Characterization of polyvinyl alcohol-borax/agarose (PVA-B/AG) double network hydrogel utilized for the cleaning of works of art

Abstract

Since cleaning of artworks may cause undesirable physicochemical alterations and is a nonreversible procedure, it is mandatory to adopt the proper cleaning procedure. Such a procedure should remove undesired materials whilst preserving the original surface. In this regard, numerous gels have been developed and exploited for the cleaning of various artwork surfaces. Lately, agarose (AG) and polyvinyl alcohol-borax (PVA-B) hydrogels have been widely employed as cleaning tools by conservators. Both hydrogels show some limitations in specific cleaning practices. In this work, we investigated the influence of including increased levels of agarose into PVA-B systems. For this reason, we performed a detailed characterization on the double network (DN) hydrogel including the chemical structure, the liquid phase retention, the rheological behavior, and the self-healing behavior of various PVA-B/AG double network hydrogels. These new hydrogels revealed better properties than PVA-B hydrogels and obviated their limitations. The inclusion of AG into PVA-B systems enhanced the liquid retention capacity, shape-stability, and mechanical strength of the blend. Furthermore, AG minimized the expelling/syneresis issue that occurs when loading PVA-B systems with low polarity solvents or chelating agents. The resultant double network hydrogel exhibits relevant self-healing properties. The PVA-B/AG double network is a new and useful cleaning tool that can be added to the conservators’ tool-kit. It is ideal for cleaning procedures dealing with porous and complex structured surfaces, vertical surfaces and for long time applications.

Non-Invasive Assessment of PVA-Borax Hydrogel Effectiveness in Removing Metal Corrosion Products on Stones by Portable NMR

“…In this work, the formulation of PVA-PEO-borax in water solution developed by Riedo et al [ 20 ] has been used for the hydrogel preparation. This has shown many weaknesses, in agreement with previous studies [ 20 , 21 , 29 , 41 , 42 , 43 ]. First of all, it does not seem suitable for the surface cleaning of macro-porous materials, such as the Travertine samples, because of the difficulty in the complete removal of the hydrogel layer, which leads to solid-like residues (see Section 4.1 ).…”

“…First of all, it does not seem suitable for the surface cleaning of macro-porous materials, such as the Travertine samples, because of the difficulty in the complete removal of the hydrogel layer, which leads to solid-like residues (see Section 4.1 ). Despite the fact that the addition of PEO increases the pore size and the liquid phase retention of the gel network, as well as improves its mechanical properties, it has been observed that the residues left on the stone surface may be due to the fact that PEO is the only polymer not chemically bonded to the network [ 20 , 21 , 29 , 42 ]. So, PEO seems the major responsible for residues together with the type and state of conservation of the sample analyzed.…”

“…The PVA-borax hydrogel properties can also be improved by adding another polymer. Some studies [ 21 , 43 ] investigated the effect of agarose on the PVA-borax gel network. Agarose seems to increase the shape stability of the gel.…”

“…Among these, there are gel-systems based on polyvinyl alcohol (PVA). PVA is a water soluble and biocompatible polymer with good resistance to mechanical stress, capable to form hydrogen bonds, thanks to its hydroxyl groups, and ion complexes [ 19 , 20 , 21 ]. It has emerged as a potential adsorbent because of its high swelling capacity and its resistance to dissolution, mainly due to the formation of cross-links between network chains [ 22 ].…”

“…Moreover, it has been used together with both natural and synthetic compounds to produce different types of hydrogels, which may also be physically or chemically cross-linked. One of these, the PVA-borax hydrogel, obtained by cross-linking of PVA with borate ions [ 18 , 20 , 21 , 25 ], can be described as a viscoelastic dispersion with a dynamic network. In fact, the increase in borax concentration expands the system network due to electrostatic repulsions in the polymer chain [ 20 , 25 , 26 ].…”