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Please use this identifier to cite or link to this item:
http://hdl.handle.net/10174/37168
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Title: | PVA/Borax-based hydrogel for stone conservation: evaluation of cleaning performance through a multi-technical approach |
Authors: | Matulac, Andrea Louise |
Advisors: | Favero, Gabriele |
Keywords: | Polymeric Dispersion Chelants Cleaning Stone Corrosion Resin |
Issue Date: | 3-Oct-2023 |
Publisher: | Universidade de Évora |
Abstract: | ABSTRACT: Carbonate stones used in connection with cultural heritage materials are subjected to different
degradation phenomena in function of their chemical and physical properties. Two important
issues that need to be addressed are: (1) the formation of corrosion products from metallic
impurities or metallic artifacts in contact with the stone and (2) the photo-oxidative
weathering of resins on stone which render them insoluble. In such cases, the choice of
cleaning method is critical because the removal has to be confined to the contaminants and
should not further damage the stone. High viscosity polymeric dispersions (HVPDs), which
have good mechanical properties, high solvent and active component retention, low toxicity,
and low environmental impact, seem to be a promising solution. For this thesis project, the
two main HVPDs evaluated were polyvinyl alcohol cross-linked with borax (PVA/B) and its
variant with agarose (PVA/B-AG) on the substrates Carrara Marble, Lecce Stone, and
Travertine. For the cleaning of bronze corrosion products, ethylenediaminetetraacetic acid
(EDTA) and potassium sodium tartrate (PST) were added as chelants. Based on
characterization studies, all of the HVPDs pass the criteria of peelability, have minimal water
desorption, retain more than half of their volatile fraction, and do not leave residues under
four hours. Regarding the first issue, SEM and FORS analysis reveal that treatment using
PVA/B-AG with EDTA or PST are both effective in the removal of corrosion products and
the restoration of the surface close to its original state. Two applications are necessary, with
the second one modulated to avoid lightening. The use of EDTA is recommended over PST
due to its higher removal efficiency. FT-IR ATR results confirm the complexation of the
chelants with copper, their sequestration, and their interaction with the HVPD components.
Regarding the second issue, FORS analysis demonstrate the significant reduction in the
redness and yellowing of the surface after the treatment with PVA/B and PVA/B-AG. Flaking
off and delamination were observed in both cases, but FT-IR ATR results show the capability
of the latter to adhere the acrylate polymer. Water vapor permeability test results also
reinforce that the resin is being removed based on the improvement of the stone's
breathability. Altogether, the results demonstrate the eco-friendliness and versatility of
PVA/B-based HVPDs as a cleaning tool. This also opens avenues for its adoption not just in
the removal of hydrophilic but also hydrophobic materials detrimental to cultural heritage
objects. |
URI: | http://hdl.handle.net/10174/37168 |
Type: | masterThesis |
Appears in Collections: | BIB - Formação Avançada - Teses de Mestrado
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