CHEMICAL ASPECTS OF THE BOOKKEEPER DEACIDIFICATION OF CELLULOSIC
MATERIALS: THE INFLUENCE OF SURFACTANTS
S. Zumbühl and S. Wuelfert
Summary—Despite its widespread use in paper deacidification, neither the exact composition of
the Bookkeeper reagent nor its time-dependent chemistry are known in sufficient detail. For this
reason, our laboratory characterized Bookkeeper reagents by X-ray powder diffraction, microinfrared spectrometry, energy-dispersive X-ray fluorescence spectrometry and polarized light
microscopy. The results clearly show that the fluorinated dispersants contained in the reagent have
a decisive influence on the reaction kinetics and probably also on the chemical species forming the
alkaline reserve.
Introduction
It is well known that the synergetic effects of oxidative degradation and acid catalyzed hydrolysis
lead to an increasing loss of mechanical stability and finally to a loss of function of paper and other
cellulosic supports. As a result, there is a large need for mass deacidification of books and archival
materials. Whereas aqueous deacidification processes are known for their high efficiency, interest in
non-aqueous treatments has grown considerably in the last few years due to the need to treat watersensitive materials and also to their greater ease of use.
Among those, the Bookkeeper® process introduced by Preservation Technologies L.P. (PTLP) has
several advantages which have led us to examine its chemistry. These are its general ease of application, lack of preconditioning, its non-swelling action and the possibility of controlled hydrolysis
leading to very 'mild' neutralization reactions [1]. In other words, neutralization is accomplished
without exposure to strongly alkaline conditions, minimizing the risk of alkaline depolymerization
of cellulose. According to Schwendener, no negative side-effects are observed during and after a
deacidification treatment using the Bookkeeper process, including retention of alkali-sensitive dyes
[1].
Despite its widespread use, neither the exact composition of the Bookkeeper reagent nor the species
forming the alkaline reserve are publicly known. Whitmore has recently pointed out that the process
chemistry and kinetics associated with the Bookkeeper treatment of cellulose are not understood in
sufficient detail [2]. We show here that the dispersion agents are not only carriers for the active
material but have a significant influence on deacidification and formation of an alkaline reserve.
Reactions of magnesium oxide
Deacidification using MgO-containing reagents and subsequent formation of alkaline reserve have
been discussed in the literature [1-24]. It is generally assumed that the suspended MgO particles are
transported onto the cellulosic fibers of the support via capillary transport. It is further assumed that
particles deposited on the fibers hydrolyze to form Mg(OH), which acts as the alkaline reserve.
Different opinions on the formation of an alkaline reserve prevail in the literature. Usdowski
generally assumes Mg(OH)2 to form a mixture of neutral and basic carbonate hydrates upon
reaction with airborne CO2 [3], whereas Whitmore postulates the formation of solid magnesium
hydroxide or a carbonate [2]. Brandt supposes excess magnesium oxide to act as an alkaline reserve
[4], and Pauk expects magnesium oxide and solid magnesium hydroxide to form the alkaline
reserve [5].
Hydrolysis of magnesium oxide
Various possible mechanisms leading to the formation of Mg(OH)2 have been proposed [6-12].
Even in the presence of small amounts of water, hydroxyl groups are formed on the surface of
magnesium oxide. The amount of chemisorbed water on MgO is dependent on particle morphology
which in turn is influenced by the choice of reactants and synthesis conditions, i.e., calcinating
temperature. Depending on the relative humidity of the surroundings, surface hydroxyl groups are
covered by a variable amount of physisorbed water. Both morphology of the MgO particles and the
availability of physisorbed water are known to determine the kinetics of Mg(OH) 2 formation [11,
13]. Under typical ambient conditions the conversion reaction MgO + H2 O -» Mg(OH) 2 takes
place on the surface of the solid. It has been shown that the inter-
action of water with the Mg(OH) 2 surface of MgO leads to the formation of solvated molecular
magnesium hydroxide [9]. Abstraction of Mg(OH) 2 (aq) molecules and subsequent surface vacancy
formation are followed by formation of new surface Mg(OH) 2 [9]. Decomposition of the individual
crystals starts at the OH-rich sites at their edges, but corrosion of crystal surfaces is also observed.
Highly dispersed MgO, as in the Bookkeeper reagent, could therefore be expected to hydrolyze
quickly. Due to the dissociation of solvated Mg(OH)2(aq), water surface layers are expected to
contain solvated magnesium and hydroxide ions [13]. Neutralization of acidic sites (mainly carboxylic oxidation products) in cellulosic materials can thus be accomplished by diffusion of
solvated hydroxide anions in physisorbed water layers on or within cellulosic materials.
Results from this study suggest that, in Bookkeeper reagents. MgO hydrolysis may be retarded by
the presence of surfactants adsorbed on particle surfaces.
Reaction with carbon dioxide
Philipp observed the formation of Mg(OH) 2 crystals on MgO surfaces in CO2-free atmospheres
[14]. The presence of CO2 leads to direct carbonatization from the solvated ions. In the presence of
hydroxide anions, the hydrogen carbonate intermediate species reacts to the hydrated 'acidic'
carbonate (nesquehonite) [15], which was previously believed to be a carbonate-trihydrate.
