EFFECTS OF ERASERS ONTHE DEGRADATION OF PAPER CELLULOSE
THI-PHUONG NGUYEN1.
STEPHANE BOUVET2, MYRIAM EVENO3
1Bibliothique nationale de France, Laboratoire Scientifique et Technique, 14 avenue Gutenberg, 77607Marne-la-Vallee Cedex 03, France e-mail:
2Bibliothcque nationale de France, Laboratoire Scientifique et Technique, 14 avenue Gutenberg, 77607 Marne-la-Vallee Cedex 03, France
3Bibliothcque nationale de France, Laboratoire du service restauration, 58 rue de Richelieu, 750S4 Paris Cedex 02, France
The purpose of this study was to evaluate the potential harmfulness of different kinds of erasers (factice, vinyl and styrene-butadiene copolymer based) on paper cellulose by following its degradation during artificial ageing treatments. The method of analysis used was the size exclusion chromatography.
INTRODUCTION
In order to evaluate the potential harmfulness of erasers on paper documents, a number of studies have been conducted to examine their composition, their effects on the changes in surface (yellowness, brightness, texture) and mechanical properties of paper.
Most of them showed:
• a more or less abrasion of the paper surface, depending on the eraser and the method used to remove visible crumbs [1,2] (vacuum cleaning or brushing),
• the amounts of residues remaining in the pores of paper depending on the author. The variations are partly due to the subjective method of evaluation used, visual examination, and depend a lot on the paper surface and the way the document is erased,
• no modification of the paper mechanical properties (fold and tensile strength) [3 ]
• no or very slight modifications of the surface pH [4,5],
• a noticeable color change of papers treated with Wishab, Groomstick [6], Kneaded Rubber and Pink Pearl [7].
In spite of some divergences, most of these studies conclude that vinyl based erasers are among the
less detrimental for paper. However, except for pH measurements, the conclusions brought by these various studies leaned essentially on physical tests (state of surface, optical properties of surfaces, mechanical properties), no study have emphasized the state of chemical degradation of the paper.
The purpose of this study was to add further information to these previous studies and especially to follow the degradation of paper cellulose mixed with different kinds of erasers during artificial ageing treatments. The method of analysis used was the size exclusion chromatography. The erasers studied belong to 3 of the main categories of erasers: styrene-butadiene based, vinyl-based and factice.
ERASERS COMPOSITION
The 10 erasers chosen for this study are among the most frequently used for dry cleaning of paper or photographic documents at the French national Library. We examined their composition using Fourier Transform Infra-Red Spectrometry (IRTF). and Energy Dispersive X-ray (EDX). The analysis conditions are described in the annexe 1.
The results are presented in the following table 1.
SEM OBSERVATION OF ERASED PAPERS
The surface of the erased papers were observed under high magnifications (l00x). The material used was a scanning electron microscope equipped with an energy dispersive x-ray facility.
We compared the surface appearance and the chemical composition of 2 parts of a same strip of paper: one was erased (20 times under a pressure of 200 g) then brushed carefully in order to remove the eraser crumbs. The other part was protected from erasing with a sheet of Mylar.
Results
For all of the erasers used, no difference in surface appearance nor in chemical composition (as analysed by EDX) was noticed between the two parts of the treated strips.
SIZE EXCLUSION CHROMATOGRAPHY
Size Exclusion Chromatography (SEC) was used to evaluate the cellulose degradation induced by the erasers. In comparison with classical methods of analy-
Tab. 1. Erases composition.
sis (mechanical tests or viscometry) this technique has proven to be particularly sensitive and well suited to the evaluation of the cellulose degradation state.
Using this technique, we followed the degradation of 2 different papers during artificial ageing treatments. Beforehand, these papers were mixed with one sample of each category of erasers: Mars Plastics for vinyl based type erasers, Wishab for styrene-butadiene based type erasers, Poudre Stouls and Design Artgum for factice type erasers.
Experimental
Papers
2 different paper samples were used: cotton pulp paper and wood pulp paper. The composition of both is listed in Tab. 2.
Before ageing, 0.1 grams of each paper was blended and mixed carefully with 0.2 grams oferaser crumbs. This mixture was then packed tightly in an
Tab. 2. Papers composition.
open 20 ml glass vial to ensure a good contact between the paper fibers and the eraser crumbs.
Accelerated ageing treatment
The bottles filled with paper fibers and eraser crumbs were aged 3 and 6 weeks at 65 % RH and 80 °C as described in the ISO 5630-3:1996 standard.
SEC analysis
After ageing, the paper samples were separated from the eraser crumbs and prepared for SEC analysis. The method used was the same as this described by Heike Jerosch [8] (see annexe 1).
Results
Each sample was analysed by SEC (the unaged and 6 weeks of ageing chromatographs are presented in the annexe 2) and the weight average of molar mass, Mw, calculated afterwards using a Microsoft Excel program.
Conclusions
• compared to the control samples, cotton or sulfite cellulose is always less degraded when treated with Mars Plastic eraser, even after 6 weeks of ageing
• after 6 weeks of artificial ageing, the 3 other types of erasers: Artgum, Poudre Stouls and Wishab have a negative effect on the paper cellulose. The most harmful seems to be the Artgum eraser; then, in decreasing order: Wishab and Poudre Stouls.
