Critical Evaluation of Mass Deacidification Processes for Book

Chapter 2

Critical Evaluation of Mass Deacidification Processes for Book Preservation

Downloaded by UNIV OF MASSACHUSETTS AMHERST on May 25, 2018 | https://pubs.acs.org Publication Date: September 28, 1989 | doi: 10.1021/bk-1989-0410.ch002

David N.-S. Hon Wood Chemistry Laboratory, Department of Forestry, Clemson University, Clemson, SC 29634-1003 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 c o l l e c t i o n s of America's l i b r a r i e s are deteriorating r a p i d l y . Thousands of books have already disappeared; m i l l i o n s are i n grave danger. On March 29, 1987, The New York Times published an a r t i c l e with an attention getting t i t l e : "Millions of Books are Turned to Dust - Can They Be Saved?" (1) This t i t l e summarized e x p l i c i t l y the actual s i t u a t i o n i n l i b r a r i e s and archives i n North America and Europe. The inherent a c i d i t y of book papers i s the major cause of deterioration. In order to salvage a book, acid must be neutralized with a l k a l i n e chemicals. The n e u t r a l i z a t i o n process i s c a l l e d deacidification. I d e a l l y , the process w i l l also deposit an a l k a l i n e reserve to prevent future a c i d attack. Many d e a c i d i f i c a t i o n processes have been developed since the 1960s (2-4). Several of these have also successfully demonstrated t h e i r p o t e n t i a l and the p o s s i b i l i t y of operating them on a p i l o t or a commercial scale. In t h i s review, a c r i t i c a l evaluation of these mass d e a c i d i f i c a t i o n processes i s made. The problems of acid deterioration of modern papers, development of d e a c i d i f i c a t i o n processes, t h e i r chemical c h a r a c t e r i s t i c s and effectiveness, as well as the need for the development of an integrated paper preservation program are discussed. The Fate of Modern Papers The cave paintings of P a l e o l i t h i c man, the hieroglyphics chiseled into the crumbling a n t i q u i t i e s of ancient Egypt, and the rune-covered a r t i f a c t s of Scandinavia and Northern Europe were to preserve forever t h e i r a c t i v i t i e s and c u l t u r a l heritage. Today, for the same purpose, 0097-6156/89A)410-0013$06.25A) e 1989 American Chemical Society

Zeronian and Needles; Historic Textile and Paper Materials II ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


14

HISTORIC TEXTILE AND PAPER MATERIALS Π

we record our knowledge, technology, a c t i v i t i e s and culture on paper. Although the cave paintings of Cro-Magnon man which were made 35,000 years ago are s t i l l i n good condition, i r o n i c a l l y , modern paper which was made less than one hundred years ago i s crumbling i n l i b r a r i e s throughout the world. The facts are that of the 20 m i l l i o n books and pamphlets i n the c o l l e c t i o n of the Library of Congress, as many as 30% are i n such a c r i t i c a l stage of deterioration that they can not be c i r c u l a t e d (5,6). A recent survey of the New York Public Library revealed that nearly 50% of i t s more than f i v e m i l l i o n books are on the brink of disintegration (7). This phenomenon can be observed i n any major u n i v e r s i t y or research l i b r a r y . M i l l i c e n t A b e l l of Yale University Library has estimated that as many as 76 m i l l i o n books nationwide may l i t e r a l l y be crumbling into dust, with more joining the l i s t every year (8). A study conducted by William Barrow sadly indicated that 97% of a l l books published between 1900 and 1949 would have a useful l i f e of f i f t y years or less (9). Why are the cave paintings of thousands of years o l d i n better condition than modern papers? Why do many early books printed i n the 15th century show no signs of serious deterioration? How can we preserve our accumulated knowledge? Are the current technologies on book preservation effective? Are the current practice on book preservation acceptable? The objective of t h i s report i s to attempt to answer these questions. Evaluation of current technologies on mass d e a c i d i f i c a t i o n processes are the main thrust of t h i s work. In addition, the need of an integrated, complete book conservation program i s discussed. Before embarking on any discussion on mass d e a c i d i f i c a t i o n , the history and development of paper making and causes that lead to deterioration of modern paper are reviewed. History and Development of Paper Making (10) Paper, one of man's most essential commodities, was f i r s t made i n the Orient about 2,000 years ago. Credit for the invention of paper has been given to T ' s a i Lun, a member of the Imperial Guard and Privy C o u n c i l l o r , who conceived the idea of making paper from o l d rags, f l a x , hemp, r i c e stalks and tree bark (11). The Chinese macerated fibers from these materials i n water and drained the suspension on a mold covered with s i l k c l o t h . The f i b e r mats were removed and dried i n the sun to form paper. This uniqueness i s attested to by i t s slow communication to other parts of the world: f i v e hundred years to reach Korea and Japan; six hundred years to Samarkand and the Arab world; and one thousand years to Europe, and even l a t e r to America i n 1690. During that p e r i o d , rags of cotton, f l a x , jute, and hemp comprised the sole source of raw materials used i n paper manufacture. From the advent of papermaking, the use of rags or bast fibers grew r a p i d l y p r i o r to 1800, creating a shortage of papermaking raw materials. It has been reported that during that period, even linen shrouds from exhumed corpses were sold for papermaking (12). In 1719, Rene de Reaumur, a b r i l l i a n t French s c i e n t i s t , suggested that paper could be made from the fibers of plants without using rags or l i n e n . However, i t took u n t i l 1764 for a German clergyman, Dr. Jacob Scaffer, to make paper experimentally from a wide variety of plant



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Mass Deacidification Processes

