Testing CSC Book Saver®, a Commercial Deacidification Spray

Restaurator, 2002, 39–47 Printed in Germany · All rights reserved Copyright  Saur 2002 _______________________________________________________________________ ISSN 0034-5806 Testing CSC Book Saver , a Commercial Deacidification Spray ® by A-L. DUPONT, J. BARTHEZ, H. JEROSCH & B. LAVÉDRINE INTRODUCTION Washing acidic paper documents in aqueous baths in order to rid them of soluble acids is a common conservation treatment. Often, alkaline salts are added to the wash water to neutralize all the acids and leave an alkaline reserve in the paper. Depending on the sensitivity of the writing or drawing medium to water, alkaline salts can alternatively be dissolved in alcohol or in a mix of alcohol and water. However, in a museum or a library/archive context such procedures are not always possible because they are time consuming. When working in terms of collection priorities preventive conservation measures must prevail over lengthy treatments. In some cases, when treatment is necessary, but time is limited, the use of a deacidification spray is appealing, since it is fast and does not require unbinding. It seemed interesting to test the efficiency of the deacidification spray CSC Book Saver® as a new deacidification alternative recently introduced on the European market. This study is not intended as a thorough product review but rather as a technical note to help paper conservators and, more generally, library and archives collection keepers form their own opinion. Cold extract pH1 and alkaline reserve2 were measured on deacidified papers. The paper surface was analysed by scanning electron microscopy and energy dispersive X-ray (SEM/EDX) to evaluate the homogeneity of the alkaline deposit. The consumption of the buffer reserve over time was simulated by exposing the papers to nitrogen dioxide3 in a pollution chamber4. Changes in pH and colour were monitored and the protective effect of the neutralizing agent on the cellulose was analysed by size exclusion chromatography. PAPERS TESTED We tested a mechanical pulp paper, sized with alum and rosin, taken from a book edited in 1931, which was very acidic and yellow. Such paper would be a typical 39 Restaurator 23: 39–47  2002 Saur, Munich etc. Brought to you by | University of Michigan Authenticated Download Date | 5/20/15 10:59 AM ® Testing CSC Book Saver candidate for deacidification and was chosen in order to simulate a real case study. In order to perform size exclusion chromatography we also studied Whatman No.1 qualitative filter paper, a well known pure cellulose paper widely used for laboratory testing. The papers were treated either on one side or on both sides of the sheet. THE DEACIDIFICATION SPRAY The deacidification solution is composed of the neutralizing agent, and a carbonated magnesium di-n-propylate [(CH3CH2CH2O)2MgOCO] dissolved 70% in npropanol (w/w). It has a grey colour. The propellant is HFC 227 (1,1,1,2,3,3,3heptafluoropropane). HFC 227 is a non-toxic non-flammable odourless gas used for pharmaceutical inhalers and has no ozone depletion potential. The magnesium complex forms a salt with the organic acids present in the paper (Mg(RCOO)2). The reaction releases carbon dioxide and n-propanol. The neutralizing agent reacts with moisture in the paper to form the alkaline reserve, a magnesium car* bonate hydroxide [MgCO3)4 Mg(OH)25H2O] . Propanol has a mid-alcohol-like odour and is an irritant to the eyes, the skin and the respiratory tract. It is therefore recommended to wear gloves (neoprene or rubber), chemical safety goggles and to use the spray in a fume hood or wearing a mask in a well ventilated room. The amount of solvent sprayed was not easy to control and treating both sides of a sheet of paper resulted in a total soaking of the substrate. Although the evaporation was fast (15 to 30 minutes), this total impregnation by the solvent resulted in a white powdery deposit on the paper. This problem should be avoided in order to obtain an even alkaline