Measurements of the cohesive and piezoresistive responses of polylactide/carbon nanotube nanocomposites made from solution-casting

• Acetone was applied to produce polylactide nanocomposite via solution-casting. • A low percolation threshold of 0.098 wt% for electrical conductivity was achieved. • The piezoresistivity of nanocomposite was studied under three loading conditions. • The nanocomposite first showed a negative piezoresistive response under tension. Carbon nanotube reinforced polylactide (CNT/PLA) nanocomposites were manufactured by solution-casting followed by hot-pressing. Acetone was used to dissolve PLA and disperse CNTs; a uniform filler distribution was obtained by ultrasonication and mechanical stirring of the liquid mixture. This allowed achieving a low percolation threshold of 0.098 wt% for the electrical conductivity, which was generally high at all CNT weight fractions. The resulting material was characterised by different test protocols, including monotonic, cyclic and stiffness-sensing tests. The stiffness sensing tests allowed measurements of the damage evolution on the material, through intermittent measurement of the material’s stiffness; simultaneously, they allowed measurements of the material’s electrical conductivity as a function of the applied strain. The material’s conductivity was found to first increase with applied tensile strains, to later decrease at large strains as a result of damage processes in the material. The proposed test technique allows gaining great insight into the electro-mechanical response of the composites and into their possible applications in structural health monitoring.