Effects of Hot Water Treatment on the Structure and Properties of Cork
Keywords:Cork, hot water treatment of cork
The cork used for stoppers (reproduction cork) is subjected to a boiling operation before processing, which consists of immersing the cork boards in boiling water for approximately one hour. An experimental study of the hot water treatment was undertaken with the purpose of characterizing the alterations that it may cause in the structure, dimensions, mass and compression properties of cork.
Various parameters related to the treatment were investigated, including water temperature, time, cork quality, and the kinetics of open air-drying.
The major structural alteration due to boiling is the attenuation of cell-wall corrugations. This leads to an expansion of 10-15% in the radial direction and 5-7% in directions perpendicular to this, including the axial and tangential directions. The mass is virtually unaffected. Boiling causes a softening of cork and also a reduction of its elastic anisotropy. These and other observed changes in the stress-strain curves in compression can be explained in terms of the structural changes.
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