Chemistry in the Comics Part 4. The Preservation and Deacidification of Comic Books Henry A. Carter Camrose Lutheran College, Camrose. AB, Canada, T4V 2R3 The acid-catalvzed hvdrolvtic demadation of cellulose, as discussed in p a r t 3 of th& series, is l&gely responsible for the aeina and deterioration of pulp paper .. . found in comic books &d library collections. other interrelated factors such as heat, liaht, relative humidity, atmospheric oxidation, and of metallic ration impurities can contribute the both to the degradation of cellulose fibers and to an increase in the overall icidity of paper. Comic books manufactured from high-yield pulp paper contain laree amounts of lienin and other i m ~ u r i t i eand, s ~ as such,ares~scept~hle toenhaoced deterioratlbn. Considering the rauid erowth of comic book collrcting as a hohbv over the i t isnot surprising thatthecomic bookindustry last 1i is now offering a variety of preservation materials such as acid-free storage hags and boxes, nonaqueous sprays and solutions for deacidification, pH indicator test strips, and other miscellaneous archival supplies. These same products are also being made available to libraries for the conservation of historic documents, maps, and rare books. This paper will examine the recommended procedures for the storage of comic hooks from a chemical viewpoint and will also discuss a number of methods for deacidification. The Storage of Comic Books In 1976, a large collection of approximately 22,000 old comic books, dating between the years 1937 and 1952, was discovered in Denver ( I , 2). Surprisingly, these comic books all contained snow-white pages and appeared to be virtually unchanged by time. In fact, these hooks had the appearance of having just been printed and placed on the newsstands. This valuable group of comics became known as the Mile High collection and later the Edgar Church collection. Today, these books command very high premiums with many selling at over three times the normal market value.
Figwe 1. The effect of different storage conditions on a group of old Classics lllu~rraredcomics. From top to Donam: (a) Classlcs Iflustrated No. 39,July 1947; (b) Classics IllushatedNo. 38. June 1947; (c)Classics itlushatedNo. 61. July 1949: (dl Classics llfustrated No. 19, April 1944 (@ 1944. 1947, 1949 Giiberlon Company).
Nearly ideal storage conditions were responsible for the outstanding condition of the Mile High collection. Certainly, the low relative humidity and higb altitude of the Denver area were significant factors. In addition, the books had heen carefully selected from the newsstands and then immediately stored in a cedar closet where they remained under cool conditions for many years. The DroDer . . storaee of comic hooks can dramaticallv slow down thechemical reactions that lead to their deterioration. A number of old comic books are shown in Fiaure 1. As can be seen, the condition of these comic book; varies quite markedly. The comic hooks in Figures l a and l c show signs of advanced deterioration as is evident from severe browning of the inside covers and brittleness a t the spines. On the other hand, the comic books in Figures l h and i d appear with relatively white pages and inside covers. Interestingly enough, the comic hook in Figure i d which appears to he least affected by the ravages of time is also the oldest of the group. It seems reasonable to assume that the differences in the apparent deterioration of these books lies in the history of their storage conditions. One could, of course, suggest that the conditions of acidity might have been different during the manufacture of these four books. However, many copies of the books shown in Figures l a and l c containing relatively white pages do exist (3).In fact, Figure 2 shows two copies of "The Woman in White", CfassicsIlLuslstratedNo. 61 (1949). The relative conditions of these two comic books can he attributed to different circumstances of storage. On the basis of the factors that are responsible for the agingof comic hooks and the deterioration of books in general as described in Part 3 of this miniseries, a number of recommendations can be made for the proper storage of books as follows:
Figure 2. A comparison of two copies of "The Woman in White" (Classics IllustratedNo 61).The book at the top is brown and brittle. while the book at the bonam is relatively white withsupple pages (@ 1949Gilberton Company).
