Holzforschung, Vol. 63, pp. 40–46, 2009 • Copyright  by Walter de Gruyter • Berlin • New York. DOI 10.1515/HF.2009.008 Article in press - uncorrected proof Cellulose supramolecular structure changes during chemical activation and sulfation 2 nd ICC 2007, Tokyo, Japan, October 25–29, 2007 Nodirali Sokhobatalievich Normakhamatov 1, *, Abbaskhan Sabirkhanovich Turaev 1 and Neyla Djalalovna Burkhanova 2 1 Institute of Bioorganic Chemistry of Uzbek Academy of Science, Tashkent, Uzbekistan 2 Institute of Polymer Chemistry and Physics of Uzbek Academy of Sciences, Tashkent, Uzbekistan *Corresponding author. Institute of Bioorganic Chemistry of Uzbek Academy of Science, Tashkent-100125, Uzbekistan Phone: q99871-262-35-40 Fax: q99871-262-70-63 E-mail: nodirali@gmail.com Abstract 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 interfibril- lar 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 stud- ies 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, sul- fation changed its crimped fibers with different thick- nesses, length and defects which were visible in a polarized light as bright luminescence. Fibers become short, thick, and straightened. Moreover, degree of ani- sotropy and crystallinity of the modified fibers decreased. Their size and degree of crimping are dependent on con- dition 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 A ˚ , respectively. Keywords: activation; cellulose; electron microscopy; polarized optical microscopy; sorption-desorption invest- igations; sulfation; X-ray diffraction (XRD). Introduction Cellulose is the most abundant renewable organic mater- ial (Hon 1994). Pulp and paper, textile fibers, film mater- ials, varnishes, plastics, etc., are examples of their indus- trial utilization which often needs chemical and structural modification (Klemm et al. 2005). The reactivity and thus processability of cellulose materials depends on the fiber morphology and its reg- ularity, its porosity, and the degree of crystallinity (DC) within the cell wall. Pulp, linters or other cellulose raw materials are frequently activated aiming at improving the accessibility and the reactivity of cellulose on various structural levels (Guo and Gray 1994). Thereby, a higher degree of substitution, a more homogeneous substituent distribution, a higher reaction rate and thus a higher yield of product with better properties can be achieved. The most frequently used activation methods include swelling agents which improve the accessibility of pores, pene- trate into the highly ordered regions, and split bonds between glucan chains and fibrils (Merchant 1957). The mechanism of reagents penetration in cellulose fibers is not always clear (Klenkova 1976). In the context of cellulose pretreatment, the term ‘‘reactivity’’ does not refer to kinetic constants of chemical reactions, but to the speed of reactants which modify hydroxyl groups. The sulfation process leading to cellulose sulfate (CS) is very fast, and consequently the limitation factor is the transport of the sulfate groups through the large supra- molecular aggregations of cellulose in the cell wall (Nevell and Zeronian 1985). CS is known for more than 100 years, but the process is still not well investigated. One of the reasons is that CS in the acid form is unstable and easily split up further to low molecular weight products. Moreover, the synthe- sis of CS is complicated and destruction processes accompany the sulfating reaction. To control these reac- tions is rather problematic (Cart and Carlton 1954). The crystal lattice of natural cellulose fibers can be changed by treatment with some hydrophilic organic substances with low molecular weight (such as aliphatic alcohols, amines, etc.), in the course of which the inter- plane distances are increased. On the other hand, the fibrous structure of cellulose and its average degree of polymerization (DP) is kept well (Klenkova and Kulakova 1967). Our group is engaged in a search for increasing the reactivity of cotton cellulose against sulfation by its acti- vation with aliphatic alcohols and tertiary amines. The main focus of our interest is a better understanding of the change of morphology of cellulose during activation and sulfation. In this paper, the morphological changes are observed by polarized light microscopy and electron microscopy. IR spectroscopy and X-ray diffraction (XRD) were the methods available for measuring the changes in crystallinity. Observation of the sorption-desorption behavior of the derivatives complement the results. Brought to you by | Tokyo Daigaku Authenticated Download Date | 5/29/15 2:11 AM