Construction of Aramid Engineering Materials via Polymerization-Induced para-Aramid Nanofiber Hydrogel

The processing of poly(p-phenylene terephthalamide) (PPTA) has long been a great challenge. This work reports a simple "monomers-nanofibers-macroscopic product" (MNM) hierarchical self-assembly approach to build 3D all-PPTA engineering materials. This approach mainly includes the preparation of polymerization-induced aramid nanofibers (PANFs) from monomers and the fabrication of all-PPTA materials from PANF hydrogel. Various 3D architectures, including simple solid bulks and sophisticated honeycombs (HCs), are obtained after the dehydration and shrinking of the PANF hydrogel. The tensile strength and compressive yield strength of PANF bulk are more than 62 and 90 MPa, respectively, which are comparable to typical engineering plastics. The compressive strength of PANF HC with a density of 360 kg m^-3 is more than 24 MPa. The thermal stability of PANF bulk and PANF HC are as good as that of Kevlar fiber and almost no decomposition occurred before 500 °C in a nitrogen atmosphere. Furthermore, the MNM process is performed under mild conditions, without high temperature, high pressure, or corrosive solvent. The MNM process is a novel strategy for the processing of all aromatic polyamide materials with complex structures and high performances and would be another development since the breakthrough of liquid crystal spinning technology of PPTA.