Cellulose supramolecular structure changes during chemical activation and sulfation

Cotton cellulose has been sulfated in the presence of organic solvents (methanol, ethanol, iso-propanol and via chlorosulfonic acid-pyridine complex, and a mixture of concentrated sulfuric acid and ethanol) and the effects were studied by polarized light microscopy, electron microscopy, IR spectroscopy, and X-ray diffraction. Sorption-desorption behavior of the sulfonated cellulose was also observed. These processes enhance interfibrillar swelling, weaken intermolecular hydrogen bonds, and loosen the packing density of microfibrils. As a result, the accessibility of esterification reagents was improved depending on the activation method. Microscopic studies showed that the surface of the initial cotton cellulose is wrinkled. The fibrillar structure of the primary fiber wall was not observed. In the case of cotton cellulose, sulfation changed its crimped fibers with different thicknesses, length and defects which were visible in a polarized light as bright luminescence. Fibers become short, thick, and straightened. Moreover, degree of anisotropy and crystallinity of the modified fibers decreased. Their size and degree of crimping are dependent on condition of modification. All pre-activation processes were successful. Thickness of fibers was increased up to 20% and the length was decreased to one-third or one-fourth. The sorption capability of cellulose was increased 2.1-3.4-fold in pre-activated samples, which is due to the increasing specific surface area (45.0-109.1 m(2) g(-1)). Volume and radius of the pores increased up to 0.1164-0.410 m(3) g(-1) and 36.2-133.3 angstrom, respectively.