Preparation and Characterization of Nanocrystalline Cellulose by Acid Hydrolysis of Cotton Linter

Abstract

The purpose of this study was to use acid hydrolysis of cotton linter to generate nanocrystal-line cellulose (NCC). Based on a 2^4 factorial design, the effects of sulfuric acid concentration, temperature, hydrolysis time, and the solid/liquid ratio on the NCC yield were examined. NCC specimens obtained from different sulfuric acid concentrations were subjected to a battery of analyses, including dynamic light scattering (DLS), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), 13C solid-state nuclear magnetic resonance (13CSNMR), and a thermal gravimetric analysis (TGA) to probe the particle size distribution, morphology, functional group shifts, position of the carbon, and thermal degradation properties of the ensuing NCC. The results indicated that the sulfuric acid concentration and solid/liquid ratio at higher levels, and temperature and reaction time at lower levels were significantly conducive to increases in NCC yields. The main effects in diminishing order were the acid concentration, temperature, hydrolysis time, and solid/liquid ratio. Results of DLS and TEM observations suggested that the NCC had a size distribution centered around 20~200 nm, with length-to-width ratios ranging 1:1~1:30. The FTIR analysis indicated that absorption peaks at 1010~1080 and 1150~1260 cm^(-1) were derived from sulfate ester bonds on the cellulosic chains. Solid state 13CNMR spectra indicated that the C4 atoms along the cellulosic chain were shifted from 87.4 ppm to a lower magnetic domain, indicating the sulfonic ester bonding position. The TGA indicated that the lower-sulfuric-acid NCC specimen began step 1 weight loss at ca. 149℃, whereas its starting temperature of step 2 weight loss was generally higher than the mid- and high-acid NCC, at 337 and 205℃, respectively. The high-acid NCC only showed marked weight loss at 243℃. The study found that a sulfuric acid concentration of 60%, a solid/liquid ratio of 1:20, a hydrolysis temperature of 45℃, and a hydrolysis time of 5 min produced the best yield of 54.4%.