Performance Evaluation of 4-Ply Rag Boards Containing Calcium

Performance Evaluation of 4-ply Rag Board Containing Calcium Carbonate and Zeolites May 30, 2012 www.loc.gov/preservation/ Library of Congress ♦ Preservation Directorate

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Performance Evaluation of 4‐Ply Rag Boards Containing

Calcium Carbonate and Zeolites

Preservation Research and Testing Division

Library of Congress

101 Independence Ave SE, Washington D.C 20540‐4560

May 30, 2012


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CONTENTS

Page

Executive Summary 3

1. Introduction 4

2. Experimental 6

3. Results 9

4. Conclusions 16

Acknowledgements 17

References 17


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EXECUTIVE SUMMARY

Research conducted from January‐May 2006 investigated the properties of rag boards containing zeolite

molecular sieves, and examined the boardsʹ ability to absorb and retain pollutants at conditions

comparable to those encountered in library and archive settings. Rag board samples containing a calcium

carbonate buffer, calcium carbonate plus zeolite, or only rag fiber were obtained from one commercial

supplier to provide samples directly comparable in all aspects other than the presence of the zeolite. A

sample of the proprietary zeolite used by both current manufacturers of sorbent‐loaded boards was

analyzed to determine its elemental composition, alkaline buffering capacity, and other properties.

Previous research on zeolites and other sorbents for museum applications has been conducted using high

pollution concentrations, or a physical model that forces contaminated air to pass through the sorbent

before reaching a detector. These approaches are not ideal for studying adsorption effectiveness at low

concentrations, or in unforced physical systems, such as would be encountered in a library collection. A

new exposure method was developed, in which the changes in vapor concentration are measured in the

air surrounding a board sample in a small test chamber. After a contaminant is added to the chamber,

timed measurements reveal the rate and limiting equilibrium value of its uptake by the board sample.

Acetic acid was selected as a model contaminant for the study, as it is one of the major organic acids

known to be associated with deterioration of library and archive materials. An ion chromatography

method was optimized for measurement of acetic acid levels, and was demonstrated to give linear results

over the range of 0.5 – 100 parts per million. The study did not assess other pollutant compounds.

Four‐ply rag board samples were exposed to varied acetic acid vapor concentrations, focusing on the 2‐20

ppm range. Levels of 2‐25 ppm have been previously observed in archives, and are considered to

represent a range of low to high risk to collection items. Absorption rates and total uptake were compared

for the three types of rag board under study. Samples which had adsorbed large amounts of acetic acid

were transferred to uncontaminated chambers, and the rate and total amount of acetic acid vapor

subsequently released from the rag boards were monitored. Differences were observed in both the rate of

uptake and the extent of desorption for the zeolite‐loaded rag boards, compared to the plain rag and

buffered rag boards.

Zeolites and zeolite‐loaded housing materials can be effective pollution sorbents in library and archival

environments, provided that their application is made with an understanding of their limitations. This

pilot study of rag board with and without calcium carbonate and zeolite sorbents has demonstrated

sorption effectiveness at real‐world, low concentrations of acetic acid in an unforced physical system.


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1. INTRODUCTION

1.1 Air quality issues in storage environments The impact of environment on collection materials, particularly the presence and deleterious effects of

volatile oxidative or corrosive volatiles, is an active concern and area of study in the museum, library, and

archive fields (1). It has long been recognized that low quality housing materials can release volatile

organic acids that accelerate the deterioration of collection items stored within them. By contrast, mat

boards, boxes, folders and related materials which contain alkaline buffers degrade more slowly, and thus

minimize adverse impact on the contents. These buffered housing materials may also absorb volatiles

released by the collection items themselves as they degrade, while additionally providing protection from

external pollution. In recent years, housing materials incorporating sorbents have appeared on the

commercial market. These materials purport to offer an enhanced level of stabilization for collections

stored in them, both from collection degradation products and from indoor air pollutants such as ozone

and oxidizing gases. Pollution‐scavenging materials have been used for some time by museums and

archives as filters in air‐handling systems or as sachets of sorbent material incorporated into display cases.

The introduction of activated carbon or zeolites directly into the housing material itself translates this

practice to item‐level storage. However, sorbent‐loaded housings have received relatively little technical

study during their fifteen years of availability.