salt distribution in the paper. A lighter spraying on one side of a sheet of paper resulted in no soaking of the substrate and no white deposit after drying. Practice on test paper is therefore recommended before spraying valuable documents. EFFECT OF TREATMENT The treatment significantly increased the pH to values ranging from 8.78 to 10.51 (Table 1). Achieving a pH as high as 10.5 in a deacidification treatment is not recommended but it should be kept in mind that Whatman No.1 paper was used as a test paper, its cold extract pH of 6.33 would not justify a deacidification treat* Information from the manufacturer 40 Brought to you by | University of Michigan Authenticated Download Date | 5/20/15 10:59 AM A-L. DUPONT ET AL. ment in conservation practice. For the ligneous paper a heavier spraying (recto and verso) resulted in a pH value (9.93), which was slightly too high, whereas a lighter treatment (recto only) resulted in very acceptable pH value (8.78). After spraying one side of a paper sheet, the alkaline reserve varied from 1.2 * to 1.8% CaCO3 . On the other hand, spraying both sides achieved an alkaline reserve of 6.9% CaCO3 for mechanical pulp paper and 9.6% CaCO3 for Whatman No.1 paper. Based on this experience and as stated earlier, it seems advisable to avoid saturating the paper substrate with solvent in order to obtain reasonable and similar levels of alkaline reserve for different types of paper. ** SEM element maps showed a homogeneous distribution of the alkaline salt on the paper surface and between the fibres. X-ray microanalysis confirmed the neutralizing agent to be a magnesium salt. Our results showed that there was no correlation between the pH and the amount of the alkaline magnesium salt in the paper. Whatman No.1 papers, one with an alkaline reserve of 1.2% (treated on one side only) and the other with 9.6% CaCO3 (treated on both sides) both had a cold extract pH around 10.5. Ligneous papers with alkaline reserves of 1.8% and 6.9% CaCO3 had a pH of about 8.8 and 9.9 respectively. An alkaline reserve of 1.8% CaCO3 significantly raised the pH, but higher salt deposits did not significantly increase the pH further. BEHAVIOUR OF DEACIDIFIED PAPER IN A NO2 ATMOSPHERE A deacidification treatment has to be efficient in protecting the paper from acids, whether originating from the paper constituents themselves or whether formed upon exposure to an external source of acids, e.g. pollution. In order to evaluate the impact of pollution, deacidified and non deacidified papers were exposed to 50 ppm nitrogen dioxide (NO2) at 23ºC and 50% relative humidity for 5 days3. The CRCDG pollution chamber4 delivered a laminar flow of NO2 and was controlled at both ends by a chemiluminescence analyser AC 31 M for nitrogen dioxides (Environment SA). Samples treated with CSC Book Saver® and untreated reference samples were placed in the chamber at the same time. The polluted papers were degassed in a dry oven at 100ºC for 15 minutes before analysis. * Alkaline reserve is calculated in calcium carbonate (CaCO3) equivalent regardless of the cation (Mg2+, Ca2+) ** The SEM is a JEOL JSM 5410 LV. EDX data is acquired with ISIS software. The surface areas observed were 30 µm2. 41 Brought to you by | University of Michigan Authenticated Download Date | 5/20/15 10:59 AM ® Testing CSC Book Saver 1,5 95 b* 1,2 90 0,9 85 0,6 80 0,3 75 0 70 untreated untreated, polluted treated, polluted L* untreated untreated, polluted treated, polluted Fig. 1 Chromatic measurements (CIE b*, CIE L* and ISO brightness R 457) of the Whatman no. 1 paper. pH and alkaline reserve After pollution the acidity of the untreated ligneous paper increased slightly. The acidity of the untreated Whatman No.1 paper, on the other hand, increased much more drastically. The alkaline reserve decreased, after pollution, by 62% in Whatman No.1 paper and by 26% in the ligneous paper. We believe this difference in behaviour, facing pollution attack, to be related to the initial amount of alkaline salt deposited in the