Volume 67 Number 1 January 1990
3
1. Books should be stored in a relatiuely cool place to slow down the acid-catalyzed hydrolysis of cellulose and to minimize the effect of atmospheric oxygen on the deterioration of paper. In Part 3 of this miniseries, it was shown that the reported activation energies for the deterioration of paper tend to vary from about 25 to 30 Kcallmol (105-126 KJImol) depending on the nature of the accelerated aging test and the paper. The logarithmic form of the Arrhenius equation suggests that the rate of deterioration of paper increases by a factor of a~oroximatelvP 5 for a corresnondina increase in temperat& from 20 t i 30 OC. A temperature flktuation of 10 OC or more is easily exoerienced by most non-air-conditioned libraries, especialli during the-summers in northern climates. For protection against large increases in temperature, rare library hooks should he stored in the lower levels, preferably in air-conditioned rooms. At the same time, comic books should be kept in cooler parts of the houses and not stored in hot attics. While not highly practical, it has been suggested that the best way to preserve a book is to wrap it in plastic and place it in a deep freeze a t -20 to -30 OF (4). In fact. a book frozen in the Antarctic for several years was found to be much better preserved than other existing copies of the same book that had been stored a t ambient temperatures (5). 2. Books should be stored in dark areas not exposed to natural sunlight or artificial sources of ultraviolet radiation. It was pointed out in Part 3 of this series that modern paper tends to discolor when exposed to natural sunliaht as a ; e k t of photoinduced chemical reactions. ~onc&tant with thisdiscolorment is a lowerina in thedegreeof polymerization of the cellulose chains andsubsequent deterioration of the paper. The contribution of various components in pulp paper toward its discoloration and degradation continues to be a subject of seriousstudy (6,7).The effect of light is expected to be particularly severe for comic books that contain large amounts of light-sensitive lignin. Nevertheless, the author has occasionally observed valuable comic books being showcased in store windows while exposed to sunlight and the accompanying heating effects.
3. Books should be protected from atmospheric oxygen by storage in polyester sleeues. Comic books, which are easily torn or damaged by improper handling, are generally stored in bags. This offers protection not only from dust and pollutants but also limits the permeation of atmospheric oxygen into paper. The effect of oxygen in contributing to the deterioration of paper is also enhanced by sunlight, elevated temperatures, metallic cation impurities, and the presence of lignin. Polyethylene, polypropylene, poly(vinyl chloride), and other types of plastic hags are commonly used for the storage of comic books. However, many plastic bags contain chemical additives and plasticizers, such as bis(2-ethyl hexyl) which can ca"secomic phthalate for poly(;inylchloride) (8), bonks to discolor and deteriorate slowly. In addition, plastic hags tend to lose their clarity with time and turn yellow and sticky. As a result, poly(ethylene terephthalate) is often used for the storage of comic books and archival documents. Marketed under the trade name of Mylar (9), poly(ethy1ene terephthalate) is a stable and relatively inert polyester film. Mylar is virtually impermeable to oxygen, moisture, and also to acidic pollutants such as sulfur dioxide (10). 4. Books should be stored under dry conditions. Hieh relative humidities. which tend to increase sienificant& the rate of the acid-datalyzed hydrolysis of cell;lose, should be avoided. A relative humidity of 5090has often been recommended, but paper permanence would probably be improved by much lower relative humidities (10.11). 4
Journal of Chemical Education