To determine whether these sorbent‐loaded materials offer concrete benefits for collections storage under

conditions of normal use, this study investigated the effectiveness of zeolite‐loaded housing materials to

absorb and retain pollutants at conditions comparable to those encountered in library and archive settings.

1.2 Current uses of sorbents in museum contexts and housing materials

Activated carbon, zeolitic molecular sieves, silica gels, and other classes of sorbents have a multitude of

commercial and industrial uses: as dessicants, air filters, in chemical purification, spill cleanup, etc. Many

of these uses are found in museum and library settings. Zeolites are allumino‐silicate minerals, with

micro‐porous structures that give them a large surface‐to‐volume ratio. The allumino‐silicate molecular

framework has a net negative charge, and positively charged cations will be found trapped in the pores or

substituted into the framework. These cations give the zeolites their ion‐exchange capability. Micro‐

porous molecular sieve materials selectively adsorb compounds based on their size and charge. This

interaction is a combination of physisorption, since the small pore size makes diffusion back out of pores

thermodynamically unfavorable, and ion‐exchange chemisorption (2).

Archival housing materials incorporating sorbents were first offered commercially in 1992, when

Conservation Resources (CRI) introduced the MicroChamber® product line, incorporating both zeolites

and activated carbon (3). Nielsen Bainbridge introduced the ArtCare® line, incorporating zeolites, in

1995. Numerous paper and board products are now available in each of these lines, combining sorbents

with different fiber furnishes and physical configurations for diverse applications. Patents for the use of

“organophillic, hydrophobic, acid‐resistantʺ molecular sieves in conservation housing materials were

granted to William Hollinger of CRI in 1996 and 1997 (4). Both manufacturers presently use the same


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zeolitic material, CR‐SPZ, in their boards and papers. Although “CR‐SPZ” appears to be a standard

abbreviation, it is apparently a product name. See section 3.2 below for further discussion.

1.3 Previous performance studies

Previously published studies of housing materials containing zeolites (5, 6, 7) have demonstrated the

ability of zeolite‐loaded products to effectively adsorb high‐concentration doses of pollutants in acute

exposure tests. A wide‐reaching study examined eighteen different sorbents of several types, and

compared their absorbance of common museum pollutants using permeation tube studies (8). In that

study, CR‐SPZ was the most effective sorbent for acetic and formic acid of the zeolites and clay minerals

examined. Some pollutants were more effectively removed by other sorbents, and activated carbon had

the best broad‐spectrum effectiveness. Similar work using lead coupon dosimeters to gauge protection by

sorbent sachets in a sealed chamber test also found that activated carbon and one zeolite were most

effective at removing saturated acetic acid vapor (9, 10). Sealed‐vessel studies of paper degradation rates

have demonstrated accelerated degradation in the presence of volatile organic compounds (VOCʹs), which

for some paper types may be mitigated by the addition of sorbents (11).

However, questions remain about sorption effectiveness in real‐world applications. Calcium carbonate,

for example, readily neutralizes acids in solution, but studies conducted at National Institute of Standards

and Technology (NIST) have shown that calcium carbonate buffered boards do not significantly inhibit

the flow of acids in gas phase in and out of a box (12). Modeling studies have demonstrated that air

exchange in an archival box is a combination of diffusion through the board and airflow through the gaps,

with the diffusion constant of the board determined by its density, thickness, and other factors (13). The

effectiveness of zeolites dispersed in a board to neutralize pollutants which may diffuse through pores of

the board or bypass the board completely, remains to be demonstrated.

A further limitation of the previously published studies of zeolite‐loaded products is that the sorbent‐

loaded paper and boards examined were compared to conventional buffered and unbuffered paper

products whose fiber composition, grammage, and porosity differed from that of the sorbent‐loaded

products. Since all of these factors affect vapor diffusion rates, direct comparison is difficult.

To address these limitations of previous studies, this pilot study was developed using low pollutant

concentrations representative of library conditions, a set of samples that matched each other closely in all

characteristics other than the presence of sorbents, and a test chamber configuration that allowed free air

circulation but does not force the pollutant through the boards.


