TY - JOUR

T1 - Mechanical Amorphization of Chitosan with Different Molecular Weights

AU - Podgorbunskikh, Ekaterina

AU - Kuskov, Timofei

AU - Rychkov, Denis

AU - Lomovskii, Oleg

AU - Bychkov, Aleksey

N1 - Funding Information: Mechanical treatment of chitosan samples was supported by the Russian Science Foundation (project no. 22-73-00124). XRD analysis and crystal structure optimization (DFT calculations) and determination of specific energy consumption for amorphization were supported by the grant of the President of the Russian Federation for governmental support of Young Doctors of Sciences (project No. MD-2330.2022.1.3). Publisher Copyright: © 2022 by the authors.

PY - 2022/10

Y1 - 2022/10

N2 - Mechanical amorphization of three chitosan samples with high, medium, and low molecular weight was studied. It is shown that there are no significant differences between the course of amorphization process in a planetary ball mill of chitosan with different molecular weights, and the maximum degree of amorphization was achieved in 600 s of high intensity mechanical action. Specific energy consumption was 28 kJ/g, being comparable to power consumption for amorphization of cellulose determined previously (29 kJ/g) and 5–7-fold higher than that for amorphization of starch (4–6 kJ/g). Different techniques for determining the crystallinity index (CrI) of chitosan (analysis of the X-ray diffraction (XRD) data, the peak height method, the amorphous standard method, peak deconvolution, and full-profile Rietveld analysis) were compared. The peak height method is characterized by a broader working range but provides deviated CrI values. The peak deconvolution method (with the amorphous Voigt function) makes it possible to calculate the crystallinity index of chitosan with greater accuracy, but the analysis becomes more difficult with samples subjected to mechanical processing. In order to refine the structure and calculation of CrI by the Rietveld method, an attempt to optimize the structure file by the density functional theory (DFT) method was performed. The averaged profile of amorphous chitosan approximated by an eighth-order Fourier model improved the correctness of the description of the amorphous contribution for XRD data processing. The proposed equation may be used as a universal standard model of amorphous chitosan to determine the crystallinity index both for the amorphous standard method and for peak deconvolution of XRD patterns for arbitrary chitosan samples.

AB - Mechanical amorphization of three chitosan samples with high, medium, and low molecular weight was studied. It is shown that there are no significant differences between the course of amorphization process in a planetary ball mill of chitosan with different molecular weights, and the maximum degree of amorphization was achieved in 600 s of high intensity mechanical action. Specific energy consumption was 28 kJ/g, being comparable to power consumption for amorphization of cellulose determined previously (29 kJ/g) and 5–7-fold higher than that for amorphization of starch (4–6 kJ/g). Different techniques for determining the crystallinity index (CrI) of chitosan (analysis of the X-ray diffraction (XRD) data, the peak height method, the amorphous standard method, peak deconvolution, and full-profile Rietveld analysis) were compared. The peak height method is characterized by a broader working range but provides deviated CrI values. The peak deconvolution method (with the amorphous Voigt function) makes it possible to calculate the crystallinity index of chitosan with greater accuracy, but the analysis becomes more difficult with samples subjected to mechanical processing. In order to refine the structure and calculation of CrI by the Rietveld method, an attempt to optimize the structure file by the density functional theory (DFT) method was performed. The averaged profile of amorphous chitosan approximated by an eighth-order Fourier model improved the correctness of the description of the amorphous contribution for XRD data processing. The proposed equation may be used as a universal standard model of amorphous chitosan to determine the crystallinity index both for the amorphous standard method and for peak deconvolution of XRD patterns for arbitrary chitosan samples.

KW - amorphization

KW - chitosan

KW - crystal structure

KW - degree of crystallinity

KW - disordering

KW - mechanochemistry

KW - molecular weight

UR - http://www.scopus.com/inward/record.url?scp=85140880800&partnerID=8YFLogxK

UR - https://www.mendeley.com/catalogue/85e0344d-d99e-3c60-82de-ac8ca1757d5b/

U2 - 10.3390/polym14204438

DO - 10.3390/polym14204438

M3 - Article

C2 - 36298017

AN - SCOPUS:85140880800

VL - 14

JO - Polymers

JF - Polymers

SN - 2073-4360

IS - 20

M1 - 4438

ER -