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materials and to demonstrate that these vegetable fibers could be a substitute for rags, yet no interest was aroused apparently at that time. At the beginning of the nineteenth century, with the use of paper and p r i n t i n g presses increasing r a p i d l y , the demand for paper outstripped the production of handmade paper, and mass production techniques were c a l l e d f o r . In 1840, Scaffer's idea was picked up by a German bookbinder named C h r i s t i a n V o l t e r . He developed a wood grinder to produce groundwood pulp i n 1844 and patented i t i n 1847. This was the beginning of mechanical pulp production. This development rapidly increased the production of newsprint, although the pulp was poor i n q u a l i t y , especially i n strength and d u r a b i l i t y , being i n f e r i o r to present-day mechanical pulp. In 1851, two Englishmen, Hugh Burgess and Charles Watt, produced pulp from willow shavings boiled i n a solution of l y e , making the f i r s t soda pulp from wood. This was the beginning of chemical pulp production. The advantages of chemical wood pulp over mechanical pulps were soon appreciated. Following t h i s invention, the s u l f i t e process was invented by an American chemist, Benjamin Tilgman, in 1867. The sulfate (kraft) process was invented i n 1889 by a German chemist, C a r l Dahl of Danzig. From t h i s we can r e a l i z e that within only a few years, a revolutionary change had taken place i n the pulp and paper world. Now, about one hundred years has elapsed. The fundamental pulping and papermaking p r i n c i p l e s established then s t i l l remain the basics of today's modern papermaking. Advances i n engineering and technology have made i t possible to produce increasingly larger tonnages and a vast variety of paper products by very c o s t - e f f e c t i v e methods. Today, world consumption of paper amounts to about 200 m i l l i o n tons annually, of which 94%-95% i s produced from wood, and the remainder mainly from other vegetable f i b e r s . I r o n i c a l l y , the h i s t o r i c a l event seems to be repeated today; under the severe constraints of p o l l u t i o n control and energy conservation, we are experiencing a shortage of f i b e r raw materials. The r e s u l t of t h i s i s the production of h i g h - y i e l d fibers that r e t a i n high amounts of l i g n i n (or even extractives) i n the pulp f i b e r s . And the newest development i n t h i s area i s the appearance of thermomechanical pulps that obtain pulp y i e l d s as high as 100%. With the development of the chemical pulping technology of wood at the end of the nineteen century, animal g e l a t i n , which had been used as the s i z i n g agent, was replaced by alum. The main advantages of using alum-rosin s i z i n g are that i t does not need to be p u r i f i e d ; when i t i s mixed into a s l u r r y i t acts to d i s t r i b u t e rag or wood fibers evenly i n water, and thus contributes to the making of an even textured paper; and paper sized i n i t dries quickly (13). The shortcoming of alum-rosin s i z i n g i s that s l u r r i e s to which i t i s added, regardless of t h e i r makeup, y i e l d a c i d i c paper (14,15). For more than a century nearly a l l book papers have been sized t h i s way. I r o n i c a l l y , modern papers, which were invented after the revolutionary changes of one hundred years ago, have serious problems—either i n permanence or i n d u r a b i l i t y . Most paper produced from wood fibers does not show the permanence of rag papers and d i s c o l o r a t i o n i s more c r i t i c a l than i n rag papers. It has been noted that modern writing papers and books tend to have a much shorter l i f e expectancy than those manufactured one hundred years ago.


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Permanence of Paper (16-18) The permanence of paper i s determined by "internal" and "external" factors (19). The i n t e r n a l factors are established during manufac ture of paper and include kind and q u a l i t y of the f i b e r , s i z i n g materials, coatings and presence of a c i d i c and m e t a l l i c compounds, and other components of the sheets. The external factors are r e l a t e d to conditions during storage or use, e . g . , temperature, r e l a t i v e humidity (which determines the moisture content of the paper), l i g h t , and contaminants i n the atmosphere. The manufacturer i s responsible for production of a paper having p o t e n t i a l permanence; the user i s responsible for storage of the product under conditions which are r e q u i s i t e for long l i f e . A lack of permanence i n paper can be manifested by d i s c o l o r a t i o n , loss i n strength and change i n chemical properties, such as increase i n copper number, decrease i n alpha c e l l u l o s e , and decrease i n degree of polymerization (DP) of the c e l l u l o s e . In evaluating permanence, consideration should be given to changes i n both the c e l l u l o s e , hemicelluloses and l i g n i n (chemical changes) and paper (physical p r o p e r t i e s ) . Although many investigators have been concerned with permanence, the factors influencing the s t a b i l i t y and permanence of paper have not been f u l l y established. Both the q u a l i t y of the c e l l u l o s e f i b e r s and the nature of the nonfibrous components contribute to the character of the finished sheet. Owing to the complex composition of papers and variations from grade to grade, many types of degradation are possible. For the c e l l u l o s e f i b e r s , these include hydrolysis, oxidation, c r o s s - l i n k i n g , change i n c r y s t a l l i n i t y , photolysis, photo-oxidation, thermal decomposition and even microbiological attack under c e r t a i n conditions (20). These factors combined with i n i t i a l paper q u a l i t y w i l l severely reduce the permanence of paper. Acid Formation One of the most s i g n i f i c a n t factors that contribute to deterioration and embrittlement i s the introduction of a c i d elements into the paper (21). Acid catalyzed hydrolysis of c e l l u l o s e causes 80-90% of paper deterioration (22). The rate of hydrolysis depends on various f a c t o r s , including the nature of the c e l l u l o s e and the conditions under which the paper i s stored. Under most conditions, however, most papers deteriorate progressively. The aging c h a r a c t e r i s t i c s of a c i d i c paper are d i s c o l o r a t i o n , embrittlement and steadily increasing fragility. L i g n i n - r i c h high y i e l d papers suffer p a r t i c u l a r l y badly. The acid problem i n l i b r a r i e s i s much more acute than i t was half a century ago. Books of the 1920 s and 1930 s are now entering a c r i t i c a l period. For the most part they can s t i l l be restored, but i f they are not also protected from acid attack they w i l l neverthe less become unusable i n the foreseeable future (23). The chief source of a c i d i t y i n paper i s the alum used i n the papermaking process. Paper (largely c e l l u l o s e ) i s a very hydrophilic substance, and i t s surface has a high s p e c i f i c energy. Thus, water readily wets paper surfaces. The very porous structure of paper makes i t act l i k e a sponge i n the presence of l i q u i d s . Hence, various chemicals have been developed to make paper reasonably water 1

