Ultrasound-Stimulated PVA Microbubbles as a Green and Handy Tool for the Cleaning of Cellulose-Based Materials.

One of the main issues in the cultural heritage field of restoration chemistry is the identification of greener and more effective methods for the wet cleaning of paper artefacts, which serve as witnesses to human history and custodians of cultural values. In this context, we propose a biocompatible method to perform wet cleaning on paper based on the use of 1 MHz ultrasound in combination with water-dispersed polyvinyl alcohol microbubbles (PVAMBs), followed by dabbing with PVA-based hydrogel. This method can be applied to both old and new papers. FTIR spectroscopy, X-ray diffraction, HPLC analysis, pH measurements and tensile tests were performed on paper samples, to assess the efficacy of the cleaning system. According to the results, ultrasound-activated PVAMB application allows for an efficient interaction with rough and porous cellulose paper profiles, promoting the removal of cellulose degradation byproducts, while the following hydrogel dabbing treatment guarantees the removal of cleaning materials residues. Moreover, the results also pointed out that after the treatment no thermal or mechanical damages had affected the paper. In conclusion, the readability of these kinds of artifacts can be improved without causing an alteration of their structural properties, while mitigating the risk of ink diffusion.

Ultrasound-Stimulated PVA Microbubbles for Adhesive Removal from Cellulose-Based Materials: A Groundbreaking Low-Impact Methodology.

In this work, we shed new light on ultrasound contrast agents applied to the field of cultural heritage as an invaluable fine-tune cleaning tool for paper artworks. In this context, one of the primary and challenging issues is the removal of modern adhesives from paper artifacts. Modern adhesives are synthetic polymers whose presence enhances paper degradation and worsens its optical features. A thorough analytical and high-spatial-resolution combined study was successfully performed to test the capability of poly(vinyl alcohol)-based microbubbles stimulated by a proper noninvasive 1 MHz ultrasound field exposure in removing these adhesives from paper surfaces, in the absence of volatile invasive and toxic chemicals and without damaging paper and/or leaving residues. We demonstrate that poly(vinyl alcohol)-shelled microbubbles are suitable for interacting with paper surfaces, targeting and boosting in a few minutes the nondamaging removal of adhesive particles from paper samples thanks to their peculiar shell composition together with their ultrasound dynamics.

Efficiency of an elliptically shaped x-ray mirror.

Curved reflecting mirrors are widely used as x-ray optical elements for both laboratory and synchrotron radiation sources. In general, the mirror parameters are optimized by numerical simulation. We discuss an analytical approach that is useful for deriving the mirror parameters, including eccentricity, length, angular acceptance, and magnification. We have examined in particular an elliptical surface from which we learned that, given the distance between the foci of the ellipse, the magnification, and the critical angle of total external reflection, it is possible to find analytically the optimal eccentricity that maximizes the angular acceptance and the optimal mirror length. We found that the last-named parameter, in a first approximation, depends only on the distance between the foci of the ellipse and on the magnification factor. We present as well a comparison of optimal parameters obtained with analytical calculation and with ray-tracing simulation that yielded good agreement.