Note that reaction (2) also depends on the concentration of solvated hydroxide anions. In the
presence of water, nesquehonite has been observed to lose small amounts of CO2 and to partially
convert to basic carbonates [3, 15, 16].
Composition of Bookkeeper reagents
Bookkeeper reagents contain a highly dispersed magnesium oxide. As discussed above, surface
reactions determine the hydrolysis of MgO. Since commercial Bookkeeper reagents are also known
to contain surfactants, their role in MgO hydrolysis needs to be taken into account. In this context it
is important to consider the composition of the medium of the reagents in some detail. What follows
is a compilation of available information on the constituents of Bookkeeper reagents.
It should be noted that PTLP has previously marketed two different reagents under the Bookkeeper trademark. One was used in closed mass deacidification machines, the other was intended
for open spray application. A recently introduced spray reagent is called Archival Mist™ but a socalled 'Bookkeeper-Spray' is also available. The trade mark 'Bookkeeper' also denotes the mass
deacidification reagent. All reagents are suspensions of highly dispersed MgO in an inert, non-polar
fluid. There may be or have been a difference in the composition of the fluids. It was believed to be
perfluo-roheptane C7F16 in the case of the closed-system reagent [17], and a mixture of per- and
polyfluorinated hydrocarbons with stabilizing additives in the spray reagents. In a new brochure
issued by PTLP 'a blend of fluorinated materials' is said to be used for the mass deacidification
product [18].
PTLP claims that their spray reagent basically consists of three groups of components [19-21]:
• The solid component: MgO (CAS No. 01309-48-4) at a concentration of 4-3gl~' (in spray
product) [22], and with a particle size below 1 urn [21, 23]
• The dispersing fluid: a blend of C5-Cl8 perfluo-roalkanes (CAS No. 86508-42-1 [21, 23]) furnished by 3M® Company [20], probably 3M PF-5060. It is defined as containing less than 1% of
non-specified byproducts [24].
•
Several additives. Less than 0-1% surfactant [21], in the form of a perfluorinated Mg-soap: CnFn+1-COO-Mg-OH [17]. Other sources claim the surfactant to be a perfluoropolyether derivative
[25] or a non-ionic, fluorinated acyl ester [4]. In addition, nonafluoromethoxybutane [21] in two
non-separable isomers C4F9-OCH3 (CAS No. 163702-07-6) and (CF3)2-CF-CF2-OCH3(CAS No.
163702-08-7) [24] is present.
The latter substances could also be products of the 3M Company. 3M product numbers HFE8401HT and HFE-7100 are specified as containing up to 2 ppm of non-volatile components [24].
The influence of the fluorinated dispersant and other components of the carrier fluid on the MgO
conversion in the Bookkeeper process has been experimentally investigated in this work.
Experimental
Analytical instrumentation
X-ray powder diffraction (XRD) measurements were taken using a Stoe Stadi P powder diffractometer. Energy dispersive X-ray fluorescence (EDXRF) spectra were recorded in a Leo-430 REM
equipped with a Roentec EDR 288 elemental
analyzer. The μFTIR spectrometer (Perkin Elmer System 2000) was coupled to a Cassegrain microscope (Perkin Elmer IR-microscope) allowing very small samples to be characterized. A standard
polarized light microscope (Olympus BH2-Pol) was used for polarized light microscopy (PLM).
Simulations of the aging behavior were carried out in a Heraeus VC0020 oven, equipped with CTCE4 temperature and humidity control.
Break loads were measured using a Zwick Z2.5/TN1S computer-controlled tensile tester.
Analysis of the composition of Bookkeeper spray reagents
To characterize the reagent, it had to be separated into its components. To examine the solid part,
volatile components of a small sample were evaporated under vacuum and the solid transferred to a
glass capillary tube under argon. The liquid components were separated from the solids by
centrifugation. IR spectra were taken of a thin layer between KBr windows.
While trying to isolate the clear liquid portion of the reagent, it became evident that different
reagent lots had different sedimentation behaviors. With some reagent lots it was possible to
completely separate liquid and solid by centrifugation. With other lots, a certain amount of solid
was found in the liquid phase even after centrifugation. In both cases, 20ml of the liquid were
evaporated on a glass slide to examine possible non-volatile residues. Residues were transferred to a
small diamond plate and characterized by μFTIR. While evaporating 20ml of the clear liquid,
formation of a small droplet (10mg) of a transparent material was observed.
Investigation of the products formed during conversion
To examine the chemical conversion of the Bookkeeper reagent under normal ambient conditions,
the commercial spray fluid was airbrushed onto filter paper (Glaswarenfabrik Karl Hecht, Assistent
1250/58), a 100-year-old jute textile, glass microscope slides (Assistent 2400) and low density
polyethene sheets (Nittel Stan-O-Nit). The clean paper was used to examine the formation of the
alkaline reserve by the effects of aging products or additives. Glass and LDPE were chosen for ease
of sampling and differences in surface polarity and surface water content.