papers. NO2 reacts with the salt present, a higher alkaline reserve represents more reactive medium for the oxidizing gas. Nevertheless, alkaline reserves of 3.7% and 5.1% CaCO3 in the paper after pollution are thought to be sufficient enough to protect the paper when facing further acidity. Pollution did not lower the pH of the deacidified papers, which remained at 10.37 for Whatman No.1 paper and 9.58 for ligneous paper. Colour measurements Figs. 1 and 2 show the changes in the CIE Lab* values and ISO Brightness measured at 457nm (R457)*. Values on the graphs are averages of 5 chromatic measurements. * Spectrophotometer Elrepho 2000 (Datacolor Int.) using illuminant D65 and the 27 mm aperture. 42 Brought to you by | University of Michigan Authenticated Download Date | 5/20/15 10:59 AM A-L. DUPONT ET AL. 35 b* 90 28 75 21 60 14 45 7 30 0 15 untreated 10 untreated, polluted treated, polluted L* untreated untreated, polluted treated, polluted a* 8 6 4 2 0 untreated untreated, polluted treated, polluted Fig. 2: Chromatic measurements (CIE a*, CIE b*, CIE L* and ISO brightness R 457) of the lignin containing paper. Browning of the ligneous paper increased after pollution with a total chromatic change delta E (∆E) above 9. We observed that for the deacidified ligneous paper the browning increased also, but to a lesser extent. The yellowing of Whatman No.1 paper as a result of NO2 pollution was less significant, with ∆E < 2. However, we noted that, within this narrow range of minute colour change, the yellowing was slightly more pronounced in the treated than for the untreated paper. This observation is consistent with results of other authors5–7 on the yellowing, after accelerated ageing, of paper deacidified with magnesium salts. On some of the ligneous papers we observed that after treatment the ink on the recto became more visible on the verso. We attributed this slight transfer to the sensitivity of the printing ink to n-propanol. According to the manufacturer, HFC 227 is chemically inert and has no interaction with inks and adhesives. 43 Brought to you by | University of Michigan Authenticated Download Date | 5/20/15 10:59 AM ® Testing CSC Book Saver Table 1: Chemical and optical data of the samples. _______________________________________________________________________________________________________________ lignin containing Whatman no.1 treated treated polluted with pH** alkaline reserve ∆E* Mw Mw decrease ** *** 2 3) recto verso NO (% CaCO (gmol-1) (%) _______________________________________________________________________________________________________________ 6.33 x x x x x 829 000 10.44 1.20 10.51 9.60 x 3.68 x 10.37 3.70 0.24 108 500 -87% 0.69 383 000 -54% 4.20 x x x x x 8.78 1.80 9.93 6.90 x 3.26 x 9.58 10.8 5.10 9.45 _______________________________________________________________________________________________________________ ** Average of two analyses *** Average of four analyses Size exclusion chromatography (SEC) Cellulose, like most polymers, is composed of a mixture of molecules of different size. The characterization of the size and molar mass distribution of the molecules is important because physical properties are closely related to the structure and composition of a polymer. In SEC, molecules are separated according to their size in solution, i.e. their hydrodynamic volume. SEC provides molar mass distribution of a polymer: data which provides exact information on the behaviour of cellulose to particular treatments. Only Whatman No.1 paper was analysed by SEC because it easily dissolved in the solvent used (lithium chloride/N,N-dimethylacetamide). The mechanical pulp paper only partially dissolved because of the presence of lignin. Sample preparation included defibrillation in a blender and activation in water. Water was later replaced by N,N-dimethylacetamide (DMAc). Dissolution was achieved at 4°C for 4 days in 8% LiCl/DMAc (w/v). Before injection, samples were diluted with DMAc to 1% LiCl, which resulted in 0.05% cellulose in the solutions. The impact of NO2 on Whatman No.1 paper was drastic on the molar mass with 87% decrease of the weight average molecular mass (Mw) (Table 1; also Fig. 3). The deacidification treatment considerably reduced this drop, to 54%. We noted that this significant decrease in polymerisation had no impact on the value of the pH of the treated paper, which was 10.51 before pollution and 10.37 after pollution. 