Polyvinylidene fluoride / Zirconium phosphate sulphophenylphosphonate nanocompites: microstructure and mechanical properties

Nanocomposite films made of polyvinylidene fluoride (PVDF) filled with layered zirconium phosphate sulfophenylphosphonate (ZrSPP), with filler loadings up to 20 wt%, were prepared by casting solutions containing the polymer and a ZrSPP precursor. The films were characterised by solid state 31P MAS NMR, X-ray diffraction, DSC determination, Raman spectroscopy and static stress-strain mechanical tests. The presence of the filler has two main effects on the polymer structure: (i) the fraction of crystalline polymer decreases with increasing filler loading; (ii) while the trans-trans-trans-gauche (T3G) chain conformation is predominant in neat PVDF, the composite films mainly contain TnG sequences with n appreciably larger than 3. The elastic modulus and the yield stress of all composites are higher than those of neat PVDF: in both cases a maximum is observed for 1-3 wt% ZrSPP followed by an almost linear decrease for higher loadings. The evolution of the elastic modulus of the composites is discussed on the basis of the changes in the polymer conformation and in the polymer crystalline fraction induced by the filler.