On the potential of using nanocellulose for consolidation of painting canvases
Graphical abstract
Introduction
Painting canvases made from natural fibers (e.g., linen, hemp, cotton or jute), used by artists as painting support, age over time. The ageing occurs due to temperature and humidity variations, and hence the dimensional changes of the painting mounted on a stretcher (Hedley, 1988; Hendrickx, Desmarais, Weder, Ferreira, & Derome, 2016), as well as chemical processes caused by acidity, which originate from primers, paints, glues and absorption of acidic gases from the environment (Ryder, 1986; Oriola et al., 2014). The ageing results in canvas degradation, particularly the reduction of its mechanical properties, which may lead to cracking of the paint layer as well as accidental tears of the canvas, resulting in irreversible damage of the painting.
In order to consolidate degraded canvases two options can be used: (i) consolidating the original canvas with an adhesive and (ii) lining of the original canvas with a new one, i.e. gluing the new canvas over the old one (Stoner & Rushfield, 2012). In both strategies, the damaged substrate on the back side of the painting is treated by an adhesive, which may be natural, such as animal glue and glue-paste, or synthetic, such as acrylic (Plexisol PB550, Paraloid B72 or Plextol B500) or complex wax-resin formulations (Beva 371) (Ackroyd, 2002; Berger, 1972; Ploeger et al., 2014). Generally, water-based adhesives are less favorable due to the hygroscopic character of the cellulosic canvas. Swelling and shrinkage of the canvas occur as a response to interactions with water, resulting in dimensional changes of the painting. The choice of proper material for canvas restoration is a major concern for conservators and the ideal properties of such materials are still under debate. One of the opinions with respect to lining and lining adhesive is to provide the painting with a stiffer support to which the mechanical stress is transferred (Ackroyd, 2002; Berger & Russell, 1988; Young, 1999). This reduces the load accumulated in the paint layer and minimizes the future degradation of the painting. At the same time, it is important to allow elongation of the lining from 0.3 to 3.0%, which is the elongation range to which paintings are exposed when mounted on a stretcher. It varies depending on the type of canvas, warp or weft direction, the pigments used and the age of the painting (Mecklenburg, 1982, Mecklenburg, 2005; Mecklenburg & Fuster Lopez, 2008).
Lining has traditionally been used for canvas restoration. However, with the growing interest in methods that provide minimal intervention of the painting, other treatments have become popular in the last decades (Ackroyd, Phenix, & Villers, 2002; Villers, 2004). The alternative treatments become favorable mainly due to the issues of reversibility, aesthetic concerns, excess of added new materials and no access to the original canvas with a lining. Another reason is that some of the widely used synthetic adhesives, such as Beva 371, are questionable from health and environmental point of view due to their toxicity (Bianco et al., 2015). Some synthetic adhesives, such as poly(vinyl acetate), promote canvas degradation due to acidic products formed during their own degradation (Chelazzi et al., 2014) and are therefore no longer used. These concerns have resulted in an increased use of natural polymers, such as animal or fish glue, for canvas reinforcement (Ackroyd, 2002).
The degraded canvas generally possesses defects at different length scales, e.g., fiber cracks on the micrometer scale and depolymerization of cellulose chains on the nanometer scale. In order to restore the mechanical properties of the original canvas, these issues should be tackled (Kolman, Nechyporchuk, Persson, Holmberg, & Bordes, 2017). In addition to the physico-chemical properties of the canvas fibers, the morphology of woven fabric has a strong influence on the mechanical properties (Young & Jardine, 2012). Taking into consideration that the paint layer, as well as the ground or size, are much stiffer than the canvas, the conservation treatment may aim at an efficient reinforcement for the canvas, rather than at restoration of the original properties, including high stretchability and flexibility, as these properties have been lost with the application of the different preparative layers. In parallel to the mechanical reinforcement, deacidification of the canvas needs to be carried out in order to arrest further degradation (Giorgi, Dei, Ceccato, Schettino, & Baglioni, 2002).
In the recent development of cellulose-based materials, nanocellulose has emerged and generated a strong interest, often due to its unique mechanical properties. Nanocellulose can be divided into three main categories: (i) cellulose nanocrystals (CNC), also referred to as nanocrystalline cellulose (NCC) or cellulose whiskers (Habibi, Lucia, & Rojas, 2010; Rånby, 1949); (ii) cellulose nanofibrils (CNF), also known as nanofibrillated cellulose (NFC) or microfibrillated cellulose (MFC) (Nechyporchuk, Belgacem, & Bras, 2016; Turbak, Snyder, & Sandberg, 1983), and (iii) bacterial nanocellulose. CNC and CNF are much more common, since they are produced by delamination of cellulose microscopic fibers (generally, from wood) into nanomaterial (top–down process), whereas bacterial nanocellulose is generated by a buildup (bottom–up process) from low molecular weight sugars by bacteria (Nechyporchuk, Belgacem, & Bras, 2016). Bacterial cellulose is produced in the form of biofilms (pellicles) of determined dimensions that contain interconnected nanofibrils (Klemm, Heublein, Fink, & Bohn, 2005), whereas CNC and CNF are separate nanoparticles, thus their deposition is not limited by the physical dimensions of the artifacts. In order to deposit bacterial nanocellulose from suspensions, post-fibrillation should be performed.
The different types of nanocellulose present appealing features for the purpose of canvas consolidation: they have high strength and form transparent/translucent and lightweight films. Their non-toxic character and non-abrasiveness for processing equipment, as well as renewable and biodegradable character, are additional features of interest for the field. Nanocellulose also has a large surface area and there are well-developed methods for its surface modification (Habibi et al., 2010; Moon, Martini, Nairn, Simonsen, & Youngblood, 2011; Nechyporchuk, Belgacem, & Bras, 2016). Reinforcing a cellulosic canvas with a material of similar nature can be beneficial for future preservation of canvas paintings.