44 Brought to you by | University of Michigan Authenticated Download Date | 5/20/15 10:59 AM A-L. DUPONT ET AL. treated and polluted 80 reference polluted 60 40 20 normalised distribution (%) 100 0 7 6 5 log molar mass 4 3 Fig. 3: Molar mass distribution of Whatman no. 1 cellulose paper. Molar mass was determined using a differential refractometre (Kontron Instruments) by standard calibration with 8 pullulan standards (Showa Denko K. K., Shodex). Peak molecular mass (Mp) of the pullulans were 788 kDa, 404 kDa, 212 kDa, 112 kDa, 47.3 kDa, 22.8 kDa, 11.8 kDa and 5.9 kDa. Glucose was used as lowest molecular weight standard (0.18 kDa). Pullulans were prepared 0.05% (w/v) in DMAc/1% LiCl (w/v). The columns set was composed of 4 poly (styrene-divinyl benzene), Phenogel (Phenomenex), 5µm mixed bed columns, 300 mm x 2 7 4.6 mm, pore size 10 to 10 Å; preceded by a guard column Phenogel 5µm 30 mm x 4.6 mm. Temperature of the runs was 55°C, mobile phase was 0.5%LiCl in N,N-dimethylacetamide -1 (w/v). Flow rate was set to 0.3 ml.min and runs lasted 60 minutes. Injection loop was 20 µL. Each paper was dissolved twice and each dissolved sample was analysed in duplicate runs. CONCLUSIONS ® Our study showed that the spray CSC Book Saver can efficiently deacidify acid papers. The treatment significantly protected the cellulose from chain cleavage caused by NO2 attack and the alkaline reserve deposited was quite remarkable. In a broader perspective, an important observation is that there is no direct correlation between pH and alkaline reserve and between pH and the rate of hydrolysis of the deacidified paper. The application of the spray requires some practice but is fairly easy. However, we recommend working in a well ventilated area. The spray has to be applied carefully and not too heavily in order to avoid solvent saturation of the paper and obtain uniform salt deposits, with no powdery traces on the surface, as well as an acceptable pH increase. A treatment on one side of a sheet of paper achieved an acceptable alkaline reserve albeit slightly below the usual recommendation of 45 Brought to you by | University of Michigan Authenticated Download Date | 5/20/15 10:59 AM ® Testing CSC Book Saver 2%. Heavy solvent impregnation resulted in alkaline reserve values that were too high. Somewhere in between, such as a light spraying on both sides of a sheet of paper, should be a safe choice. In cases where deacidification is considered necessary but lengthy immersion treatments in aqueous or alcohol solutions are not possible, the spray can be an alternative worth considering. It was beyond the scope of this technical study to include ink stability tests but the user must be aware of potential problems of transfer or discolouration of inks. It is strongly recommended that the sensitivity to the product of inks and other media is tested before treatment. Future experi® ments could include comparisons of the performances of CSC Book Saver with other commercial deacidification sprays such as Wei T’o (Wei T’o Associates, Inc.) and Bookkeeper (Preseservation Technologies). SUMMARIES ® Testing CSC Book Saver , a Commercial Deacidification Spray ® The effect of the deacidification spray CSC Book Saver on a mechanical pulp paper and a pure cellulose paper was tested and the consumption of the magnesium based alkaline reserve over time was simulated by exposing the papers to nitrogen dioxide. Scanning electron microscopy and energy dispersive X-ray analysis (SEM/EDX) showed uniform salt deposits were achieved. The alkaline reserve, albeit too high when the paper was heavily impregnated by the solvent during