Nanomechanics of Shape Memory Polymer Nanocomposites with Carbon Nanofibre and Carbon Nanotube

Micro and nanoscale deformation behaviour of nanorods enhanced shape memory polymer nanocomposites have been investigated through microstructure analysis, thermal-mechanical characterization, nanoindentation, micromechanics testing and recovery efficiency assessment. The relationships between mechanical property and microstructure have been studied and microstructure characterization showed that the formation of CNF bundles with knots structure in CNF/polysterene (PS) composites, whereas the MWCNT/PS composites showed the separated individual MWCNT rods in a polymer matrix. The micromechanical analysis revealed that although both the CNF and MWCNT enhanced the PS matrix, the MWCNT shows a better reinforcing capability and the enhancement is significant with CNT concentration up to 3 wt%. Energy distribution dependency on the nano-filler content were characterized by nanoindentation. The micro-mechanics analysis on the calculated E/σ_Y and h_p/h_max showed that the pile-up effect did not significantly affect the reliability of nanoindentation results with the load above 1 mN. The h_p/h_max ratio analysis was proved as a better evaluation parameter than the E/σ_Y ones for identifying the pile-up and sink-in effects. Thermal cyclic tensile results indicated that the shape recovery rates were reduced by adding nano-fillers into polymer. MWCNT/PS nanocomposites exhibit a higher recovery rate and yield strength than those of the CNF/PS, because of their better organic-inorganic interface and uniformity.