Aramid nanofibers (ANFs), typically produced by exfoliating aramid microfibers (Kevlar) in alkaline media, exhibit excellent mechanical properties and have therefore attracted increased attention as nanoscale building blocks. However, the preparation of aramid microfibers involves laborious and hazardous processes, which limits the industrial-scale use of ANFs. This work describes a facile and direct monomer-to-ANF synthesis via an as-synthesized intermediate low-molecular-weight poly­(p-phenylene terephthalamide) (PPTA) without requiring the environmentally destructive acids and high-order shearing processes. Under the employed conditions, PPTA immediately dissociates and self-assembles into ANFs within a time period of 15 h, which is much shorter than the time of 180 h (not including the Kevlar preparation time) required for the Kevlar-to-ANF conversion. Interestingly, the fabricated ANFs exhibit nanoscale dimensions and thermoplastic polyurethane (TPU) reinforcing effects similar to those of Kevlar-derived ANFs; i.e., a 1.5-fold TPU toughness improvement and a maximum ultimate tensile strength of 84 MPa are achieved at an ANF content of only 0.04 wt %. Remarkable reinforcement ability investigated by comprehensive analytical data comes from ANFs, which disturb ordered hydrogen bonding in hard segments and induce strain hardening along the elongation pathway. Thus, the developed approach paves the way to industrial-scale production of ANFs and related nanocomposites.

The performance limits of conventional super engineering plastics with inorganic nanofillers are surpassed by all-organic nanocomposites prepared via in situ SNAr polymerization of polysulfone (PSU) in the presence of a highly dispersed aramid nanofiber (ANF) solution. The latter is directly used, bypassing the energy-consuming, nanostructure-damaging workup process. Using only a 0.15 wt % nanofiller, the all-organic nanocomposite shows an ultimate tensile strength 1.6× higher and 3.4× tougher than neat PSU and its blending counterpart due to the mutually interactive filler and maximally homogenized matrix. The exceptional toughness of the ANF/PSU nanocomposite originates from the grafted PSU on the surface of ANF; it drives stress-delocalized deformation, as revealed by stress-absorbable viscoelastic behavior and ductile elongation of materials. This material is a promising candidate for use as a filler-interactive, high-performance nanocomposite.