Mechanical properties of polymeric microfiltration membranes

The influence of the pore topology and polymer properties on mechanical characteristics of asymmetric polyethersulfone (PES) and symmetric polyvinylidene fluoride (PVDF) microfiltration membranes was investigated by conducting elongation, creep, stress relaxation, small-amplitude oscillatory and bubble point pressure tests. The main aspects of the membrane stress-strain curves were found to be similar despite significant differences in the pore topology and polymer properties. While the Kelvin-Voigt model for solid polymers described the membrane viscoelastic response below the transition to ductile yielding, the stress-strain curves of membranes and solid polymers above the yield point appeared to be drastically different. All tested membranes demonstrated weak strain hardening, low sensitivity to strain rate, significant elastic recovery, stress relaxation and reduction of the bubble point pressure with accumulation of plastic deformation. Therefore, tensile stresses exerted on a membrane under assembling and process conditions should be smaller than the yield stress to assure that they will not impair filter performance. The novelty of our approach is the use of models for perforated plates to evaluate membrane mechanical properties as ductile yielding for both proceeds via localized plastic deformation around pores. Presented results provide a reliable framework for development of membranes with properties tailored to applications.