Solvent-free acetylation of CNFS and CMFS using different catalysts

Nanocellulose has several advantages, including hydrophilicity, low density, high strength property, and large specific-surface area. However, its hydrophilicity becomes a problem when it comes in contact with a polymer matrix in nanocomposites. Therefore, the transformation of hydrophilicity into hydrophobicity through chemical modifications is important. This study focused on the impacts of two solvent-free acetylation methods using iodine (Method 1) and sulfuric acid (Method 2) as catalysts. Moreover, herein, the characteristics of acetylated cellulose nanofibrils (A-CNFs) and cellulose microfibrils (A-CMFs) produced via an aqueous counter collision (ACC) are compared. The degree of substitution (DS) of acetylated samples increased with the reaction time. Furthermore, the DS of Method 2 was higher than that of Method 1. After acetylation, the X-ray diffraction patterns of the samples were semicrystalline and amorphous owing to the destruction of crystalline cellulose. Moreover, the crystallinity of all acetylated samples decreased. Excluding a few cases of Method 2, the thermal stability increased after acetylation. Excluding the CMFs treated with Method 2, the contact angle increased with the reaction time. This indicates that the samples were transformed to exhibit hydrophobic surfaces. In addition, the cases of Method 1 exhibited higher crystallinity, thermal stability, and wettability than those of Method 2.