Volatile Organic Compound Emissions from Museum Showcase Materials

Mapelli E.¹, Pedrocchi-Fantoni G.², Strini A.<sup>1

1</sup> Consiglio Nazionale delle Ricerche - Institute for Building Technology, Italy
² Fondazione Fantoni, Italy

Introduction
A case-study carried out in a small museum -Fantoni House-Museum- in the North of Italy is described. In particular the volatile organic compounds inside and outside new showcases were analysed and the results were compared with laboratory measurements of some materials used to produce them.
The Fantoni House- Museum is located in the family's homestead in Rovetta, a small village in the Pre-Alpine area not far from the town of Bergamo. In the 15th century the Fantonis started their activity in Rovetta as sculptors of wood and later of marble and occasionally worked as architects. Their studio and workshop went on in the same location for 400 years without interruption. Nowadays the museum has a rich collection of drawings, terracotta models, sketches, and architectural projects mainly realised in the period from the 16th to the 18th century. The museum's library holds ledger books and a large collection of letters, work contracts, and descriptions of artworks and production processes.

Showcases feature
Some sketches are held in two new showcases equipped with humidity monitoring and control system and soft diffusion light system.
They have an internal volume of about 5-6 m³ and building materials were selected and studied for the best arrangement from functional and aesthetic requirement.
The project of Astarte, the showcase manufacturer, is for a totally sealed showcases with the main structure made of metallic materials varnished with epoxy-paint to reduce the VOC impact coming from the varnish.
The large glass area is sealed with silicon adhesive without acetic acid emissions as required for museum products and the internal covering is made of PVC-coated plywood. The PVC used to cover the plywood is certified for museum use.

Field survey
The concentration of the VOC inside and outside the showcases was determined by sampling the air with active sampling method. Sampling tubes, with Tenax as adsorbent material, were used with a manual sampling pump and different sampling volumes were taken.
The sampling tubes were then analysed by thermal desorption and gaschromatographic analysis with mass spectrometer detector for qualitative analysis and flame ionisation detector for quantitative analysis.
Inside the showcases were found considerable amounts of acidic and carbonylic compounds as well as phenol, alcohols and phthalates (Table 2). Outside the showcases were found low concentrations of aromatic hydrocarbons and carbonylic compounds.
The outside survey permits to check the VOC presence in the room and to establish possible sources of volatile compounds. In the present study, the outside results show that the carbonylic and carboxylic compounds inside the showcase have not origin from external contamination, but coming from manufacturing showcase materials.

Laboratory survey
The main components of the showcases were analysed in laboratory with respect to their emissions by using a 30 l test chamber both in static and dynamic conditions. The materials analysed were: the epoxy-paint used to varnish the metallic load bearing structure, the silicon sealing adhesive, PVC tube used for the dehumidification system, the plywood used for internal wall and floor covering and the PVC coating of the wood board used as finishing aesthetic material.
The chamber is realised with cylindrical glass chemical reactor with a sealed glass cover (Figure 1). It is supplied with chromatographic grade air and a custom stainless steel fan driven by a standard chemical laboratory stirrer obtains the internal air mixing. The inlet air system consists of a stainless steel tube and the outlet of a silcosteel tube. The temperature of the system and the humidity of the inlet gas are controlled and could be monitored inside the chamber during the test [1].

The chamber working conditions are:

chamber volume:	30 l
chamber air flow:	15 l/h
relative humidity:	50 % U.R.
sample area:	113 cm2
loading factor:	0.38 m2/m3

Static working conditions, without air exchange, allow a rapid classification of the materials according to their emission potential. It is relatively simple and the VOC equilibrium concentrations are not influenced by sink effects, chamber loading, air velocity within the chamber. In static conditions the VOC equilibrium concentrations represent the maximum concentrations which may be found in an indoors ambient [2].
Dynamic conditions, with air exchange, are affected by sink effects, chamber loading, air exchange rate and are strongly time-dependant. The test gives information about the evolution of VOC emissions over the time, which may be very different for each compound depending on its volatility [3].
When the chamber works in dynamic conditions the Specific Emission Rate for every compounds can be calculated.

Results
The main interesting results of chamber test studies of the showcase manufacturing materials concerning their VOC emissions, are those obtained for PVC-coating and plywood. The emissions from PVC- coating was studied over a 10 days period and the most significant PVC emissions were found for phenol, N-methyl-pyrrolidone, 2-ethylhexanol, 2-ethylhexanoic acid, diethylene glycol monobuthyl ether.
For plywood, the main emissions were acetic acid, hexaldehyde and minor compounds in the class of hydrocarbons and carbonyls.
For every compound, the emission profile in static and dynamic conditions was drawn. As an example the emission profile for phenol is reported in Figure 2

The Specific Emission Rate (SER) was calculated at the steady state concentration with Equation (1) and the results are reported with the Maximum Concentration, for every compound, in Table 1.