1



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17

r e p e l l e n t , so that paper can be printed or written with inks. The process i n which a chemical additive provides paper with resistance to wetting and penetration i s c a l l e d s i z i n g (13). Papermaker's alum [Al^iSO^)^ 14^0] i s the most popular chemical used i n s i z i n g (14,15). It i s introduced into the furnish to p r e c i p i t a t e r o s i n s i z e ; to r e t a i n r e s i n s , starch, or pigments; and to control p i t c h (24). Unfortunately, aluminium sulfate i s sensitive to humidity and undergoes hydrolysis to generate s u l f u r i c acid (25). The s u l f u r i c acid generated decomposes the c e l l u l o s e molecule by breaking g l y c o s i d i c bonds. The chain-shortening of c e l l u l o s e leads to a corresponding decline of the mechanical strength of the paper. Additional sources of acid contamination include carboxyl group i n the c e l l u l o s e , a c i d i c carbohydrate gums, bleach and pulping chemical residues, and some constituents of coating c o l o r s . Acids may be introduced after the paper i s manufactured by atmospheric contamination, p a r t i c u l a r l y sulfur dioxide which i s absorbed by the paper and, i n the presence of moisture, w i l l generate s u l f u r i c a c i d . Development and Need of Book Deacidification If acid i s present i n paper, hydrolysis of c e l l u l o s e fibers would be inevitable. Hence the removal of acid from paper i s imperative. The f i r s t attempt to s t a b i l i z e paper by a d e a c i d i f i c a t i o n treatment was undertaken by S i r Arthur Church i n 1891 using a solution of barium hydroxide i n methanol to deacidify the backing of Raphael cartoons. In the early f o r t i e s , Barrow recognized that the b u i l t - i n a c i d i t y of paper had a greater effect on i t s deterioration than atmospheric contamination and advocated the d e a c i d i f i c a t i o n of documents (26). Since then, a number of workers throughout the world have contributed to much of our present knowledge of deterioration due to a c i d i t y and of d e a c i d i f i c a t i o n processes (2-4). It i s known today that the inherent a c i d i t y i s responsible for eighty-five to ninety percent of destruction i n book papers, causing them to lose an estimated f i f t y percent of t h e i r f o l d strength every 7.5 years and ultimately reduces them into a state of embrittlement i n which they w i l l break at a touch (27). It has been observed by Smith (28) that the pH value required for stable, permanent paper has altered with the passage of time. In the early twentieth century, permanent book papers required a pH of 4 (hot water e x t r a c t ) . In 1928, t h i s figure was set at 4.7 or preferably higher. By 1935, i t was r e a l i z e d that low pH was a cause of early deterioration i n paper and the figure was raised to a minimum pH of 5 for good q u a l i t y book paper. In 1937 Grant observed that for permanent paper the value of the hot water extract should not be less than pH 6. Lewis, i n 1959, stated, on the basis of t e s t s , that papers i n good condition had a pH of 6.3 and 6.5. Barrow l a t e r also stated that the most stable papers show a pH of about 7 (cold extraction) while the least stable show a pH of 5, and that a pH of about 7 i s desirable for maximum conservation. Smith also suggests that the most desirable pH value i s 7, i . e . , neutral. An evaluation by Kathpalia of papers dating from the fourteenth to nineteenth centuries has shown that papers with pH above 6.7 are i n excellent condition while those with pH ranging from 6.2 to 6.7 are i n good condition, and that a l l these papers are free from fungus stains.



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As a r e s u l t of the above studies, a number of processes have been developed for introducing a strong a l k a l i n e base to react with the acid i n paper to form neutral s a l t s . The process also deposits a neutral substance or buffer on the treated product that w i l l r e s i s t future acid contamination from any source. The various processes developed may be c l a s s i f i e d as aqueous d e a c i d i f i c a t i o n , nonaqueous d e a c i d i f i c a t i o n and gaseous d e a c i d i f i c a t i o n (5,29). It should be borne i n mind that d e a c i d i f i c a t i o n i s e f f e c t i v e for treating books which are already i n the c o l l e c t i o n s that have not yet been dangerously damaged by a c i d . B r i t t l e books are beyond saving by d e a c i d i f i c a t i o n only. For such books, a paper strengthening treatment has to be conducted also. Aqueous D e a c i d i f i c a t i o n Aqueous d e a c i d i f i c a t i o n technique consisted of immersing paper i n , or spraying i t with, an aqueous solution of barium, calcium or strontium bicarbonates or hydroxides. The immersion time varied from f i v e seconds to about two minutes. The wetted paper i s then d r i e d . As a r e s u l t , carbonates of these metals are deposited on the treated paper. Pioneering work was done over f i f t y years ago by Schierholtz at the Ontario Research Foundation i n Toronto. The process was patented i n 1936. To increase the n e u t r a l i z i n g p o t e n t i a l of the chemicals used, Schierholtz recommended carbon-dioxide treatment to convert hydroxides to carbonates and that the suspension of carbonates be allowed to s e t t l e on the treated sheets. He reported that a more concentrated bicarbonate solution could be prepared by using carbon dioxide gas under pressure and advised that the pH of a water extract from paper treated by t h i s process should exceed a value of 6.5 and that a deposit of up to 2 percent by weight might be required for s t a b i l i z i n g groundwood papers l i k e newsprint. Based on the patent, Barrow of Richmond, V i r g i n i a , developed a two-step process (26), i n which materials were f i r s t neutralized with calcium hydroxide and then a l k a l i z e d with calcium bicarbonate. Many other approaches have been devised since that time, including the use of magnesium bicarbonate by Gear of the National Archives i n Washington. His one-step process, developed i n 1957, i s the form of aqueous d e a c i d i f i c a t i o n s t i l l practiced by many small l i b r a r i e s and archives. In 1978 t h i s process was further improved by substituting the more soluble magnesium hydroxide for magnesium bicarbonate (30). The Library of Congress has used the aqueous d e a c i d i f i c a t i o n method i n the past for much of i t s paper and manuscript d e a c i d i f i c a t i o n because of i t s safety and r e l i a b i l i t y (31). Aqueous d e a c i d i f i c a t i o n i s an e f f e c t i v e means to remove a c i d . Some of the a c i d and impurities can be washed out during the treatment. However, i t i s a painstaking process. Because water w i l l swell paper, i t w i l l damage bindings. I t requires taking books completely apart, soaking them i n the s o l u t i o n , drying, and then rebinding. Moreover, water can be very damaging to certain inks used for color or for w r i t i n g . Hence, the treatment require special handling s k i l l s for c r i t i c a l l y embrittled papers. For these reasons, a nonaqueous d e a c i d i f i c a t i o n treatment has been developed to avoid such d i f f i c u l t i e s .


