VOCs in paper-based cultural heritage collections -
source of information or risk?
Paper is one of the most important carriers of cultural heritage, and its preservation is of vital importance. As a consequence of its degradation, volatile organic compounds (VOCs) are formed, which give rise to the memorable smell of old books. Their identity and quantity depends on paper composition and VOCs have been shown to be a source of information on paper quality and condition. This discovery enables the development of non-destructive 'sniffing' tools to rapidly identify the objects which are most at risk.
On the other hand, many simple organic acids, aldehydes and even aromatic compounds, formed during paper degradation, may also initiate or accelerate the degradation of cellulose, even from one document to another. A testing procedure was designed to quantify this effect and numerous preventive storage strategies were evaluated, from the use of VOC scavengers to hypoxia.
A number of factors are known to influence the degradation of historical paper, among which the environment undoubtedly plays a crucial role, along with paper composition. During paper degradation, a variety of low molecular weight products are formed, several of which are volatile and thus have an increased mobility not only within the material, but also within a collection. In the figure on the left, we summarise the numerous exogenous and endogenous factors influencing cellulose degradation-among which volatile degradation products (VOCs) can be both emitted but also absorbed by paper.
Lately, the interest in determination of VOCs emitted from paper has increased, however, there are only limited studies available on the information which can be extracted from VOCs and on their effect on cellulose degradation. For this reason, the PaperVOC project was funded (1.1.2007-31.12.2009).
Studies of the impact of several identified VOCs on degradation of paper were performed in closed vessels at elevated temperature. The effect of removal of VOCs using scavengers or adsorbent media was also studied using the same procedure. Additionally the effect of oxygen removal was evaluated . A new test procedure for determination of compatibility of storage and display materials with heritage materials of organic origin based on closed vial degradation has been developed .
The complex role of volatile degradation products in mixed paper collections should not be underestimated. Our results show that cross-infection due to emission and re-absorption of VOCs can be significant and removal of VOCs from storage facilities/enclosures should be considered .
A non-destructive and potentially non-contact method for paper characterisation based on book aroma was developed on the basis of VOCs emissions. We quantitatively correlated volatile degradation products with properties important for preservation of historic paper .
Investigations were extended to real storage facilities and amounts of volatile aldehydes in libraries were evaluated  and compared to other pollutants, such as the typical traffic-generated pollutants: NOx, SO2, O3.
Volatile organic compounds (VOCs) formed during paper degradation are numerous and varied [3,4] and their identity and quantity depends on paper composition . Research has shown that the quantity of furfural (with a pungent smell, typically produced during caramelisation of sugar) is indicative of paper acidity. Thus, VOCs may be regarded as a source of information on paper quality.
On the other hand, many simple organic acids, aldehydes and even aromatic compounds, which have been shown to form during degradation [3,4], may also initiate or accelerate degradation of cellulose. The usual and often used technique for analysis of VOCs in paper makes use of solid-phase micro-extraction (SPME) coupled to GC-MS although other ways of sampling have also been employed, e.g. cryotrapping and thermal desorption. Studies of the impact of several identified VOCs on degradation of paper can easily be performed in closed vessels at elevated temperatures. We evaluated the impact of the following: furfural, iso-butylbenzol, 1,4-diethylbenzen, acetic acid, formic acid, toluene, hexanal, 2-pentylfuran, formaldehyde and vanillin, on papers of three different qualities . Apart from volatile acids, a statistically significant negative effect of all compounds with a carbonyl group in the structure was noticed.
The effect of removal of VOCs using VOC scavengers or absorbent media (left: activated charcoal cloth and a filter medium - chemisorbent) was also studied in closed vessels at elevated temperature. Similarly, the effect of oxygen removal was also evaluated. In our study, we included several commercially available products and compared their effect on degradation of cellulose in a closed vessel at an elevated temperature. The complex role of volatile degradation products in mixed paper collections should not be underestimated .
Our research also shows that the effect of cross-infection due to emission and re-absorption of these compounds may be significant and strategies for removal and monitoring of VOCs from storage facilities should be given due consideration [2,5].
The project received extraordinary media attention, as the developed concept of characterisation of heritage objects by their smell is innovative and at the same time entirely non-destructive for the object.
Development of the concept into a usable tool would require further investment, but it is realistic, since technologically advanced portable tools, which would be suitable for the application, already exist on the market.
Following the major scientific publication (Further Reading no. 4), the news spread in the general media, and was published in The New York Times (left), The Times, The Guardian, Daily Telegraph, BBC, Le Temps Suisse, Scientific American, CBC Radio, Daily Planet, Discovery Channel, Radio Noorderlicht, and more than 50 other national and international media. It was also featured in the major scientific journal Science.
