The interaction of water with archaeological and ethnographic birch bark and its effects on swelling, shrinkage and deformations

Abstract

The aim of this study is to gain specific information on the water vapour interaction with archaeological and ethnographic birch bark. Water is involved in a number of curative and preventive conservation measurements e.g. when re-shaping or drying objects and when defining climate directives for long-term storage. We measured the sorption isotherm of archaeological, ethnographic and contemporary birch bark at different temperatures and analysed the moisture-induced size and shape changes (swelling, shrinkage, deformation) during humidification and drying. The analysis revealed that, compared to other organic materials like wood, the moisture uptake of outer birch bark is modest. This can be attributed to the cell structure and composition: outer birch bark is composed of closed cells made to a large extent of hydrophobic components (suberin, lignin). The equilibrium moisture content is higher if lenticels or inner bark are present. The extent of brittleness and delamination of the sample influences the sorption behaviour: the less brittle and delaminated archaeological birch bark is, the lower the equilibrium moisture content (EMC). Since the moisture uptake is modest, the related swelling of the outer bark is also modest, but anisotropic due to the cellular arrangement. Swelling is largest in the radial direction, smaller in longitudinal and negligible in tangential direction. Water vapour can plasticize birch bark and as birch bark becomes flexible, it bends towards the outside of the bark. This deformation takes place at high moisture contents and the adsorption process is slow. Based on these results recommendations on how best to perform treatments involving moisture and on relative humidity ranges for birch bark objects are provided.

Numerical Modelling of Moisture Loss during Controlled Drying of Marine Archaeological Wood

“…The results of this further modelling are described statically in Figure 4, while the simulation can be viewed dynamically as Supplementary Video S1. The most intuitive explanation for the more rapid drying of surface samples is their higher degree of atmospheric exposure; indeed, these results accord well with recent reports that kinetically studied the drying of marine archaeological wood using sorption isotherms, which revealed extremely rapid evaporation and geometric distortion even at high environmental relative humidity levels [25]. Others have noted that under high humidity, marine archaeological wood can leach PEG from the surface [15], which may also help explain these differential drying rates compared with the interior.…”

Utilization of Birch Bark as an Eco-Friendly Filler in Urea-Formaldehyde Adhesives for Plywood Manufacturing

“…This is caused by most suitable concentration of soaked water, that is bounded in bark. In case of BB10 and Ref10, still high amount of water (explained in DSC and TGA part) is part of the resin and is continuously evaporated during isothermal heating at 105 • C. On the other hand, in case of BB20, there is very large amount of water soaked by bark which is not sufficiently bonded and evaporates quickly during isothermal heating at 105 • C [127]. The results of TGA and DTG analysis confirmed the results in DSC part, that the addition of 15% BB as a filler in UF resin is the best option and should not be exceeded.…”

Uniform Water Potential Induced by Salt, Alkali, and Drought Stresses Has Different Impacts on the Seedling of Hordeum jubatum: From Growth, Photosynthesis, and Chlorophyll Fluorescence

“…The early seedling stage is an extremely crucial period of plants, and is susceptible to the adverse environments (Wang et al, 2019;Ocvirk et al, 2020;Ren et al, 2020). During this period, water absorption is a determining factor and it regulates various physiological processes in the plant (Klugl and Di Pietro, 2021). In general, both salt-alkali and drought stresses can induce lower water potential, which limits water uptake and inhibits growth of plants.…”