Cellulose Fibers water adsorption

The water retention of cellulose fibers at a given relative humidity varies depending on whether the equilibration has taken place by desorption or adsorption. (hysteresis). The water uptake also continuously decreases after repeated drying and moistening of the fibers. Additional factors influencing the ability of pulp fibers to swell are their chemical composition, such as their hemicellulose and lignin content. 

The dependence of the retention volume on the adsorbate concentration in the gas phase has proved to be a useful and rapid way to determine adsorption Isotherms (12). The adsorption of organic molecules and water on glassy polymers (13), cellulose fibers, paper (14-16), cellophane (17), glass fiber TlS.), textile fibers (8 ), and carbons (19) has been measured by IGC. 

The distinction between fiber saturation point (the maximum water content of swollen cell walls) and the maximum possible moisture content has a diminishing value for degraded wood, which may eventually have no effective fiber saturation point at all. The ordered and disordered cellulose in sound wood are the main sites for water adsorption (ii). As they diminish over time, their relative role in determining fiber saturation also diminishes. Nevertheless, the measurement of relative water adsorption will have some value in determining the relative degradation in a wood sample. 

Paper chromatography of amino acids is best described as partition chromatography between the stationary aqueous (most polar) phase in the cellulose fibers and the mobile (least polar) phase formed by the solvent system used. The actual situation is somewhat more complicated. The stationary phase cannot be described as pure water but rather as a concentrated aqueous carbohydrate solution. Elements of adsorption chromatography are involved as shown by the relatively small/ f values for aromatic amino acids and by the possibility of separating enantiomers (mirror images) of amino acids depending on the chirality of the cellulose in the paper. 

Y. Lei, X. Qian, J. Shen, X. An, Integrated reductive/adsorptive detoxification of Cr (Vl)-contaminated water by polypyrrole/cellulose fiber composite. Ind EngChem Res 2012,51 (31), 10408-10415. 

Free water only exists when all sites for the adsorption of bound water in the cell wall are filled. This point is called the fiber saturation point (FSP) and all the water added to fibers after the FSP has been reached exists as free water. Thus the total moisture content is the sum of the bound and free water. AAfhen a cellulose fiber remains at a constant relative humidity (RFl) and temperature for a long enough period of time, the proportion of water reaches a steady state known as the equilibrium moisture content (EMC). Test results show that, typically, for small pieces of wood at a constant RH, the EMC is reached in about 14 days [17]. The EMC varies significantly with the somce of the fibers and values for some of the most widely used fibers (at typical ambient conditions of 65% RH and 21°C) are given in Table 15.6. 

Poly(acrylic acid) (PAA) was grafted onto the ultra-fine cellulose fiber surfaces via ceric ion initiation (Scheme 5). The carboxylic acid concentration could be controlled by varying monomer AA and/or ceric ion concentrations, and was determined by NaOH-HCl titration using phenophthlein as the indicator. Unless otherwise indicated, fibers with 3.6 mmol of COOH per g cellulose (lAA]/[Ce(IV)]-30) were used for enzyme adsorption and assay. The PAA activated cellulose fibers were immersed in 1.0 mg/ml lipase solution (pH 7.0) at room temperature for 24 hrs. The lipase adsorbed cellulose fibers were rinsed by pH 7 buffer and deionized water to remove loose lipase, then dried under vacuum at room temperature for 12 hrs. 

The following commercially available fillers were used Kaolin Spex IF, calcium carbonates of the type Hydrocarb 90 OG (powder and slurry). The specific surface area of the fillers used for adsorption was determined by the BET method (Sorptomatik 1800, Carlo Erba Strumentazione, Italy). It was 7.5 m /g for kaolin and 10.3 mVg for Hydrocarb 90 OG. Fibers Sulfate-bleached cellulose from soft wood was used for the adsorption experiments. The cellulose fibers were disintegrated and left to swell after several treatments with distilled water. The water-soluble impurities were removed from the material by hot water extraction for 1 h, which was repeated two times. 

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