WATER-ABSORPTION BY CORK

A study of liquid water absorption by cork was carried out in which the anisotropy of cork was taken into account. The changes with time of the mass, volume, and linear dimensions were measured for different orientations of the sections in cork exposed to liquid water at room temperature (20 C) and at 90-100 C. Two regimes of water absorption were identified, namely, a period involving dimensional change and a period with only mass change. Diffusion coefficients at both temperatures were estimated using a special technique. There is a small anisotropy with a faster diffusion in the radial direction. Diffusion coefficients at 90 C are two orders of magnitude larger than at room temperature. Water absorption in the cell walls causes the expansion of cork, which (for the boiled specimens tested) is slightly smaller in the radial direction. The volume increase is proportional to the mass increase and ceases after relatively short immersion times. At this stage, the cell walls are apparently saturated with water. Further immersion results in penetration of water into the cells. The kinetics of absorption is rather slow at long times, but eventually the cells become full of water, the density increases above that of water, and the cork sinks.