Influence of structure on piezoelectric properties of polypropylene-montmorillonite electrets

The effect of the structure, mechanical properties and filler content of isotactic polypropylene (i-PP)/modified montmorillonite (MMT) composite films on their piezoelectric properties was investigated. The introduction of MMT mineral filler into the i-PP allowed to produce the films with cellular structure, confirmed by scanning electron microscopy (SEM), using extrusion method. The uniaxial orientation of the film increased its degree of crystallinity. After polarization in an electric field of intensity ca. 100 V/μm the films showed piezoelectric properties. The stability of obtained electrets was evaluated based on piezoelectric voltage measured during the storage of films at room temperature. The cellular structure and increase in crystallinity degree of the films influenced the increase in piezoelectric charge coefficient d33 compared to neat i-PP. The d33 values obtained under higher and lower stresses of tested specimens are almost twice higher than those determined for solid (compact) poly(vinylidene fluoride) (PVDF) film and non-oriented i-PP film. This opens up the possibility of application of the obtained composite films for pressure sensors with wide applicability due to the relatively not complicated manufacturing method.