34—MOISTURE RELATIONS OF CELLULOSE V—STABILIZATION OF CELLULOSE AND THE VARIATION WITH TEMPERATURE OF ITS HEAT OF WETTING IN WATER

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Abstract
The heat of wetting of stabilized and of unstabilized cellulose in water was measured at different temperatures between 0°C and 45°C by breaking a vacuum-sealed glass ampoule containing a known weight of dry cellulose under the liquid in a calorimeter and measuring the rise of temperature by means of a thermistor. Stabilization of cellulose was brought about by repeated immersion in water at 60°C and drying in vacuo. The evolution of heat is slower the lower the temperature, indicating that the diffusion of water through the cellulose gel is governed by some reaction between the two materials, the rate of reaction increasing with rise of temperature. Stabilization of cellulose brings about the reproducibility of its heat of wetting, as well as of the sorption isotherms. The heat of wetting of stabilized cellulose decreases with rise of temperature in a way that can be represented by two straight lines meeting at 23°C, the line on the lower temperature side being steeper. The break of the curve denotes the transition temperature, which marks the increase of activity of cellulose with rise of temperature, and it agrees with the same conclusion drawn from sorption isotherms. The heat of wetting-temperature curve of unstabilized cellulose is similar, though less definite, and it shows a transition temperature practically the same as that of stabilized cellulose. Stabilization has no appreciable effect on the heat of wetting below the transition temperature and decreases it at higher temperatures, the decrease being greater the higher the temperature. This effect is discussed in terms of the reorientation of chain molecules in the amorphous regions of the cellulose, in accordance with the effect of stabilization in displacing the adsorption isotherms.