engleski

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 characteristics of truly "amorphous" cellulose is needed. So far, such scattering curves have not been available. It was the aim of this study to arrive at an experimentally determined scattering curve of amorphous cellulose. Tor this purpose, two cellulose samples (a pine wood pulp and microcrystalline powder) were ball milled in a high energy equipment in order to destroy the crystalline structure. The structural changes in the cellulose samples and kinetics of amorphization were followed by taking the X-ray diffractograms. After a 30 min milling, no more change , in the structure could be observed and the diffraction curve of amorphous cellulose with two diffuse maxima at spacing 0.427 nm (strong) and at 0.247 nm (weak) was obtained. The amorphization was found to follow a first order kinetics, the rate constant k = (0.0033ą0.0004)/s holding for both samples. however, while the amorphization of the microcrystalline cellulose started immediately, with the wood pulp sample an introduction period of about 300 s was observed, which is probably due to residual morphological structures present in this sample.

Amorphous and crystalline cellulose; High-energy dry ball milling; Kinetics of amorphization of cellulose; Wide angle X-ray diffraction analysis.

nije evidentirano