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Nonaqueous D e a c i d i f i c a t i o n A number of investigators have voiced the theory that a d e a c i d i f i c a t i o n solution containing organic solvents might provide a remedy for d i f f i c u l t i e s caused by the use of water. Similar hopes were expressed by the International I n s t i t u t e for Conservation of H i s t o r i c and A r t i s t i c Works i n 1968, when i t s Committee for Paper Problems reported that "a nonaqueous means of d e a c i d i f i c a t i o n that would not be harmful to paper, pigments and the various media must be developed." As a matter of f a c t , nonaqueous d e a c i d i f i c a t i o n began i n England about the end of the 19th century. Barium hydroxide i n methanol was used as a d e a c i d i f i c a t i o n agent i n the V i c t o r i a and Albert Museum. Baynes-Cope of the B r i t i s h Museum reinvented t h i s method i n the middle of the 1960s (32). Considerable research i s being devoted to improve existing techniques, to accelerate the d e a c i d i f i c a t i o n process, render i t applicable for the treatment of bound volumes and reduce the cost of operations. Nonaqueous d e a c i d i f i c a t i o n has been improved i n the past ten years and has reached commercial success. The new process i s conducted by introducing " l i q u i f i e d gas" into a chamber containing books. Once the a c i d ions i n the paper have been neutralized, the "gas" i s pumped out of the compression chamber and returned to a storage tank. The books can then be dried and return to the shelves. Since a nonaqueous d e a c i d i f i c a t i o n process does not require books to be unbound as does an aqueous process, i t s development dramatically reduced the cost of operation. Nonaqueous d e a c i d i f i c a t i o n treatments involve the use of a nonaqueous solution containing a d e a c i d i f i c a t i o n agent and an organic solvent. The advantage of using organic solvents i s that they are available as l i q u i d s over a wide range of temperature and may be blended to obtain the desired working requirements and properties. One of the major features of t h i s method i s the r a p i d i t y of penetration of chemicals into paper and the extreme r a p i d i t y of drying the paper even at room temperature. This can avoid the problems of drying and crocking. On the other hand, a l l the organic solvents used are either flammable or toxic or expensive. Some are poisonous, or hazardous to health, and others dissolve, or cause feathering i n , dyes and inks used on paper. Substances such as magnesium acetate, barium hydroxide, cyclohexylamine and i t s carbonate and acetate and magnesium methoxide have been tested for t h e i r safety and effectiveness. Magnesium methoxide has been found to be a very effective n e u t r a l i z e r . However, on a damp day or with a damp paper, the solution tends to p r e c i p i t a t e prematurely and leave surface deposits on the treated paper. Methyl magnesium carbonate i s also effective but much less sensitive to water. Both these products produce adequate a l k a l i n e reserves i n paper. Since methanol i s used as the solvent, the d e a c i d i f i c a t i o n should be conducted i n a w e l l - v e n t i l a t e d hood. The most successful nonaqueous d e a c i d i f i c a t i o n treatment i s the Wei T O process which uses solutions of methoxy magnesium methyl carbonate i n alcohol and Freon as the s t a r t i n g materials (33). The spray d e a c i d i f i c a t i o n of the solution on books i s now i n use at the


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Princeton University L i b r a r i e s and at the B r i t i s h L i b r a r y . The mass d e a c i d i f i c a t i o n of the Wei T O process has been used i n the National Library and Public Archives of Canada (34). Just l i k e any method, Wei T o process does have i t s l i m i t a t i o n s . Details of the chemical process and i t s l i m i t a t i o n s w i l l be discussed elsewhere i n t h i s report. A s i m i l a r process using magnesium alkoxides and alkoxy carbonates dissolved i n mixtures of methanol and Freons was developed i n the B i b l i o t h è q u e Nationale at Chateau de Sable i n France. f


Gas D e a c i d i f i c a t i o n In consideration of the damage of paper by l i q u i d s (solvents) as well as the l i m i t a t i o n and effectiveness of transfer chemicals into the f i b e r s , d e a c i d i f i c a t i o n by gas has been devised. Although there are a great many v o l a t i l e organic compounds which appear to be s u f f i c i e n t a l k a l i n e for vapor-phase d e a c i d i f i c a t i o n , only a very few appear to be p r a c t i c a l . Kathpalia (35), at the Nehru Library i n New D e l h i , exposed books to high concentrations of ammonia vapor for d e a c i d i f i cation. However, i t was found that ammonia i s a too weak base to completely neutralize strong acid i n paper, and ammonia v o l a t i l i z e d from treated books i n a few days. I t has not been considered as a permanent d e a c i d i f i c a t i o n method. Langwell (36-38) worked with eyelohexylamine carbonate as the neutralizing amine s a l t . It has achieved some success. Although t h i s method i s not s t r i c t l y a mass d e a c i d i f i c a t i o n process, i t can be e a s i l y applied to whole books, rather than single sheets. D e t a i l of i t s chemistry w i l l be discussed i n the subsequent mass d e a c i d i f i c a t i o n section. The Barrow Laboratory investigated the use of several amines and f i n a l l y s e t t l e d on morpholine as the most effective vapor-phase treating agent (39). It appeared that the morpholine penetrates books well and deacidifies them e f f e c t i v e l y . However, t h i s method has not been considered as a permanent method due to the rapid drop of pH of treated products. The process does not introduce a buffering chemical into books. They have to be redeacidified every few years to maintain protection. Morpholine also may cause s i g n i f i cant d i s c o l o r a t i o n of papers. The Library of Congress has attempted to use ethyleneimine as a gaseous treating materials, but no s i g n i f i c a n t improvement i n aging c h a r a c t e r i s t i c s was achieved, and the paper was seriously discolored. Since then, the Library of Congress had developed a promising vapor-phase process using an organometallic compound, d i e t h y l z i n c , to deacidify books (40). D e t a i l of t h i s process w i l l be discussed i n a subsequent section. Chemical Characteristics of Mass D e a c i d i f i c a t i o n With respect to the quantity of book materials to be neutralized i n l i b r a r i e s , i t i s too laborious to treat books i n a single-sheet operation. Only a mass scale d e a c i d i f i c a t i o n process i s acceptable. Hence, several mass d e a c i d i f i c a t i o n processes have been developed. They are discussed further.



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The Library of Congress Diethyl Zinc D e a c i d i f i c a t i o n Process (40,41). The Diethyl Zinc (DEZ) Mass D e a c i d i f i c a t i o n Process was developed by the Library of Congress at the beginning of 1970s. Diethyl zinc gas i s used to deacidify paper by permeating such gas i n a vacuum environment. D i e t h y l zinc i s an organometallic compound which has been used by the chemical industry since i t s discovery i n 1849. One of the most important chemical properties of DEZ i s i t s r e a c t i v i t y to acids (even very weak acids such as water) and i t s r e a c t i v i t y to oxygen. Hence i t reacts extremely rapidly with both strong and weak acids present i n paper, neutralizing them and l i b e r a t i n g gaseous ethane. Strong acids: Weak acids:

H S0„ + ( C H ) Z n ζ 4 Ζ D Ζ 2CH (X> H + ( C ^ ^ Z n o

0

3

c

ZnSO, + 2C.H. 4 Ζ Ό Zn(CH C0 ) + 2 C H

0

2

3

2

2

2

(1) 6

(2)

Moreover, the reaction of DEZ with l i q u i d water or vapor i s very rapid y i e l d i n g ZnO which i s non-volatile and only s l i g h t l y soluble i n water to y i e l d a solution of pH 7.2-7.4. H 0 + (C H ) Zn 2

2

5

ZnO + 2 C H

2

2

(3)

6

Zinc oxide deposited i n paper provides an "alkaline reserve" (which i s more nearly neutral i n pH than the more commonly used calcium and magnesium reserves) by reacting with any strong or weak acids introduced into the paper subsequent to the d e a c i d i f i c a t i o n process : ZnO