1. Volatile organic compounds (VOCs) are formed during degradation of paper and significantly contribute to its degradation.
2. Considering that the cumulative concentration of internally generated VOCs exceeds the concentrations of externally generated SO2, NOx and O3, the strategies of pollution mitigation in libraries and archives need to be reassessed, along with relevant standards. It has recently been shown that the stability of colour photographic is most affected by acetic acid .
3. The presence of groundwood-containing paper can up to double the rate of degradation of cellulose degraded in its proximity. While in repositories, separation of objects according to paper composition might therefore help, it is a resource intensive operation and would probably negatively affect collection management efficiency. However, alkaline sleeves could be used for groundwood-containing documents, thus beneficially affecting the object itself and those in the vicinity.
4. Strategies of removal of VOCs from the immediate proximity of paper have a positive effect on paper durability. The presence of moleculite and activated carbon, and hypoxic conditions have the same beneficial effect, which is most pronounced in the case of groundwood containing paper (up to 20% benefit). Paper sleeves with a good alkaline reserve also have a positive effect.
5. Different VOCs have different effects on the degradation of paper, with the effects of formic and acetic acid being comparable to that of some aldehydes (formaldehyde, vanillin and furfural). The negative effects of these compounds are most pronounced in the case of alkaline and neutral papers and less so in the case of acidic groundwood containing papers, which are themselves good emitters of VOCs.
6. Historic iron gall ink emits less VOCs than the surrounding paper (left, top), however, its effect on the degradation of paper stored in the proximity is still slightly negative because of the emission of reactive oxygen species (H2O2).
7. Archival boxes shield the documents from traffic-generated pollutants, however VOCs accumulate in the internal box environment. The concentration of acetic acid in boxes can thus exceed 100x that of NO2. Boxing materials should have a good alkaline reserve to absorb this acidity. Boxes with openings retain less VOCs (left, middle).
8. The VOCs emitted by paper have been shown to be a useful source of information on paper quality. Our research has shown, for the first time, that VOC emissions contain information on paper composition and condition. Based on this, development of sniffers to quickly identify the most endangered objects is possible.
9. There are no health concerns in view of aldehyde concentrations in libraries and archives (left, bottom). In poorly ventilated high-load repositories, the concentrations can exceed USA-NIOSH occupational limits (TWA - average value of exposure over the course of an 8 h work shift that is not to be exceeded) of 16 ppb.
10. A new test procedure has been proposed to evaluate the cross infection effect of storage materials in close proximity to organic heritage materials .
University of Ljubljana, Faculty of Chemistry and Chemical Technology, Ljubljana, Slovenia
Contact: Irena Kralj-Cigic (Scientific coordination: Matija Strlic)
National and University Library, Ljubljana, Slovenia
Contact: Jana Kolar
Nationaal Archief, Tha Hague, The Netherlands
Contact: Gerrit de Bruin
The authors gratefully acknowledge financial support of the Slovenian Research Agency and of Nationaal Archief, The Netherlands.
1. M. Strlič, I. Kralj Cigić, A. Možir, G. de Bruin, J. Kolar, M. Cassar: “The Effect of VOCs and Hypoxia on Paper Degradation”, submitted.
2. M. Strlič, I. Kralj Cigić, A. Možir, D. Thickett, G. de Bruin, J. Kolar, M. Cassar: “Test for Compatibility with Organic Heritage Materials – A Proposed Procedure”, e-Preservation Science, 7 (2010) 78-86. OPEN ACCESS.
3. M. Strlič, E. Menart, I. Kralj Cigić, G. de Bruin, J. Kolar, M. Cassar: “Emission of volatiles and reactive oxygen species during degradation of iron gall ink”, Polym. Degrad. Stab., 95 (2010) 66-71.
4. M. Strlič, J. Thomas, T. Trafela, L. Cséfalvayová, I. Kralj Cigić, J. Kolar, M. Cassar: “Material Degradomics: on the Smell of Old Books”, Anal Chem. 81 (2009) 8617-8622.
5. A. Fenech, M. Strlič, I. Kralj Cigić, A. Levart, L. Gibson, G. de Bruin, K. Ntanos, J. Kolar, M. Cassar: “Volatile Aldehydes in Libraries and Archives”, Atm. Environ., 44 (2010) 2067-2073.
6. M. Strlič, I. Kralj Cigić, J. Kolar, G. de Bruin, B. Pihlar: "Non-Destructive Evaluation of Historical Paper Based on pH Estimation from VOC Emissions”, Sensors, 7 (2007) 3136-3145. OPEN ACCESS.