A comparison between micro- and nanocellulose-filled composite adhesives for oil paintings restoration

Annalisa Cataldi,Lars Berglund,Flavio Deflorian,Alessandro Pegoretti

doi:10.1080/20550324.2015.1117239

Annalisa Cataldi, Lars Berglund + Show 2 more

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https://doi.org/10.1080/20550324.2015.1117239

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Abstract

Cellulose nanocrystals (CNC) and microcrystals (CMC) were selected as reinforcing fillers for poly(2-ethyl-2-oxazoline), a water-soluble thermoplastic adhesive widely used in the restoration of oil paintings. Thin composite films containing 5, 10, and 30 wt% of CNC or CMC were produced by solution mixing and casting. UV-vis spectroscopy showed how CNC preserved the adhesive transparency even at the highest CNC content, while for CMC, a progressive loss of transparency was observed. Thermal analysis evidenced a progressive increase of the glass transition temperature of the polymer matrix induced by CNC, while no effects were observed for CMC. Both micro- and nanocellulose were able to improve the elastic modulus and reduce the thermal expansion coefficient and creep compliance of the adhesive, with effects more pronounced for CNC nanoparticles. Finally, single-lap shear test on bonded ancient oil painting substrates confirmed the improved dimensional stability of the joint imparted by CNC in the adhesive under both quasi-static and creep conditions.

Highlights

The restoration of oil paintings on canvas, involving various constituting components such as textile substrates, preparation layers, paint films, and varnish layers, is a major concern for conservators.[1]
field emission scanning electron microscopy (FESEM) images of formulations filled with Cellulose microcrystals (CMC) and cellulose microcrystals (MCC) and nanocrystals (CNC) are showed in Fig. 3a and b, respectively
The viscoelastic properties of unfilled Aquazol 500 (AQ500) and CMC and CNC composites are listed in Table 3, while the representative Dynamic mechanical thermal analysis (DMTA) thermograms of compositions filled with CMC and CNC are showed in Fig. 5a and b

Summary

Introduction

The restoration of oil paintings on canvas, involving various constituting components such as textile substrates, preparation layers, paint films, and varnish layers, is a major concern for conservators.[1]. Thermoplastic heat-seal adhesives are the mostly used for their good physical properties and Aquazol 500, a poly (2-ethyl-2-oxazoline), is another versatile adhesive introduced in the field of conservation in the 1990s for its high transparency, good flexibility, and easy removability, being a water soluble polymer, and widely used in the restoration of oil paintings.[12,13] Considering the specific mechanical performance required to an oil paintings adhesive, such as a good dimensional stability and a high resistance to long-lasting stresses, and the well-known reinforcing properties of cellulose-based fillers on polymers,[14,15,16,17] this work proposes the application of the composite technology to artwork restoration issues. Considering the recent attention of composite scientists toward cellulose-based fibers reinforcements as renewable alternative to their synthetic equivalents, cellulose microcrystals (MCC) and nanocrystals (CNC) were chosen as fillers in this work

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