+

H^SO, ZnSO, + H 0 (4) 2 4 4 2 There i s l i t t l e or no reaction of d i e t h y l zinc with dry c e l l u l o s e or l i g n i n under process conditions. The amount of zinc oxide i n the treated paper, and hence the a l k a l i n e reserve, can be controlled by the amount of moisture i n the paper at the time of treatment; s u f f i c i e n t DEZ i s added to react with a l l the acid and water present. DEZ can also produce ZnO by reaction with oxygen i n a i r : (C H ) Zn 2

5

2

o

+

70

2

ZnO + 4C0

2

+

5H 0 2

(5)

This r e a c t i o n , too, i s extremely rapid and liberates a great deal of heat. If l i q u i d DEZ i s exposed to a i r , i t w i l l spontaneously ignite. Consequently, i t i s essential that l i q u i d DEZ be i s o l a t e d from contact with the atmosphere. B a s i c a l l y , the DEZ process consists of three simple steps: 1. Preconditioning: displacement of oxygen from the chamber and reduction of moisture content of book to 0.5%. 2. DEZ permeation: reaction of acids and moisture i n books with DEZ; removal of the ethane produced. 3. Postconditioning: removal of excess DEZ and return of moisture to books. It takes about f i f t y to f i f t y - f i v e hours to complete the three steps.



22


The Wei T O Nonaqueous Book D e a c i d i f i c a t i o n Process (42,43). The Wei T O Nonaqueous Book D e a c i d i f i c a t i o n System i s a l i q u i f i e d gas process using methoxy magnesium methyl carbonate, which i s dissolved i n methanol, t r i c h l o r o t r i f l u o r o e t h a n e (Freon 12) and d i c h l o r o d i f l u o r o methane (Freon 113). After the books have been dried for 24 hours i n warm a i r , followed by an overnight vacuum drying process, to reduce t h e i r moisture to 0.5%, they are impregnated with the d e a c i d i f i c a t i o n solution for an hour, the solvents are then removed as vapors by techniques that f a c i l i t a t e rapid drying and uniform deposition of the deacidifying and buffering agents i n the pages. The methoxy magnesium methyl carbonate (H C0Mg0C00CH ) after being deposited i n the fibers by the solvents, reacts with water from the a i r to form a mixture of magnesium carbonate (NgCO^), magnesium hydroxide [Ng(0H )], and magnesium oxide (NgO): 3

2

H COMgOCOOCH + 2H 0 3

H

2°

3

+

H

°°2

Mg(0H) + H C 0 2

2

MgC0

2

C 0

2

3

(6)

2

7

3

( ) MgC0 + 2H 0

3

3

MgO + C 0

3

Mg(0H) + 2CH OH + C0

2

(8)

2

(9)

2

The magnesium hydroxide, carbonate and oxide then react with strong acids i n the paper to form a neutral s a l t . Sulfuric acid (H S0^), for instance, i s converted to magnesium sulfate (MgSO^ [Epsom Salts]) and water, when i t reacts with magnesium hydroxide: 2

Mg(0H) + H S 0 2

2

MgS0

4

4

+ 2H 0

(10)

2

At the same time, magnesium carbonate reacts with the a c i d , forming more magnesium sulfate and carbonic acid ( H C 0 ) , which decompose r a p i d l y into water and carbon dioxide: 2

MgC0 + H S 0 3

Η

2

H

2°°3

MgS0 + H C 0

4

2°

4

+

C

2

3

(11)

3

°2

(

1

2

)

After the books are removed from the processing chamber, during the overnight recovery, or subsequently i n the l i b r a r y , the magnesium hydroxide and magnesium carbonate can release moisture or carbon dioxide to the ambient a i r to form the basic magnesium carbonate [MgO* MgC0 »Mg(0H )] and function as the a l k a l i n e reserve. 3

2

Koppers Process (44). In the Koppers "Book Keeper" process, the books are treated with submicron p a r t i c l e s of basic metal oxides, hydroxides, or s a l t s of calcium, magnesium, or z i n c . The p a r t i c l e s can be applied i n the paper making process or to the finished paper by e l e c t r o s t a t i c transfer such as i n a xerographic process, by a dispersion i n a gas, or by a suspension i n an i n e r t l i q u i d . In the case of a l i q u i d suspension of the p a r t i c l e s , the l i q u i d s chosen are halogenated hydrocarbons. Typical l i q u i d s include Dupont Freon Fluorocarbons such as Freon 11 (trichloromonofluoromethane), Freon 113 ( 1 , 1 , 2 - t r i c h l o r o - l , 2 , 2 - t r i f l u o r o e t h a n e ) , and Freon 114


2. HON


23


( 1 , 2 - d i c h l o r o - l , 1 , 2 , 2 - t e t r a f l u o r o e t h a n e ) , and A l l i e d Chemical Genetron 11 and 113 and mixtures. Surfactants, such as ICI Solsperse 6000 and 3000 and 3M Fluorad FC 740 and 721, can be employed to overcome surface tension and charge a t t r a c t i o n effects of p a r t i c l e s . This process does not require drying of the book and the t e s t r e s u l t s showed that treated books are s a t i s f a c t o r i l y d e a c i d i f i e d and buffered, with no adverse effects on paper, p r i n t , covers or bindings. Interleaf Vapor Phase Deacidification (Langwell) Process (37,38,45). Although i t i s known that weak-base ammonia i s not a suitable d e a c i d i f i c a t i o n agent, Langwell of England believed that c e r t a i n organic derivatives of ammonia—the amines—are much more a l k a l i n e than ammonia and could therefore be r e l i e d on to reduce the a c i d i t y of acid paper to a degree believed to be s a t i s f a c t o r y for long storage. He found that eyelohexylamine carbonate (CHC) i s effective i n deacidifying books i n the vapor phase. I t has been reported that the Vapor Phase Deacidification (VPD) process i s v e r s a t i l e and lends i t s e l f to a wide, range of techniques which may be adapted to s u i t the diverse needs of p r a c t i c a l document r e p a i r ; for example, the active material CHC may be absorbed on sheets of absorbent paper which can then be used as interleaving i n books. By t h i s method, a few sheets of VPD paper, e.g. one sheet to every 50-100 pages of the book, may be evenly spaced throughout the book which i s then closed and replaced on i t s shelf for a week or two. The interleaving process takes only a few minutes and the book should be evenly and completely d e a c i d i f i e d with no appreciable change i n i t s appearance. A cheaper method well suited to boxed papers and f i l e s i s to use the CHC i n powder form enclosed i n small paper envelopes. These packets are simply placed i n the boxes with the loose papers and put aside u n t i l needed again for reference. The vapor from the CHC should permeate the whole box i n a few weeks time and give uniform and s a t i s f a c t o r y d e a c i d i f i c a t i o n . The permanence of the d e a c i d i f i c a t i o n has been tested by heating the d e a c i d i f i e d paper samples to 150 C (300 F) without increasing the a c i d i t y . The vapor from CHC has a very disagreeable odor, that would create an unpleasant atmosphere not only for those handling the material, but also i n the stacks of books treated with CHC. CHC i s reported to cause nausea and skin and eye i r r i t a t i o n (46-54). More importantly, chronic and acute toxic effects have been observed i n experimental animals exposed to varying concentration of CHC vapor, sometimes r e s u l t i n g i n death (50,54). Effective Means of Book Protection from Acid Degradation One of the most i n d u s t r i a l l y important c h a r a c t e r i s t i c s of papers i s t h e i r chemical s t a b i l i t y , which enables them to withstand degradation with i t s consequential loss of t e n s i l e and tear strength and f o l d endurance under normal conditions of use. However, t h i s s t a b i l i t y i s not absolute. Cellulose i s susceptible to oxidation and the g l y c o s i d i c linkage i s susceptible to h y d r o l y s i s . In order to protect book papers from a c i d degradation, they must not be exposed to a c i d . Acids are generated from the alum-rosin s i z e as well as from such


