Control of reinforcing efficiency in thermoplastic polyurethane/aramid nanofiber nanocomposites: Rheological and two-dimensional correlation spectroscopic approaches

Abstract

To overcome the demerits of thermoplastic polyurethanes (TPUs), such as softness and low thermal stability, they are typically prepared as composites reinforced by stiff p-aramid. Although aramid nanofibers (ANFs) provide reinforcement superior to that of conventional microfibers, their reinforcing efficiency depends on their loading and dispersion. Herein, we establish rheological and spectroscopic strategies for the precise control of the reinforcing efficiency of ANF in TPU nanocomposites. ANF exhibits the maximum mechanical reinforcing efficiency at 1.5 w/w% in the range of 0.5–6.0 w/w%. Rheologically, the optimal filler amount is just above the percolation threshold (1.0 w/w%). Based on Fourier-transform infrared spectroscopy and its two-dimensional correlation analysis, while ANF produces intermolecular hydrogen bonds with TPU until 1.5 w/w%, it favors intramolecular interaction as the content increases. The intermolecular TPU-ANF interaction contributes to the high reinforcing efficiency of ANF (<1.5 w/w%), whereas the evolution of intramolecular ANF–ANF bonds above 2.0 w/w% results in aggregation and associated efficiency deterioration. Thus, the reinforcing efficiency of ANF-containing polymer nanocomposites can be accurately tailored using rheological and spectroscopic approaches.