Carbon-based piezoresistive polymer composites: Structure and electrical properties

Piezoresistive polymeric composites were prepared by melt mixing of polypropylene (PP) with expanded graphite (EG) (10-15 wt%) and/or multiwalled carbon nanotubes (MWCNTs) (1-2 wt%). The composites were extruded at a temperature of 185 C, by adopting 2.5-10 rpm screw speeds, and fibres with diameters of 0.2, 1.5 and 3 mm, were obtained. An integrated piezoresistive sensor device was obtained by hot pressing the extruded fibres into two sandwiched PP panels. Structure and morphology of the carbon fillers (EG and MWCNTs) and of the fibres, were investigated by means of X-ray diffraction, optical microscopy, scanning electron microscopy (conventional and conductive SEM) and atomic force microscopy. Piezoelectric properties of fibres and sensor devices were detected through a set up made by a dynamometer, a potentiometer and a digital multimeter. It was shown, that mechanical deformations, due to the applied loads, affect remarkably the resistivity of the materials.