Cellulose systems

Chitosan samples with degrees of deacetylation of 65,73,85, and 92% were almost completely adsorbed onto the surfaces of cellulosic fibers, especially onto the surfaces of fines in a variety of cellulosic systems used in industrial operations. Adsorption increased as the degree of deacetylation of chitosan increased. The aggregation of the fine cellulosic particles was maximum at a dosage of about 10 mg/kg. The interactions between chitosan and the cellulosic substrates were dominated by a bridging mechanism at about pH 7 [32]. 

Cx enzymes occur in multiple forms in most cellulose systems, and they appear to be different enzymes with different relative activities on a number of cellulose substrates. It was always possible, then, but not necessarily likely, that a completely different Cx system was being synthesized in each case and that this would account for the difference in synergism. This possibility was excluded, however, when it was found that each Cx system was identical in terms of CM-cellulase activity in each case the number of reducing end groups produced per unit decrease in viscosity was the same. 

Figure 2. Schematic diagram of the general procedures used in purifying cellulose system components (1, 2, 4)...

The two-stage sorption behavior is not a unique characteristic of the cellulosic systems investigated by Long et al. Subsequent studies, by... 

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. 

Wells, J.I. Langridge, J.R. Dicalcium phosphate dihydrate-microcrystalline cellulose systems in direct compression tabletting. Int. J. Pharm. Tech, and Prod. Manuf. 1981, 2 (2), 1-8. 

There is obviously an important consequence of using char absorpUvitites of 0.95-0.98 as implied in Figure 4, as opposed to using the value of 0.77 which better describes the real situation in a fire. The former will not result in as rapid heating of the sample. Rarely has much concern been shown for such important departures from near-black char surface behavior in the modeling of pyrolysis in cellulosic systems. 

Fig. 6. Equilibrium pH variation as a function of initial pH for HgCl,. Solutions chemically modified cellulose systems.

Numerous investigators have proposed theories for the temperature dependence of pitch. " However, none completely explain the experimental results obtained for the various cellulosic systems. Of those proposed, Osipov s approach, which is based on a molecular statistical theory,takes into account steric and chiral interactions in solution to predict the influence of temperature and solvent on the pitch and twist sense of cellulose deiivatives. Assuming the cellulosic chain adopts a twisted belt as opposed to a helix, and the persistence length, /, of the cellulose chains is much smaller than that of a rigid chain, the twisting power could be expressed by... 

Siekmeyer, M. Steinmeier, H. Zugenmaier, P. Structural investigations and phase behavior of a ternary lyotropic liquid-crystalline cellulosic system cellulose tricarbanilate/3-chlorophenyl-urethane of cellulose/triethylene glycol monomethyl ether. Makromol. Chem. 1989, 190 (5), 1037-1045. 

In summary, the results which are presented in this section suggest that the charge transport of ions within paper and paperlike structures is essentially the same as that of the transport properties associated with aqueous electrolyte systems. Furthermore, the transient current behaviour which has been observed in these fibrous cellulosic systems show characteristics similar to the ionic transient current conduction exhibited in both dielectric fluids and aqueous ionic systems. 

At sufficiently high penetrant partial pressures in glassy polymers, the onset of plasticization produces the upturn in permeability seen in Fig. 2d. While this behavior is shown for the acetone-ethyl cellulose system, it is also typical of many other systems. In fact, if one extends the pressure range of the measurements in Fig. 2c to 900 psia, an upturn in permeability like that seen in Fig. 2d is observed (29). This response is, therefore, a combination of the dual mode response in Fig. 2c and the plasticization response in Fig. 2b at high sorbed concentrations. 

The fourth avenue of research is even more conjectural. Here we see the cellulase-cellulose system as a physico-chemical model of flux. It depicts the transition between the structure and the structureless, between the reserve solids and the mobile solutes. Such transitions exist throughout nature. 

If our conventional thinking about the reversibility of enzymic reactions in general holds in the case of the cellulase-cellulose system, it would follow that the system would not only hydrolyze cellulose into glucose but also synthesize cellulose from glucose. This would relate... 

In any case, the deeper study of the cellulase-cellulose system puts us face to face with a most important facet of a most challenging problem of science and philosophy—i.e., putting form into the formless. 

Hydrophobically modified alkali-swellable latex thickeners (Chapter 25) can also be used as cothickeners for HEURs, and, like hydrophobically modified HEC, do not suppress the ICI viscosity of HEURs. Therefore, blend ratios of HEUR/hydrophobically modified alkali-swellable latex systems will have less HEUR thickener and be less expensive than HEUR/cellulosic systems. Some hydrophobically modified alkali-swellable latexes are even more cost-efficient than cellulosic thickeners, so a further savings may be realized. Another advantage to this approach is that the HEUR/hydrophobically modified alkali-swellable latex thickener systems are not biodegradable however. 

Computer simulations which may mimic aggregation processes in 3 d space yield values of 0 = 2.5 for OLA and 0 = 1.8 for CA (33, 35-38). Clearly neither the OLA or CA model describes the cotton cellulose system. A possibility that so far has not been included in the simulations is that the aggregates might restructure after formation. Schaefer et al. (42,43) suggested that additional attachments will lead to an increased 0 so... 

When the nonaqueous cellulose solvent was used as a medium, the order of reactivities was 6-OH>2-OH 3-OH. This order is similar to observations in the case of simple alcohols. Thus, although the primary hydroxyl group 6-OH has the highest reactivity, and the secondary hydroj l groups 2-OH and 3-OH have almost equal reactivities, the difference of reactivities between 6-OH, 2-OH and 3-OH is small. On the other hand, when heterogeneous alkali cellulose systems were used, where cellulose was swollen in aqueous alkali rather than being in solution, the order of reactivity was... 

I provides a speclnim that differs from that of the native form. Eleetron microscopy shows that cellulose I complexed wifli EDA is composed of nonuniform crystalline domains, whereas die IIIi allomorph is characterized by well-defined crystalline zones. The conformational changes observed for die primary hydroxyl groups are of interest, as they provide possible markers for study of die various conformational transitions associated with cellulosic systems. 

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