Deacidification

It is believed that the water-soluble acidity in paper can be washed out using water. Alternatively, if water is thought to be too hazardous to use on the paper, then the acidity may be neutralised while still in the paper, possibly by using a non-aqueous deacidifying treatment. Not all the acidity can be washed out of oxidised paper as some of the cellulose will have produced carboxylic acid groups on the cellulose chain. Many conservators at this stage of a conservation process prefer to introduce some alkaline material into the paper to neutralise any acids not washed out and which will remain behind to neutralise any acidity that may develop in the future. 

Barrow s examinations of stable, old papers found that most had a significant calcium or magnesium carbonate content. Today, some of the best aqueous deacidification treatments introduce these compounds. There are several popular materials used for aqueous deacidification, one of these is calcium hydroxide solution (lime water). Calcium hydroxide is not very soluble in water a saturated solution contains 1.85 gL 1 in ambient conditions and has a pH of 12.4 which is quite high. Severely degraded papers are suspected to undergo alkaline hydrolysis and some inks can bleed at such a high pH. While the paper is in the solution, the acids are neutralised. When treated paper is removed from the solution, the imbibed calcium hydroxide reacts with carbon dioxide in the air to form stable calcium carbonate. If the object has a very black area, e.g. as in some mezzotint prints, the dried precipitated carbonate may sometimes be visible as a white bloom, however, usually it is not seen. The eventual pH of the paper is in the range 8.0-9.0. 

If carbon dioxide is bubbled through the calcium hydroxide solution, the carbonate is precipitated at first but later it dissolves again with the formation of calcium bicarbonate solution. This solution varies in pH depending on the quantity of carbon dioxide in solution but the pH is generally about 7. It can be used as a deacidifying treatment when a high pH must be avoided. 

A process called the Barrow two-stage treatment deposits twice as much CaC03 by first immersing in calcium hydroxide, then calcium bicarbonate  

Barrow s method is seldom used now, as the quantity of CaC03 deposited with the single step processes is considered adequate. 

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Sulfite paper has a relatively short life span, since residual acid will continue to hydrolyze the cellulose and cause embrittlement. Further sources of acid include aluminum sulfate (which is added together with resin to suppress bleeding or feathering of ink into the paper) and S02 and NO from the atmosphere. Much of the world s library collections and archives will soon be lost as the paper crumbles. Various deacidification treatments (e.g., with ammonia, morpholine, cyclohexylamine carbamate, or diethyl-zinc) have been proposed and tried, but at best they can only halt the process of embrittlement and cannot reverse it.14 With the move to kraft pulping, alkaline peroxide bleaching, and increasing use of precipitated calcium carbonate as a filler, the high quality papers produced today are intrinsically acid free and should also resist subsequent acidification by S02-polluted air fairly well. 

The product, after filtration, is conveyed mechanically to another filter on which the cyclonite is washed with cold water until deacidification is as complete as pos-... 

Desirability of Malo-Lactic Fermentation. Three important aspects of malo-lactic fermentation must be considered in appraising its desirability deacidification, bacteriological stability, and increased flavor complexity (4). 

In addition to malo-lactic fermentation, another biological method for deacidification of high-acid must is to use malic acid-metabolizing Schizo-saccharomyces yeast for the alcoholic fermentation. Benda and Schmidt (33) have selected strains of these yeasts which produce wines with no off-flavors. In using some of these same strains we have also been able to make wines of sound character (18). 

The supercritical fluid extraction of oil seeds has been investigated extensively by several authors [34,98]. Possible applications of supercritical fluids in the edible-oil industry include deacidification, deodorization, and fractionation of crude oils and chemical conversion (like hydrogenation, and enzymatic reactions). 

The present ED industry has experienced a steady growth rate of about 15% since 15 years (Srikanth, 2004). The most important industrial ED application is still the production of potable water from brackish water. However, other applications either in the semiconductor industry for the production of ultrapure, that is, completely deionized water without the chemical regenerations of IERs or in the food industry (i.e., whey demineralization, tartaric stabilization of wine, fruit juice deacidification, and molasses desalting) are gaining increasing importance with large-scale industrial installations. 

Cheese whey demineralization Desalting of protein hydrolysates (i.e., soy sauce), sugar solutions, molasses, and polysaccharide dispersions Deacidification of fruit juices Tartaric wine stabilization Flavor recover from pickle brines... 

FIG. 17 Schematic layout of a three-compartment ED stack for the deacidification of fruit juices a, anionic membrane c, cationic membrane R , generic anion X+, generic cation. 

Kang, Y.J. and Rhee, K.C. 2002. Deacidification of mandarin orange juice by electrodialysis combined with ultrafiltration. Nutraceuticals and Food 7, 411—416. 

Vera, E., Ruales, J., Domier, M., Sandeaux, J., Sandeaux, R., and Pourcelly, G. 2003. Deacidification of clarified passion fruit juice using different configurations of electrodialysis. J. Chem. Technol. Biotechnol. 78, 918-925. 

Voss, H. 1986. Deacidification of citric acid solutions by electrodialysis. J. Membr. Sci. 27, 165-171. 

Figure 10.17 Flow schematic of electrodialysis systems used to exchange target ions in the feed solution, (a) An all-cation exchange membrane stack to exchange sodium ions for calcium ions in water softening, (b) An all-anion exchange membrane stack to exchange hydroxyl ions for citrate ions in deacidification of fruit juice...

Critical Evaluation of Mass Deacidification Processes for Book Preservation... 

Four mass deacidification processes for book preservation namely, the Library of Congress diethyl zine process, Wei T o nonaqueous process, Kopper s "Book Keeper" process, and Langwell interleaf vapor phase process, are critically evaluated, based on their chemical characteristics and effectiveness on deacidification. 

The objective of this report is to attempt to answer these questions. Evaluation of current technologies on mass deacidification processes are the main thrust of this work. In addition, the need of an integrated, complete book conservation program is discussed. 

Before embarking on any discussion on mass deacidification, the history and development of paper making and causes that lead to deterioration of modern paper are reviewed. 

If acid is present in paper, hydrolysis of cellulose fibers would be inevitable. Hence the removal of acid from paper is imperative. The first attempt to stabilize paper by a deacidification treatment was undertaken by Sir Arthur Church in 1891 using a solution of barium hydroxide in methanol to deacidify the backing of Raphael cartoons. 

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