spraying, fell within a more commonly accepted range after lighter sprayings. The treatment significantly raised the pH in all cases. The total chromatic change of the mechanical pulp paper, after nitrogen dioxide exposure, was significant, whether the paper was treated or not. Size exclusion chromatography (SEC) of the cellulose showed that the neutralizing agent protected the macromolecule from chain cleavage caused by the pollution, very efficiently. ® Essais avec le CSC Book Saver , un spray commercial de désacidification ® Nous avons étudié l’effet du spray de désacidification CSC Book Saver sur des papiers de pâte mécanique et de pâte pure cellulose. La consommation de la réserve alcaline à base de magnésium au cours du temps a été simulée par l’exposition des papiers au dioxyde d’azote. Les analyses au microscope électronique à balayage couplé à un analyseur X à énergie dispersive (MEB/EDS) ont montré un dépôt uniforme des sels alcalins. La réserve alcaline, bien que trop élevée dans le cas d’une imprégnation totale par le solvant, s’est montrée acceptable suite à une pulvérisation plus légère. Dans tous les cas Le pH des papiers a augmenté considérablement suite au traitement. Qu’il soit traité ou non, le papier de pâte mécanique a subi un changement chromatique total (∆E) élevé suite à l’exposition au dioxyde d’azote. L’analyse en chromatographie d’exclusion stérique (CES) de la cellulose a montré un effet protecteur de l’agent neutralisant vis à vis des coupures de chaînes dues à la pollution. 46 Brought to you by | University of Michigan Authenticated Download Date | 5/20/15 10:59 AM A-L. DUPONT ET AL. ® Untersuchungen zu CSC Book Saver , ein kommerzielles Neutralisierungsspray ® Es wurde die Wirkung des Neutralisierungsspray „CSC Book Saver “ auf Holzschliff- und reines Zellstoffpapier untersucht. Zur Ermittlung, in welchem Ausmaß die durch die Behandlung erzielte auf Magnesium basierenden alkalischen Reserve im Laufe der Zeit unter Umwelteinfluß reduziert werden dürfte, wurden die Proben einer NO2-haltigen Atmosphäre ausgesetzt. Strahlungschemische Analyse (SEM/EDX) zeigte eine gleichmäßige Verteilung des als alkalische Reserve dienenden Salzes. Dessen Menge ist nach starker Imprägnierung mit der Lösung zu hoch, nach leichterer aber innerhalb des allgemein akzeptierten Bereichs. Das pH wird durch die Behandlung deutlich angehoben. Nach der Begasung mit NO2 zeigte das Holzschliffpapier eine deutliche Farbveränderung, und zwar sowohl die mit dem Spray behandelten als auch die nicht behandelten Proben. Mit Hilfe von SEC (size exclusion chromatography) wurde gezeigt, daß das neutralisierende Agens das Cellulosemolekül sehr wirksam gegen Kettenbruch infolge von Luftverschmutzung schützt. REFERENCES 1. TAPPI T 509 om-88. Hydrogen ion concentration (pH) of paper extracts (cold extraction method. TAPPI Test Methods. Atlanta: TAPPI Press 1988. 2. ISO/CD 10716. Paper and board. Determination of alkali reserve. 1994 3. Reilly, J.M., Zinn, E. and Adelstein, P., Atmospheric pollutant aging test method development. Poster th presented at the 67 Council and General Conference of the International Federation of Library Association and Institutions (IFLA), Boston, Mass., August 16–25 (2001). 4. Daniel, F., A pollution chamber for the accelerated deterioration of materials, Restaurator 17 (1996): 193–202. 5. Kolar, J., Novak, G., Effect of various deacidification solutions on the stability of cellulose pulps, Restaurator 17 (1996): 25–31. 6. Bukovský, V., Yellowing of newspaper after deacidification with methyl magnesium carbonate, Restaurator 18 (1997): 25–38. 7. Bansa, H., Aqueous deacidification – With Calcium or with Magnesium ? Restaurator 19 (1998): 1–40. A-L. Dupont, J. Barthez, H. Jerosch, B. Lavédrine CNRS UMR 8573 / Centre de Recherches sur la Conservation des Documents Graphiques 36, rue Geoffroy Saint Hilaire 75005 Paris France Tel + 33 1 44 08 69 92 E-mail : [email protected] 47 Brought to you by | University of Michigan Authenticated Download Date | 5/20/15 10:59 AM