During the conversion process all samples were stored under typical ambient conditions (50% RH.
20°C. 0-3% CO,). To monitor chemical changes, a small quantity of reagent material was sampled
weekly using a tungsten needle. Samples were taken from paper by extracting a piece of the paper
in clear Bookkeeper fluid. While it is clear that different species presumably have different
extractabilities, their measurements nevertheless were helpful to monitor the formation of the
alkaline reserve. As long as MgO can be identified, the conversion process is considered
incomplete. Additional spectra were taken from samples on glass after 18 months of storage. All
FTIR spectra except the liquid were taken from samples after mechanically flattening them on a
diamond window. At the same time the samples were characterized by optical microscopy at a
magnification of up to 1000X. Examination of the alkaline reserve formed was accomplished by
EDXRF and XRD.
To investigate water sorption and the water-repellent effect of the fluorinated surfactant, samples on
glass slides were heated to 180°C/'2h immediately after application, while a second sample was
kept at ambient conditions. Both samples were stored for 24 hours at room conditions and then
characterized by μFTIR.
Observations concerning deacidification
The jute samples were used to monitor the effectiveness of the deacidification process. The jute textile used was strongly acidic: a cold water extract had a pH of 4. The amount of reagent needed to
achieve deacidification was determined by titration of the extracts. To enable the formation of an
alkaline reserve, a somewhat larger amount than calculated (1-5X) was applied to the samples. Two
months after treatment, samples were aged at 80°C/60% RH for six weeks. Samples were then
characterized by FTIR spectrometry and by tensile tests. The corresponding break load
measurements were taken using 20mm strips. Elongation rates were lOmm.min"1, the gauge length
was 100mm and pre-tensioning was set to IN. The results were calculated from 16 individual
measurements.
Results and discussion
The composition of Bookkeeper-Spray
Solid fraction
The diffractogram in Figure 1 shows fine-grained MgO to be the main component with some
Mg(OH)2 in coarser particles. Large amounts of amorphous material could be excluded by comparison with a reference measurement of the capillary alone. As expected, fresh Bookkeeper reagent
also contains a small amount of Mg(OH) 2 due to the hydrolysis of some MgO during production of
the reagent [17]. No carbonates were detected using XRD.
Figure 1 XRD diffractogram of the solid portion of fresh Bookkeeper. Solid magnesium oxide in
small crystals is accompanied by a small amount of magnesium hydroxide.
Figure 2A shows the corresponding FTIR spectrum. MgO is not expected to show significant
absorption within the spectral range of the instrument [26-30]. The OH-stretches at 3700cm-1 and
around 3400cm-1 are attributed to chemically and physically bonded surface water as well as to the
Figure 2 (A) FTIR spectrum of fresh Bookkeeper reagent, one hour after application and
evaporation of volatile components under normal room conditions. (B) FTIR spectrum of the clear
fluid of Bookkeeper reagent after centrifugation. Note that the strongest bands are saturated.
Mg(OH)2 content of the sample [31-37]. Other bands in this spectrum are due to additives, as discussed below.
Liquid fraction
Figure 2B shows several strong characteristic signals of fluorinated hydrocarbons [38, 39]. The
broad band of C-C and C-F streching vibrations appears between 1360 and 1090cm-1, and the signals between 730 and 750cm-' are due to C-F deformation vibrations. However, we also observed
several bands due to C-H vibrations. The bands between 1050 and 900cm-1 as well as above
3000cm-1 are typical of C-H- streches in polyfluorinated compounds. Hence, as expected, the liquid
is not completely fluorinated. The signals at 2977 and 2879cm-1 are methyl streching vibrations [38,
39]. Their presence could be due to a significant amount of nonafluoromethoxybutane.
Non-volatile residues in liquid component
The corresponding FTIR spectrum is shown in Figure 3A. The signals observed are attributed to
unsubstituted hydrocarbons [39-41]. The same signals occur in spectrum 3B which was obtained
from the residue containing some solid. Samples of five different reagent lots were tested. They all
contained unsubstituted hydrocarbons. Measurements by the PTLP laboratories could not confirm
the
Figure 3 FTIR spectra of hydrocarbon residues from two different batches of Bookkeeper
reagent:
(A) residues contained in well-separated liquid and
(B) residues on an inseparable content of solids.
Figure 4 EDXRF elemental analysis of Bookkeeper reagents after six weeks and 24 months on glass
slides (20keV excitation). Error bars indicate signal fluctuations within the domains characterized.
presence of hydrocarbons. We therefore conclude that different reagent lots may contain different
amounts of this impurity. This point is addressed in some detail in the discussion section.
Conversion processes and formation of the alkaline reserve
Hydrolysis and hydrophobic effects Concerning the composition of the reagent, we assumed that the
reactions of the Bookkeeper reagent may depend strongly on the fluorinated dispersants. Soon after
application of the reagent the blend of fluorinated solvents completely evaporates. Boone et al.
suggest that the surfactants also evaporate rapidly after application [25]. However, our FTIR spectra
(Figure 2B) as well as the EDXRF results (Figure 4) clearly indicate that a significant amount of
fluorinated compounds remains after application. These may be the fluorinated carboxylates
mentioned earlier or possibly other surfactants bound to the surface of the solid content of the
reagent. Examination of samples stored for 24 months at ambient conditions still showed fluorinated residues.