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2. EXPERIMENTAL

2.1 Samples

With the cooperation of a mat‐board manufacturer, the Library obtained three specimens of 4‐ply rag

boards, all made from the same fiber furnish, and from the same production batch, so that they were as

directly comparable as possible. The first board sample is made from a lignin‐free rag furnish (ʺRʺ); the

second contains a calcium carbonate buffer (CaCO3), providing a 3% alkaline reserve (ʺRBʺ); and the third

contained both calcium carbonate and a sorbent, zeolite CR‐SPZ (ʺRBZʺ). Sample ʺRBZʺ represents

Nielsen‐Bainbridgeʹs ʺAlphaRagʺ product line. Its tested performance in this study relates specifically to

this product as manufactured in 2005‐6. The scope of this project was limited to 4‐ply rag mat boards with

and without sorbents, and therefore cannot be extrapolated without further testing to the numerous other

paper and board products incorporating ArtCare® and MicroChamber® materials.

Table 1: Composition of the three rag board types compared in this study

Abbreviation Mat board type

R rag fiber

RB rag fiber + buffer (calcium carbonate)

RBZ rag fiber + buffer (calcium carbonate) + zeolite (CR‐SPZ)

2.2 Pollutant vapor and concentrations

Acetic acid has been identified as one of the primary pollutants in indoor environments (14); it is emitted

by building materials and coatings, and is a major volatile generated by paper and film materials as they

deteriorate (15,16). It in turn accelerates deterioration rates of these library materials, both paper and

photographic materials (11,16,17), as well as having well‐known deleterious effects on metal, stone, and

natural history specimens in museum collections (1). Thus, acetic acid was selected as the pollutant of

interest for this project. Exposures were conducted at concentrations in the range of 2‐21 ppm, which

correspond to levels of acetic acid vapor concentrations frequently observed in storage areas containing

degrading acetate film (16). Results from this pilot study cannot be directly extrapolated to other specific

pollutant compounds.

2.3 Instrumentation

2.3.1 pH and alkaline reserve

PH and alkaline reserve measurements were conducted following ASTM method D 4988‐96 (18), using a

Metrohm automated titrator equipped with sample changer 730, Titrando‐809 dosing unit, and Tiamo 1.0

control software.

2.3.2 Scanning Electron Microscopy‐ Energy Dispersive X‐ray Spectroscopy (SEM‐EDX)


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A small rectangle of each rag board was cut with a diamond blade, bent into an L‐shape, and mounted

with carbon tape so that the exposed cross‐section of the four ply‐board samples projected straight up

from the mounting stud. The samples were viewed with a Cambridge S‐200 scanning electron microscope

with no coating. Elemental analyses and elemental distribution maps were collected using Cambridge

Quantex software.

2.3.3 Ion chromatography

Headspace vapor samples drawn from the reaction vials with gas‐tight syringes were slowly bubbled

through sodium hydroxide to fix the acetate ion in solution, and the acetate concentration determined by

ion chromatography. 20‐microliter samples were injected onto a Dionex AS‐11 column in a DX‐500 ion

chromatography system, running a modification of a separation method optimized for organic acids (19).

Step‐wise dilutions of sodium acetate from 500 ‐ 0.5 ppm were analyzed in replicate to establish a

calibration curve, permitting quantitative evaluation of the test aliquots. This instrumental calibration

curve was created with five replicates, repeated at two periods over the course of the study, and selected

standards were repeat tested daily to verify instrument performance baselines. Under these conditions

acetic acid was successfully quantified at concentrations from 250 ppm to 2 ppm, and its presence detected

at levels as low as fractions of 1 ppm.

2.3.4 Volatile organic pollutant exposure tests

Exposure tests were conducted using 10ml Pierce Reacti‐Vials as reaction chambers. These small vials

maintain their seals under moderate pressure or vacuum, while the valve design permits sampling or

introduction of material into the vial. All exposure experiments were repeated in duplicate or triplicate.

Rag board samples were cut to uniform size using an automated mat cutter, preconditioned to 50%

relative humidity following ASTM method D865‐93 (20), and suspended on stainless steel pins for free

circulation around all faces.

Acetic acid vapor was collected from the saturated headspace above a reservoir of concentrated acetic acid

in a sealed vessel, and injected into the miniature reaction chambers. This approach permits precise

control over the relative humidity and acetic acid levels in the test chamber. It should be simple to

calculate the vapor concentration above a liquid in a sealed vessel from fundamental principles. However,

published values of the relevant physical constant for acetic acid are inconsistent, as other workers have

also noted (10). Heuristic experimentation was therefore carried out with empty vials to determine the

correlation of injected vapor volume to the resulting pollutant concentration, and the repeatability of this

dosing method. Experiments with rag board samples were conducted using acetic acid vapor doses of 2.5

and 1 ml. These acetic acid vapor volumes yielded 20 ppm and 7 ppm measured acetate concentrations,

with a +/‐5% accuracy level. Acetate levels in this range correspond to the worst‐case ʺdanger levelʺ

conditions for a film archive (18‐20 ppm) and an intermediate danger level for other materials (16).

