Hybrid Cellulose Nanocrystal-Bonded Carbon Nanotubes/Carbon Fiber Polymer Composites for Structural Applications

Integrating carbon nanotubes (CNTs) in carbon-fiber-reinforced-polymer (CFRP) composites enhances structural and functional properties; however, it often involves chemical functionalization or processes that lead to inhomogeneous dispersion and nonuniform distribution of CNTs that impair the final properties and hinder manufacturing scalability. Herein, we present a novel and scalable processing technique to integrate pristine CNTs (pCNTs) into CFRP composites without the need for chemical functionalization or addition of surfactants. We use cellulose nanocrystals (CNCs) as assisting nanomaterials to uniformly disperse and stabilize pCNTs in water, and then we coat carbon fibers (CFs) with CNC-pCNT prior to resin infusion. Two coating methods are used: simple immersion (I-coating) and simultaneous immersion and sonication (IS-coating). The surface chemistry of coated CFs reveals that I-coating provides a higher quantity of polar oxygen groups in coated CFs containing CNC-pCNT compared to IS-coating. We show that fabricating hybrid CFRPs by incorporating 0.2 wt % CNC–0.2 wt % pCNT in CFRP composites using this simple technique enhances the flexural strength by 33% and the interlaminar shear strength (ILSS) by 35% compared to those of neat CFRPs. Significantly, 0.2CNC-0.2pCNT-CFRPs show ∼25% higher flexural strength and ILSS compared to the largest enhancement in composites with individual functionalized CNTs (fCNTs) or CNCs, demonstrating a synergistic effect of CNC-pCNT in enhancing properties. Moreover, our results indicate that incorporating CNC-pCNT increases the thermal stability of CFs compared to those of fCNTs. These are specifically crucial in composites used in structural applications. These results highlight that the introduced CNC-enabled processing technique is a potential scalable path toward the fabrication of hybrid composites that can enhance properties higher than individual CNTs or CNCs, avoiding costly and/or time-inefficient functionalization processes.