Studies on Collapse of Wood Cells and Negative Pressure in Cell Lumen by Yoshiaki HATTORI* and Yasushi KANAGAWA** The negative pressure, that is liquid-tension, to cause cell-collapse was estimated with osmotic pressure at 20 Ž, and the behavior of cell-collapsing and the radius of opening in the cell wall were discussed. The concentration dependence of the osmotic pressure of polyethylene glycol (PEG-20000) was determined over a wide range of concentration up to 0.557g/ml. On the basis of this result, the shrinkage behavior of the collapsing samples in the solution was compared with the amount of cellcollapse in air-drying and with the results of compression tests perpendicular to the grain. The results obtained were summerized as follows. When the negative pressure in the cell lumen exceeded a certain magnitude, the cells deformed and then the sample shrank abruptly, as if the sample yieled to the stress. The limiting magnitude was about 2kg/cm2 in the case of Balsa (Ochroma sp., R=60kg/m3), and 35kg/cm2 in Almon (Shorea almon Foxw., R=430kg/m3). According to the magnitude of negative pressure to cause cell-collapse and the permeability of the cell wall to PEG, it was considered that the maximum radius of opening in the cells collapsed at normal temperature was order of 10mƒÊ at the utmost.
Note; a: Pressure sensor, b: Semi-permeable membrane, c: O-ring, d: Support screen, e: Solution, f: Solvent. Fig. 2. Osmometer cell. Fig. 1. Schematic diagram of the method to obtain the maximum shrinkage caused by cell-collapse.
932 Note; Numerals show each concentration of solutions in unit of g/ml. Fig. 3. Pressure curves in the osmometer cell. Fig. 5. Concentration dependence of osmotic pressure plotted according to equation (2). Note; Broken line shows the data quoted from reference No.3. Fig. 4. Concentration dependence of osmotic pressure.
Note; Numerals show each concentration of solutions in unit of g/ml. Broken line represents the maximum shrinkage caused only by cell-collapse in air-drying. Fig. 6. Shrinkage curves of Balsa in concentrated solutions. Note; Refer to Fig. 6. Fig. 7. Shrinkage curves of Red meranti in concentrated solutions. Fig. 9. Negative pressure-shrinkage curve (solid line) and compressive stress-strain curve (broken line) in tangential direction of Balsa. Note; Refer to Fig. 6. Fig. 8. Shrinkage curves of Whit lauan in concentrated solutions. Fig. 10. Negative pressure-shrinkage curve (solid line) and compressive stress-strain curve (bro- line) in tangential direction of ken Almon.
Fig. 11. The difference in the mechanism of cell-collapse by immersing in solution (a) and air-drying (b).
Table I. Pore size distribution in the osmotic membrane15). Note; Values were calculated from the data reported in reference No.15. Fig. 12. Relationship between the maximum negative pressure and pore radius.
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