In a series of static‐dose experiments, aliquots of acetic acid vapor were injected into the reacti‐vials, and

the pollutant concentration remaining in the vial measured after equilibration times ranging from 1‐48

hours. A second series of experiments examined equilibration times ranging from 1‐60 minutes. These

were conducted in two series, one series using multiple measurements on a single vial, and a second series

using individual vials for each time interval. The data from the second set of individual vials gave better

repeatability between replicates, and only these results are discussed here.

For desorption tests, rag board samples and an equivalent weight of pure zeolite powder were exposed to

saturated acetic acid vapors for five hours, weighed to determine their mass uptake, then transferred to

clean reacti‐vials. Acetic acid concentrations in the vials were measured after 24 hours equilibration time

in the same manner described for the adsorption studies. Longer exposures to the concentrated acetic acid

resulted in saturation of the rag board samples, with visible wetting of their surfaces. Results from these

trials are not reported here.

Figure 1: Reacti‐vial miniature test chamber with a sample fixed on a stainless steel dissecting pin

0 0.50 1.00 1.50 2.00 2.50

0

1.00

2.00

3.00

4.00

5.00

6.00

7.00

µS

standard acetate solutionsstd. E 21.72 ppm acetatestd. F 6.52 ppm acetatestd. G 2.17 ppm acetatestatic vial, 2.5ml acid vapor

Figure 2: correlation of acetic acid vapor volume to acetate concentration standards E, F, and G. The pale

blue chromatogram, 2.5 ml. of vapor, corresponds closely to standard E and conditions the vial to ~20

ppm.


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3. RESULTS 3.1 Characterization of rag board samples

Samples of the three rag board types were analyzed as‐received to verify their composition and structure.

PH and alkaline reserve titrations indicated that all three rag boards examined had an alkaline pH,

ranging between 8.3‐9. Alkaline reserves between 3 and 4 wt‐%‐equivalent calcium carbonate (CaCO3)

were found in the buffered (RB) and zeolite‐plus‐buffer (RBZ) rag boards, in agreement with the

anufacturerʹs specifications of 3‐5 % alkaline reserve. The plain rag board (R) contained a negligible

alkaline reserve, approximately 0.5 wt‐%‐equivalent CaCO3.

SEM‐EDX analysis of rag board RBZ revealed the presence of titanium (Ti), calcium (Ca), silicon (Si) and

aluminum (Al), and smaller amounts of sodium (Na), with an even distribution of the zeolite and calcium

across the four plies. This is in agreement with the expected specifications of 12‐14 wt‐% zeolite in this

board (21). Buffered rag board RB likewise contained Ti and Ca, with comparatively lower amounts of Si

and Al, while plain rag board Rʹs most abundant inorganic element was Ti.


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Fig. 3: Sample RBZ: ArtCare® Alpharag, SEM image and elemental distribution of Ca, Si, and Al.

3.2 Characterization of zeolite cr‐spz

Elemental analysis was also carried out on a sample of the CR‐SPZ zeolite powder. The zeolitic framework

elements silicon and aluminum were detected with relative abundances of 78 and 17% respectively, giving

a Si:Al ratio of 4.6:1, with sodium cations present at a relative abundance of 5.2%. This framework may be

characterized as an intermediate‐silicate zeolite, that is, having a Si:Al ratio greater than 2:1. Such

intermediate‐Si zeolites may be expected to have better thermal and acid stability than low‐Si zeolites.


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Figure 4: SEM image of CR‐SPZ powder,

0

2000

4000

6000

8000

10000

12000

14000

16000

0 100 200 300 400

Potential, kV

Intensity, A

rbitrary U

nits

Silicon

Aluminum

Oxygen

Sodium

17 % Aluminum77.8 % Silicon5.2 % Sodium

3600X magnification. Image width = 20 microns

Figure 5: EDX spectrum of CR‐SPZ

Zeolite naming conventions are normally indicative of their crystalline structures, following nomenclature

defined by the International Zeolite Association Structures Committee (22). There are over 200 distinct

families of structures. Approximately 50 structural families consist of natural minerals and their

customized derivatives manufactured for specific applications; the remaining structures exist only in

synthetic products. The phrasing ʺXX‐SPZʺ appears to describe a member of the SPZ structural family;

however, no such structural family is defined by the Association. If this material is indeed an industrially

synthesized or modified zeolite, then ʺSPZʺ is most probably an abbreviation used by the producer.

