Two-Step Carboxymethylation of Cellulose from Halocynthia roretzi Using Ionic Liquid

Water-soluble carboxymethylated tunicate cellulose (CMTC) was produced using cellulose from Halocynthia roretzi, known for its uniquely high molecular weight and crystallinity. Among various known methods for cellulose carboxymethylation tested in this study, only the homogeneous method using LiClO₄ yielded water-soluble CMTC. However, industrial application of this method is hindered by LiClO₄'s toxicity, explosiveness, and high cost. Therefore, we developed a two-step carboxymethylation process utilizing [Emim][Ac], effectively converting crystalline cellulose into an amorphous form and reducing both the degree of polymerization (DP) and polydispersity index (PDI). CMTC prepared by this two-step method exhibited a high degree of substitution (DS = 1.94), excellent water solubility (>100 mg/g), and superior thermal stability. Compared to the LiClO₄-based CMTC, our product contained only 5% unmodified glucose and demonstrated significantly enhanced thickening properties, with 8-fold greater viscosity in 5% aqueous solutions. Structural properties were confirmed via HPLC, ¹H NMR, XRD, FT-IR, and TGA analyses.