Study of additive compatibility with poly(vinyl chloride) (PVC). 2: Dynamic mechanical analysis of PVC lubrication by stearic acid and its derivatives

The glass transition temperatures of PVC containing stearic acid derivatives as lubricants have been used to define two new parameters of lubrication: the saturation concentration and the efficiency constant . The saturation concentration represents the maximum amount of lubricant compatible with PVC in a specific formulation. The lubricant molecules are associated with the surface molecules of the PVC primary particles or are in the interstitial space between them. The use of lubricants at significantly lower concentration than the saturation concentration ensures their permanence in the polymer. They then act as internal lubricants reducing the viscosity of the melt. The use of lubricants at much higher concentrations than saturation concentration leads to formation of lubricant pools between PVC primary particles. Increased temperature or longer time ensures the release of lubricants from these pools at the surface of the polymer giving the lubricants an external character. At a normal usage of 0.5 to 1.5 phr (approximately 1.6–5 meq stearate) to 100 g PVC, methyl, barium and calcium stearates may be considered internal, aluminum and sodium internal/external, zinc, lithium, magnesium stearates and stearic acid itself external lubricants.