Highly Viscous Polymeric Dispersions: an innovative versatile soft matter for cleaning stone materials

The field of high-viscosity polymer dispersions (HVPDs) has seen significant advancements due to the versatility and practical applications of such materials. This PhD thesis is focused into the development and characterization of HVPDs based on polyvinyl alcohol (PVA), borax, and water, with a particular attention on the confinement of various additives, to enhance their properties and applications. The primary aim of this research is to explore how different modifications influence the performance of HVPDs, both in terms of their physical properties and their functional efficacy. The study is structured around three main areas of investigation: the use of chelators, the incorporation of essential oils, and the addition of fatty acid methyl esters. Primary, the thesis examines the effects of incorporating chelating agents into the HVPD matrix. Chelators are known to interact with metal ions, which can influence the network structure and stability of polymer dispersions. By integrating chelators such as EDTA or Rochelle salt into HVPD formulations, this research assesses changes in rheological behaviour, polymer stability, and the ability to mitigate metal ion interference. The findings reveal how these chelators impact the overall performance of HVPDs, offering insights into their potential applications in diverse industrial and environmental contexts. Subsequently, the focus shifts to the integration of essential oils into the HVPD framework. Essential oils (E.O. i.e.), known for their antimicrobial properties, are explored as functional additives to enhance the biocidal efficacy of the dispersions. This thesis evaluates how essential oil of Origanum vulgare and its carvacrol-chemotype, affect the gel-like properties of HVPDs, including their viscosity, structural integrity, and antimicrobial effectiveness. This part of the research addresses the challenges of maintaining efficacy in various environmental conditions and explores the potential benefits of using natural antimicrobial agents in polymer dispersions. The practical application of these HVPD formulations, enriched with E.O. at the Castlelaw Hill heritage site, in collaboration with prof. Dave Adams (university of Glasgow-School of chemistry), Senior Paintings Conservator Damiana Magris (Historic Environment Scotland) and Architect Clive Cruickshank, illustrates their effectiveness in situ. This case study not only tests the material's cleaning efficacy under real-world conditions but and relative chemotype also highlights the adaptability of HVPDs to challenging environmental factors such as uneven surfaces, high humidity, and variable drying times. These insights provide valuable feedback for refining the formulation, particularly to address the issue of residue formation in areas where full drying was not achieved. The final component of the study involves the addition of methyl octanoate, a fatty acid ester, to the HVPD matrix. This investigation aims to understand how methyl octanoate alters the rheological and viscoelastic properties of the dispersions. The impact on shear-thinning behaviour, elasticity, and overall material flexibility is analysed to determine the practical implications for ease of application and removal in real-world scenarios. Overall, this thesis provides a comprehensive analysis of HVPDs modified with chelators and apolar substances (E.O. and methyl octanoate). The goal is to enhance the material properties, expand their functional applications, and address specific challenges such as performance in high-humidity environments and the presence of micro-residues. This research has broad implications for the field of cultural heritage conservation, particularly in the cleaning and preservation of stone materials exposed to adverse environmental conditions. High humidity and temperature fluctuations can often hinder the effectiveness of traditional cleaning methods, making HVPDs, with their rheological and mechanical properties, ideal candidates for use in sensitive heritage environments. Additionally, the incorporation of biodegradable and non-toxic additives positions this research at the forefront of developing sustainable conservation technologies. By exploiting advanced analytical techniques and exploring innovative formulations, this research contributes valuable insights into the optimization and application of high-viscosity polymer dispersions in various fields.