PAPYLUM PROJECT: CHEMILUMINESCENCE - A NOVEL TOOL IN PAPER
CONSERVATION STUDIES
Matija Strlič*
University of Ljubljana, Faculty of Chemistry and Chemical Technology, Ljubljana, Slovenia *
corresponding author: matija.strlic@uni-lj.si
1. Introduction
Deacidification of paper is one of the most often performed active conservation procedures. The
need for optimal deacidification is well justified considering the vast quantities of acidic paper in
Western libraries and archives, e.g. in Poland.1 Due to the production process, papers produced in
the period ca. 1850-1990 are acidic, and the rate of their degradation is such that it is quite possible
that in the next century or two, most of the artistic, written and printed documentation on paper
from the period will irreversibly fall into pieces (Figure 1) if no action is taken.
Figure 1: A degraded acidic paper item from the 1900's, hardly usable due to its fragility.
However, optimisation of deacidification is a complex task, not only due to the variety of paper
materials used, but also due to the fact that the degradation processes, i.e. oxidation, taking place in
moderately alkaline paper, were relatively rarely studied2 and not well understood. Since cellulose
oxidation is a slow process, the need for extremely sensitive analytical techniques was also evident.
For these reasons, the consortium of five partners: University of Ljubljana, Faculty for Chemistry
and Chemical Technology, Slovenia; National and University Library, Slovenia; Polymer Institute
of the Slovak Academy of Sciences, Bratislava, Slovakia; The Netherlands Institute for Cultural
Heritage, Amsterdam, The Netherlands; and Centre National ď Evaluation de Photoprotection,
Aubiere, France, gathered with the goal to construct a new instrument exploiting a rarely studied
phenomenon observed during oxidation of paper, i.e. chemi-luminescence, the weak light emitted
by molecules as a result of a chemical reaction. This innovative approach, combined with
comprehensive studies of thermooxidative and photooxidative degradation of cellulose and paper
led to optimisation of aqueous deacidification techniques and new guidelines regarding evaluation
of paper stability, thus increasing the accessibility of cultural heritage on paper.
2. Results
The consortium, driven by expertise of five research laboratories, two of them in end-user
institutions, and one in an institute involved in instrument production for the scientific market,
ensured a highly focussed approach leading to the following results:
- Construction of a state-of-the art chemiluminomctric instrument, the first of its kind. The
measurement procedure is straightforward: a sample (even a complete object) is simply inserted
into the instrument and the emitted light can readily be measured - degradation of paper at room
temperature can virtually be seen. The instrument allows the use of humid atmosphere, which is
known to affect degradation of cellulose and paper, and it also allows the observation of samples
without destructive sampling. The instrument is a valuable addition to the conservation scientist's
laboratory, and is already commercially available.3 Its use extends well beyond conservation
research, as it may be used for degradation studies of a variety of organic materials, including e.g.
food.
Figure 2: The instrument consists of two parts, connected by fibre optics. The measuring chamber
(left) serves to isolate the sample from external light and to provide constant measuring conditions
in the surrounds of the examined part. The light-sensing part (right) serves to translate light signals
to digital ones.
- Using the chemiluminomctric approach and a variety of other methods, details of the cellulose
oxidation process were elucidated, such as the influence of
carbonyl groups.4,5 It is thus recommendablc to wash any degradation products out of paper and to
perform a reduction pre-treatment of paper to be deacidified, if possible.
Application of advanced kinetic calculations to chemiluminometric data lead to development of
degradation software with which we can predict rates of degradation at room temperature6,7 These
data are of extreme importance for the collection manager, as accelerated degradation experiments
performed in ageing chambers arc of little significance for ageing during storage conditions. In
future applications, such prediction methods may allow the conservation scientist to evaluate a
conservation treatment on an original, as only a micro-sample is needed.8 Using a newly invented
analytical technique, it was shown that the content of peroxides during oxidation of cellulose is
extremely low9 - this led to the conclusion that antioxidants with the role of radical scavengers
might not be very effective for stabilisation of paper.
Relative humidity was shown to have an extremely important role during degradation of moderately
alkaline paper - by correctly adjusting the relative humidity level, an up to 10-times decreased rate
of degradation was observed at the conditions of study.10 This research indicates an important future
line of study, which should lead to better guidelines for long-term storage conditions.
A comprehensive set of experiments was performed at four temperatures of accelerated ageing,
allowing us to extrapolate the ageing behaviour of a variety of treated models and real historic
papers to room temperature. Thus, we obtained the data on stability of differently treated papers
(containing CaCO3, MgCO3 selected anlioxidants) at the conditions of use.
By comparison of natural light-ageing with three different experimental techniques of artificial
light-ageing, we produced guidelines for the conservation researcher on how to conduct studies on
photo-stability of paper. Our studies have shown an extreme sensitivity of photo-aged papers
towards later oxidative ageing in darkness." This leads to the conclusion that for exhibited objects,
the deacidifi-cation also has to be carefully selected: MgCO3 and halides showed a stabilizing
effect. Manual deacidification of paper using aqueous solutions of Ca(HCO3)2 MgíHCO3)2 and
Ca(OH)2 were carefully optimised regarding concentration of the alkali, time of immersion, the
resulting pH and alkaline reserve.
At the project completion, members of the project, in cooperation with other renowned scientists
from the field, have set to write a book on paper degradation, summing up the recent advances. The Papylum webpage became an important resource of information and literature data on paper
degradation. The database will continue to be developed in the future: http://papylum.uni-lj.si
Research within the Papylum project thus lead to construction of a new valuable tool for the
conservation researcher, the most important result. Using the tool, and a variety of other optimised
and even newly developed methods, a profound understanding of cellulose oxidation was gained.
The extensive experimental plan using altogether more than 150 different paper samples lead to
data on rates of degradation at storage conditions and during irradiation with daylight during
exhibitions - on the basis of such information, the collection manager is able to choose the optimal
treatment.
The chemiluminometric approach has already led to first useful implementations outside the
Papylum project, e.g. studies of laser-treated paper12,l3 and of cotton textiles.'4 This demonstrates the
validity of our research directions.
The project also points to topics important for future research. On one hand, guidelines and risk
assessment for storage conditions should be evaluated, especially regarding recommendations on
relative humidity. On the other hand, lignin (not an object of our study) was shown to exhibit strong
chemilumincscence during oxidation - the newly developed methodology could thus help solving
other acute problems in conservation and preservation of paper-based cultural heritage for the
future. The developed chemiluminometric technique deserves to be explored further in the area of
cultural heritage materials of organic origin, e.g. textiles, varnishes, synthetic polymers, etc.
3. Acknowledgement
The authors gratefully acknowledge the support of the European Commission, Fifth Framework
Programme, Key Action "City of tomorrow and cultural heritage" within the Energy, Environment
and Sustainable Development, Contract n" EVK4-CT-2000-00038, project Papylum. The work is
the sole responsibility of the authors and does not represent the opinion of the Community. The
Community is not responsible for any use that might be made of the data appearing herein.
4. References
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Cracow. 2003. pp. 283-285.
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3. http://www.lumipol.com, accessed 28/10/2004.
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