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What we did so far...

The knowledge obtained in the course of the Papylum project is summarised on this webpage, which will be constantly updated. A number of scientific and technical publications has been published in addition to posters at many international conferences. To the most important result, the prototype chemiluminometer, a separate page is devoted. Reprints of all the papers below can be obtained from Matija Strlic.
 

 
If you would like to obtain some basic information on the chemiluminescence phenomena taking place during cellulose degradation, you may want to consult the review paper, to be published in full in the Postprints of the Conservation Science 2002, 22-24 May, Edinburgh, Scotland.
M. Strlic, J. Kolar, J. Rychly:
Paper conservation chemistry: a review of chemiluminescence studies of cellulose stability (view it in PDF format).

Abstract: Chemiluminescence, the extremely weak light emitted during a chemical reaction, can conveniently be studied during oxidation and other degradation reactions of cellulose, thus providing us with important data on the reaction mechanisms and kinetics. While the knowledge of degradation mechanisms can lead to improved stabilisation and conservation methods, the kinetic data, most importantly activation energy, may help us to evaluate the material stability and thus compliment accelerated ageing studies of paper materials in climate chambers. The most often used experimental techniques and the so far identified mechanisms leading to chemiluminescence during degradation of cellulose are reviewed. The recent studies have mostly been conducted in atmosphere surrounding the sample being dry, however, some experiments indicate that there is a pronounced and complex influence of moisture on the chemiluminescence signal. This is especially important in the lower and, for the conservation chemist, the most interesting temperature region, <100 °C.
 

 
Results indicate that pullulan (polymaltotriose) can be used as a cellulose model in studies of the effect of molecular weight on the degradation. Namely, molecular weight is related to the concentration of end-groups and in the case of both pullulan and cellulose the end groups are aldehydes.

M. Strlic, D. Kocar, J. Kolar, J. Rychly, B. Pihlar:
Degradation of pullulans of narrow molecular weight distribution the role of aldehydes in the oxidation of polysaccharides
Carbohydrate Polymers, submitted.

Abstract: Degradation of pullulan samples of narrow molecular weight distribution was studied in O2 and N2 atmosphere at 180 °C and in air at 80 °C, 65%RH. At higher temperatures, size exclusion chromatographic analyses provided evidence for non-random degradation and formation of cross-links, a phenomenon depending on the concentration of carbonyl groups. Initial degradation rates in oxidative and inert environments were comparable, while at longer reaction times extensive cross-linking was typical of degradation in oxygen. At 80 °C, in a moderately alkaline environment, the degradation remains random, as demonstrated by the mono-modal distributions of molecular weights. Furthermore, there was no evidence of cross-linking. Correlations between the concentration of aldehyde end-groups in the pullulan samples, rates of degradation and the content of peroxides after a pre-oxidation treatment, as determined by the use of chemiluminometry, were demonstrated. This leads to the conclusion that aldehyde groups, via the peroxide intermediates, have the decisive influence on the rates of oxidative degradation of polysaccharides.
 

 
An important study of factors affecting the degradation of alkaline paper was recently published. The paper addresses a controversial topic, i.e. alkaline ageing of bleached chemical pulps.

J. Malesic, J. Kolar, M. Strlic:
Effect of pH and Carbonyls on the Degradation of Alkaline Paper
Restaurator, 23 (2002) 145-153.

Abstract: Paper is a composite material, which makes interpretation of experiments extremely difficult. Nevertheless, the data obtained so far on a limited amount of samples support the theory that higher pH values may have a negative effect on the stability of paper made from bleached chemical pulps. Higher pH accompanied by higher ageing instability was obtained for pulps deacidified with magnesium bicarbonate than calcium hydroxide. However, the additives in paper may cause a marked decrease in the pH of the former samples, resulting in less degradation in samples containing magnesium carbonate than of its calcium analogue. Contrary to the bleached chemical pulps, rag paper and paper made from purified cotton fibres do not exhibit pH sensitivity during the standard accelerated ageing conditions. The results demonstrate, that the difference in behaviour is caused by higher content of carbonyl groups in bleached chemical pulps than in rag and cotton paper.
 

