The Thermodynamic Properties of the System Cellulose – Water Vapor

Abstract

The heats of wetting by water of cotton cellulose containing various amounts of adsorbed and desorbed water were measured. These measurements together with those of the water vapor sorption isotherm were used to calculate the integral and differential enthalpies, free energies, and entropies of adsorption. Irreversible effects were avoided by vacuum-drying all samples a t room temperature. The dilfercntial enthalpy values suggest hydrogen bonding. The differential entropies are explained in terms of changes in both the adsorbate andThe surface area of the cellulose is calculated by applying the Brunauer-Em~nett-Teller and Harkins-Jura equations to the adsorption isotherm. The changes in the differential enthalpies and entropies of adsorption follow the same sequence as the changes in film formation given by the surface area calculations.No hysteresis was observed in the heats of wctting of adsorbed and desorbed samples. I t is concluded that the hysteresis of the sorption isotherm is an entropy phenomenon. This supports Barkas' explanation of hysteresis in terms of plastic deformation of a gel. INTRODUCTIONMeasurement of the amounts, the vapor pressures, and the energies involved when water vapor is added to and removed froin fibrous natural polyiners have made it possible to calculate in detail the therinodynamic properties of the systeins silk fibroin -water vapor and wool keratiil-water vapor (1, 2, 3). T h e present report includes the saine kind of ineasureinents on the system cellulose -water vapor.Wahba also made similar ineasuremellts on the cellulose -water vapor system (4). However, we believe that Wahba's drying procedures introduce a n irreversible effect. A similar but larger effect is sho\vi~ in the work of Argue and Maass ( 5 ) , who inade the first detailed measurements of the heats of wetting of cellulose by water.Babbitt (6) made a coinprehe~lsive a~lalysis of the adsorption isotherm of the cellulose -water vapor system and was the first to apply the Brunauer, Emmett, and Teller adsorptioil isotherin equatioil (7) t o this system. In the present work, surface area measurements have assisted us in interpreting the thermodynamic properties. E X P E R I M E N T A LCalori~netric measureinent of the heats of wettin:: by liquid water of cellulose equili--.

Structural and thermodynamic characterization of modified cellulose fiber-based materials and related interactions with water vapor

“…Rhim and Lee [16] reported that the maximum net isosteric heats of adsorption for vegetable parchment (VP) paper, Kraft paper, and solid-bleached-sulfite (SBS) paperboard were 18.51, 27.39 and 26.80 kJ/mol, respectively, at lower moisture content. The maximum net isosteric heat of water vapor adsorption on cotton cellulose was found at about 19 kJ/mol, at low moisture content [44].…”

The water vapor sorption behavior of natural fibers

“…[42][43][44] Water adsorption into the plant cell wall is accompanied by a release of heat into the environment due to a reduction in energy of the water molecules as they are confined within the cell wall microcapillaries. 17,45 The heat energy released is in addition to the latent heat given off when water vapor condenses to a liquid. Measurement of this ''heat of wetting'' can use calorimetric methods (integral heat of wetting), or can be estimated by application of the Clausius-Clapeyron equation (differential heat of wetting).…”

Thermal Effect of CO2 on Apoplastic Ice in Rye and Oat during Freezing

“…The following assumptions were made in the calculations: (a) the 20 oat crowns used in the analysis were cylindrical and of uniform size (height ϭ 20 mm, diameter ϭ 6 mm); (b) all the cells in the crown were spheres with a diameter of 0.01 mm; (c) the 3.6 mg of water freezing in the 20 oat crowns had a volume of 3,600 mm 3 ; and (d) a liquid water mono-layer is 3 Å thick. (Morrison and Dzieciuch, 1959). Olien (1974) reported that a liquid water layer 6 monomers thick would result in strong adhesions, and that no adhesions were present with a liquid water layer 15 monomers thick.…”