AN X-RAY-DIFFRACTION STUDY OF THE CRYSTALLINE-TO-AMORPHOUS PHASE-CHANGE IN CELLULOSE DURING HIGH-ENERGY DRY BALL-MILLING

In methods used widely for determining ''crystallinity'' of cellulose substrates by X-ray wide angle diffraction the scattering characterist ics of truly ''amorphous'' cellulose is needed. So far, such scatterin g curves have not been available. It was the aim of this study to arri ve at an experimentally determined scattering curve of amorphous cellu lose. For this purpose, two cellulose samples (a pine wood pulp and a microcrystalline powder) were ball milled in a high-energy equipment i n order to destroy the crystalline structure. The structural changes i n the cellulose samples and the kinetics of amorphization were followe d by taking X-ray diffractograms. After 30 min of milling, no more cha nge in the structure could be observed and the diffraction curve of am orphous cellulose with two diffuse maxima at spacings of 0.427 nm (str ong) and 0.247 nm tweak) was obtained. The amorphization was found to follow a first order kinetics, the rate constant of k = (0.0033 +/- 0. 0004) s(-1) holding for both samples. However, while the amorphization of the microcrystalline cellulose started immediately, with the wood pulp sample an induction period of about 300 seconds was observed, whi ch is probably due to residual morphological structures present in thi s sample.