Hydrogels from agar and citrus pectin for cleaning cultural heritage objects

Agar (AG) hydrogels are largely used for cleaning cultural heritage objects. Herein, we present the preparation of a new binary hydrogel based on agar and citrus pectin (AG/CP) and its application in an oil painting on brushed aluminium. The use of citrus pectin is justified since it is a sustainable and innovative alternative, from an economic and scientific point of view. The hydrogels AG and AG/CP were prepared and analyzed comparatively. First, their properties were investigated by FTIR, SEM and water swelling degree. Next, they were applied to remove adhesive residues and other dirt from the painting surface. Finally, they were evaluated comparatively in terms of their performance as cleaning material to the painting. It was verified that AG/CP hydrogel is homogenous, transparent, mechanically self-sustainable, and absorbs water and ethanol in a more controlled manner than AG hydrogel, leading to a better result in cleaning the painting surface. Also, AG/CP was efficient in removing tape glue residues from the aluminium surface since it softens when in contact with solvent, allowing better interaction with the glues. Taking both neat and post-cleaned brushed aluminium, the successful removal of adhesive glue was confirmed by contact angle measurements. Our main finding is the demonstration of the good performance of the hydrogels containing citrus pectin, an abundant polysaccharide in Brazil, to enhance the state of conservation of contemporary work of art, without causing any damage to the object. Besides, the binary hydrogel was obtained through a simple and reproducible method, as it is its application on the work of art.