Surface replication and characterization of ultrahigh-pressure homogenizer treated cellulose nanofiber-reinforced polyvinyl alcohol composites by thermal imprinting

In this study, cellulose nanofibers (CNFs) were treated in an ultrahigh-pressure homogenizer (UHPH) in the thermal imprinting process. After 20 passes, UHPH-treated CNFs with concentrations of 1, 2, and 5 wt% were used to reinforce polyvinyl alcohol (PVA), and PVA/CNF composite films were fabricated by solvent casting. The composite films were subjected to thermal imprinting using a fluoropolymer-treated nickel–phosphorus mold with various line/space micropatterns at different mold temperatures. In addition, the effect of the CNF contents on the viscoelastic behavior, thermomechanical properties, thermal dimensional stability, surface properties, and replication performance of the PVA/CNF composites were investigated. The viscoelastic properties and induced stiffness were improved as a result of the solid-like behavior and CNF network structure, and the coefficient of thermal expansion (CTE) decreased with the increase in the CNF content. The low modulus of the film at thermal imprinting temperatures increased transferability, while the high stiffness, molecular recovery, and low CTE of the composites secured the micropatterns and increased the replication quality of the thermal imprinted PVA/CNF composite films. Results suggested that the addition of CNFs can improve the processability of the thermal imprinting process. Notably, the high replication of films for all micropatterns was observed at a CNF content of 5 wt%. Nevertheless, the narrow micropattern of 5 wt% CNFs could be thermally imprinted at a temperature of less than 120 °C.