Desorption of Residual Ethylene Oxide from Fumigated Library Materials
Results and Discussion
Two parallel studies were completed to compare the relative capacity of selected library materials for offgassing of ethylene oxide. One of them monitored the progressive increase in ethylene oxide concentration within a contained environment after successive infusions of fresh air. In the other study, a constant vacuum was applied after the fumigation step, and the ethylene oxide concentration monitored at the vacuum pump exhaust.
Figure 1 presents the data collected by monitoring the progressive accumulation of ethylene oxide above fumigated vinyl audio records in successive changes of air. Only a few selected air changes are shown here as an illustration of the pattern that was generally observed after each change of air with the vinyl platters, as well as with other materials. As each fresh volume of air begins to interact with the fumigated material, the concentration of ethylene oxide in the air continues to increase towards an equilibrium value where it ultimately levels off. In about two hours after a fresh volume of air is introduced, the ethylene oxide concentration approaches to within 10 percent of the equilibrium value. In the interest of efficiency, it was decided to plot the data for all air changes with different materials in the manner illustrated by the data in Figure 1 and read off the near-equilibrium concentration at 2.0 hours.
Table 1 presents these experimental data for all of the materials studied here with the single exception of the data for the second motion picture film. The two sets of data obtained with the black and white film on a cellulose acetate base and the color film on a polyester base were almost identical. Therefore, the second data set has been excluded. The single data set presented here represents both the color film on a polyester base and the black and white film on acetate base. The only material that the two films had in common was the emulsion layer. The high and almost identical affinity that both the films exhibit for residual ethylene oxide suggests that it is mainly the gelatinous emulsion layer that interacts with ethylene oxide.
Besides the different materials, Table 1 also presents data for desorption of the fumigant from the empty chamber. Considering the size of the chamber and its large surface area, it would not be unexpected to find a small, but measurable concentration of ethylene oxide in the first few changes of air. However, it is surprising to note that the amount of ethylene oxide dislodged in the presence of 1.4 Kg of leather is even less than that observed for the empty chamber. When the data for each air-change for individual materials is corrected for the ethylene oxide given off by the empty chamber, the leather would appear to have actually absorbed some ethylene oxide. This fact suggests that leather probably interacts chemically with ethylene oxide. This comment is not expressed without reservation since we have not observed any direct and convincing proof for this deduction, which, however, does appear logical. These data suggest the need for further work to clarify this issue. However, such work was beyond the scope our immediate objective.
The data from Table 1 were corrected for the ethylene oxide given off by the empty chamber. The corrected data are presented in Figure 2. The book paper studied here is a commercial acidic alum-rosin-sized chemical wood pulp paper that we considered to be representative of today's acid-sized fine paper. Evidently, it does retain residual ethylene oxide to a relatively high enough extent to suggest the use of caution and adequate aeration if such paper is fumigated with ethylene oxide. Newsprint shows an even higher retention, which is exceeded by wood, probably because of its smaller porosity. The vinyl records, with an appreciably smaller surface area exposed to the fumigant, show a much smaller retention than the fine book paper. However, they need just as many air-changes to reduce the level of the ethylene oxide concentration to an acceptable level.
Figure 3 and Figure 4 show the data obtained from the second set of experiments in which the fumigated materials were subjected to a constant vacuum and the ethylene oxide concentration measured at vacuum exhaust. In these experiments too, the data for the two photographic films overlapped so closely that one set of data is presented to represent the two films. The same order for increasing affinity for residual ethylene oxide is displayed here as observed in the experimental approach in which the near-equilibrium concentration in successive air-changes was measured, namely, leather < vinyl records=book paper < newsprint < wood < photographic film. In general, paper does not pose much of a problem.
Some library books studied as a part of this work, but not reported here,
lost the residual gas even more easily than the Springhill Offset&8482; paper, for
which the ethylene oxide concentration dropped under 1 ppm after 5 air-changes.
On the other hand, the ethylene oxide concentration over pine scraps was still
over 1 ppm after 23 air changes, and it was 38 ppm over photographic film after
25 air-changes
(Table 1).
This work demonstrates that offgassing of ethylene oxide by library materials is a reality. Vigilance needs to be exercised by confining fumigated materials to a restricted, but well-ventilated area where the ethylene oxide concentration can be monitored. The fumigated materials should be added to the collections only after the ethylene oxide concentration is decisively under 1 ppm. The data presented here offer a comparison of the relative capacity of different library materials to offgas residual ethylene oxide. However, it needs to be noted that no attempt was made here to facilitate the desorption of ethylene oxide. The introduction of moisture into the chamber or raising the temperature of the air would have accelerated the rate of desorption of ethylene oxide. The optimization of this process was beyond the scope of this study.
Table of Contents - Introduction - Experimental - Results and Discussion - References - Supporting Documents