The mechanical properties of films. I. Evaluation of the mechanical properties of some surface coating polymers by the Williams, Landel and Ferry method

Abstract

AbstractThis series of papers is concerned with an evaluation of the dynamic elastic properties of typical insulating varnish and enamel films and the observation of transition temperatures in these materials.Dynamic elastic properties have been investigated in the temperature range, room temperature to 180°, and in the frequency range 40 to 2000 c/s. The results have been interpreted by the method of reduced variables. The Williams, Landel, Ferry (WLF) equation was found to be applicable to many of the materials including polyesters, silicones and epoxides; the product of the WLF parameters (C1°C2°) varied from 350 to 1300. The use of the Tg form of the WLF equation is deprecated, insofar as the relationship between Ts (the parameter in the WLF ‘universal’ equation) and Tg is demonstrably not constant.Polyurethane varnishes showed large deviations from the WLF equation and this is almost certainly connected with the existence of more than one large transition in these materials. Multiple transitions may however be detected in materials conforming to the WLF equation and it does not seem possible to decide whether or not transitions established dilatometrically will influence the less sensitive dynamic properties in such a way as to produce clear deviations from WLF behaviour.