5. Books should be stored in acid-free containers. I t has been suggested that storage in cardboard boxes has been one of the leading causes of premature deterioration of comic books and other pulp paper products (12). The acidity of cardboard that is generated during itsmanufacture can be transferred to less acidic paper products over a period of time. Thus, acid-free boxes are recommended for storage. These boxes should have a pH ranging from 8.0 to 10.3 and contain an alkaline buffering agent. The Deacldiflcatlon ot Comlc Books While proper storage methods will certainly increase the lifetimes of comic book and library collections, the problem of acidity in paper remains. However, accelerated aging tests, generally performed in the range of 60-120 "C, indicate that the use of deacidification agents can dramatically slow down the aging of cellulosic materials (13,14). Since the late 19th century, various methods have been developed to reduce the amount of acidity present in cellulose fibers. Present deacidification treatmenta for paper stem from research primarily done since 1960. The comic book industry has kept pace with these developments, and articles on deacidification have appeared frequently in The Comic Book Price Guide. Vapw Phase Deacidification A method for the deacidification of comic books first appeared in the 1975 edition of The Comic Book Price Guide (15). This method simply consisted of exposing the books to gaseous ammonia produced from crystals of ammonium carbonate. At room temperature, ammonium carbonate dissociates as follows:
(NH,),CO,
=NH,HCO, + NH,
(1)
, Thus, it was suggested that the acidity of 3 0 4 0 comic hooks could be neutralized within 4 days when placed in a closed box containing several grams of ammonium carbonate. ~nfortunatkly,this method does not yield permanent results. This is not surprising since the titration of a weak hase (ammonia) and a strong k i d (such as sulfuric acid arising from the sizing process) will produce a pH of approximately 5. Thus, once the residual ammonia dissipates from the paper, the pH begins to drop below 7. I t has also been observed by the author that ammonia fumes can cause mild browning of old comic books. Nevertheless, while this method is hardly satisfactory, it does represent asimple introduction to the technique of vapor phase deacidification (VPD) (16-18). Improved methods of VPD appeared in subsequent editions of The Comic Book Price Guide. The 1977 edition discusses the use of both cyclohexylamine carbonate (CHC) and morpholine as substitutes for ammonium carbonate in VPD (19). While cyclohexylamine carbonate, C ~ H ~ N H ~ + C ~ H I ~ NHC02-, is acidic, it dissociates a t room temperature to produce basic cyclohexylamine as follows: C6H,,NH,+C6H,,NHC02-+ 2C6H,,NH2+ COZ
(2)
Cyclohexylamine (pKb = 3.4) is more basic than ammonia 120). . ..but is still a relativelv weak base that is not exnected to produce permanent deacidification. Furthermore, there is some concern as to the toxicity of cyclohexylamine (21). Again, like ammonia, cyclohexylamine can cause some discoloration (22). The deacidification of hooks by impregnation with a mixture of morpholine and water vapor has previously been described (23). Morpholine (pKb = 5.67) dissociates in water as follows (24):
Accelerated aging tests a t 100 "C for 8 days indicate that the life expectancy of paper treated with morpholine is increased by a factor of 3.5. The treated paper also shows significant resistance t o aging from moist air containing 5 ppm sulfur dioxide. However, there have been instances of ground wood papers (such as comic books) showing visible yellowing following treatment with morpholine (19, 23). In addition, the degree of permanence of deacidification is based mainly on the absorption and retention of morpholine by cellulose. I t is generally recommended that deacidified paper should retain an "alkaline reserve" as a buffer against any future exposure to acid attack. One such agent that meets this condition is diethyl zinc, and its use in VPD will now he discussed.
-
(C,HS),Zn + 702
The use of diethyl zinc (DEZ) in vapor phase deacidification has received a great deal of attention compared to other VPD methods. In fact, the DEZ method is currently being investigated and developed by the world's largest library, the Library of Congress (25-33). The DEZ method essentiallv consists of three stens. The first step involves drying thebooks in an autoclave under vacuum until the moisture is reduced to about 0.5% of the initial weight of the paper. Next, the books are treated with easeous diethvl zinc, which reacts as follows with the acids in ihe paper (simply represented here as Hf):
-
(C,HS),Zn + 2Ht Zn2++ 2C2H6 (4) At the same time, diethyl zinc reacts with residual moisture in the paper to form zinc oxide as follows: (C,H,),Zn
+ H,O
ZnO + 2C2H,
(5)
