The behavior of cotton cellulose and beech wood in ammonia atmosphere

Abstract

In order to learn more about the plasticization of wood, sorption measurements on cellulose rich specimen, cotton fibers, and bending tests on beech wood were performed in ammonia atmosphere. The results showed that the sorption of NH3 on cotton was substantially hindered at low relative vapor pressure, presumably due to interaction of NH3 with hydrate water. Near the saturation pressure a reduction of the sorption capacity was observed because of developing collapse in the capillary system. In the middle relative vapor pressure range the equilibria were retarded while the active surface area was extended to more than double. Observations at different temperatures‐15, 25, 35°C, revealed that the extension of the sorptive area took place consistently at the same ammonia content of the specimen. The other mentioned diverging sorption features, however, were intensified variously by raising the temperature. No difference was found between the ammonia sorption properties of cellulose I and III. Bending tests on beech wood laths in ammonia environment displayed a dynamic progression of the plasticization. At the beginning of the exposition to ammonia the bending ability of the specimen was increasingly enhanced. When in course of the plasticization the modulus of elasticity of the laths dropped below 1/3 of the starting value, bendability changed by levelling off progressively. The conclusion thereof that the plasticization of wood can be forced only to given limits was confirmed by destructive bending tests and by porosimetric measurements. To reach a sufficiently softened state of the beech laths with dimensions 25×1×0.6 cm, 15 min appeared to be enough while further alterations could be observed even on the smallest specimen size for considerably longer periods.

Swelling of beech wood (Fagus sylvatica L.) during gaseous ammonia treatment as a function of pressure

“…It is likely, that the swelling of the crystalline areas of the cellulose is responsible for the over-swelling in the tangential direction. In relation to the test p i /p s = 0.6, the beginning of swelling the crystalline areas becomes visible by the strongly delayed swelling process (Bariska and Popper, 1971).…”