In Situ Reinforced Heterocyclic Aramid Fiber with Nanosized Graphene Whiskers: Small Addition, Big Gains

Heterocyclic aramid fibers (HAFs) with high strength and high modulus are widely used in the field of impact resistance. However, the weak interaction between molecular chains of HAFs seriously hinders the simultaneous improvement of strength and modulus. Herein, small addition (0.05 wt%) of nanosized acyl-chloride-activated graphene whiskers (NGW-Cl) is used as reinforcements to simultaneously increase the strength and modulus of HAFs. The resultant NGW-Cl/HAFs monofilament displays high tensile strength and modulus of 6.31 and 152 GPa, which are 19% and 18.8% higher than that of HAFs. The NGW-Cl/HAFs multifilaments show high tensile strength and modulus of 36.16 and 1008 cN per dtex, which are 19.34% and 24.14% higher than that of HAFs. Especially, the dynamic modulus of NGW-Cl/HAFs is up to 268.0 GPa at 200 HZ, which is increased by 92.8% compared with HAFs (139.0 GPa), showing a great application potential in high-frequency vibration fields. Additionally, the strength and modulus of NGW-Cl/HAFs impregnated multifilaments is up to 6.08 and 152 GPa, which is increased by 24.5% and 28.8% compared with HAFs. This apparent improvement is because the strong chemical bonding between NGW-Cl and heterocyclic aromatic chains enhances heterocyclic aromatic chain interaction, inducing high crystallinity and orientation of HAFs. The special nanosized and whisker-like structures of nanosized acyl-chloride-activated graphene whiskers(NGW-Cl) have highly matched between the graphene and heterocyclic aramid (HA) molecules in the size and morphology, thus improving HA's crystallinity and orientation. Additionally, the grafted OCCl in NGW-Cl can form amide bonds with NH2 in p-phenylenediamine (PPD) monomer for strengthening the intermolecular chain interactions and thus simultaneously improve fiber's strength and modulus.image