Abstract
Shellac is a natural varnish still known as one of the most elegant finishes for furniture and musical instruments, and currently used for restoration and refinishing of wooden antiques. However, it displays some limitations such as (i) sensitivity to alcoholic solvents (ii) softness of the coating, and (iii) considerable weathering due to photo- and bio-degradation. Hence, the main aim of this study was to improve the properties of shellac-based finish by introducing functionalized nanoparticles. Two inorganic nano-sized materials were considered: ZnO that was expected to reduce photo- and bio-degradation problems, and ZrO2 that was expected to improve the hardness of the varnish. Nanoparticles were synthesized and treated with a bifunctional silane coupling agent. Both plain and functionalized nanoparticles were extensively characterized using different experimental techniques. Functionalized nanoparticles were grafted on shellac through a reaction involving the epoxy-rings introduced on their surface. The resulting modified varnishes were applied on maple wood specimens according to traditional procedures. Different instrumental techniques and testing methods were used to characterize both nano-sized materials and the corresponding nanocomposites, as well as to evaluate the performance of the new coatings. The investigated composite materials display the same aesthetic appearance as plain shellac, while some other properties were improved. In particular, both nanocomposites are distinctly less soluble in alcohols than plain shellac and display antifungal properties. Moreover, coating containing functionalized ZnO nanoparticles displays photo-protection behavior, while shellac modified with ZrO2 nanoparticles exhibits a higher hardness when compared to the traditional varnish.
Highlights
Surface coating is the most common method used to protect wood against deterioration and improve and stabilize its distinctive appearance
Plain and GPTMS-functionalized NPs were characterized by different techniques in order to gain information about their chemical compositions, sizes, and shapes
Results of Fourier transform infrared spectroscopy (FTIR) investigations are substantially in agreement with data obtained by scanning electron microscopy (SEM)-energy-dispersive X-ray spectroscopy (EDS) and confirm the functionalization of the inorganic NPs with the organic moiety deriving from GPTMS
Summary
Surface coating is the most common method used to protect wood against deterioration and improve and stabilize its distinctive appearance. Shellac has been widely used as a protective material for wooden furniture and musical instruments, due to its excellent properties such as ease of application, high adhesion to the wood surface, and protective properties along with its non-poisonous nature [3,4,5]. It is still known as one of the most elegant finishes for furniture and currently used for restoration, conservation of wooden artifacts, and refinishing wooden antiques [3,6,7]. Various nanomaterials such as metal NPs (gold, copper and silver) and different metal oxide NPs are currently used in the preservation and restoration treatments of different heritage objects [11]
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