The lubrication mechanism of calcium stearate/paraffin wax systems in PVC compounds

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.

Influence of processing conditions on the leaching of thermal stabilizers from plasticized polyvinyl chloride in the presence of water

“…Indeed, it has already been shown that calcium stearate can modify the fusion process of PVC. 6 At the steady state of processing, the pressure decreases with increasing the stearates concentration, meaning that the slip amplitude increases with the stearates concentration. Furthermore, the transient time for reaching the steady state increases with the stearates concentration.…”

“…This result means that the addition of stearate at a lower concentration than 0.84 phr does not modify the viscous behaviour of the PVC compound. Calcium stearate is known to be insoluble in PVC, 6 and it can be assumed that zinc stearate is not soluble. Indeed, in the case of solid particles in low volume concentration, the bulk viscosity of the compound can be assumed to be independent of the particle concentration.…”

“…5 Furthermore, it is known that stearates can act as lubricants in plasticized PVC formulations, but there are few reports concerning the influence of processing conditions on the migration of stearates towards the surface. 6,7 This article discusses the influence of the processing conditions on the migration of zinc and calcium stearates from plasticized PVC to the PVC/metal interface. Actually, slip phenomenon of the PVC melt at the metal interface is investigated.…”

Characterization of the Interface Between Fresh Concrete and Formwork

“…Hm is more easily emulsified by soap than Hv because it does not form a soap film. However, the soap film does not create on oil film as in the case of Hv, due to deterioration of the oil film by solubilization in the presence of soaps at the interface (Rabinovitch et al 1984). The correlations established between the ability to reduce friction and physicochemical measurements make it possible to identify two processes that intervene close to the formwork: -The emulsification of hydrocarbons (Hm) and esters (Hv) by the soaps formed; and -The transformation of esters into soap (saponification), catalyzed by fatty acids (acidifiers) present in the oil, which are themselves turned into soap (salts of fatty acids).…”

“…The correlations established between the ability to reduce friction and physicochemical measurements make it possible to identify two processes that intervene close to the formwork: -The emulsification of hydrocarbons (Hm) and esters (Hv) by the soaps formed; and -The transformation of esters into soap (saponification), catalyzed by fatty acids (acidifiers) present in the oil, which are themselves turned into soap (salts of fatty acids). In the case of Hv, the interface forms two layers (Rabinovitch et al 1984). The ester molecules, owing to their polarity, adsorb preferentially on the metal wall of the formwork by chemical interactions (Jacquet et al 1974).…”