Microstructural design for enhanced mechanical and shape memory performance of polyurethane nanocomposites: Role of hybrid nanofillers of montmorillonite and halloysite nanotube

Herein, the effect of simultaneous incorporation of two silicate-based nanofillers, including montmorillonite (Mt) and halloysite nanotube (Hal), on mechanical and shape memory performance of thermoplastic polyurethane (TPU) nanocomposites was studied. Different amounts (1, 3, and 5 wt%) of Hal, Mt. and hybrid Hal:Mt. were embedded into TPU matrix, utilizing a melt mixing method. Morphological studies on the hybrid nano composites elucidated that appropriate dispersion and distribution were achieved. Higher transition temperatures, as well as lower degrees of crystallinity, were observed for TPU/Hal:Mt. nanocomposites, compared to the other counterparts. Dynamic-mechanical-analysis (DMA) results illustrated superior storage modulus in the hybrid nanocomposites in both glassy and rubbery regions owing to superlative polymer-filler interactions. According to the tensile measurements, the hybrid nanocomposites demonstrated remarkable improvements in Young's modulus as well as ultimate strength and elongation at break than those of solo-nanocomposites due to better stress transfer from the hybrid fillers to the TPU. Superior ameliorations of storage modulus, both in glassy and rubbery regions, consequently effectuated the shape memory performance of the hybrid nanocomposites. For instance, 5 wt% incorporation of the hybrid filler within the matrix enhanced shape fixity ratio, shape recovery ratio, and recovery speed by 6.1%, 2.9% and 2.3 s, respectively, compared to pristine TPU.