Viscoelastic Properties of Montmorillonite Clay/Polyimide Composite Membranes and Thin Films

Abstract

Montmorillonite clay, cloisite 30B (nanoclay), was successfully dispersed in a polyimide (PI) matrix by in situ condensation polymerization followed by solution casting and thermal imidization. Wide angle X-ray diffraction, WAXD, test was used to study the structure of cloisite 30B clay powder and nanoclay/polyimide composites. The WAXD spectra of nanoclay powder and the composites show one major diffraction peak at 4.76° and 6°, respectively, suggesting that the d-spacing of nanoclay was decreased by about 26% after composite film processing. The viscoelastic property of polyimide and nanoclay/polyimide composite was studied by using dynamic mechanical spectrometer. The storage modulus and glass–rubber transition temperature of nanoclay/polyimide composites increases with increasing volume fraction of clay. The storage modulus of the composites in the rubbery plateau region, (T > 400 °C) increased remarkably with increasing volume fraction of clay. A modulus enhancement, (E_C/E_M) of about three orders of magnitude, (E_C/E_M ~1,440) was obtained for nanoclay/polyimide composite containing 6.8 vol% of nanoclay. The tangent of the loss angle (tan δ) for the composites, decreased with increasing volume fraction of nanoclay. The observed decrease in tan δ with increasing volume fraction of clay is consistent with the established trend of increasing storage modulus and glass–rubber transition temperature with increasing volume fraction of nanoclay. The phenomenal increase in the rubbery plateau storage modulus and glass–rubber transition temperature with increasing volume fraction of clay is believed to be due to increased restriction of chain motion with increasing nanoclay volume fraction.