Abstract-Terahertz absorption by cellulose: Application to ancient paper artifacts

M. Peccianti, R. Fastampa, A. Mosca Conte, O. Pulci, C. Violante, J. Łojewska, M. Clerici, R. Morandotti, and M. Missori

https://journals.aps.org/prapplied/accepted/ce07fYc6Le011c53637216614e26e35315d5a921c

Artifacts made of cellulose, such as ancient documents, pose a significant experimental challenge in the THz transmission spectra interpretation due to their small optical thickness. In this Letter we describe a method to recover the complex refractive index of cellulose fibers from the THz transmission data obtained on single freely standing paper sheets in the 0.2\textendash 3.5~THz range. By using our technique, we were able to eliminate Fabry-Perot effects and recover the absorption coefficient of the cellulose fibers. The obtained THz absorption spectra are explained in terms of absorption peaks of the cellulose crystalline phase superimposed to a background contribution due to a disordered hydrogen bonds network. The comparison between the experimental spectra with THz vibrational properties simulated by density functional theory calculations confirms this interpretation. In addition, evident changes in the THz absorption spectra are produced by natural and artificial aging on paper samples, whose final stage is characterized by a spectral profile with only two peaks at about 2.1~THz and 3.1~THz. These results could be used to provide a quantitative assessment of the state of preservation of cellulose artifacts.

Abstract-Stabilization of the Tensile Strength of Aged Cellulose Paper by Cholinium-Amino acid Ionic Liquid Treatment

Eleonora Scarpellini, Michele Ortolani, Alessandro Nucara, Leonetta Baldassarre, Mauro Missori, Renato Fastampa, and Ruggero Caminiti

J. Phys. Chem. C, Just Accepted Manuscript

DOI: 10.1021/acs.jpcc.6b06845

Publication Date (Web): October 6, 2016

Copyright © 2016 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.6b06845

In this study, a chemical stabilization method, that preserves the tensile strength of artificially aged paper pre-treated with an aqueous solution of ionic liquid, is presented. Pure cotton cellulose papers samples were soaked with cholinium glycinate ionic-liquid solution either before or after the artificial aging process, which was based on thermal degradation in dry air. The tensile strength of artificially aged paper was measured by using the double-folding technique. The role of ionic liquids was investigated by mid-infrared and terahertz time-domain absorption spectroscopy. It was found that the tensile strength of pre-treated samples is higher than that of other aged samples. A model for changes in the cellulose structure caused by oxidation and by the binding of ionic liquid molecules is proposed, basing on the analysis of the mid-infrared absorption bands in the carbonyl/carboxyl region at 1590-1750 cm−1. Terahertz spectroscopy data indicate that the ionic liquid molecules penetrate in the larger size porosity, acting as binders among cellulose fibers to maintain the tensile strength of paper.