terms such as plasticity and recovery are used heavily as relative ratings of material processability. Plasticity is generally associated with the relative ease of deformation (i.e., the inverse of effective viscosity). In other words, a highly plastic elastomer or rubber is one that deforms or flows readily. Devices used to test for plasticity, such as the Mooney viscometer, attempt to measure resistance to deformation. Unfortunately, terminology is not always consistent, even within a particular industry. For example, the parallel plate compression test described in Chapter 2, although widely used in the rubber industry, provides a measure of material stiffness and refers to the measured value as plasticity. The ASTM standard for the parallel plate compression test refers to the measurement (i.e., the measured compressed thickness) as the plasticity number. Additional contradictory terminology stems from the fact that in unvulcanized rubbers, permanent deformation is an attractive feature. That is, the material should not be elastic. Some definitions often used by technical sales personnel include definitions of plasticity in this feature 383(e.g., material susceptibility to and retentivity of deformation). Laboratory test methods aimed at measuring the property of elastic recovery have evolved; one such example is the Goodrich plastometer. It is important to note that although such tests are a rheological characterization of the polymer, they in fact do not provide a true measure of viscosity or resistance to flow, but instead provide a measurement of a combination of viscous and elastic properties.
