Effects of ball milling on the structure of cotton cellulose

Authors: LING, ZHE - Beijing Forestry University; WANG, TUO - Louisiana State University; MAKEREM, MOHAMADAMIN - Louisiana State University; Santiago Cintron, Michael; Cheng, Huai; KANG, XUE - Louisiana State University; BACHER, MARKUS - University Of Natural Resources & Applied Life Sciences - Austria; PORTHAST, ANTJE - University Of Natural Resources & Applied Life Sciences - Austria; ROSENAU, THOMAS - University Of Natural Resources & Applied Life Sciences - Austria; King, Holly; Delhom, Christopher; Nam, Sunghyun; Edwards, Judson; KIM, SEONG H. - Pennsylvania State University; XU, FENG - Pennsylvania State University; French, Alfred - Al

Submitted to: Cellulose
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2018
Publication Date: 2/17/2019
Citation: Ling, Z., Wang, T., Makerem, M., Santiago Cintron, M., Cheng, H.N., Kang, X., Bacher, M., Porthast, A., Rosenau, T., King, H.A., Delhom, C.D., Nam, S., Edwards, J.V., Kim, S., Xu, F., French, A.D. 2019. Effects of ball milling on the structure of cotton cellulose. Cellulose. 26(1):305-328. https://doi.org/10.1007/s10570-018-02230-x.
DOI: https://doi.org/10.1007/s10570-018-02230-x

Interpretive Summary: This paper explores the relative states of crystalline and amorphous cellulose present in cotton. Crystalline cellulose may be thought of as well-organized crystallites having defined dimensions. Whereas amorphous cellulose has no defined structure based on organized shapes and size, and is thought to exist as random cellulose chains. The idea that cellulose has a crystalline component came from an analytical technique termed X-ray diffraction. The idea that everyday plant cellulose is not entirely crystalline came from various avenues of thought and analysis. In the case of spectral analysis using X-ray diffraction, the peaks of amorphous cellulose are not as sharp as crystalline cellulose. The increase in peak breadth could come from small crystallite size, from defects within the crystal lattice, or from material that lacks organization, causing the crystalline peaks to be more diffuse. Thus, shedding further light on the source of amorphous cellulose is important. In this work ball-milled cotton was an interesting sample for analyses of amorphous or non-crystalline cellulose versus crystalline because few other molecules such present to interfere with the analysis. Cotton cellulose’s initial crystal size is also bigger than for many other plants. Also, all of the samples analyzed in this study had the same history until the ball milling began, rather than choosing native materials from different sources to obtain different crystallinities. The paper sheds light on the cellulosic structure of cotton by sorting through the relative states of amorphous versus crystalline cellulose in purely defined samples using a plethora of instrumental approaches the results of which are interpreted by international authorities on cellulose structure. This work contributes to knowledge in a literature on the structure of cotton cellulose, which should improve approaches to utilizing cotton cellulose as a source of both crystalline and amorphous cellulose.

Technical Abstract: Cellulose is often described as a mixture of crystalline and amorphous material. A large part of the general understanding of the chemical, biochemical and physical properties of cellulosic materials is thought to depend on the consequences of the ratio of these components. For example, amorphous materials are said to be more reactive and have less tensile strength but comprehensive understanding remains elusive. Ball milling has been used for decades to increase the ratio of amorphous material. The present work used 13 techniques to follow the changes in cotton fibers (nearly pure cellulose) after ball milling for 15, 45 and 120 minutes. X-ray diffraction results were analyzed with the Rietveld method; DNP (Dynamic Nuclear Polarization) natural abundance 2-D NMR studies in the following paper assisted with the interpretation of the DNP 1-D analyses in the present work. A conventional NMR model’s paracrystalline and inaccessible crystallite surfaces were not needed in the model used for the DNP studies. Sum Frequency Generation spectroscopy also showed profound changes as the cellulose was decrystallized. Optical microscopy and FE-SEM results showed the changes in particle size and molecular weight, and carbonyl group analyses confirmed chemical changes. Specific surface areas and pore sizes increased. Fourier Transform IR and Raman spectroscopy also indicated progressive changes; some proposed indicators of crystallinity for FTIR were not in good agreement with our results. Thermogravimetric analysis results indicated progressive increase in initial moisture content and some loss in stability.