Comparison of Trimethylsilyl Cellulose-Stabilized Carbonate and Hydroxide Nanoparticles for Deacidification and Strengthening of Cellulose-Based Cultural Heritage.

Lunjakorn Amornkitbamrung,Tamilselvan Mohan,Doris Bračič,Alenka Vesel,Rupert Kargl,Jasna Malešič,Ulrich Hirn,Karin Stana Kleinschek,Silvo Hribernik,Matej Bračič

doi:10.1021/acsomega.0c03997

Abstract

Herein, colloidal dispersions of alkaline nanoparticles (NPs: CaCO3 and Mg(OH)2) are stabilized by trimethylsilyl cellulose (TMSC) in hexamethyldisiloxane and employed to treat historical wood pulp paper by an effortless dip-coating technique. Both alkaline NPs exhibit high stability and no size and shape changes upon stabilization with the polymer, as shown by UV–vis spectroscopy and transmission electron microscopy. The long-term effect of NP/TMSC coatings is investigated in detail using accelerated aging. The results from the pH-test and back-titration of coated papers show a complete acid neutralization (pH ∼ 7.4) and introduction of adequate alkaline reserve even after prolonged accelerated aging. Scanning electron microscopy–energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and infrared and water contact angle measurements showed the introduction of a thin and smooth hydrophobic NP/TMSC coating on the paper fibers. Acid-catalyzed desilylation of TMSC was observed by declining C-Si infrared absorbance peaks upon aging. The CaCO3 coatings are superior to Mg(OH)2 with respect to a reduced yellowing and lower cellulose degradation upon aging as shown by colorimetric measurements and degree of polymerization analysis. The tensile strength and folding endurance of coated and aged papers are improved to 200–300 and 50–70% as illustrated by tensile strength and double folding endurance measurements.

Highlights

Conservation of cultural heritage is of high importance for understanding and maintenance of human history and evolution
Both particle types settled after approximately 40 s as indicated by a strong decrease in absorbance
CaCO3 stabilized by trimethylsilyl cellulose (TMSC) in the solvent hexamethyldisiloxane (HMDSO) is utilized to simultaneously neutralize acidity, impart alkaline reserve, and impart mechanical strength to acidic cellulose-based paper

Summary

Introduction

Conservation of cultural heritage is of high importance for understanding and maintenance of human history and evolution. A large volume of historical and cellulose-based documental heritage, such as paper, books, graphical works, and manuscripts, produced since the 1850’s is deteriorating, which is becoming an important threat to libraries and archives.[1−4] The degradation proceeds mainly due to acidcatalyzed hydrolysis of cellulose. The latter is often promoted by the decomposition of the sizing agent alum (KAl(SO4)2· 12H2O), which is used in the papermaking process.[3,5,6] During hydrolysis, the cellulose β-(1 → 4)-glycosidic bonds are cleaved, resulting in the irreversible depolymerization of cellulose chains and subsequently in a substantial reduction of mechanical strength.[1,7,8] Many efforts to decrease the degradation rate of paper called “deacidification or chemical stabilization” were made. This involved the neutralization of acidity in paper to slow down the degradation rate and introduce additional alkaline compounds, namely, an alkaline reserve (AR) that neutralizes acids that may evolve in the future.[9]

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