X‐ray diffraction patterns obtained for this specimen at the Getty Conservation Institute could not be

matched perfectly to a structure in the IZA database, but showed closest similarity to the FAU family (23).

The Si:Al ratio determined for this specimen is higher than is typical for natural mineral faujasites, which

normally have ratios of approximately 2.5:1. Natural faujasites typically include Ca and Magnesium (Mg)

cations at around 5 and 1% abundance, where this specimen contains ~5% sodium but no calcium or

magnesium. These characteristics are not typical of a natural faujasite mineral; however, they are not

implausible for a custom‐modified industrial derivative.

Figure 6: structure of faujasite (FAU) and related zeolite families, after Auerbach. (2)

To assess whether zeolite CR‐SPZ was hydroscopic or hydrophobic, zeolite powder samples were oven‐

dried, then exposed to 50% and 100% RH conditions and permitted to equilibrate for 72 hours.

Equilibrium moisture contents at these two conditions were found to be 23% and 27%. From this it may be

concluded that some moisture uptake occurs.

The pH of slurries of CR‐SPZ zeolite powder were found to be alkaline, as expected from the inherent net

charge of the sodium cations. When a zeolite slurry was titrated against hydrochloric acid (0.1 M)

following the standard method to determine alkaline reserve (18), an excess volume of sodium hydroxide

was required to re‐neutralize the solution, which may indicate that the zeolite was partially dissolved by

the acid. Thus, the presence of this zeolite in a paper or board sample may slightly affect the results of

alkaline reserve titrations on such materials. Repeating the titration using acetic acid (0.1 M) instead,

affording a milder starting pH (4, rather than 2), it was found that the zeolite powder itself provides no

effective alkaline reserve.

3.3 Volatile organic pollutant exposure tests

3.3.1 Static and timed uptake series

Figure 7 shows the acetic acid levels inside the vials after 3 hours of exposure to 1 ml (~7 ppm) acetic acid.

All three rag boards successfully absorbed the entire pollutant load, in this instance. Longer equilibration

times and higher initial acid levels were also examined, with similar results. Simple physical trapping by

the rag fibers appears able to soak up some acetic acid.


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Figure 7: comparison of acetic acid remaining in the vial headspace after 3 hoursʹ equilibration

Initial uptake of the acetic acid vapor was rapid for all three rag board types. A second series of

experiments focused on the first hour, and in particular the first ten minutes. Figure 8 shows one such

timed series for a set of vials with a 2.5 ml (20 ppm) acetic acid load. Figure 9 shows a typical uptake

curve in numerical view. Similar results were observed for all three rag board types and both pollutant

levels tested. During the earliest minutes of exposure, the zeolite‐loaded rag board slightly but

consistently took up the acetic acid vapor more rapidly than the other two rag boards, as shown in Fig. 10.

This modest acetic acid vapor dose does not exceed the capacity of either type of rag board, in this single‐

dose static experiment, so the others do catch up over time.

0 0.50 1.00 1.50 2.00 2.50l i i i

0

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00µ

Sstatic vapor load adsorption - 3hrs, 1ml acid

RBZ

RB

R

vapor blank

0 0.50 1.00 1.50 2.00 2.50l i i i

-1.00

0

1.00

2.00

3.00

4.00

5.00

6.00

µS

adsorption over time, 0-45 minutesstatic 2.5ml, 0 minstatic 2.5ml, 10minstatic 2.5ml, 15minstatic 2.5ml, 45minstatic 2.5ml, 6 min

Figure 8: rate of uptake of acetic acid vapor by board R

uptake of static acetic acid load: rag

62

113.8 3.1 30

10

20

30

40

50

60

70

0 10 20 30 40 5

time, minutes

ace

tate

tota

l (IC

) x

10

4 , arb

.

un

its

0

Figure 9 : rate of uptake of acetic acid vapor by board R

uptake of acetic acid: R vs RBZ

0

20

40

60

80

0 2 4 6

time, minutes

ace

tate

IC u

nits

x10 4

rag

RBZ

Figure 10: short timescale comparison the uptake rates of boards RBZ and R

3.2 Desorption experiments

To investigate whether the acetic acid vapor taken up would be subsequently released by a contaminated

board moved to a cleaner environment, samples of the three types of rag board and an equal weight of

plain zeolite powder were exposed to saturated acetic acid vapor, then transferred into clean Reacti‐vials

and permitted to equilibrate for 24 hours.