24

HISTORIC TEXTILE AND PAPER MATERIALS II


acid impurities as carbonyl and carboxylic groups present i n oxidized c e l l u l o s e and l i g n i n . They must be neutralized with a l k a l i n e chemicals. The amount of a l k a l i n e chemicals added not only have to be enough to neutralize e x i s t i n g acids but should also provide enough reserve to react with any a c i d which may be generated l a t e r by oxidation of c e l l u l o s e by heat, l i g h t , pollutants and other means. In order to avoid oxidation of the c e l l u l o s e and l i g n i n , u v - s t a b i l i z e r s and antioxidants may need to be added to book papers together with the a l k a l i n e chemicals. How Can These C h a r a c t e r i s t i c s of Treatments Be Measured? Treated papers should maintain at a pH i n the range 7 and 8.5. The pH should not be higher than 8.5 to prevent a l k a l i n e hydrolysis of cellulose. The a c i d i t y or a l k a l i n i t y may be determined as the amount of water-soluble a c i d i t y or as the hydrogen ion concentration (pH) of the paper extract. The pH i s more i n d i c a t i v e of the s t a b i l i t y of paper than i s the t o t a l a c i d i t y . The pH can be determined by either a hot or cold extraction method. In the cold extraction method, 1 gram of paper i s macerated with a s t i r r i n g rod i n 20 ml of d i s t i l l e d water at 20 to 30°C. Then 50 ml more water i s added and the sample i s l e f t for 1 h r , after which the pH of the solution i s determined. For the hot extraction method, the paper i s digested at 95 to 100 C under reflux for 1 h r . The surface pH of paper can also be measured by using s p e c i a l pH electrodes. Litmus paper and universal pH solution can be used but w i l l not give accurate readings. The amount of a l k a l i n e reserve retained i n the f i b e r should be in the amount of 2 to 3% of the paper weight, and should be determined accurately by using c l a s s i c a l t i t r a t i o n methods or by atomic absorption. The d i s t r i b u t i o n of a l k a l i n e chemicals should be examined by using a scanning electron microscope (SEM) coupled with an energy dispersive X-ray analyzer (EDXA) f a c i l i t y . The cross-section of treated papers should be examined by using SEM to confirm the deposition of a l k a l i n e reserve i n the center of the papers. The mechanical and physical properties before and after d e a c i d i f i c a t i o n of the papers should be examined for t h e i r t e n s i l e and tear strengths and f o l d endurance. The color should be measured by using a colorimeter or a reflectance spectrophotometer. The chemical nature of paper should be examined i n terms of molecular weight d i s t r i b u t i o n , carbonyl, carboxyl and aldehyde groups and the t o t a l acid content. The effectiveness of the d e a c i d i f i c a t i o n should be evaluated by studying the aging c h a r a c t e r i s t i c s of treated papers by using standard accelerated aging t e s t s . C r i t e r i a for Mass D e a c i d i f i c a t i o n An i d e a l mass deacidfication process should preserve book papers i n a usable condition. For best r e s u l t s , any mass d e a c i d i f i c a t i o n developed must meet the following c r i t e r i a : 1. No preselection or sorting of books. 2. Should apply to most i f not a l l types of paper ( f i b e r ) . 3. No transfer of color bodies or s o l i d s between books.


2. HON 4. 5. 6. 7. 8.


9. 10. 11.

12.

13.

14.


25

Chemicals used should be safe for personnel at the treatment site. The treatment should not leave an odor i n the books. The treated books should be non-toxic to humans. The treatment should have no deleterious changes i n appearance, f e e l , or p h y s i c a l i n t e g r i t y of the books. The treatment should not influence the properties of binding adhesives, leather and p l a s t i c i z e d covers. Chemicals discharged should not create environmental p o l l u t i o n problems. Should achieve complete d e a c i d i f i c a t i o n i n a reasonable length of time. Should uniformly neutralize and uniformly deposit a l k a l i n e reserve. The a l k a l i n e reserve should be two to three percent i n concentration for maximum permanence. The paper must be buffered at a pH of 7 to 8.5 for minimal effect on a c i d / a l k a l i hydrolysis of paper and on inks and colors. The expected l i f e of the paper should be s i g n i f i c a n t l y improved. A minimum of a five time increase i n accelerated aging l i f e t i m e must be achieved. The treatment should be economically feasible for treating large quantity of books, i . e . , > 50,000 volumes/year.

