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

Abstract

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.

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

“…Moreover, a shift in the maximum of the band at 1095 cm −1 due to the co-presence in the hydrogel and PVAMBs not only of the C-O of alcohol groups but also of acetal ones is found, confirming the presence of reticulation. Acoustic, viscoelastic, and shell thickness properties of PVAMBs have been already shown in the literature by authors [30,31,35]. Accordingly, PVAMBs' resonance frequency (ω 0 ) is found to be centered at about 11 MHz, as measured via acoustic attenuation spectroscopy [30]; their shear modulus and the shell thickness are, respectively, ~0.16 MPa and ~350 nm, as measured via attenuation spectroscopy and atomic force microscopy (AFM) [31,35].…”

“…During the last decade, research has focused on expanding the use of echogenic PVA microbubbles (PVAMBs), i.e., micrometer-sized spheres made of an air core stabilized by a hydrophilic cross-linked PVA shell, from biomedicine (e.g., molecular imaging and targeted therapy) to cultural heritage [30][31][32]. Among the main reasons to use cross-linked polymer shell microbubbles (MBs), there are their robustness, chemical versatility, and biocompatibility.…”

“…Due to these peculiar properties, PVAMBs are herein the subject of investigation as a promising cleaning tool for paper artifacts. In a previous work of our group, PVAMBS have been proposed for the localized removal of aged polystyrene-based synthetic adhesive residues from modern paper samples, thus constituting an environmentally friendly alternative to the use of organic solvents, which are toxic for operators [31]. Indeed, according to D'Andrea et al, thanks to the responsive properties induced by US action and their micrometric size (and therefore dimensions comparable to those of paper pores), PVAMBs perform a micro-mechanical action leading to a removal process resulting in yellow and brittle aged adhesive residues, present on the sample, in about 2 min (Figure S1) [31].…”

“…In a previous work of our group, PVAMBS have been proposed for the localized removal of aged polystyrene-based synthetic adhesive residues from modern paper samples, thus constituting an environmentally friendly alternative to the use of organic solvents, which are toxic for operators [31]. Indeed, according to D'Andrea et al, thanks to the responsive properties induced by US action and their micrometric size (and therefore dimensions comparable to those of paper pores), PVAMBs perform a micro-mechanical action leading to a removal process resulting in yellow and brittle aged adhesive residues, present on the sample, in about 2 min (Figure S1) [31]. The aim of this work is to overcome a fundamental drawback in the restoration field, which is the optimization of an ad hoc cleaning protocol according to each different sample's composition and the possible presence of contaminants (see above).…”

“…The aim of this work is to overcome a fundamental drawback in the restoration field, which is the optimization of an ad hoc cleaning protocol according to each different sample's composition and the possible presence of contaminants (see above). Indeed, as already discussed, adhesive residues could be removed by means of net organic solvents, complex fluid media, or PVAMBS [17,31,33], while the cleaning of an aged paper sample, without specific contaminants, could be achieved using Gellan gum, poly(vinyl pyrrolidone) chains embedded in a poly(2-hydroxyethyl methacrylate) and/or PVA based hydrogel systems [13,15,29,34]. This means that a satisfying cleaning treatment consists of several successive steps.…”