Tuning the Mechanical Properties of Composites from Elastomeric to Rigid Thermoplastic by Controlled Addition of Carbon Nanotubes

A commercial thermoplastic polyurethane is identified for which the addition of nanotubes dramatically improves its mechanical properties. Increasing the nanotube content from 0% to 40% results in an increase in modulus, Y, (0.4-2.2 GPa) and stress at 3% strain, sigma(epsilon) (= 3%), (10-50 MPa), no significant change in ultimate tensile strength, sigma(B), (approximate to 50 MPa) and decreases in strain at break, epsilon(B), (555-3%) and toughness, T, (177-1 MJ m(-3)). This variation in properties spans the range from compliant and ductile, like an elastomer, at low mass fractions to stiff and brittle, like a rigid thermoplastic, at high nanotube content. For mid-range nanotube contents (approximate to 15%) the material behaves like a rigid thermoplastic with large ductility: Y = 1.5 GPa, sigma(epsilon = 3%) = 36 MPa, sigma(B) = 55 MPa, sigma(B) = 100% and T = 50 MJ m(-3). Analysis suggests that soft polyurethane segments are immobilized by adsorption onto the nanotubes, resulting in large changes in mechanical properties.