| Abstract | The removal of polar solvents previously proposed as swelling agents for wood was followed by means of weight and volume changes. The degree of swelling and quantities of dimethyl sulfoxide, dimethylformamide, N-methyl pyrrolidone, and pyridine left in yellow birch, beech, white pine, and Douglas-fir after exposure for various times to evaporation at 100 and 50 percent relative humidities, ovendrying, and vacuum were determined. For the most strongly held solvent, water extraction was also used. Pine was found to release solvents most quickly and fir most slowly. Pyridine evaporated rapidly and dimethylformamide fairly rapidly at 50 percent RH, but even after ovendrying, 2 to 4 percent by weight of these solvents was retained except in pine. Eleven to 19 percent dimethylsulfoxide and methyl pyrrolidone was retained in birch and beech after ovendrying, and application of moderate vacuum had little effect on the retention. Preliminary evaporation at 100 percent RH is unnecessary, and evaporation at 50 percent RH is not practical with the slower solvents. Beech, which swells rapidly, is prone to cracking. Sufficient material is extracted from birch to cause volumetric shrinkage. Treatment of white pine with dimethylformamide appears to be the most practical system. |
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