Thermal, Mechanical, Morphological and Piezoresistive Properties of Poly(ethylene-Co-Methacrylic Acid) (EMAA) with Carbon Nanotubes and Expanded Graphite

This paper deals with a comparative study of the effect of carbon nanotubes (CNTs) and expanded graphite (EG) on the thermal, mechanical, morphological, electrical, and piezoresistive properties of poly(ethylene-co-methacrylic acid) (EMAA) nano-composites. To this end, different amounts of carbonaceous fillers (5, 10, 15 wt% of CNT and 10, 15, 30 wt% of EG) have been added to the EMAA thermoplastic matrix. The electrical percolation threshold (EPT) was determined to know the percentages of nanofillers capable of forming a continuous electrical conductive network through the matrix. The thermogravimetric analysis (TGA) highlights that the conductive network behaves like a protective mesh against thermo-oxidative degradation. Differential scanning calorimetry (DSC) evidences how the presence of carbon nanoparticles af-fects the crystallinity of the EMAA matrix. From a mechanical point of view, the stress-strain curves, the storage modulus, and the graph of tan  demonstrate that both the fillers determine an enhancement in the Yang and storage moduli and in the glass transition temperature. A quantitative comparison between the different fillers evi-dences greater improvements for the bidimensional nanofiller, most likely due to the cumulative effect of more extended filler-matrix interactions. Field Emission Scanning Electron Microscopy (FESEM) and Tunnelling Atomic Force Microscopy (TUNA) were used to study the interaction between the filler nanoparticles and the polymeric chains of the hosting thermoplastic matrix. Among all the experimented filler concentrations, EMAA 10% CNT and EMAA 15% EG have been selected for studying the piezoresis-tive response of the formulated nanocomposites. The electrical parameters were found to depend sensitively on the aspect ratio and the structural and morphological features of the nanofillers. A very relevant difference was detected in the Gauge Factor (G.F.) of the two typologies of nanocomposites. The G.F. of EMAA 10% CNT and EMAA 15% EG, were found to be 0.5 and 165, respectively.