 
A study of chemiluminescent phenomena and their rigorous kinetic evaluation based on experimental data in the temperature region above 100 °C was published. The research of degradation kinetics will form the basis of future modelling studies.

J. Rychly, M. Strlic, L. Matisova-Rychla, J. Kolar:
Chemiluminescence from paper. I. Kinetic analysis of thermal oxidation of cellulose
Polymer Degradation and Stability, 78 (2002) 357-356.

Abstract: Kinetic analysis of chemiluminescence intensity - time and chemiluminescence intensity - temperature runs for oxidation of cellulose at elevated temperatures is presented showing a good coincidence of rate constants of the first order from non-isothermal chemiluminescence experiments with those obtained from polymerisation degree determinations and from the literature. Rate constants from isothermal runs are lower than those from non-isothermal runs, however, when repeating non-isothermal runs several times in so-called temperature cycling experiments, the non-isothermal rate constants approach isothermal ones. The method enabling the differentiation of faster and slower process in oxidation of cellulose based on non-isothermal chemiluminescence runs is demonstrated.
 

 
A new method for determination of hydroperoxides in cellulose was developed. Hydroperoxides play an extremely important role in the autoxidative degradation route and their quantification may be quintessential for further studies.

D. Kocar, M. Strlic, J. Kolar, B. Pihlar:
A new method for determination of hydroperoxides in cellulose
Anal. Bioanal. Chem., 374 (2002) 1218-1222.

Abstract: A new chromatographic method for the determination of hydroperoxide groups in cellulose is described, whereby the sample is dispersed in a phosphate buffer solution (pH 7) of FeCl3, EDTA and a hydroxyl radical scavenger, N,N' - (5-nitro,1,3-phenylene) bisglutaramide. The reaction time, concentration of reagents and chromatographic conditions for the subsequent separation and quantitation of the hydroxylated products are optimised. The limit of detection is 0.14 µmol l-1 H2O2 which corresponds to 2.1 µmol peroxides per kg of cellulose (mass of sample: 0.4 g). It was shown that in the concentration range of H2O2 up to 15 µmol/l the method gives linear response and that the adsorption of reaction products on the fibres is negligible. For cellulose samples, this corresponds to a linear range of 2.1 - 225 µmol of hydroperoxides per kg. Due to the possible side reactions of hydroxyl radicals in the suspension of analyte, it is recommended that the standard addition technique is used. In purified cotton cellulose, the steady state concentration of hydroperoxides at room conditions was found to be 15.1±1.5 µmol/kg.
 

 
A comprehensive study of size exclusion chromatography of cellulose was performed in order to be able to optimise the determination of molecular weight (or degree of polymerisation), an extremely important parameter followed during degradation of cellulose.

M. Strlic, J. Kolenc, J. Kolar, B. Pihlar:
Enthalpic interactions in size exclusion chromatography of pullulan and cellulose in LiCl/DMAc
Journal of Chromatography A, 964 (2002) 47-54.

Abstract: Enthalpic phenomena were shown to contribute to the size exclusion separation mechanisms during chromatographic analysis of solutions of pullulans and cellulose in LiCl/DMAc solvent and eluent. The effects of LiCl concentration in the sample solutions and the effects of temperature were of the same order of magnitude for both pullulan and cellulose samples leading to systematic errors in the determination of mean molecular weight of up to a few 10%, depending on the conditions and on the molecular mass of the analyte. The systematic error is much higher than the random errors, the typical values of the latter being up to a few % (RSD). Low column temperature and a higher content of LiCl in the sample solution lead to lower determined mean molecular mass values. This could be explained by a decrease in the interactions between dissolved macromolecules, although interactions polymer-stationary phase and preferential solvation should also be taken into account. Furthermore, the cellulose stability in solution was determined, the first order random degradation constant being k = 6.9·10-8 /mol (monomer) / day.
 

 
In Slovenia, a TV programme was devoted to Papylum and InkCor, both 5th Framework Programme projects, and both under Slovenian coordination. Alas, only the Slovenian version currently exists, but we are working on a translation.

Nevarno crnilo (Dangerous Ink)
Zenit, May 26, 2002, Slovenian radiotelevision

View the recording of the programme as a Real Media clip

 

 
 
Papylum. Anno MMII