Gravimetric analysis showed that acetic acid mass transfer into the zeolite powder, normalized to %

uptake per gram, was significantly greater than the amount taken up by the three types of rag board, as


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shown in Fig. 11. These results are averages over only two replicates, so the difference seen here between

boards RB and RBZ is not numerically significant.

Re‐release of acidic vapor at levels corresponding to 1‐2 ppm was observed for all three rag boards and for

the zeolite powder, as shown in Fig. 12. Although the RBZ board takes up as much acid per gram as the

other two rag board types, and the zeolite powder takes up twice as much, they release less of the acetic

acid, as shown by the overlay chromatogram. Similar desorption effects have been reported in a prior

study of acetic uptake by zeolite beads, activated charcoal filters, papers impregnated with potassium

hydroxide or calcium carbonate, and MicroChamber® paper (24).

mass uptake, wt%/gram of sample

1.2

1.5

1.3

2.2

0

0.5

1

1.5

2

2.5

R RB RBZ Z

% o

f s

tart

ing

we

igh

t g

ain

ed

Figure 11: mass uptake of acetic acid vapor, normalized to % uptake per gram of board sample. ʺZʺ

indicates plain zeolite powder

0 0.50 1.00 1.50 2.00 2.50Mi

-0.20

0

0.20

0.40

0.60

0.80

1.00

1.20

µS

acetic acid released after 5-hour exposureRRBRBZZ

Figure 12: measured acetic acid concentrations released by contaminated specimens after 5 hoursʹ

exposure to concentrated acid vapor, then 24 hoursʹ equilibrium in a Reacti‐vial


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3.3 Interpretation and practical considerations

To adsorb, physically trap, or chemically neutralize acetic acid or any other volatile pollutant, a sorbent

material must interact with the pollutant. Industrial air filtering materials using sorbents force the air to

pass through a filter bed, disc, or other barrier of the active material, affording numerous molecular

collisions and numerous opportunities for interaction. This is also the case in permeation tube experiments

and showcase designs incorporating sorbents into active air circulation systems.

In library storage conditions, however, airflow is often passive rather than active, and not constrained. A

mixture of air movement through housing gaps and diffusion through the housing materials will be

observed. Air permeability constants of papers and boards also affect the opportunity for sorbents to

encounter and interact with the pollutant vapor, as demonstrated in a study of sulfur dioxide, and thus

impact the sorbentsʹ practical effectiveness (7). Deterioration studies conducted in well‐sealed

passepartout mats incorporating sorbents indicated that in the absence of any airflow, the volatiles

emitted by degrading materials interacted with other items immediately adjacent, rather than being

neutralized by the sorbent a few inches away (25).

This study has demonstrated the complete uptake of low concentrations of acetic acid vapor by rag boards

in an unconstrained system, and that under the conditions examined, most of the acetic acid adsorbed by

zeolites will be retained rather than released to establish an equilibrium. However, any approach to the

reduction of reactive volatile vapors in collection storage environments requires thoughtful consideration

of the physical placement of the sorbent relative to the source of the volatile contaminant, and to the air

flow patterns and rate of air exchange in the environment under consideration.


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4. CONCLUSIONS 4.1 Effectiveness of pollutant absorption by sorbent-loaded rag boards under mild conditions In real‐world applications, sorbents experience a constantly replenishing supply of pollutant vapors,

which may fluctuate and potentially increase over time. Replicating such conditions exceeds the scope of

this pilot study. These single‐dose experiments do, however, support some conclusion that will have

relevance to a constant‐supply situation.

Rag board fibers have demonstrated some ability to adsorb pollutant vapors, even when no additives are

present. Buffered rag boards demonstrated modestly improved acetic acid vapor uptake and retention

over the plain board. At the moderate concentrations examined (2‐20 ppm acetic acid), the zeolite‐loaded

rag boards adsorbed acetic acid vapor faster than the plain or buffered boards with the same fiber furnish.

