Prevention of Aggregation of Pectin‐Containing Cellulose Nanofibers Prepared from Mandarin Peel

In this study, pectin‐containing cellulose nanofibers (CNFs) were prepared from mandarin peel (MP), and the effect of pectin, which remained in purified cellulose after a purification treatment, on the aggregation of CNFs was investigated. Cellulose samples with different pectin concentrations were prepared by bleaching and a hydrothermal treatment with an acid solvent. Following the preparation of the different pectin‐containing cellulose samples, each cellulose sample was fibrillated by a high‐pressure homogenizer treatment. The morphological structures of CNF samples were observed using atomic force microscopy (AFM) and scanning electronic microscopy (SEM). The AFM images of the pectin‐containing CNFs showed that the pectin covered the surfaces of the CNFs and that the CNFs obtained from MP were finer than those obtained from wood cellulose. Further, the SEM images of the oven‐dried samples showed that the pectin‐containing CNFs were finer than the purified CNFs obtained from MP. Moreover, the oven‐dried pectin‐containing CNFs could be redispersed in water. This indicated that pectin has a potential to prevent the aggregation of CNFs. However, the addition of commercial pectin to a CNF suspension did not inhibit CNF aggregation. Although an interaction between the CNFs and pectin were confirmed in the case of the pectin‐containing CNFs prepared from MP, the commercial pectin did not interact with the purified CNFs. This CNF‐pectin interaction, which is based on their original structures, probably results in the pectin covering the surfaces of the CNFs. It is likely that this is the reason that the aggregation of the CNFs was inhibited.