Fluorinated carboxylates are often used as surface active compounds to improve the wetting of
metals with fluorinated solvents [42]. Also, their hydrophobic and oil-repellent nature is exploited
for a large variety of materials, e.g., in textile impregnation [43, 44]. The coverage of porous substrates is a very important variable affecting water-repellency. Hence the amount of fluorochemical
needed for a good repellency depends on both the substrate and the composition of the fluorocarbon
structure. For example, for fabrics, a structure containing approximately 10 fully fluorinated carbon
atoms is needed for maximum repellency [44].
Figure 5 shows FTIR spectra of Bookkeeper
Figure 5 FTIR spectra of a sample heated to 180°C (spectrum A). Note the water band around
1600cm-1and the absence of signals attributable to surfactants. Spectrum B was taken from
Bookkeeper reagent dried under normal room conditions: the signals of the surfactants (1241,
1149, 983cm-1) are clearly present whereas the water band is lacking, showing the hydrophobic
effect of the surfactant.
reagents on glass supports. One of the samples (spectrum A) was heated to 180°C immediately after
application, while the other was held at room conditions (spectrum B). Both samples were then
stored for 24 hours at ambient conditions prior to FTIR analysis. The spectra show marked differences which we attribute to the evaporation of additives during heating.
In the non-heated sample, a noticeable absence is the water absorption around 1600cm-1 which is
assigned to H-bonded water [45]. This assignment is consistent with the signal intensity expected
for magnesium oxide particles with large surfaces. This correlates with the shift and intensity of the
OH band around 3400cm -1 which is affected by bonding type and quantity of water [36].
In contrast, the FTIR spectrum of the heated sample (Figure 5A) is almost free of fluorinated
residues and shows the expected water content. This is a clear indication of the water-repellent
effect of fluorinated dispersants adsorbed on the solid. We conclude that the fluorinated residues act
as retarders, slowing down the hydrolysis of MgO and the diffusion of Mg2+ and OH- ions into
cellulose-bound water layers. They probably are the key to the 'mildness' of Bookkeeper
neutralization.
Not all of the surfactant in the commercial
Figure 6 FTIR spectra of magnesium oxide (A), basic magnesium carbonate (B) and calcium
carbonate (C), 24 hours after treatment with Bookkeeper fluid. Spectra show the different
adsorption capacity for fluorinated compounds. Typical spectral features of fluorinated compounds
are marked by dashed lines.
reagents is bound to the MgO/Mg(OH)2 content. We treated magnesium oxide, basic magnesium
carbonate and neutral calcium carbonate of comparable particle sizes with some of the separated
fluid. FTIR spectra of the treated solids showed interesting differences in binding capacity: the
oxide showed a much larger surfactant content (Figure 6A) than the basic carbonate (Figure 6B).
Note that the pure carbonate did not bind any measurable amount of surfactant (Figure 6C).
Figure 7 shows the corresponding measurements of cellulosic materials by ATR/FTIR. Both transmission FTIR spectrometry and ATR surface measurements established that paper and jute textiles
do not bind any measurable amount of the fluorinated dispersants. We conclude that the
physisorbed water content in cellulosic materials will not be influenced by a Bookkeeper treatment.
Species found in hydrolyzing Bookkeeper reagent
Figure 8 shows FTIR spectra of the Bookkeeper reagent on glass slides as a function of aging time.
Figure 7 A TR/FTIR spectra of cellulose from a filter paper (A) and the same sample after
treatment with Bookkeeper fluid (B). The latter does not show any measurable amounts of
fluorinated compounds. Typical spectral features of fluorinated compounds are marked by dashed
lines.
Spectra correspond to two weeks, six weeks and 18 months of storage at 20°C and 50% RH.
Hydrolysis of MgO to Mg(OH)2 could not be monitored by FTIR due to the absence of specific
MgO vibrations in the range over 600cm-1. The most important spectral changes are:
•
•
•
•
The disappearance of the OH-stretch of Mg(OH)x at 3700cm-1
New bands appearing around 1400cm-1 and in the range between 700 and 800cm -1
Reduction of the signals attributable to fluorinated compounds at 1240 and 1150cm-1
The growth of the water bands around 3300 and around 1600cm-1
As the sharp band around 3700cm-1 is attributed to hydroxyl groups coordinated to three or four
Mg2+ ions [46], we conclude that neither MgO nor Mg(OH)2 are present in the reaction products.
The new bands around 1400cm-1 and between 700 and 800cm-' are an indication of the formation of
a carbonate species [47, 48]. The weakening of the 1240cm-1 and 1150cm-1 bands is well explained
by the previously observed smaller affinity of carbonates for the fluorinated surfactants. As a
logical consequence of the loss of surfactant, the water content of the product species rises.