All the rag boards tested will subsequently release acetic acid vapors if they are moved to a less polluted

environment; however, the released fraction was lower for the zeolite‐loaded rag boards than the others.

The zeolite powder, examined in isolation, absorbs significantly more acetic acid vapor than equivalent

weights of rag fiber or calcium carbonate, and releases a lower percentage of its total uptake. The zeolite

loaded rag board similarly released a lower quantity of acetic acid vapor than plain and buffered rag

board when dosed with comparable initial amounts.

Zeolites and zeolite‐loaded housing materials can be effective pollution sorbents in library and archival

environments, provided that their application is made with an understanding of their limitations. This

pilot study of rag board with and without calcium carbonate and zeolite sorbents has demonstrated

sorption effectiveness at real‐world, low concentrations of acetic acid in an unforced physical.

Commercial products often change in composition and manufacturing method, so testing studies of

commercial samples need to be interpreted conservatively as representing the composition of materials at

a specific time. As part of the Quality Assurance Program, the Library constantly re‐tests any materials

used in housing and exhibition to ensure their consistency with approved conservation material

specifications. Pollutant mitigation remains an important topic in heritage conservation science, and PRTD

has received numerous inquiries relating to the test methods developed and final findings from this 2006

pilot project. In 2012 this report was updated to include recent references and pollutant studies.

Future research being developed and identified as critical for the field includes the assessment of the rate

at which each sorbent material becomes saturated with pollutant materials, and the subsequent re‐release

of a range of common pollutants known to have degradative effects on cultural heritage materials.


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ACKNOWLEDGEMENTS

The financial support of this fellowship by the Nielsen Bainbridge Company is gratefully acknowledged,

as well as assistance with technical specifications and samples of ArtCare® AlphaRag from Norman Boris.

Jim Druzik at the Getty Conservation Institute kindly shared a specimen of zeolite CR‐SPZ, unpublished

X‐ray diffraction (XRD) results, and several thought‐provoking discussions.

PRTD colleague Frank Hengemihle performed the SEM‐EDX analyses, and project advisor Lambertus van

Zelst provided an invaluable source of advice and support throughout the project.

REFERENCES

1. An extensive bibliography on indoor air quality and effects of pollutants on materials, focused on problems

in museums and libraries, is regularly updated by the Indoor Air Pollution Working Group, and may be

consulted at http://iaq.dk/biblio/biblio.htm ʺBibliography on Indoor Air Pollution, Detection Methods,

Material Deterioration, Mitigation Methods, Case Stories, Etc.ʺ

Last accessed 4/14/2011.

2. Auerbach, S.M., Carrado, K.A., and Dutta, P.K., Eds. Handbook of Zeolite Science and Technology. Marcel

Dekker, Inc, NY, 2003.

3. Vine, M.G., and Hollinger, W., ʺActive Archival Housingʺ, Restaurator 14 (1993) 212‐216.

4. United States Patent # 5,525,296 and #5,683,662.

# 5,525,296, June 11, 1996, ʹArticle and method for archival preservation with an organophilic, hydrophobic or

acid‐resistant molecular sieveʹ.

#5,683,662, November 4, 1997, ʹArticle and method for archival preservation with an organophilic,

hydrophobic or acid‐resistant molecular sieveʹ.

5. Hollinger, W., ʺMicrochamber Papers Used as a Preventive Conservation Materialʺ, in: Preventive

Conservation: Practice, Theory and Research. Preprints of the Contributions to the Ottawa Congress, 12‐16 September

1994. A. Roy and P. Smith, Eds. International Institute for Conservation, London, 1994. pp 212‐216.

6. Rempel, Siegfried. “Zeolite Molecular Traps and Their Use in Preventive Conservation”, Western Association

for Art Conservation Newsletter 18 (1996).

7. Daniel, F., Hatzigeorgiou, V., Copy, S., and Flieder, F., ʺEtude de lʹEfficacité dʹun Nouveau Produit

dʹArchive: le Microchamber®ʺ, in: Les Documents Graphiques at Photographiques: Analyse et Conservation. Traveaux

du Centre de Recherches sur la Conservation des Documents Graphiques 1994‐1998. Paris, Direction des Archives de

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8. Druzik, J.M “Performance of Pollutant Adsorbents (2001‐2003)”; project summary posted at

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