Adsorption isotherm cellulose fibers

The data of the polymer adsorption on cellulose fibers are represented in Fig. 4. They show a Langmuir-type adsorption isotherm. The plateau value obtained from Fig. 4 is more than 25 mg/g. Somewhat lower values have been reported for the adsorption of other cationic polymers such as poly-DADMAC or poly(ethylenimine) on various cellulosic materials [26, 27]. The cationic... 

More recentfy Mohlin and Gray (9J) determined adsorption isotherms on cellulose fibers for a variety of adsorbates (solutes). From the experimental type II isotherms specific surface areas of the fibers were computed, for eadi solute, with the results en in Table 11. The agreement observed between the different solutes is quite remarkable considering that the area of the solute molecule on the potymer surface must be known or estimated. Hie sirface area determined by nitrogen adsorption measurements at —196° was included for the purpose of comparison. The sli t di arity could possibly indicate that the area available to the smaller nitrogen molecule may be somewhat larger (1.9 compared to 1.6 m g" ). 

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. 

Figure 17.4 Adsorption isotherm of ODTMA and coadsorption of 2-naphthol onto cellulose fibers. ...

Figure 17.7 Adsorption isotherms of organic solutes on cellulose fibers treated with hexadecyammonium brimide C16 (coverage ratio 9 = 75%). (a) virgin cellulose Cel-0, (b) oxidized cellulose Cel-600. ...

Abstract High contents of fillers such as kaolin or calcium carbonate limit the use of waste paper, especially in tissue paper production. In order to determine the effect of flotation reagents on the removal of fillers, adsorption, zeta potential, and particle size measurements, as well as flotation experiments using model dispersions of calcium carbonate, kaolin, and cellulose fibers were carried out. The adsorption of the cationic polymer starts at low initial concentrations on the negatively charged filler surfaces and cellulose fibers. However, due to the steeper slope of the adsorption isotherm on the fillers, the polymer is preferentially adsorbed on the fillers. Furthermore, the adsorption of the polymer causes an increase... 

Nevertheless, for waste paper recycling the plateau values of the isotherm are not decisive. With 0.2% dosage of the cationic polymer and 1 % stock consistency, the initial concentration is only 20 mg/1. Due to the steeper slope of the adsorption isotherm on the fillers, the polymer should preferentially be adsorbed on the fillers. Figure 5 shows the flotation recovery of all three solid materials — calcium carbonate, kaolin, and cellulose. These flotation tests were performed with pure systems. The solid content was the same as in waste paper recycling 1 and 0.2% for fibers and fillers, respectively. At a concentration of 20 mg/1, the recovery of kaolin is higher than 90%, while 70% of calcium carbonate are floated. However, with the same initial concentration the recovery of the cellulose fibers is below 20%. In comparison with the adsorption isotherms it can be concluded that the adsorbed amount of the cationic polymer is too low in order to hydrophobize the cellulose surface. Thus, the cationic polymer is a selective collector with respect to filler pigments. This fact has been confirmed by flotation tests with synthetic mixtures of cellulose and fillers [30]. 

The sorption isotherms of the vapor of -hexane by cotton cellulose (COC) and viscose fibers (VI were similar to F-shape isotherms of type 1 having the saturation plateau (Fig. 7.31). Despite lower degree of amorphicity, COC-sample had increased sorption value than the more amorphous VF-sample. This provides evidence that just surface adsorption occurs in the cellulose-hexane system. 

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