Evaluation of Different Mass D e a c i d i f i c a t i o n Processes Although many mass deacidifications have been developed, i t can be stated that none of the technologies offered meets a l l the c r i t e r i a . Nevertheless, the DEZ process, Wei T O process, Kopper Process and VPD have demonstrated independently t h e i r p o t e n t i a l for arresting paper deterioration from a c i d . To what extent these processes meet the c r i t e r i a to be used for a p r a c t i c a l mass d e a c i d i f i c a t i o n process i s the question that has to be answered. Accordingly, a comparison of the c h a r a c t e r i s t i c features of these processes i s tabulated i n Table I . The evaluation i s based on t h e i r neutralization chemistry and effectiveness. The engineering design, safety and costs of these processes are not considered i n t h i s evaluation. DEZ Process. DEZ process has been developed and refined by chemists at the Library of Congress since 1974. It i s a very impressive method of deacidifying book papers e f f e c t i v e l y and uniformly. There i s no doubt that the d e a c i d i f i c a t i o n chemistry i s workable. As shown i n Table I , the DEZ process i s the process that met most of the "ideal" c r i t e r i a . In essence, the DEZ process uniformly and consistently neutralizes a l l excess acid i n the paper, leaves a uniformly d i s t r i b u t e d a l k a l i n e reserve i n a l l regions of the book page and the paper f i b e r . Unfortunately, d i e t h y l zinc i s not a chemical with great " s t a b i l i t y " to work with. Because of i t s pyrophoric properties, DEZ must be handled with great caution and subsequently cannot be operated within l i b r a r i e s . This w i l l l i m i t p o t e n t i a l l i b r a r y users. The end-product of d e a c i d i f i c a t i o n i s the conversion of s u l f u r i c acid i n paper to zinc sulfate. Just l i k e aluminum s u l f a t e , zinc sulfate i s prone to dissociate into acid i n the presence of water or



1

a

No Yes Long Complex None No Complete 7.0-7.5 1.5-2.0% Risk of f i r e Low Operating p i l o t plant (2 mo.) ^ Moderate to high

DEZ

e

f

9

Yes Yes Short Less complex Some Yes Needs v e r i f i c a t i o n 8.5-9.5® 0.7-0.8% Uncertain Uncertain Operating p i l o t plant (7 years)^ Low to moderate

Wei T O

e

9

Minimal^ None Short Simple ^ Minimal^ Minimal Needs v e r i f i c a t i o n 8.0-9.0® 2% Uncertain Uncertain Lab tested p i l g t design Low

Bookkeeper^

As of January 1988

C

Low

n

Yes None Very long Very simple Some Yes Partial 5.0-8.7 None Uncertain Low Commercial

VPD

H

^Library of Congress DEZ process. "Bookkeeper" submicron p a r t i c l e process. Langwell vapor phase d e a c i d i f i c a t i o n process—distributed by I n t e r l e a f , Inc. Based on telephone conservation with Dr. J . J . Kozak of Koppers (Nov. 2, 1987). No independent assessment. No formal independent analyses have been made. Manufacturer's data indicates complete n e u t r a l i z a t i o n under ^laboratory conditions. I n i t i a l indications are good but no formal assessments have been made, rjsome concern about the future regulation of fluorocarbons used i n these processes. Based on OTA analysis and extrapolation of l i m i t e d cost data furnished by developer of each system.

————

No None Short Simple None No Complete 7.0-8.5 About 2% None None

Preselection of books Predrying Impregnation time Treatment plant Effect on inks and colors Effect on p l a s t i c covers Neutralization pH of treated paper Alkaline reserve Danger to health Impact on environment Stage of development

Cost

Ideal

Comparison of A l t e r n a t i v e Mass D e a c i d i f i c a t i o n Processes,

Criteria

Table I .



2. HON


27

moisture (55). This act i s undesirable. The fate of zinc sulfate and the regeneration of acid i n paper, unfortunately, has not been considered by the Library of Congress. The reaction of d i e t h y l zinc with water produces zinc oxide, and then zinc carbonate, as the a l k a l i n e reserve. These chemicals have antiseptic properties which may also prevent the growth of mold i n paper. They may also improve the brightness of treated papers. However, i t i s also known that zine oxide i s a photosensitizer (56) which may trigger photo-oxidation of treated papers to i n i t i a t e a chemical chain reaction that w i l l lead eventually to the formation of a c i d i c products (57). Moreover, the interaction of zinc oxide and zinc carbonate with copper, iron and cobalt present i n the paper and t h e i r subsequent effects on paper s t a b i l i t y have not been studied. Wei T'o Process. Wei T'o process i s the only mass d e a c i d i f i c a t i o n process currently available commercially. The " l i q u i d gas" d e a c i d i f i c a t i o n solution of t h i s process consists of methoxy magnesium methyl carbonate dissolved i n a mixture of Freon and methyl a l c o h o l . The process has been proven by six years of production operation at the National Library and Public Archives of Canada. It u t i l i z e s a less complex system than the DEZ process to achieve d e a c i d i f i c a t i o n . National Library and Public Archives of Canada are s a t i s f i e d with the deacidification results. Nevertheless, as a mass d e a c i d i f i c a t i o n process, i t does have some l i m i t a t i o n s . The process requires a manual, item-by-item preselection procedure to remove books with p l a s t i c i z e d covers, and books printed with unstable inks, to avoid color and ink transfer problems. Books with colored i l l u s t r a t i o n (using unstable inks) can also cause problems. Testing has shown that some p l a s t i c s used on modern paperback books react adversely. The f i n i s h might crack and flake. Examination of randomly selected books treated with the Wei T O solution has shown nonuniform d e a c i d i f i c a t i o n . Although the deacidifying agent does not harm leather, leather bound books are not recommend for the treatment. It i s anticipated that during pre-drying process, leather can be i r r e v e r s i b l y damaged. The other concern with the Wei T O process i s i t s use of Freon (chlorofluorocarbons). It i s known that Freon vapor escaping to the atmosphere w i l l lead to the depletion of the ozone layer i n the stratosphere. Although the process i s operated i n a closed system, immediately after d e a c i d i f i c a t i o n , books are stacked i n shelves for drying. The escape of Freon to the atmosphere can be s i g n i f i c a n t . Wei T'o Associates announced that i t has improved i t s nonaqueous d e a c i d i f i c a t i o n solution to eliminate the ink i n s t a b i l i t y problems, p a r t i c u l a r l y i n the graphic a r t s . The new formulation avoids the use of an alcohol co-solvent and the higher a l k a l i n i t y of magnesium that may cause color changes or smudging on sensitive inks. Other solvents may replace chlorofluorocarbon solvents. This new formulation seems to solve a l l the problems that the Wei T'o process has. However, the refusal of Dr. Smith of Wei T'o to discuss or define i t s technology prevents us from evaluating i t s improved system. Hence, the improved system was not included i n t h i s evaluation, as Dr. Smith s a i d , "If there i s no d e f i n i t i v e information about the idea or product, no consideration should be given i t " (36).



