Controlled Environment Neutron Radiography of Moisture Sorption/Desorption in Nanocellulose-Treated Cotton Painting Canvases

Abstract

Nanocellulose-based materials have recently been used to consolidate degraded cotton painting canvases. Canvas-supported paintings consist of materials that are sensitive to moisture and especially susceptible to environmental fluctuations in temperature and relative humidity (RH). These environmental fluctuations occur in uncontrolled environments found in historic houses and palaces and can lead to hydrolytic degradation and mechanical damage to canvases. To simulate this situation in an experimental setting, canvas samples were mounted in a custom-made closed-cell and subjected to programmed cycles of RH at a controlled temperature while exposed to the neutron beam. Results are presented for both untreated samples and those treated with a polar consolidant, cellulose nanofibrils (CNF(aq)) in water, and an apolar consolidant, a composite of persilylated methyl cellulose with surface silylated cellulose nanocrystals (MC+CNC(h)) in heptane. They were then compared with changes in ionic conductivities as measured by dielectric analysis (DEA) with the same cyclic RH program and temperature. Although the samples were exposed to the same experimental conditions, they presented treatment-specific responses. CNF-treated canvas showed higher hygroscopicity than the untreated sample and facilitated moisture diffusion across the sample to areas not exposed to the environment. A sample treated with MC+CNC(h) retarded moisture diffusion during the increase in RH and could, therefore, afford protection to moisture absorption in uncontrolled environments. Thus, the experimental setup and resulting data provide a pilot study demonstrating the potential of neutron radiography in following and comparing real-time moisture diffusion dynamics in untreated and nanocellulose-consolidated cotton canvases and assisting in validating the overall benefit of the treatment.

The Critical Roles of Water in the Processing, Structure, and Properties of Nanocellulose

“…(C) Tracking moisture diffusion in untreated and nanocellulose-consolidated cotton canvases by neutron radiography. Reprinted with permission under Creative Commons Attribution 4.0 International license () from ref . Copyright 2021 American Chemical Society.…”

“…However, their application in cellulosic material analysis requires further verification study. Setting aside the purpose of discriminating between FW and BW, as shown in Figure , MRI, X-ray topography, neutron radiography, and terahertz (THz) time-domain spectroscopy have found extensive use in visualizing water distribution and moisture content within cellulosic materials. ,,, These advanced techniques can visualize samples at a resolution of 1 μm and water at a resolution of tens of micrometers. ,− ,,,− …”

“…Setting aside the purpose of discriminating between FW and BW, as shown in Figure 3, MRI, X-ray topography, neutron radiography, and terahertz (THz) time-domain spectroscopy have found extensive use in visualizing water distribution and moisture content within cellulosic materials. 33,35,36,40 These advanced techniques can visualize samples at a resolution of 1 μm and water at a resolution of tens of micrometers. 31,34−36,38,39,52−54 NIR-HIS and CRM are capable of assessing water content and distinguishing between FW and BW in cellulosic materials, but achieving a higher accuracy requires extensive data collection and computational processing.…”

How can Neutron Imaging contribute to Heritage Science? An overview at the ISIS Neutron and Muon Source

“…This is a particularly relevant property as water, polymers, and hydroxides associated with corrosion phases show low contrast when using X-rays but can readily be visualized by neutrons. This allows neutrons to be used, for example, to monitor moisture content for cultural heritage materials [3], reveal light organic components encased in dense materials [4], [5], track corrosion in metals [6], and visualise repairs and fillings due to casting defects or broken elements.…”

A Review of Applications of Nanocellulose to Preserve and Protect Cultural Heritage Wood, Paintings, and Historical Papers

“…For the sake of clarity, Table 4 summarizes some advantages and disadvantages of nanocellulose applications for wood, paintings, and paper conservation. Here, several examples of different applications of nanocellulose are reported, such as the consolidation and reinforcement of ancient degraded wood [21], the chemical modification of wood adhesive [66], the preparation of cellulose and lignin nano-scale consolidants for waterlogged archaeological wood [18], the consolidation of cotton painting canvases [24,25,67], the combined stabilization and deacidification of cellulosic materials [61], and the increase in watercolor painting efficiency on paper [68].…”