Using polarized light microscopy (PLM), we observed the formation of small birefringent crystals
in direct proximity to isotropic crystals of
Figure 8 FTIR spectra showing the conversion of Bookkeeper magnesium oxide on glass slide into
the species of the alkaline reserve under normal room conditions. The spectra were taken two
weeks (spectrum A), six weeks (spectrum B) and 18 months (spectrum C) after application of the
reagent.
figure 9 Micrograph of Bookkeeper sprays on a glass slide one hour after application (left) and
after 18 months under normal room conditions (right). After application, the fine-grained material
is homogeneously distributed. Upon conversion into the alkaline reserve, much coarser, rosetteshaped, birefringent structures form.
Figure 10 FTIR spectra showing Bookkeeper reagents sprayed on different substrates, i.e., glass
slide (A), LDPE (B) and cellulose (C), after 12 months storage under normal ambient conditions.
MgO. The latter convert to larger spherical aggregates of anisotropic, elongated crystals (Figure 9)
after 18 months. The large distances between aggregates indicate extended ion migration within the
water layers on the glass surfaces.
Regarding the formation of the alkaline reserve, no dependence on the substrate used (paper, glass
slides and LDPE) was observed by FTIR. However, the substrate type has an influence on the
conversion rate. The FTIR spectra in Figure 10 show conversion product species after one year on
different substrates (glass slide: spectrum A, LDPE: spectrum B and cellulose: spectrum C). In one
case (LDPE) we observed the formation of a small quantity of an additional crystalline cubic
species by PLM although these species were not characterized further.
FTIR spectra and PLM observations are in accordance with the reactions presented in the introduction: solid MgO converts via intermediate solvated hydroxides into a hydrated carbonate. Note that
no MgO/Mg(OH)2 remains after 18 months (on glass). However, the exact composition of the
alkaline reserve formed remains unclear. FTIR spectra and
Figure II (A) FTIR spectra of an unidentified alkaline reserve compound (similar to the one in
Figure 6). (B) FTIR of the species formed in hydrocarbon domains identified as nesquehonite,
Mg(HCO3)(OH)-2H20.
XRD diffractograms of the crystalline products were compared to reference data for the expected
product species. On this basis we exclude the formation of the neutral carbonate-pentahydrate
MgCO3-5H2O (lansfordite), the acid carbonate-hydrate Mg(HCO3) (OH) 2H2O (nesquehonite), as
well as the basic species Mg5(CO3)4(OH) 2 4H2O (hydromagnesite) and Mg2 (CO3)(OH) 2-3H2O
(artiriite) [16, 47-51]. Sulfates and hydroxides are also not present. Alternatives include the
formation of co-crystals with organic species, as is known from the literature. For example,
fluorinated solvents are known to be included into crystals, leading to dislocations [52, 53]. EDXRF
results confirm the content of fluorinated compounds in the alkaline reserve (Figure 4). A
Figure 12 Break loads of Bookkeeper-treated jute textile strips and untreated controls after
accelerated aging. Error bars indicate two standard deviations.
significant oxygenated fraction is also present. FTIR spectra show structured OH-streching and
possibly also carbonate vibrations in combination with EDXRF results showing a marked oxygen
and fluorine content. PLM observations of birefringence also indicate that the alkaline reserve could
be composed of co-crystals of hydrated magnesium carbonates and fluorinated materials.
Deacidification of cellulose
The deacidification reactions of the Bookkeeper reagent were studied on a jute sample (Figure 11).
The FTIR spectrum of the untreated cellulose (spectrum 11 A) shows a significant amount of oxidation in the form of strong signals in the carbonyl-streching region (around 1720cm-1) as well as
absorptions attributed to lignin and adsorbed water (1655-1600cm-1). Six weeks after treatment we
observed a strong decrease in the carbonyl region and increased intensity around 1643cm-1 (Figure
11B). As shown before, cellulose does not adsorb measurable amounts of Bookkeeper additives
(Figure 7). Hence, the observed spectral changes are interpreted as being due to the saponification
of acids (conversion of carboxyl groups into carboxylates).
This stabilizing effect of deacidification was also confirmed by testing the stress-strain behavior of
treated and untreated jute samples after accelerated aging. Break loads of treated samples were
clearly higher than those of untreated controls (Figure 12).
Impurities
While producing test sprays on glass slides we observed the formation of separate micro-domains
Figure 13 Micrograph of deposits of hydrocarbon residues which separated as micro-domains on a
glass slide 18 months after application of Bookkeeper reagent (lot no. 711131).
Figure 14 FTIR spectra showing the saponification of carboxylic acids (six weeks after application
of Bookkeeper reagent). Signal changes show the conversion of carboxyl stretches (1722cm-1) into
car-boxylates (1643cm-1).
of unsubstituted hydrocarbons (Figure 13). While characterizing these samples microscopically, we
noted the presence of inclusions of solid materials within the hydrocarbon domains. As
unsubstituted hydrocarbons do not mix with fluorinated solvents and compounds, we expected the
formation of different conversion species within these hydrocarbon domains.