• the behaviour of cotton and sulfite pulps towards erasers are slightly different: after 3 weeks of artificial ageing, compared to the aged reference, sulfite cellulose is less degraded than cotton cellulose -for example, in contact with Design Artgum, a sulfile paper lose 10 % of its Mw whereas a cotton paper lose 50 % of its Mw. However, we can notice that after 6 weeks of artificial ageing, compared to the reference, the decrease in Mw is almost the same for the 2 types of papers, whatever the eraser used.
CONCLUSION
The results of SEC analysis confirm those obtained by previous studies: in a chemical point of view, vinyl based are the less detrimental erasers for paper cellulose.
Fig. 1. Mw of cotton pulp paper mixed with eraser crumbs and artificially aged (65 % RH; 80 °C).
Fig. 2. Mw of sulfite pulp paper mixed with eraser crumbs and artificially aged (65 % RH; 80 °C).
We showed that among the 3 other erasers tested, Design Artgum seems to be the most harmful; then in decreasing order: Wishab and Poudre Stouls. Because of the complexity and the large variation in composition between the different erasers, it is difficult to generalise the effects of a particular eraser to a whole category (Mars Plastic for vinyl based erasers, Design Artgum for factice erasers, etc.).
To confirm these tendencies, more tests should be performed.
However, these results must be relativized. The artificial ageing conditions are considered as "extremes" and an observation at a high magnification shows that not much crumbs remain in the pores of the paper after erasing and brushing.
So, these tests do not aim at preventing the use of some erasers in paper conservation but they should rather help the conservator in choosing the less harmful eraser for a given document or a given treatment.
REFERENCES
1. Pearlstein, E. J.. Cabelli, D., King, A., Indictor, N., "Effects of eraser treatment on paper", J.A.I.C, 22: 1-12(1982)
2. Sterlini, P., "Surface cleaning products and their effects on paper", Paper conservation news, 3(76): 3-7 (1995)
3. Pearlstein, E. J., Op. Cit.
4. Estabrook, E., "Considerations of the effect of eraser on cotton fabric", J.A.I.C, 28: 79-96 (1989)
5. Roelofs, W. G. Th.. De Groot, S., Hofenk De Graaf, J. H., "Die Auswirkung von Radierpulvern, Knetgummi und Radiergummi auf Papier", in Preprints vom 9"' internationalen Kongress der IADA: 131-136(1999)
6. Roelofs, W. G. Th.. A. Ibid.
7. Estabrook, E., Op. Cit.
8. Jerosch, H., Lavedrine. B., Cherton, J. C, "Study on the correlation between SEC and mechanical tests of different paper types for degradation state evaluation", Restaurator, 23: 222-239 (2002)
ACKNOWLEDGMENTS
We gratefully acknowledge Dr. Heike Jerosch for her help and advice throughout this study. Warm thanks to Bertrand Lavedrine for use of the SEC apparatus for preliminary tests.
ANNEXE 1 SEM-EDX ANALYSIS
EDX analysis were done using an ISIS system (Oxford Instruments) coupled with a SEM JEOL 840.
IRTF ANALYSIS
The erasers polymer was directly determined using a Spectrum 2000 Infra-Red Spectrometer (Perkin-Elmer) equipped with a Golden Gate Single Reflection ATR Diamond crystal system (Specac).
The same samples were afterwards extracted with ether and the soluble part was dried and analysed as previously mentioned.
The spectrum obtained were finally compared to references.
SIZE EXCLUSION CHROMATOGRAPHY
Technique
SEC was carried out on 3 Phenogel GPC mixed bed columns 5 mm particle size. 300 x 7.80 mm (ref: OOH-3259-KO) plus a guard column 30 x 7.80 mm. These columns were maintained at 50 °C during analysis. The pump system was a Gold 126 (Beckman) fitted with a Waters 2414 differential refractometer detector. 0.5 % w/v LiCl in DMAC was used as the eluant (0.6 ml/min).
The injection volume was 50 \x\, which corresponds to approximately 25 µg of cellulose. 2 injections were made per sample.
Column calibration was carried out using Pullulan standards (Showa Denko, Shodex)
Mw calculation
The molecular mass averages, Mw was calculated according to the following formula:
with n, the number of the molecules with the molecular weight Mi.
Sample preparation
An aliquot of 5 mg of paper fibers is placed in 4 ml extract clean reservoir fitted with a Nylon frit (Alltech), and hydrated with 1 ml water during 1 night. Then the water is sucked up and replaced with successively 3 x 1 ml of pure DMAC. After the 3rd DMAC washing, the fibers are translated in a glass vial filled with 1.25 ml of a 8 % (w/v) LiCl in DMAC solution, stirred and placed at least 48 h at 4 °C. Before injecting, each sample is diluted 5 times with pure DMAC then filtered with a 0.45 µm, 13 mm regenerated cellulose filter (Alllech)
ANNEXE 2
Fig. 3. SEC chromatographs of sulfile and cotton pulp papers imaged
Fig. 4. SEC chromatographs of cotton pulp papers mixed with different types of erasers. Artificially aged for 6 weeks (80 °C, 65 % RH)
Fig. 5. SEC chromatographs of sulfile pulp papers mixed with different types of erasers. Artificially aged for 6 weeks (80 °C, 65 % RH).