| Abstract: | The lubrication mechanism in PVC was studied using calcium stearate and paraffin wax lubricants. Based on the results of the differential thermal analyses, percent haze, microscopy, metal release, Brabender fusion, and extrusion studies we have developed a new theory of PVC lubrication based on molecular structure. Lubricants containing polar groups, which preferentially wet the metal surface in the presence of PVC, such as calcium stearate, are excellent metal lubricants. Non-polar lubricants which do not wet the metal surface, such as paraffin wax, allow PVC to stick to the metal surface. However, these lubricants work in combination with the metal wetting lubricants to make the lubricant layer more fluid, providing a better lubricating system than either lubricant alone. Lubrication between PVC primary particle flow units is similar to that at the metal surface with the polar PVC surface acting in a similar manner as the metal surface. We find the common classification of lubricants as internal or external to be deficient in explaining performance. |