The zinc oxide, present in the paper to the extent of I S % (in addition to the zinc salts of the acids that were originally present in the paper), acts as an alkaline buffer against any further acidity that might be generated in the paper. Finally, the excess diethyf zinc and ethane are removed, and the books are allowed to rehumidify by injecting water into the chamber. It has been previously reported that diethyl zinc might react with hydroxyl groups present in cellulose to form ethylzincoxycelluIose groups, CzHsZnO-R (34). Hydrolysis of these C2H5ZnO-R groups on rehumidification would yield zinc oxide. However, recent investigations indicate that there is no observable reaction between cellulose and diethyl zinc under process conditions, and that the reaction between diethyl zinc and residual moisture (0.345%) in the paper is responsible for the deposition of zinc oxide as seen in eq 5 (33,351. While zinc oxide provides an excellent alkaline reserve against further acid attack in paper, there is evidence to show that zinc oxide in the presence of water vapor can enhance the UV ohotodeeradation of cellulose (36). Thus, attempts have been made to modify the DEZ method by convertine zinc oxide to zinc carbonate by the addition of carbon dGxide during the third step (34).However, recent tests have indicated that only very small amounts of zinc carbonate form under process conditions and that the zinc oxide remains essentially unaltered (33). Since the exposure of books to UV light is generally minimal under proper storage conditions, the DEZ method will continue toemploy zinc oxide as an alkaline reserve (32). Incontrast tn the tinal products that are uniformly depoaited throuehout the treated books (viz. ZnO and zinc snlts), the starting material, diethyl zinc, is very reactive and must be handled with a areat deal of care. Liquid diethyl zinc reacts violently with water according t o e q 5, producing combustible ethane zas, which can ignite from the heat of the reaction. Furthermore, liquid diethyl zinc is pyrophoric, ignitina on contact with air to form clouds of zinc oxide as
(6)
I t should be noted that gaseous diethyl zinc a t the low pressure of 20 Torr used in the DEZ method is easier to handle and is not pyrophoric (33,351. Unfortunately, two accidents involving the inadvertent mixing of diethyl zinc with water (or brine in the second accident) occurred (on December 5,1985, and Februarv 14, 1986) a t a pilot DEZ plant located at the Goddard $ace Flight Center in Maryland ( 2 5 , 3 7 4 ) . While the first accidegt produced a fire that was quickly brought under control, an explosion occurred in the second mishap that created a major difficulty in removing the residual diethyl zinc from the process piping. Subsequently, the DEZ pilot plant was demolished with ex~losivesbv an armv demolition team. Despite this initial serbark, experimentation is nowproreedine smoothlv at the new . d o t -olant run hv Texas Alkvls in (2,: 33). Data from the Library of Congress Preservation Research andTesting Office indicate that the DEZ method produces a consistent neutralization of excess acidity in paper, leaves a uniformly distributed alkaline reserve, doeshot cause discoloration, has no resulting toxicological effects, and increases the life expectancy of all types of paper by a factor of 3-5 (32). In addition, the DEZ method has the potential to be applied on a large scale (by the Library of Congress possibly in 1991) so that 1.5 million volumes can he deacidified per year (35). If the facilities could be made available, the DEZ method could probably be used successfully in the deacidification of comic hooks. The zinc oxide used as an alkaline reserve results in a favorable nH ranee of the treated naner between 7.2 and 7.3 (32). ~ x c e i l e nresults t have been obtsned by the Libram of Conaress in the DEZ treatment of "dime novels" and other ground wood pulp papers (35). ~~~
Diethyl Zinc
ZnO + 4C02+ 5H,O
.
~
ousto on
The Wei T'o Process
