The effect of halloysite nanotubes dispersions on vegetable-tanned leather thermal stability

Leather artefacts in historical collections and old leather bookbindings in archives and libraries frequently show a variety of visible changes which alter their appearance and ability to be used, such as powdery surface, weakened structure, complete or partial loss of the grain layer. However, historical leather stabilization and consolidation yet represent a challenging problem for conservators due to the sensitivity of collagen to the action of most of the conservation and restoration formulations currently used. In this paper we report our recent research concerning the development of halloysite nanoparticles dispersions for enhancing the hydrothermal stability of weakened historical vegetable tanned leather. The effects of halloysite nanotubes (HNTs) dispersed in various aqueous and non-aqueous mediums on the thermal stability of collagen in historical leather were tested using thermal microscopy, thermogravimetry and micro differential scanning calorimetry. Unilateral nuclear magnetic resonance was used to evaluate the changes in water dynamics due to collagen matrix interaction with dispersion media. The treated samples were also characterized using infrared spectroscopy and scanning electron microscopy. The analytical assessment confirmed the leather thermal stability increase and a partial recovery of fibres cohesion, thus validating the use of HNT dispersions as a basic tool for the preservation of collagen-based materials. Further functionalisation and encapsulation using antimicrobials, fungicides and pH adjustment nanoparticles will deliver novel and more durable HNTs-based conservation treatments.