After 18 months storage at normal room conditions, the formation of nesquehonite
(Mg(HCO3)(OH) 2H2O) [47] was observed within these domains using μFTIR (Figure 14). To our
surprise, signals of fluorinated compounds were evident even within the hydrocarbon domains.
Conclusions
The positive effects of Bookkeeper spray reagents in the conservation of cellulosic materials seem
to be well established and are confirmed by our accelerated aging tests. However, current models of
the Bookkeeper chemistry are insufficient to account for the observations and data reported here. In
particular, the fluorinated additives used appear to be of much greater importance than previously
realized: they act as retarders for the hydrolysis of MgO and thus appear to be largely responsible
for the 'mildness' of deacidification using the Bookkeeper reagent.
On treated surfaces, the additives have a permanence of several months, and very probably form an
important part of the alkaline reserve. The species involved have not yet been precisely defined.
However, some previously proposed candidates can be excluded. Neither magnesium oxides,
hydroxides or sulfates, nor neutral, basic or acidic carbonate hydrates were formed under normal
ambient conditions.
It should be noted that conclusions drawn from single-sheet spray experiments do not necessarily
apply to Bookkeeper-based mass deacidification processes, especially in the case of book
deacidification. Further investigations into the chemical and physical mechanisms of Bookkeeper
action are clearly indicated, in order to utilize this important conservation tool more intelligently.
Experiments which try to quantify the influence of water concentration and CO, diffusion on the
conversion speed and the products formed are in progress.
Acknowledgements
The authors would like to thank Dr M. Woerle (Laboratory for Inorganic Chemistry, ETH Zurich)
for X-ray powder diffraction analysis and Dr H. Scheidiger (Berner Fachhochschule, HTA
Burgdorf) for EDXRF analysis. We also thank Dr R.D. Knochenmuss (Institute of Organic
Chemistry, ETH Zurich) for corrections of the typescript as well as helpful comments and
discussions.
Manufacturer
Preservation Technologies L.P. (PTLP). Ill Thomson Park Drive. Cranberry Township, PA
16066, USA.
References
1 SCHWENDENER, C., 'Die Bookkeeper-Neutrali-sierung — Moglichkeiten und Grenzen der
Anwendung im Bereich der Einzelblatt-konservierung von Grafik', Diplomarbeit, Berner
Fachhochschule, Studiengang Kon-servierung und Restaurierung, Fachrichtung Graphik und
Photographic, Bern (1999).
2 WHITMORE. P.M., 'Evaluation of the Bookkeeper process chemistry'. http://palimpsest.
stanford.edu/byorg/lc/massdeac/whitmore.html (27 January 1997)7
3 USDOWSKI, H.E., 'Zur Entsauerung von Papier mil Carbonaten', Dauerhaftigkeit von Papier,
Zeitschrift fur Bibliothekswesen und Biblio-graphie. Sonderheft 31, 46-54.
4 BRANDT, A.-C., Mass Deacidification of Paper — A Comparative Study of Existing Processes,
Bibliotheque Nationale, Pro Eibris, Paris (1992).
5 PAUK, S., The Bookkeeper mass deacidification — some effects on 20th century library mater-
ial'. http://ftp.konbib.nl/kb/sbo7cons/bokkeep/ rappeng.htm (accessed 23 January 2000).
6 BRATTON, R.J., and BRINDLEY G.W., "Kinetics of vapor phase hydration of magnesium oxide —
Part 2, Dependence on temperature and water vapor pressure'. Transactions of the Faraday Society
61 No. 505. Part 1 (1965) 1017-1025.
7 COLUCCIA, S., and TENCH, A., "Surface structure and surface state in magnesium oxide powders',
Journal of the Chemical Society — Faraday Transactions 115 (1979) 1669-1779.
8 DULEY, W.W., "Photoluminescence study of the dehydroxylation of magnesium oxide', Journal
of the Chemical Societv — Faraday Transactions 180 (1984) 1173-1179.
9 LONGO, E., VARELA, J.A., SENAPESCHI, A.N., and WHITEMORE. O.J., 'Mechanisms of water
interaction with an MgO surface'. Langmuir 1 (1985)456-461.
10 RAZOUK, R.I., and MIKHAIL, R.SH., The hydration of magnesium oxide from the vapor phase'.
The Journal of Phvsical Chemistrv 62 (1958)920-925.
11 ROYEN, P., and TROMEL. M., 'Rontgeno-graphische und elektronenmikroskopische Untersuchung
von Magnesiumoxiden ver-schiedener Herkunft', Berichte der Bunsengesellschaft 67 (1963) 908918.
12 DURIEZ. C., CHAPON, C. HENRY, C.R.. and RICKARD J.M., 'Structural characterization of
MgO(lOO) surface'. Surface Science 230 (1990) 123-136.
13 FEITKNECHT, W., and BRAUN. H., 'Der Mech-anismus der Hydradation von Magnesiumoxid mil
Wasserdampf, Helvetica Chimica Acta 50 (1967) 2040-2053.
14 PHILIPP, W.R., 'Phasenbeziehungen im System MgO - H,O - CO, - NaCl'. dissertation. ETHZ.
Zurich (1988):
15 'Magnesiumverbindungen', Ullmann Encyklo-padie der Technischen Chemie, 3rd edition.