An alternative to the use of vaoor nhase deacidification for comic books first appeared in t i e l&32 edition of The Comic Book Price Guide (40). This nonaqueous method, developed by Wei T'o Associates, involves the use of methoxy magnesium methvl carbonate (MMMC) dissolved in methanol, Freon 12, a i d Freon 113. Presently, the Wei T'o process is being used for mass deacidification by a numher of libraries including the National Library and Public Archives in Canada (33). Similar processes based on MMMC are employed by the British Library and the Bibliothsque Nationale in France. As a mass deacidification svstem (4144). the Wei T o process basically consists of th;ee step$. First; the books are vacuum dried for approximately 36 h. Next, the books are impregnated for 50 min with a solution of MMMC dissolved in methanol, Freon 12 (dichlorodifluoromethane), and Freon 113 (trichlorotrifluoroethane), under pressure in a processina tank. Finallv, the liquefied eas solvents are removed from the books under vacu"m andrecycled for further use. The books then rehumidify on standing open to the air. Wei T'o solutions and sprays are also available for small scale applications, and these have been successfully used for the deacidification of comic books (45,46). The deacidification agent in the Wei T'o system, methoxy magnesium methyl carbonate, is prepared by the reaction of magnesium methoxide with carbon dioxide (47.48). Magnesium methoxide is first prepared by the reaction of dry methanol with magnesium: 2CH,OH
+ Mg
-
Mg(OCH,),
+ H2
(7)
The resulting slurry of magnesium methoxide is then saturated with carbon dioxide resultina- in the formation of MMMC as follows: Mg(OCH,),
+ CO, +CH,OMgOC(O)OCH,
Volume 67
Number 1 January 1990
(8)
5
Unless higher pressures of carbon dioxide are used, the compound Mg(OC(O)OCH3)2does not form, although MMMC is probably best represented by the formula, CH30MgOC(0)OCHrxC02 where x may vary with solvent and temperature (47,48). MMMC is much more stable toward water than magnesium methoxide, the original nonaqueous deacidification agent proposed by Smith (13). During the Wei T'o process, MMMC is deposited on the paper of the books. On exposure to air, MMMC reacts with moisture t o form a mixture of magnesium oxide, magnesium hydroxide, and magnesium carbonate as according to the following reactions:
+ H,O CH,OMgOC(O)OCH, + 2H20 CH,OMgOC(O)OCH,
CH,OMgOC(O)OCH,
+ H,O
-
MgO + C02 + 2CH30H Mg(OH),
(9)
+ CO, + 2CH,OH (10)
MgCO,
+ 2CH30H
(11)
The magnesium oxide, hydroxide, or carbonate can then neutralize acids in the paper to form Mg2+salts. At the same time, a number of basic magnesium carbonates, such as MgCOrMg(OH)23HzO can form. These basic carbonates provide an alkaline reserve of 0.7-0.8% and a pH of book paper ranging from 8.5 to 9.5 (33). There is also considerable evidence to indicate that the presence of magnesium salts provides added protection against oxidative degradation of cellulose (49-52). While excellent results have been reported for the treatment of comic hooks by the Wei T'o process, slight yellowing can occur for comic hooks as well as other ground w w d pulp paper products containing lignin (33). Sometimes, smudging of sensitive inks can result and the paper sizing can be affected. While the interior pages of comic books can be relatively easily treated by the Wei T'o method, the covers are more difficult and sometimes have to be resized (46). Currently, new solvents are being sought to eliminate problems associated with alcohol-soluble inks and to replace chlorofluorocarbons that are potentially dangerous to the ozone layer (33,53,54). Conclusions
The deterioration of hook paper as a result of acid attack is a serious problem that cannot be ignored. This problem is even more acute for comic bwks, newsprint, and other mound wood ouln e~ . . Daners . . that contain larae - amounts of lignin. The storage procedures recommended in this paper can certainlv retard the rateof acid-catalwed hydrolysis and oxidative digradation of cellulose. In addition, ai;-conditionine. oroducina a cooler and drier environment, is recommendLd'for libraries and for comic colkctions. While proper storage conditions can slow down acid degradation; deacidification can stop acid attack and prevent future problems with acidity arising from environmental pollutants such as sulfur dioxide. A number of deacidification methods have been proposed in the past, and, undoubtedly, new methods will be developed in the future. Meanwhile, the DEZ and Wei T'o methods, both of which offer an alkaline reserve.. are oresentlv beina used or developed for . mass deacidification in our n&ions'iihraries. only the Wei T'o nrocess is currently available for comic book collections and small-scale operations. The results that have been obtained for both methods are very encouraging. I t should be emphasized that i t is not thermodynamically possible to reverse the acid hydrolysis and oxidative deterioration of cellulose fibers. Thus, steps should be taken toward the preservation and deacidification of books long before browning and brittleness occur. At the same time, studies have shown that deteriorated or brittle books can be strengthened by gas phase treatment with p-xylylene (or parylene) polymers (55). This process essentially involves ~