The interest in using nanocellulose for restauration of cellulosic materials has been increasing lately. Nanocellulose has recently been employed for consolidation of historical papers (Dreyfuss-Deseigne, 2017; Santos et al., 2015; Völkel, Ahn, Hähner, Gindl-Altmutter, & Potthast, 2017). Bacterial nanocellulose has been also reported for reinforcement of historical silk fabrics (Wu, Li, Fang, & Tong, 2012). To the best of our knowledge, the use of nanocellulose for consolidation of painting canvases remains unexplored.
In this work, different types of nanocellulose, namely mechanically isolated cellulose nanofibrils (CNF), carboxymethylated cellulose nanofibrils (CCNF) and cellulose nanocrystals (CNC), were tested and compared in terms of structural reinforcement of degraded canvases. The mechanical properties of newly prepared and real paintings were first studied to determine the elongation regime where canvas consolidation should act. Then, model aged canvases were treated with different nanocellulose-based formulations to investigate their film-forming properties on canvases and their response to static and periodic uniaxial stress at different relative humidity values. The reinforcing effect of the nanocelluloses was also compared with that obtained with different traditional consolidants.
Section snippets
Materials
CNF in the form of an aqueous suspension was kindly provided by Stora Enso AB (Sweden). The CNF was produced from softwood pulp (ca. 75% of pine and 25% of spruce, containing 85% of cellulose, 15% of hemicellulose, and traces of lignin, as determined by the supplier). CCNF, also in the form of an aqueous suspension, was kindly provided by RISE Bioeconomy (Sweden). The CCNF was produced from a softwood sulphite dissolving pulp (Domsjö Dissolving plus, Domsjö Fabriker AB, Sweden) by
Mechanical properties of canvas paintings
In order to provide a rational reinforcement of the degraded canvases, it was necessary to determine the elongation regime where the reinforcement should be provided, i.e., to specify whether the initial stretchable character of the canvas should be reproduced or if the consolidation treatment should stiffen the canvas. New cotton canvas was coated with prime, paint and varnish, and was examined after each layer deposition in both warp and weft directions using tensile testing.
The
Conclusions
Canvas degradation is one of the crucial issues of easel paintings, which leads to their irreversible damage. In this work, we demonstrate for the first time that different types of natural cellulose nanomaterials have a potential for use as a mechanical reinforcement of degraded cellulosic canvases. Such treatments are also in line with the strategy of minimal intervention. The results show that nanocellulose can provide a substantial reinforcement in the low elongation region, i.e. below 3%,
Acknowledgements
This work has been performed in the frame of NANORESTART (NANOmaterials for the RESToration works of ART) project funded by Horizon 2020 European Union Framework Program for Research and Innovation (Grant Agreement No. 646063). The authors express their gratitude to RISE Bioeconomy (Sweden) and Stora Enso AB (Sweden) for providing the nanocellulose samples.
References (47)
- et al.
A study on reversibility of BEVA®371 in the lining of paintings
Journal of Cultural Heritage
(2015) - et al.
Characterization and degradation of poly(vinyl acetate)-based adhesives for canvas paintings
Polymer Degradation and Stability
(2014) - et al.
Evaluation of the effects of environmental conditions and preventive conservation treatment on painting canvases
Thermochimica Acta
(1997) - et al.
Moisture uptake and permeability of canvas paintings and their components
Journal of Cultural Heritage
(2016) - et al.
Preparation of silica/polyelectrolyte complexes for textile strengthening applied to painting canvas restoration
Colloids and Surfaces A: Physicochemical and Engineering Aspects
(2017) - et al.
Production of cellulose nanofibrils: A review of recent advances
Industrial Crops and Products
(2016) - et al.
Current progress in rheology of cellulose nanofibril suspensions
Biomacromolecules
(2016) - et al.
Accelerated ageing of cotton canvas as a model for further consolidation practices
Journal of Cultural Heritage
(2017) - et al.
The long-term stability of a popular heat-seal adhesive for the conservation of painted cultural objects
Polymer Degradation and Stability
(2014) Deformation mechanisms and yield strength in amorphous polymers
Progress in Polymer Science
(1997)
Reinforcement of vulnerable historic silk fabrics with bacterial cellulose film and its light aging behavior
Carbohydrate Polymers
Standard Test Method for Breaking Strength and Elongation of Textile Fabrics (Grab Test)
Not lining in the twenty-first century: Attitudes to the structural conservation of canvas paintings
The Conservator
The structural conservation of canvas paintings: Changes in attitude and practice since the early 1970
Studies in Conservation
An evaluation of the preparation of canvas paintings using stress measurements
Studies in Conservation
Deterioration of surfaces exposed to environmental changes
Journal of the American Institute for Conservation
Formulating adhesives for the conservation of paintings
Studies in Conservation
Cation-Induced hydrogels of cellulose nanofibrils with tunable moduli
Biomacromolecules
Nanocellulose films in art conservation
Journal of Paper Conservation
Nanotechnologies for conservation of cultural heritage: Paper and canvas deacidification
Langmuir
Cellulose nanocrystals: Chemistry, self-assembly, and applications
Chemical Reviews
Relative humidity and the stress/strain response of canvas paintings: Uniaxial measurements of naturally aged samples
Studies in Conservation
Cellulose nanopaper structures of high toughness
Biomacromolecules
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Present address: Swerea IVF AB, Box 104, SE-431 22 Mölndal, Sweden.
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Present address: Department of Chemistry and Molecular Biology, University of Gothenburg, Göteborg, Sweden.