Urban und Schwarzenberg. Mtinchen (1960) 115-133.
16 Gmelins Handbuch der Anorganischen Chemie. System-Nummer 27, 'Magnesium - Teil B, Die
Verbindungen des Magnesiums'. 8th edition, Verlag Chemie, BerlhT(1939) 301-327.
17 BURD, J.E., Preservation Technologies PTLP, personal written communications (21 June 1999,
23 June 1999).
18 Preservation Technologies PTLP. http://www. ptlp.com/base.html (accessed 15 January 2000).
19 Preservation Technologies PTLP. http://www. bookkeeper-pti.com/mass.html (accessed 12
March 1999).
20 DOMACH, M.M., Technical evaluation of PTI mass deacidification technology — an evaluation
of the Bookkeeper mass deacidification process', Technical Evaluation Team Report for the
Preservation Directorate, Library of Congress, Pittsburgh 1994. gopher://marvel. loc.gov:
70/00/services/preserv/massdead/mass dead.ptl (accessed 24 August 1999).
21 Material Safety Data Sheet - Bookkeeper Deacidification Mist. La Route du Papier (27 January
1998).
22 BURD. J.E.. Preservation Technologies PTLP, personal written communication (3 June 1998).
23 Preservation Technologies PTLP, Declaration on Deacidification Spray (1998).
24 3M Special Fluids, http://www.mmm.com/ marcet/industrial/fluids.7100.html (accessed 19
September 1999).
25 BOOSE. T., KIDDER, L., and RUSSICK, S., 'Bookkeeper® for spray use in single item treatments'.
The Book and Paper Group Annual 17. American Institute for Conservation (1998) 29^13.
26 ANDERMANN, G., and DUESLER, E., 'Improved infrared optical-index values for MgO', Journal
Optical Society America 60 (1970) 53-57.
27 FARMER, V.C.. The anhydrous oxide minerals' in The Infrared Spectra of Minerals,
Mineralogical Society, London (1974).
28 MCDEVITT, NT., and BAUN, W.L., The characteristic frequencies of 52 metal oxides (700-240
cm"1)'- Spectrochimica Acta 20 (1964) 799-808.
29 PECKHAM, G., The phonon dispersion relation for MgO', Proceeding Physical Society 90 (1967)
657-670.
30 RUPIN, R., and ENGELMANN, R., 'Optical phonons of small crystals'. Rep. Prog. Phys. 33 (1970)
149-196.
31 ANDERSON, P.J., HORLOCK, R.F., and OLIVER, J.F.. 'Interaction of water with the magnesium
oxide surface'. Transactions of the Faraday Society 61 (1965) 2754-2762.
32 CABIGON, E.G., 'Fourier-Transform-Infrarot-Spektroskopische Untersuchungen der Wechselwirkung von Wasserdampf mit MgO(lOO)-Einkristall und mit supraleitendem YBa,Cu,O7 xPellet unter Ultrahochvakuum-bedingungen", dissertation, Universitat Hannover (1990).
33 TAKEZAWA, N., MIYAHARA, K., and TOYOSHIMA, I., 'Infrared diffuse reflectance spectra of
surface hydroxyl groups on magnesium oxide', Hokkaido University, Journal of the Institute for
Research of Cathalvsis 19 (1) (1971) 56-61.
34 COLUCCIA, S., MARCHESE, L., LAVAGNINO, S., and ANPO, M., 'Hydroxyls on the surface of MgO
powders'. Spectrochimica Ada 43A (12) (1987) 1573-1576.
35 ITO, T., KANEHORI, K., and TOKUDA, T., 'Infrared study of the adsorption of water vapor on
magnesium oxide at elevated temperatures', Zeitschrift fur Physikalische Chemie 103(1976)203206.
36 RICE, R.W., and HALLER, G.L.. 'Adsorbed water on single crystal oxides'. Proceedings of the
Fifth International Congress on Catalysis, Miami Beach 1972, Vol. L Amsterdam (1973) 17/317324.
37 BUSCA. G., "Vibrational spectroscopy of adsorbed molecules and surface species on metal
oxides". Catalysis Today 21 (3. 4) (1996) 323-545 [special issue, Elsevier. Amsterdam].
38 HUMMEL, D.O.. 'Band 1 — Polymere, Struktur und Spektrum' in Atlas der Polymer und
Kunststoffanalyse, 2nd edition. Carl Hanser Verlag. Munchen (1978).
39 SOCRATES. G., Infrared Characteristic Group Frequencies — Tables and Charts, 2nd edition,
Wiley, Chichester (1994).
40 POUCHERT, C.J., The Aldrich Library of Infrared Spectra, Aldrich Chemical Company,
Milwaukee (1975).
41 LOVELACE, A.M., RAUSCH, D.A., and POSTELNEK, A.. Aliphatic Fluorine Compounds, ACS
Monograph 138. Reinhold Publication Corporation, New York (1958).
