Nanofiber cellulose di- and tri-acetate using ferric chloride as a catalyst promoting highly efficient synthesis under microwave irradiation

An efficient method for the generation of cellulose di- and tri-acetate nano-structures is obtained through testing ferric chloride hydrate (FeCl₃·6H₂O) as a valuable Lewis acid catalyst with acetic anhydride under microwave irradiation. Our target was to evaluate the effects of the reaction conditions on the products' properties such as surface area and particle size distribution. It was found that changes in the degree of substitution (DS), the surface area, the degree of polymerization and the particle size distribution of the products correlated with reaction conditions. Cellulose tri-acetate nanofibers with DS of 2.94 with 98.03% yield was prepared using 200 mg of FeCl₃·6H₂O, 25 ml of Ac₂O and 4 minutes of microwave irradiation. Also, cellulose di-acetate nanofibers were prepared with DS values ranged between 2.37 and 2.72 with yield ranged between 78.92 and 90.58%. The percentage of acetyl groups (Ac%) as well as the BET specific surface area, total pore volume, mean pore diameter, mono layer volume and the mean particle size of the products were determined. The maximum specific surface area obtained for the acetylated cellulose was about ten times larger than that measured for the commercial cotton cellulose and about six times larger than that of the commercial cellulose acetate. The lowest mean particle size (34.90 nm) was about eleven times smaller than the mean particle size of the commercial cellulose acetate (394 nm). The present work has proved that FeCl₃·6H₂O was a highly active catalyst for the esterification of cellulose with unexpected yields and for the formation of nanofibers with low molecular weight.