Scalable coating methods for enhancing glass fiber–epoxy interactions with cellulose nanocrystals

Two scalable coating techniques, slot die and spray coating (SC), are used to apply cellulose nanocrystals (CNCs) to the surface of glass fibers with the goal of enhancing interfacial interactions between glass fibers and epoxy and, consequently, the strength of fiber-reinforced composites. The quality of the cellulose coatings and the interfacial shear strength, assessed via the single fiber fragmentation test, are determined as a function of the method and conditions used to coat the fibers. In addition, a comparison with glass fibers coated with identical CNC formulations using a laboratory-scale dip coating (DC) technique is provided. Results from both scalable methods were found to be comparable or superior to the DC technique, with SC outperforming DC by up to 18% on average depending on the coating applied. Further analysis was conducted on coating morphology, fracture behavior, elemental composition, and surface loading. The observed differences can be used to determine which technique is most appropriate for a given application. This work demonstrates the viability in adapting existing, scalable processes for CNC glass fiber coatings and establishes key avenues for future process optimization.