42 NEUMULLER, O.-A., Rompps Chemie-Lexikon, Ranck'sche Verlagshandlung. Stuttgart (1981)
1345, 3045.
43 HALASZ, S.P.. and MILLAUER, H.. 'Fluorver-bindungen — organische", Ullmann Encyclo-pddie
der technischen Chemie, 4th edition, Volume 11, Verlag Chemie, Weinheim (1976) 631-656.
44 KlSSA. E., Fluorinated Surfactants — Synthesis, Properties, Application, Surfactant Science
Series, Volume 50. Dekker Inc.. New York (1994).
45 DAENE. M.A., GRIFFITHS, D.L., LEWIS, LA., WINTER, J.A., and TENCH, A.J., 'Infra-red study of
the interaction of hydrogen sulphide and water with a magnesium oxide surface", Journal of the
Chemical Society, Faraday Transactions III (1975) 1005-1012'.
46 COLUCCIA, S., MARCHESE, L., LAVAGNINO, S., and ANPO, M., 'Hydroxyls on the surface of MgO
powders', Spectrochimica Ada 43A (12) (1987) 1573-1576.
47 JONES, G.C., and JACKSON, B., Infrared Transmission Spectra of Carbonate Minerals, NMS,
The Natural History Museum, Chapman & Hall, London (1993)".
48 WHITE. W.B.. The carbonate minerals' in V.C. FARMER. The Infrared Spectra of Minerals,
Mineraloaical Society Monograph 4, London (1983) 227-284.
49 WHITE, W.B., 'Infrared characterisation of water and hydroxyl ion in the basic magnesium carbonate mineral'. The American Mineralogist 56 (Jan-Feb) (1971) 46-53.
50 GADSDEN, J.A., Infrared Spectra of Minerals and Related Compounds. Butterworths. London
(1975).
51 NYQUIST, R.A., PUTZIG, C.L., and LEUGERS, A.M., Infrared and Raman Spectral Atlas of
Inorganic Compounds and Organic Salts, Academic Press, San Diego (1997).
52 HURLE, D.T.J., (ed.), Handbook of Crystal Growth, Vol. 1-2, North-Holland. Amsterdam
(1993).
53 BOYLE, P.D., 'Growing crystals that will make your crystallographer happy', http://laue.
chem.ncsu.edu/web/GrowXtal.html (accessed 16 November 1999).
Authors
STEFAN ZUMBUHL has
a diploma in conservation and restoration of cultural heritage from the
Technical University of Applied Sciences of Berne. Since 1997 he has been a scientific collaborator
at the Art Technical Laboratory of the University. Address: Technical University of Applied
Sciences of Berne, Department of Conservation and Restoration, Studerstrasse 56, 3004 Bern,
Switzerland.
STEFAN WUELFERT has
a PhD in physical chemistry from the University of Berne. Since 1995 he has
been head of the Art Technological Laboratory of the Technical University of Applied Sciences of
Berne, Department of Conservation and Restoration. Address as for Zumbiihl.
Resume—Malgre son usage tres repandu en desacidification du papier, on ne connait avec
precision ni la composition du reactif Bookkeeper, ni son evolution chimique dans le temps. Pour
cette raison, notre laboratoire a procede a la caracterisation des composants du reactif Bookkeeper
par diffraction des rayons X, micro-spec-trometrie IR, spectrometrie de fluorescence des rayons X a
dispersion d'energie et microscopie en lumiere polarisee. Les resultats montrent clairement que les
dispersants fluores contenus dans le reactif ont une influ-
ence decisive sur la cinetique de la reaction ainsi probablement que sur les especes chimiques
constituant la reserve alcaline.
Zusammenfassung—Trotz der weit verbreiteten Verwendung in der Massenentsauerung van
Papier, ist weder die exakte Zusammensetzung der im Bookkeeper- Verfahren verwendeten
Reagenzien, noch die Chemie des Verfahrens hinreichend genau bekannt. Daher wurden in
unserem Labor die Reagenzien des Bookkeeper- Verfahrens durch Rdntgenpulverdiffraktometrie,
energiedispersive Rontgenfloureszenzanalyse und Polarisationsmikroskopie charakterisiert. Die
Ergebnisse zeigen, daft die fluorierten Dispergierungsmittel, die bei dem Verfahren verwendete
\verden, einen erheblichen Einflufl auf die Reaktionskinetik und \vahrscheinlich auch die die
alkalische Reserve bildenden Reaktionsprodukte haben.
Resumen—A pesar de su extendido uso en desacidificacion de papel, no se conoce con suficiente
details ni la composition exacta del reactivo Bookkeeper ni su quimica en relation al paso del
tiempo. For esta razon nuestro laboratorio analizo los reactivos Bookkeeper par media de
difraccion de rayos X de la muestra en po/vo, microespectrometria infrarroja, espectrometria de
energia dispersiva par fluorescencia de rayos X y microscopia de luz polarizada. Los resultados
claramente muestran que los dispersantes fluorinados contenidos en el reactivo tienen una
influencia decisiva en las reacciones cineticas y tambien, probablemente, en las especies quimicas
que forman la reserva alcalina.