(1)                                SER_240h = C_240h (Fc/As)

with:
      C_240h = concentration of the compound after 240 hours in µg/m³
      Fc = chamber air flow in m³/h
      As = sample area in m²

Table 1: Specific Emission Rate after 240 h and Maximum Concentration of PVC and plywood VOC emissions

	SER 240h	Max Conc.
PVC emissions	µg/m2h	µg/m3
phenol	55	1000
N-methylpyrrolidone	24	190
2-ethylhexanol	4	310
2-ethylhexanoic acid	48	230
diethylene glycol monobuthyl ether	33	235
Plywood emissions
acetic acid	1980	1430
hexaldehyde	35	970

In static conditions the VOC concentration can reach very high levels. This is the most common way showcases work. Static chamber studies are important to predict materials behaviours in working conditions.
To compare field and laboratory results, the 1-litre volume air sampling inside the showcase was considered because it doesn't put breakthrough problems for acid and carbonylic compounds (Table 2).

Table 2: Comparison of field and laboratory results
VOC concentration in µg/m³

Compounds	Conc. inside showcase	Max Conc. in static cond.	Conc. (240 h) in dynamic cond.
acetic acid	627	1430	1531	wood
toluene	60
hexhaldehyde	137	970	27	wood
ethylbenzene	46
m+p-xilene	198
o-xilene	98
phenol	42	1000	42	PVC
2-ethylhexanol	23	310	3	PVC
2-ethylhexanoic acid	40	230	36	PVC
diethylene glycol monobuthyl ether	10	235	25	PVC
diisobuthylphthalate	36

Discussion
The field survey allows identifying the critical compounds in the museum atmosphere, inside and outside the showcases; on the other hand, the laboratory survey allows to identify the critical materials that emit dangerous compounds and to estimate their potential risk.
In the comparison of the results it is very important to take into account some parameters like the air exchange rate, the emitter-loading factor, the presence of sink effects. In particular the loading factor of the covering materials in the showcase is greater than in the chamber, but the sinks can be particularly meaningful especially when paper sketches are inside.
When the survey was carried out, the showcases weren't completely finished and some indoor/outdoor air exchange was present. When the showcases are totally sealed, the VOC concentration might increase and the acetic acid concentration might as well exceed the recommended values [4-5].

Conclusions
The VOC found in the showcases are in relationship with the materials used to manufacture them (Table 3).
In particular the large amount of acetic acid and aldheyde is done to the presence of wood panel with great exposed surface (showcase loading factor is 2.8 m²/m³ ). This makes fruitless every precaution to reduce the environmental impact adopted for other materials like the silicon adhesive acetic acid-free used to seal the glasses.
The PVC used to cover the plywood panels is certified for museum use, but its emission behaviour is not negligible. The main component of the PVC emissions is done to phenol, a reactive and weakly acid aromatic compound (Ka 10^-10), but also the 2-ethylhexanoic acid (Ka 10^-5) is present in considerable amount.
An other interesting compound found in the internal air of the showcases is diisobuthylphthalate. Phthalates and plasticised in general are studied concerning to the museum ambient with particular regard to their interactions with objects based on cellulose nitrate like paints, photographic slides and metals [6].
The chamber studies don't point out the presence of plasticised in the construction materials and in particular in the PVC covering sample and in the PVC tube used for air dehumidification system. It was observed that when the paper sketches are in the showcases the phthalate concentration is higher than in the empty showcases. For this reason the source of diisobuthylphthalate is probably to check in the paper sketches and in particular in the conservative treatments make at the paper in the years (i.e. the paper reparation in the early fifty with sellotape).

Acknowledgements
The authors would like to thank the showcases manufacturer Astarte S.r.l., (Molinetto di Mazzano, BS, Italy) for their technical information.

References
[1] A. Strini, E. Mapelli, L. Bignami
A Volatile Organic compounds Emission Test Chamber Based on a Standard Chemical Reactor Vessel. Procceding of the 8th Conference on Indoor Air Quality and Climate - Indoor Air '99, vol. 5, pp. 137-142.

[2] S. Sollinger, K. Levsen, G. Wunsch
Indoor Air pollution by Organic Emissions from Textile Floor Coverings. Climate Chamber Studies under Static Conditions. Atmospheric Environment, vol. 28, n. 14, pp. 2369-2378, (1994).

[3] S. Sollinger, K. Levsen, G. Wunsch
Indoor Air pollution by Organic Emissions from Textile Floor Coverings. Climate Chamber Studies under Dynamic Conditions. Atmospheric Environment, vol. 27B, n. 2, pp. 183-192, (1993).

[4] J. Tétreault, J. Sirois, E. Stamatopoulou
Studies of Lead Corrosion in Acetic Acid Environments. Studies in Conservation, vol. 43, pp. 17-32, (1998).

[5] A-L. Dupont, J. Tétreault
Cellulose Degradation in an Acetic Acid Environment. Studies in Conservation, vol. 45, pp. 201-210, (2000).

[6] R. Scott Williams
Plasticized PVC in Museums: Don't Use It. (1993). Canadian Conservation Institute
It descibe some exemple of artefacts damged by PVC plasticized. Available on the Canadian Conservation Institute website: www.cci-icc.gc.ca

Author to whom correspondence may be addressed:

Emanuela Mapelli
CNR-ITC
via Lombardia, 49
I-20098 S.Giuliano Milanese (MI)
Italy

E-mail: emanuela.mapelli@itc.cnr.it