Multiscale approach in the assessment of nanocellulose-based materials as consolidants for painting canvases

This thesis investigates mainly the use of nanocellulose-based treatment for the consolidation of degraded cotton canvases of modern paintings and includes within this some case studies on linen canvases (sized and unsized) and 19th cent. historical samples from paintings. It. uses a multi-scale analytical approach where primarily controlled relative humidity dynamic mechanical analysis (DMA-RH) was used to evaluate the effect of the novel nanocellulose based preparations. It aims at quantifying the advantages, disadvantages, and limitations of their application. Initially, the baseline viscoelastic response to RH variations of a degraded cotton canvas was measured by DMA-RH. This technique was used further together with SEM to assess morphologically and mechanically 6 traditional consolidants including natural such as animal glue and synthetic materials. Following the same protocol, two solutions of nanocellulose-based consolidants developed in the frame of the Nanorestart project were assessed. These materials consisted of nanocellulose dispersions in water or water/ethanol and nanocomposites of nanocellulose-reinforced cellulose derivatives in polar/apolar solvents. Overall, higher consolidation at lower weight added was measured for the nanocellulose-based treatments tested when compared to the traditional consolidants. The penetration of the consolidant in the canvas also shows to greatly differ between treatments with the nanocellulose showing low penetration. Higher mechanical response to RH was also measured after treatment in particular with the water-based treatment. The results demonstrate how the adhesion, measured here at the nanoscale, and consolidant penetration into the canvas are dominant factors for the development of consolidation treatment for painting canvases. The assessment of the novel consolidants was finally carried out on historical canvases. Most treatments show to perform well on historical paintings in terms of handling properties, penetration and surface appearance and consolidation. Preliminary time-resolved neutron radiography with new purpose built sample chamber and RH controller provided visual information on time-dependent moisture response of the samples

Nanocellulose-based materials for the reinforcement of modern canvas-supported paintings

The aim of this work was to evaluate the use of novel nanocellulose-based consolidants for modern easel paintings as a possible alternative to lining and to the use of common adhesives. Two dispersions of consolidants were tested: nanofibrillated (CNF) and nanocrystalline cellulose (CNC). A model cotton canvas was used to evaluate the effect of these consolidants following treatment by the nanocellulose-based formulations. The surface appearance of the canvases was assessed before and after treatment using colorimetry and scanning electron microscopy (SEM). Additionally, the characterisation of the mechanical properties of the samples was performed using tensile testing and dynamic mechanical analysis (DMA-RH) at controlled relative humidity (RH) (3 RH cycles, 20-60-20% RH at 25 °C) before and after treatment. Finally, colour changes undergone by the samples upon accelerated ageing were measured by colorimetry. Taking into account the individual outcomes of each of these tests, it was possible to evaluate the merits and limitations of the use of nanocellulose treatments for the consolidation of modern painting canvases

Evaluation of the adhesion and performance of natural consolidants for cotton canvas conservation

Recent developments in paper and canvas conservation have seen the introduction of nanocellulose (NC) as a compatible treatment for the consolidation of historical cellulosic artefacts and manuscripts. However, as part of the assessment of these new materials for canvas consolidation, the adhesion of the consolidation treatment (which takes place between the applied material and the substrate) has not yet been evaluated, and as a result, it is poorly understood by both the scientific and conservation communities. After evaluating the potential of NC treatments for the consolidation of cotton painting canvas, we investigate a route to promote the interaction between the existing canvas and the nanocellulose treatment, which is in our case made of cellulose nanofibrils (CNF). This was carried out by introducing a cationic polymer polyamidoamine-epichlorohydrin (PAAE) as an intermediate layer between the canvas and the CNF. The morphological, chemical and mechanical evaluation of the canvas samples at different relative humidity (RH) levels demonstrated how the adhesion of the added PAAE layer is a dominant factor in the consolidation process. Improvement in the coating of canvas single fibres by the CNF, higher adhesion energy between the canvas fibres and the CNF treatment and finally overall stronger canvas reinforcement were observed following the introduction of PAAE. However, an increase in mechanical response to moisture sorption and desorption was also observed for the PAAE-treated canvases. Overall, this study shows the complexity of such systems and, as such, the relevance of using a multi-scale approach for their assessment

Nanocellulose-based materials for the reinforcement of modern canvas-supported paintings

The aim of this work was to evaluate the use of novel nanocellulose-based consolidants for modern easel paintings as a possible alternative to lining and to the use of common adhesives. Two dispersions of consolidants were tested: nanofibrillated (CNF) and nanocrystalline cellulose (CNC). A model cotton canvas was used to evaluate the effect of these consolidants following treatment by the nanocellulose-based formulations. The surface appearance of the canvases was assessed before and after treatment using colorimetry and scanning electron microscopy (SEM). Additionally, the characterisation of the mechanical properties of the samples was performed using tensile testing and dynamic mechanical analysis (DMA-RH) at controlled relative humidity (RH) (3 RH cycles, 20-60-20% RH at 25 °C) before and after treatment. Finally, colour changes undergone by the samples upon accelerated ageing were measured by colorimetry. Taking into account the individual outcomes of each of these tests, it was possible to evaluate the merits and limitations of the use of nanocellulose treatments for the consolidation of modern painting canvases

On the potential of using nanocellulose for consolidation of painting canvases

Nanocellulose has been recently proposed as a novel consolidant for historical papers. Its use for painting canvas consolidation, however, remains unexplored. Here, we show for the first time how different nanocelluloses, namely mechanically isolated cellulose nanofibrils (CNF), carboxymethylated cellulose nanofibrils (CCNF) and cellulose nanocrystals (CNC), act as a bio-based alternative to synthetic resins and other conventional canvas consolidants. Importantly, we demonstrate that compared to some traditional consolidants, all tested nanocelluloses provided reinforcement in the adequate elongation regime. CCNF showed the best consolidation per added weight; however, it had to be handled at very low solids content compared to other nanocelluloses, exposing canvases to larger water volumes. CNC reinforced the least per added weight but could be used in more concentrated suspensions, giving the strongest consolidation after an equivalent number of coatings. CNF performed between CNC and CCNF. All nanocelluloses showed better consolidation than lining with synthetic adhesive (Beva 371) and linen canvas in the elongation region of interest