28


Koppers "Book Keeping" Process. In view of the l i m i t a t i o n of the Wei T'o process, chemists at the Koppers Company developed a "Book Keeper" process by dispersing submicron p a r t i c l e s of basic metal oxides, hydroxides or s a l t s of calcium, magnesium, or z i n c , i n a suitable gas such as Freon or l i q u i d medium, so that the active chemicals can be transferred and deposited e l e c t r o s t a t i c a l l y on the surface of paper. It also does not require pre-drying of books as i s required for both the DEZ and Wei T'o processes. The testing r e s u l t s appear satisfactory as shown i n Table I . The major concern with t h i s process i s the d i s t r i b u t i o n of the a l k a l i n e reserve on the paper. It appears the process deposits a l k a l i n e chemicals on the surface of paper and achieves surface d e a c i d i f i c a t i o n . However, acid formed i n the core of the paper i s not neutralized. Koppers intends to prove the degrees of chemical penetration and n e u t r a l i z a t i o n of acid i n the center layers by examination of the cross-section of paper by SEM. No reports have been released yet. The effects of the chemical process on paper, covers and inks have not been published. The Koppers process appears to be a unique one with great p o t e n t i a l for mass d e a c i d i f i c a t i o n with success. More testings are required. As with the Wei T'o process, the effect of Freon on the ozone layer of the stratosphere i s a concern. Langwell Vapor Phase D e a c i d i f i c a t i o n Process. Langwell"s VPD process i s a very simple process. Cyclohexylamine carbonate i s inserted between book pages to achieve p a r t i a l d e a c i d i f i c a t i o n . However, t h i s process does not create an a l k a l i n e reserve i n treated products to prevent future acid attack. Cyclohexylamine carbonate w i l l react with some p l a s t i c covers, inks and c o l o r s . Preselection of books i s required. The odor and the carcinogenic nature of the vapor are also c r i t i c a l factors that l i m i t the use of VPD process as a mass d e a c i d i f i c a t i o n process (46-54). To conclude, i t i s c l e a r l y evident that none of the mass d e a c i d i f i c a t i o n processes just discussed meet the "ideal" c r i t e r i a set forth i n Table I . Without consideration of cost effectiveness and safety of operation, the Library of Congress" DEZ process seems to be the winner. However, as a mass d e a c i d i f i c a t i o n process the Koppers "Book Keeping" process may have more p o t e n t i a l due to i t s straightforward and danger-free operation. Moreover, recently Book Preservation Associates and Lithco have announced new mass d e a c i d i f i c a t i o n methods. These processes should be considered i f data are a v a i l a b l e . Integrated Complete Book Preservation Program A l l of the d e a c i d i f i c a t i o n techniques discussed above w i l l remove acid and provide a deposition of a l k a l i n e reserve to protect further acid attack. Although these methods undoubtedly work, from least to most e f f e c t i v e , they do not attempt to improve or restore the mechanical properties of the paper treated. Hence, mass d e a c i d i f i cation i s only a part of a complete mass preservation program that i s needed by l i b r a r i e s and archives i n order to extend the l i f e t i m e and u s a b i l i t y of t h e i r holdings. Although d e a c i d i f i c a t i o n of paper i s a very important step i n order to i n h i b i t further d e t e r i o r a t i o n , restrengthening of embrittled stocks i s necessary as well as protection against detrimental oxidizing and b i o l o g i c a l attacks.



2. HON


29

Accordingly, a complete book preservation program should consider (a) complete d e a c i d i f i c a t i o n ; (b) improving f o l d endurance, tear and t e n s i l e strength of paper; and (c) i n h i b i t i n g oxidation. The strengthening of paper can be done by deposition of polymers onto fibers or by grafting polymers onto f i b e r s . Smith has mentioned b r i e f l y i n many of his papers impregnating the paper i n books with a c r y l i c r e s i n and ethyl hydroxy1-ethyl c e l l u l o s e solution to increase f o l d endurance (no actual publications have been seen). Salz and Skrivanek have used p o l y v i n y l butyrate for the same purpose. Sodium s a l t of carboxymethylcellulose (CMC) has been used by Raff and his co-workers (58). The Austrian National Library uses methylcellulose of low v i s c o s i t y as the strengthening agent together with calcium hydroxide as the neutralizing agent (59-61). The B r i t i s h Library has grafted ethyl acrylate and methyl methacrylate onto book paper by g a m m a - i r r a d i â t i o n (62). V i n y l monomers have been used at Clemson University with a heat- and light-induced graft copolymerization techniques to strengthening paper documents (63). Antioxidants and photostabilizers may need to be added to treated books to avoid future acid generation i n book papers. Accordingly, without complete deacidifying and strengthening, a book conservation program should not be considered complete. Recommendations Based on the information available today on the DEZ process, Wei T'o process, Koppers process, and VPD process, i t i s very d i f f i c u l t to judge which process i s the best suited to a mass d e a c i d i f i c a t i o n process. In addition to the l i m i t a t i o n s of each process which has been discussed, data are lacking to support long-term effects on treated papers. In order to select a v i a b l e mass d e a c i d i f i c a t i o n process, the following parameters have to be considered: 1.

The effects of the reagents on the chemical properties of the paper components, such as c e l l u l o s e , hemicelluloses, and l i g n i n are not known. For example, the change i n degree of polymerizat i o n , i . e . , the chain length of c e l l u l o s e polymer before and after treatments. The changes i n functional groups, such as carbonyl, carboxyl, and conjugated double bonds i n c e l l u l o s e and l i g n i n have not been considered, despite t h e i r importance on acid formation and d i s c o l o r a t i o n reactions. 2. The o p t i c a l properties of treated papers have to be studied. A colorimeter or reflectance spectrophotometer can be employed to examine the change i n o p t i c a l and color c h a r a c t e r i s t i c s before and after treatments. 3. The mechanical properties have not been reported conclusively. Most of the available data provided was based on f o l d endurance testing. Although i t i s an important property that should be determined, studies of t e n s i l e , tear and burst strengths are important as w e l l . 4. The o x i d i z a b i l i t y of treated papers due to heat, l i g h t and a i r pollutants need to be evaluated. A l l these important parameters must be established for treated papers so that a meaningful evaluation can be made. Before making any decision on selecting an e f f e c t i v e mass d e a c i d i f i c a t i o n process,


30



a comprehensive t e s t i n g , which i s based on the above-mentioned parameters, of the treated books from the DEZ process, Wei T'o process, Koppers process, and VPD process must be made by an independent group which i s not associated with any of the developers of the d e a c i d i f i c a t i o n process. In addition to the d e a c i d i f i c a t i o n chemistry, the f i n a l decision should also be based on the evaluation of the engineering design, safety of operation and cost factors which have not been considered i n t h i s paper. Acknowledgment This project was funded by the U.S. Congress, Office of Technology Assessment (OTC). This support i s g r a t e f u l l y acknowledged.

Literature Cited 1. 2. 3. 4.

5. 6. 7. 8. 9. 10.

11. 12. 13. 14.

15.

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33

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Critical Evaluation of Mass Deacidification Processes for Book

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