ow ever,
6
Journal of Chemical Education
the deoosition and subsequent polymerization of monomeric pxilylene onto book paper. This formation of the poly@xylylene) coating does not involve a chemical reaction with c~liuloseor anyother component of paper. The parylene polymer simply surrounds and strengthens the cellulose chains and "welds" the paper fibers together. While the parylene process has the disadvantage of being irreversible, i t mav have meat ootential in strenethenine rare books and documents &at have become brittle. A few comments should be made about the possibility of "whitening" old and discolored pages of comic books. In Part 3 of this series, it was suggested that the main cause of the discoloration or yellowing of paper was due to the formation of aldehyde groups on the anhydroglucose units of cellu. . lose. For hi&yield pulps such as comic books, however, discoloration can also occur by the oxidation of the phenolic hvdroxvl erouns of lienin to colored auinonoid oroducts " " (56). Thus, if one could reduce the carbonyl groups on cellulose and lienin to the corres~ondinaalcohols. then i t should be possibl;! to brighten agLd pap& In this regard, some success has been obtained by the treatment of old papers with sodium horohydride (57, 58). While carboxylic acid groups are unaffected by NaBH4, the carbonyl groups are reduced to hydroxyl groups with improved brightness. In addition, the removal of carbonyl groups, which enhance the autooxidation of cellulose, greatly increases the stability of paper. The use of oxidizing agents to bleach discolored paper should be approached with some caution as oxidative degradation of cellulose mav also result. In anv case. while the appearance of paper I&be improved, i t s a g h i d u e to the deoolvmerization of cellulose fibers cannot be reversed. the use of alkaline paper in new books might be the lona-term solution to the problem of acid deterioration of hook;. A number of sizing &aterials exist that can he used together with calcium carhonate as a filler in the manufacture of alkaline paper (32). Unfortunately, the switch to alkaline paper in paper manufacturing is not likely to take place very quickly 4 the market for &id-free paper is not particularly strong. While the demand for alkaline paper has come maidv fro&the libraries. the amount of oaner used in library boois constitutes less than 0.3% of thk total paper production in the United States (32). ~d~~
~
.
-
Acknowledgment The nhotoeraohs that anoear in this oaoer were used with , current the kind pe;mksion of rawl ley ~ o r p o r i t i o n the owner of the co~vrights .. - to Classics Illustrated. Thanks are due to the following people for their advice and helpful discussions: Susan Cicconi (The Restoration Lab), Jef Hinds (Comic Conservation Lab), Georgina Lewis (U. of Alberta), Dan Malan (Malan Classical Enterprises), Richard Smith (Wei T'o Associates), Peter Sparks (Library of Congress), and Joe Vereneault (Sparkle City Comics). Finally, the author is indebted to Lynn J. Carter for encouragement and helpful suggestions during the writing of this miniseries. Llterature Clted 1. Overatrpet. R.M.The Comic Book Prim Guide. 12th ed.: Overstreet: Cleveland.. TN.. 1982:p A-21. 2. Vereneault, J., Sparkle City Comics, Swd,NJ: pemnalcommunication, 1988. 1986. 3. Malan,O.,MelanClaasieal Enterprises. St. Louis,MO,p~onalcommunicstion, 4. Rsloff,J.Sci.N~w 1981,121,154. 5. Carltan. A. M. Handbook olPulp ond Pope? Technology, 2nd sd.; Britt, K. W., Ed.; Van Nostrand Reinhold: New York, 1570:Chapter9-6. 6, h a . S. R.: Feller. R. L. Historic Textile ond Paper Mafatiols Conservotion end Chorocfetiiotion:Needles, H.L.:Zemnian,S. H.Eds.;AmericanChemicalSaeiety: Wsahingtan. DC. 1986;Chapter 21. 7. H o n D. N.-S. Preraruotion o/Popor and Textiles of Historic and Artistic Vduq Williams, J. C., Ed.; American Chemical Society: Wehihingtan, DC, 1981: Voi. 2, Chapter 10.
8.
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Cerpar.A.:Giiioia,J.:Guillerm. G.:Sauignac,M . ; V ~ Q u a n g , L .J. Chem Educ. 1986, 6, RII S o l u m ~ . n 3 . 7 I V C Ordonlr Ch~mr.rr,. 4th ed \I.lr\ h e w Ysrk 19M. 1 1 hmSn.C ~ Sm~tl..flD L.br U 1969..19 I.
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