Synergistic effect of hemiacetal crosslinking and crystallinity on wet strength of cellulose nanofiber-reinforced starch films

Starch is the most abundant biomass and potential replacement of single-use packaging; however, the lack of water durability and wet strength restrict the applicability of starches. Hemiacetal/acetals cross-linked starch film have water stability, however, the film possess poor wet strength owing to lack of crystallinity. In this study, we prepared TEMPO-oxidized cellulose nanofiber (TCNF)/starch composite films by mixing different-storage-duration native tapioca starch (NTS), hydroxypropyl starch (HPS), and di-aldehyde starch (Di-aldS) with TCNF. We demonstrate that the films prepared with the stored starch pastes exhibit improved mechanical properties and wet strength owing to the synergistic effect of enhanced crystallinity and hemiacetal crosslinking. However, long-term storage of the starch pastes negatively affected their properties. Thus, improving the film properties by optimizing the starch paste storage time is an environmentally friendly and energy-conserving method. Moreover, our experimental results suggest that TCNF/HPS films prepared with the HPS paste stored for three days (~22 °C, ~25% RH) can be a potential alternative to single-use packaging films.