Cellulose concentrations

Continuous deaeration occurs when the viscose is warmed and pumped into thin films over cones in a large vacuum tank. The combination of the thinness of the Hquid film and the dismption caused by the boiling of volatile components allows the air to get out quickly. Loss of water and CS2 lower the gamma value and raise the cellulose concentration of the viscose slightly. Older systems use batch deaeration where the air bubbles have to rise through several feet of viscose before they are Hberated. 

Figure 20 AFM image (tapping mode, height image) of a dry cellulose film. The cellulose concentration was 0.5%w/w. The root-mean-square surface roughness was 5.0 nm (courtesy of M. Liu, University of Birmingham, UK).

In Fig. 12 the stability of the concentrated emulsions is plotted against the concentration of methyl cellulose in the aqueous continuous phase. Obviously the viscosity of the continuous phase increases with increasing concentration. Concentrated emulsions did not form for high concentrations of methyl cellulose owing to the difficulty of incorporating the dispersed phase into the continuous phase. For instance, styrene-water and n-butyl methacrylate-water did not form concentrated emulsions for methyl cellulose concentrations in the... 

Figure 2. Nematic phase patterns formed in the cellulose solutions prepared from solvent composition of 24.5/75.5 cellulose concentration, 14g/100mL DP, 450 (a and b) immediately after dissolution.

Figure 3a. Conjugated pattern solvent composition, 27.0/73.0 cellulose concentration, 12g/100mL DP, 210 storage time at 25"C, 14 days.

Figure 3b c. Conjugated patterns formed at relatively high cellulose concentration solvent composition, 24.5/75.5 cellulose concentration, 18g/100mL (b), 20g/100mL (c) DP, 210 storage time at 25 C, 10 days, with 1" red plate , direction of the highest refractive index of the 1 red plate. 

Figure 5. Aggregated anisotropic phase pattern solvent composition, 23.6/75.0/1.4, NH3/NH4SCN/H2O cellulose concentration, 20g/100mL, immediately after dissolution.

Figure 6. Minimum cellulose concentration for mesophase formation as determined by solvent composition DP, 210 storage time at 25 C, 30...

Cellulose based mesophases have displayed a somewhat steeper inverse dependence of pitch to concentration than that reported by Toriumi (29). A value of x = 3 has been reported for hydroxypropyl cellulose in water (31), for acetoxypropyl cellulose in acetone (32) and for hydroxypropyl cellulose in acetic acid and in methanol (28). Our data for cellulose in NH3/NH4SCN show a reasonably straight line when p l/3 was plotted vs. cellulose concentration (Figure 11), which is in accord with earlier reports (28,29,31,32). 

Figure 13. Specific rotation dependence at 25 C on solvent composition and on storage time cellulose concentration, 12g/100ml DP, 210 1 hour ( ), 24 hours (o), 213 hours (n).

Plotting [0] against l/X gives a linear relationship as shown in Figure 12. The values for An were calculated from the slope and the cholesteric pitch and are shown in Table II. An (corrected for cellulose concentration) increased with increasing cellulose concentration and with decreasing NH4SCN content. 

In the current study, the aggregated anisotropic phase occurred in solutions prepared from acid hydrolyzed cellulose of dp 35. The higher minimum cellulose concentration for mesophase formation was observed in cellulose solutions richer in NH4SCN (see Figure 6). In these aspects, the cellulose/NH3/NH4SCN system resembles the DMAC/LiCl/cellulose system. 

The former prediction is now discussed. In the cellulose/NH3/NH4SCN system, the observation that the minimum cellulose concentration for mesophase formation increased with increasing NH4SCN in the solvent up to approximately 75.5%, indicates that this specific solvent composition may be regarded as a good solvent composition. 

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