Nanotechnologies for conservation of cultural heritage: Paper and canvas deacidification

The aging of cellulose, the main constituent of paper, is due to depolymerization of cellulose fibers and is promoted by acid pH. Paper deacidification is a fundamental process for the conservation and restoration of probably the most important material used to transmit cultural heritage. Several methods are currently used for paper deacidification. We applied nanotechnologies to produce kinetically stable dispersions of nano- and micron-sized calcium hydroxide particles in alcohol media. Although calcium hydroxide possesses the best deacidification properties, it has never been used so far as dispersion in nonaqueous media. Calcium hydroxide particles, once deposited onto paper cellulose fibers, deacidify them and react with carbon dioxide from the air, forming a calcium carbonate reservoir on the paper fibers. This process allows a long-term control of paper pH, with excellent deacidification properties. Deacidification of 14th, 17th, 19th, and 20th century acid yellowed paper samples coming from rag and wood pulp (20th century) has been performed with excellent results. Moreover, the nano- and microparticle dispersions can be applied to paper or canvases using conventional procedures. This new method is environmentally clean, is inexpensive, and can also be used for industrial applications.