Small Angle X-Ray Study of Cellulose in Cotton Using Correlation Functions

Abstract

ABSTRACT:This work shows that the small angle X-ray scattering (SAXS) intensity of dewaxed cotton of local origin at 25°C deviates from Porod's law establishing that cotton at 25°C falls under non-ideal two-phase structure characterised by continuous variation of electron density at the phase boundary. Therefore the mean square of the electron density gradient <I grad 1' / 1 2 ) in isotropic structure is proportional to the fourth moment J s4 I(s)ds, of the SAXS intensity distribution in the reciprocal space and to the second derivative of the correlation function in the origin. The above relation given by Vonk has been used to find the thickness E of the transition region along with the following important physical parameters. They are D, the average periodicity transverse to the layer, S/ V, the specific inner surface, </> 1 and </>2 , the volume fraction of two phases, i.e., matter and void, le, the length of coherence, T,_ and T,_, the transversal lengths, T,, the range of inhomogeneity and 2E/D, the volume fraction of the transition layer. Two values of E have been obtained by the method of Vonk and Ruland. The SAXS intensity data of cotton sample was obtained by a technique using a compact Kratky camera.KEY WORDS Back Ground Corrected SAXS Intensity/ Cellulose/ Width of Transition Layer / Correlation Functions / Transverse Periodicity / Cotton as a natural fibre finds extensive use in day to day life. Cotton fibres, like most vegetable fibres are essentially cellulosic in nature and the percentage of cellulose is as high as 96% in unpurified cotton. The other components of cotton are protein 1.1-1.9%, pectic substance 0.7-1.2%, ash 0.7-1.6%, wax 0.4-1.0% and few other trace materials. However purified cotton contains 99. 7% pure cellulose. 4 The cellulose in cotton is in the form of fibrils which spiral at an angle to the length axis of the cell. It is arranged in several ordered levels of orientation in the fibre. At the molecular level, the long molecules are shown by Xray diffraction to be arranged into highly ordered crystalline regions. X-Ray diffraction is considered the basic method for the structural studies of polymer solids, because of direct relationship between the diffraction pattern and order. 5 As cotton is cellulosic in nature and comes under macromolecular system, a small an-gle X-ray scattering (SAXS) study has been undertaken to throw some light on its macromolecular structure.Small angle X-ray scattering takes place in systems having macromolecular structure. The electron density difference between the two phases of the system, which occurs over a distance of 100 to 1000 A, causes small angle X-ray scattering. This phenomenon was first observed by Krishnamurti,6 were applied to obtain physical parameters of densely packed system for an ideal two-phase structure having sharply defined phase boundaries, where it was observed that the product /(_0). 0 3 comes out to be a constant at a large scattering angle. Here, 0 is half the scattering angle and l is the smeared-out intensity.However, ...

The effect of temperature on the fine structural characteristics of cotton fibre – a small-angle X-ray scattering investigation using correlation functions

“…in our previous paper (Misra, Bisoyi, Patel, Patra & Patel, 1988) using the theories of Vonk (1973) and Ruland (1971), treating the cotton as a pseudo-twophase lamellar structure (see Fig. 1).…”

“…Using a three-dimensional correlation function C(r), the value of -3[d2C(r)/ dr2],=o = R' can be computed. If the value of R' exactly or nearly coincides with R [R = (3/2)(2-n'/ Misra et al (1988), equation (4)], then the system can be treated as an isotropic system. The fine structural characteristics, typically known as macromolecular parameters of dewaxed cotton at five temperatures (298, 310, 319, 327 and 334 K) were computed under identical experimental conditions and are displayed in Table 1.…”

Fine Structure Analysis of Ramie Fibres by Small Angle X-Ray Scattering Technique

“…The work of Misra et al 3 • 4 on natural cellulosic fibre like cotton, sisal etc. shows that natural cellulosic macromolecules possess non-ideal two phase structure.…”

“…2 As Ramie is mostly cellulosic, it comes under the macromolecular system. We present here the SAXS studies on ramie fibres to compare the macromolecular structure of natural fibre with fibres treated in sodium hydroxide solution at different concentration.The work of Misra et al 3 • 4 on natural cellulosic fibre like cotton, sisal etc. shows that natural cellulosic macromolecules possess non-ideal two phase structure.…”

Background correction of the SAXS intensities scattered by semicrystalline materials

“…Porod's (1951) law is sensitive to background error, therefore background correction is important. Some authors have used the following equation to represent the background scattering of some polymers (Korltleve, Tuijnman & Vonk, 1972;Misra, Bisoyi, Patel, Patra & Patel, 1988;Stroble, Schneider & Voigt-Martin, 1980):…”