Improvement options for archive boxes in tropical climates

Summary

Preserving archives in countries like India, Indonesia, Sri-Lanka, Brazil, and Suriname is challenging because of tropical climate conditions (high relative humidity (RH) and high temperature (T)), especially in combination with often non-reliable climate control systems. Variable (and fast changing) climate conditions in combination with high RH pose a serious threat to archival records. The National Archives of the Netherlands (NAN) cooperates with local archive institutions to preserve the archives originating from the Dutch presence in these countries. The aim of this project is to investigate the packaging concept of archive boxes and to come with possible solutions to protect archived documents better against (fast changing) variable climate conditions and insect intrusion, thereby taking into account also other requirements such as economy (low price), possibility for local production (less transportation), sustainability, and lifetime. For good preservation it is important that the RH (or water activity) inside the box and of the archived material is below about 60%. Starting point of this project was the wish to create a packaging (archive box) that protects its content against varying climatic environmental conditions. A hypothesis was that this could be obtained by a suitable packaging material and coating with optimal moisture permeability in combination with an absorber. This could result in a lower RH and lower RH variability inside the packaging upon changes in environmental conditions. Wageningen Food and Biobased Research (WFBR) performed a study to possible solutions, including an investigation to the state of the art knowledge on the moisture migration phenomena relevant for the archive box. Based on these results, WFBR developed a quantitative physical model describing moisture transport through and inside an archive box, to get insight in the key factors that control water migration and moisture content of the archived materials and to test the starting hypotheses. With this model the effects of different packaging options, including coating and usage of moisture absorbers, were evaluated in relation to (changes in) environmental RH and T. WFBR found that application of polymer coatings on cardboard archival boxes will indeed decrease the water vapor flux between the inside and outside environment of the box, but that it will only be effective on a time scale of hours to days and not on longer desired time scale of months. For boxes that need to withstand moisture migration on a time scale of months, other materials are needed, like metals or plastics, that do not comply with additional requirements like cost effectiveness and/or the possibility of local production. Furthermore, in case of relatively high humidity inside the box due to e.g. adding a relative wet paper to the box or due to a mal functioning of the climate control system for a period longer than about a few days, the outflux of water from the box is also decreased when a coating is applied. This results in the counter effective result that when the coating on an archival box is improved to decrease water vapour permeability, the archival content (upon a temporarily increase of the humidity in the storage room) will be subjected for a longer duration to high humidity inside the box. Concerning the role of absorbers, it is concluded that the effect of common absorbers is very limited. This because they are already saturated at RH’s around 50%, which are common RH’s in tropical archival storage rooms. Therefore their buffering capacity when the environmental RH increase above 50% is very limiting. Ideally, a special absorber is needed that does not absorb at storage room humidities (below about 55%) but absorbs at higher RH’s that may occur either during transport or during defects in the climate control of a storage room. However these are specific and expensive and do not match the boundary conditions set in this project. In general, the archives of the NAN experience different types of problems due to the tropical climate, which require different types of solutions. There is no archive box or material that can solve all of these problems at the same time. This because the effect of a certain adaptation, like application of a coating or absorber, on the moisture exposure of the archived documents, depends on the details and timescale of the experienced problem. So, because tropical archives experience different types of problems of different durations, no general advice for the construction of an archive box can be given to minimize the exposure of the archived materials to high humidities. However, recommendations depending on the situation and duration can be and are given. These include changing the currently used corrugated cardboard to solid board and closing gaps in the box to minimize insect intrusion as well as stabilize the storage conditions and improve handling protocols.