Polymer induced strengthening and toughening of aramid nanofiber film: The importance of densification and hydrogen bonding

In this contribution, polyacrylic acid (PAA), polyacrylamide (PAM), thermoplastic polyurethane (TPU), and polyvinylpyrrolidone (PVP) were selected as additives to improve the mechanical strength and toughness of the aramid nanofiber (ANF) film. The results show that all these polymers can improve the strength, elongation at break, and toughness of the ANF film. Compared with pure film, the ANFs/TPU composite shows the highest strength of 273.14 MPa, an increase of 67.53%, and the ANFs/PAA exhibits the highest elongation of 30.02% and the highest toughness of 49.18 MJ.m(-3), increased by 251.52% and 304.77%, respectively. The enhancing mechanisms can be attributed to the structural densification, hydrogen bonding, and dipole-dipole interactions. The TPU and PAM that contain amide structures can form ordered networks of hydrogen bonds and show strong enhancing capacities on strength, while the PAA and PVP show robust enhancing capacities on toughness. Meanwhile, taking polystyrene (PS) as additive, we proved that the nonpolar polymer shows weak enhancing ability on the mechanical strength of ANF film due to the poor interfacial compatibility and severe phase separation.