| Numerous archives and libraries all over the world, including China, have focused on a large number of decrepit and damaged documents. Many precious documents, such as archive materials, books, manuscripts, prints, and paintings on paper, are affected by the hydrolytic breakdown of cellulose catalyzed with acids. Acids are mainly derived from four aspects, namely, the product of photo-oxidation, oxidation, inorganic acid from air, organic acid from bio-deterioration, and additives, such as aluminum sulfate. Since the mid-19th and20th centuries, more and more papers, especially most newspapers, have been industrially manufactured from mechanical pulp containing large amounts of additives, which can lead to the accumulation of acidic substances. Thus, these manufactured papers have been facing serious acidification, and they would also evoke the acid-induced depolymerization of cellulose fibers through hydrolysis. Currently, more and more researchers have been contributing to the conservation, particularly deacidification, using their scientific knowledge to create solutions that could increase the expected lifetime of documents.In general, the final pH value of papers should be in the range of7.0-8.5after the deacidification treatments. If the pH value of the paper surface is too high, it would undergo alkaline depolymerization, leading to the decrease in the chain lengths of the cellulose. Moreover, many deacidification treatment processes are suspects for diminishing paper strength and degrading paper because they damage the fiber structures and inks.Selecting an appropriate paper deacidification agent is very important for the deacidification of paper. The use of three deacidification agents (i.e., iso-butylamine, calcium propionate, and borax) is studied for the deacidification of paper using the immersion treatment by investigating the paper surface pH, alkaline residue, paper whiteness, strength, and other performance indicators. Results show the deacidification by borax solution not only results in the promotion of a proper pH range, high level of alkali reserves, and ignorable influence to paper appearance, but also to the enhancement of the mechanical intensities of paper even after artificial aging.Borax, as an antibacterial agent, is known to effectively control the growth of microorganisms in the paper, which is also favorable for the long-term preservation of papers. Borax has been drawing considerable interests as mild and moderate alkaline agent. Moreover, it has shown a remarkable ability to accept electrons and form molecule interplay among the polyhydroxy cellulose molecules that can make papers stronger.In the recent30to40years, CO2SCF has been successfully used either as a nontoxic or an excellent inflammable solvent in other applications. CO2SCF can be used at relatively low costs and just above room temperature, and it does not cause any deterioration in inks, pictures, adhesives, or leather bindings of books. Fortunately, the processing of paper in CO2SCF has been verified highly efficient, safe, and practices wasteless conservation in the neutralizing treatment of acidic paper because of the different deacidification agents, and its efficiency showed quite a difference.Supercritical carbon dioxide (CO2SCF), as a solvent system, is used in the deacidification of acidic papers using the borax solution of water and alcohol. CO2SCF improved the deacidification process by significantly improving the pH value and the base residual value. The borax in supercritical fluids can be better combined with cellulose hydroxyl to improve the mechanical properties of paper substantially. The treatment of borax in CO2SCF could be an alternative for acidic papers. Aside from improving the pH and depositing a sufficient alkaline residual, CO2SCF also strengthens the mechanical properties of treated papers.The current study showed that borax, aside from being an optimal mild deacidification agent to neutralize the acidic functions of the papers, not only controlled the proper pH range but also led to a steady increase in the base stock. Borax was also beneficial to the mechanical strength, especially in its perfect performance in the artificial aging, and it exhibited good durability. Moreover, as an antibacterial agent, borax could effectively control the growth of microorganisms on papers, which would be conducive to the long-term preservation of aged papers.The use of CO2SCF combined with borax alcoholic solutions allowed the substantial improvement of mechanical strength and minimization of the negative effect of solvents on the color intensity and tint of ink compared with the immersion treatments commonly used for neutralizing paper. These findings are very promising since borax is known to be economically cost effective and the CO2SCF treatment is easy to perform and gives excellent results in paper conservation. All these advantages will be favorable for the long-term preservation of aging papers. |
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