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HE
SIGNIFICANCE of new approaches to the problem of oxidative paper degradation
processes in order to be able to design adequate conservation methods is
well recognised. In the frame of Papylum project, a research group of organic,
analytical, physical, polymer and conservation chemists, conservators, and
producers of scientific equipment was formed. Photon-counting
chemiluminometry is an established experimental technique, which opened
new routes in the understanding of degradation processes in synthetic macromolecular
systems. Is it believed that:(i) New tools and techniques to investigate the paper degradation at temperatures closer to the room temperature are needed. Accelerated ageing at elevated temperatures (typically at 80 °C) has in many studies proved inadequate to mimic natural ageing.
(ii) Further research into the thermo- and photo-oxidative degradation of cellulose should be carried out.
(iii) New strategies to extend the useful life of paper should be developed to inhibit its decay and methodologies for their systematic study and standardisation developed.
AS RECENTLY SHOWN by research consortium members, cellulose
luminescence depends on temperature, previous irradiation, concentration
of oxygen in the surrounding atmosphere, and on the relative humidity
of the atmosphere. Three different luminescent phenomena were identified.
However, a systematic study of the chemiluminescence phenomena during
long-term ageing experiments accompanied by comprehensive use of spectroscopic
techniques, should still be performed. ¶
It is well known that the degradation kinetics of cellulose
(and, consequently, of the corresponding chemiluminescence) greatly depends
on the environmental moisture. For an adequate analysis of the degradation
behaviour the moisture content should be controlled both in the atmosphere
surrounding the sample, and in the sample itself, since the relationship
is not linear. According to the data available in the literature, moisture
accelerates degradation of cellulose, although the mechanism is not at
all well understood.
The application of chemiluminescence to the studies of paper degradation
is the main objective of Papylum. The method has provided valuable new
insight into the degradation of synthetic polymers, therefore this novel
technique, applied to studies of problems in conservation is likely to
prove advantageous to the existing methods of study. ¶
For a comprehensive listing of relevant literature please
see the corresponding page and the
review
article.
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Chemiluminescence of three differently pre-treated samples of sulphate bleached chemical pulp during dynamic experiments (with constantly increasing temperature) in nitrogen atmosphere. While sample A was irradiated with incandescent light source and sample B was oxidised in air at 100 °C prior to the experiment, sample C was used as obtained. Chemiluminescence peaks were obtained and associated with different chemical reactions for all three phenomena observed - the technique is therefore useful in the studies of photo-degradation, oxidative degradation and thermal degradation in inert atmosphere. |
A SIGNIFICANT IMPROVEMENT of the current knowledge about
the degradation mechanisms of cellulose and paper due to the action of
oxygen under the influence of different factors such as light, humidity
and temperature is expected. This will allow a better estimation of the
degradation state and of the future degradation rate of cellulose-based
historical artefacts. The following questions will be addressed during
the project:
(i) What role is played by humidity, pH, peroxides and present carbonyl groups in the oxidation of alkaline paper and cellulose?
(ii) Sensitivity of cellulose towards visible light is typically manifested by chemiluminescence after irradiation. Further studies of photochemical degradation processes taking place in cellulosic materials will be performed.
(iii) How is the thermally initiated oxidation of low molecular model saccharides related to the oxidation of cellulose? May such studies help us understand the phenomena in a complex organic matrix?
(iv) What is the relation between chemiluminescence phenomena and accelerated oven ageing?
The published results of our work will be summarised
on the corresponding page, which will
be constantly updated.
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General workplan of the Papylum Project. |
BASED ON THE KNOWLEDGE obtained, possible future elaboration
of a comprehensive chemiluminometry-based test method to assess the (residual)
service life of paper would be a major advancement. The development and
testing of conservation treatments based on the impregnation of paper
with efficient antioxidant formulations, will thus be made much easier
and faster. This benefit can be extended to the segment of the papermaking
industry devoted to the production of permanent paper. To sum up, the
following major advances in damage assessment of paper artefacts are foreseeable:
(i) A new chemiluminescence instrument with a moisture-controlled reaction chamber and non-destructive sampling, which will offer shorter experimental times and better quality data than the present thermal ageing experiments (oven ageing).
(ii) An extensive knowledge on thermo- and photo-oxidative degradation of cellulose, summarised in a software that will allow us to estimate the rate of degradation of a certain sample at room conditions.
At the end of the project, a workshop was held, accompanied by publisation of a book on ageing and degradation of paper. Please see the separate page for more details.