Different Effects of Mixing Manners on the Porous Structures and Dense Films of Waterborne Polyurethane Modified with Recycled Aramid Nanofibers

Para-aramid nanofibers have received much attention in recent years, including the low-cost preparation method and the control of the dispersing of the long, self-associating product in highly viscous polymer matrices for polymer composites. In this work, recycled aramid nanofibers (RANF) were prepared through selective chemical cracking of discarded para-aramid composite panels. Two manners of mixing RANF into waterborne polyurethane (WPU) are proposed, and different dispersing effects are compared in both the composite aerogels and films. It has been found that the controlled coalescence of RANF in WPU prepared by the gel mixing (GM) method gave out a particular cellular structured aerogel with high strength (790 kPa), toughness (2.06 MJ·m–3), and damping functions; meanwhile, finer dispersed RANF were obtained by the solution mixing (SM) method, and RANF-reinforced WPU solid films were obtained by the 3D porous structure-mediated composite method at an RANF content of 0.66 wt %, with tensile strength, modulus, and toughness increasing to ∼150% of the original levels, providing the clue to the solve the dispersing problems of the associative 1D nanofillers.