The crystalline character of Saudi Arabian cotton fibers was studied using a wide angle x-ray diffraction technique. The purified cotton fibers were examined in their native state and after treatment with urea or caustic soda (NaOH). Cellulosic phases in Saudi Arabian cotton were identified by measuring and indexing the reflections 101, 101, and 002. The x-ray diffractograms showed a cellulose I structure in native cotton fibers as well as those treated with urea. Cotton fibers treated with NaOH and with urea followed by NaOH showed a cellulose II structure. Computer data processing was used to determine the percent crystallinity, lattice spacings, disorder parameter, and crystallite sizes. The percent crystallinity of native cotton decreased from 64% to 47% with mercerization (NaOH). The lattice spacings calculated from the resolved peak positions indicated that d101 for each phase increased by 1 %, while both d101 and d002 decreased with treatment. The disorder parameter increased from 0.0094 to 0.0123 with mercerization. The crystallite sizes L101 and L101 were 3.75 and 2.61 nm, respec tively, for native cotton, and changed to 3.39 and 2.64 nm with the urea treatment. With mercerization, L101 and L101 were 4.35 and 3.15 nm, respectively, but with mercerization after the urea treatment, the crystallite sizes dropped to 1.27 and 2.85 nm, respectively. In the direction perpendicular to the c-axis, the crystallite sizes (L002) were 4.32, 3.7, 3.07, and 2.94 nm for the untreated cotton, urea treated, mercerized, and mercerized after urea treatment, respectively.

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T HE PRESENT work focused on modifying the chitosan structure which has noticeable places in advanced research. The effect of UV-ozone irradiation with different exposure doses (9.68 x 10-14 , 19.35 x 10-14 , 29.03 x 10-14 and 38.75 x 10-14 J/m 2) on the microstructural, thermal stability and optical properties of chitosan was studied. X-ray diffraction (XRD), selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM), optical parameters techniques as well as differential thermal analysis (DTA) and thermogravimetric analysis (TGA and DTG), were performed. The obtained results indicated that, effects on semi-crystalline structures have occurred. Detected variations in XRD, SAED, HRTEM, DTA and TGA analyses under investigation may be attributed to the different degrees of crystallinity, induction of structural changes and molecular configuration of chitosan upon exposure to UV-ozone. The results confirmed that the UV-ozone irradiation plays a role in refining the microstructure and changes occurring in chitosan matrix for future biomedical applications.

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