Determination of fluidity

Among the various solvents suggested for dissolution of cellulose, cuprammonium solution is recommended as a general solvent having 15 0.1 g/1 Cu, 200 5 g/1 NHj and less than 0.5 g/1 nitrous oxide. The fluidity in this solvent of the solution of cotton is given by 

The kinetic energy correction is unnecessary for times of flow greater than 200 sec. In actual practice 0.5 g of finely cut dry cotton sample is dissolved in 100 ml of standardised cuprammonium hydroxide solution. The viscometer (Fig. 16-2) is 

Chemically undamaged cotton has a fluidity of 3 to 5. A value of 10 or more can be taken as an indication of excessive degradation during chemical pre-treatment processes. It is usual to work with 2% solution in the case of regenerated cellulose. Unprocessed viscose has a fluidity of 10 to 12. The fluidity values can be expressed in terms of DP of cellulose by the following equation [14]  

Fluidity results determined in Cuxam and Cuen for chemically damaged cotton are correlated with viscosity values obtained in Cadoxen and FeTNa solvents [16]. The comparison and conversion of the viscosity values to apparent cuprammonium fluidity is a quick method of determining degradation of cotton occured in pretreatment processes [16]. 

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Tab. 8.1. Main fluorescence techniques for the determination of fluidity (from Valeur, 1993)...

The various fluorescence-based methods for the determination of fluidity and molecular mobility are summarised in Table 8.1. Attention should be paid to the comments indicated in the last column. 

The red blood cell must be able to squeeze through some tight spots in the microcirculation during its numerous passages around the body the sinusoids of the spleen are of special importance in this regard. For the red cell to be easily and reversibly deformable, its membrane must be both fluid and flexible it should also preserve its biconcave shape, since this facilitates gas exchange. Membrane lipids help determine membrane fluidity. Attached to the inner aspect of the membrane of the red blood cell are a number of peripheral cytoskeletal proteins (Table 52-6) that play important roles in respect to preserving shape and flexibility these will now be described. 

Major determinants of membrane fluidity may be grouped within two categories [53] (1) intrinsic determinants, i.e., those quantifying the membrane composition and phase behavior, and (2) extrinsic determinants, i.e., environmental factors (Table 1). In general, any manipulation that induces an increase in the molal volume of the lipids, e.g., increase in temperature or increase in the fraction of unsaturated acyl chains, will lead to an increase in membrane fluidity. In addition, several intrinsic and extrinsic factors presented in Table 1 determine the temperature at which the lipid molecules undergo a transition from the gel state to liquid crystalline state, a transition associated with a large increase in bilayer fluidity. 

Biological membranes Fluidity and order parameters Determination of the phase transition temperature Effect of additives (e.g. cholesterol)... 

Two main types of viscometers are suitable for the determination of the viscosity of a polymer melt The rotation viscometer (Couette viscometer, cone-plate viscometer) and the capillary viscometer or capillary extrusiometer. The latter are especially suitable for laboratory use since they are relatively easy to handle and are also applicable in the case of high shear rates. With the capillary extrusiometer the measure of fluidity is not expressed in terms of the melt viscosity q but as the amount of material extruded in a given time (10 min). The amount of ex-trudate per unit of time is called the melt index or melt flow index i (MFI). It is also necessary to specify the temperature and the shearing stress or load. Thus MFI/2 (190 °C)=9.2 g/10 min means that at 190 °C and 2 kg load, 9.2 g of poly-... 

Pyrene carboxaldehyde and a series of pyrene carboxylic acids were found useful as fluorescence probes in describing the constitution of inverted micelles of certain calcium alkarylsulfonates in hydrocarbon media. 1-Pyrene carboxaldehyde is a convenient probe for studying the particle sizes of micelles in the region of lOOA. A series of graded probes, pyrene carboxylic acids with varying alkyl chain length, have been used to determine internal fluidity and micro-polarity as a function of distance from the polar core of these Inverted micelles. Pyrene exclmer to monomer fluorescence intensity ratio and fluorescene lifetime provided the means of measurement of internal fluidity and micropolarity, respectively. 

Lipid-free (Na+, K+)-ATPase is incapable of hydrolyzing ATP or p-nitrophenyl phosphate. The precise role of the lipid and the specificity for the lipid have not yet been determined. The addition of lipid to the delipidated enzyme brings about conformational changes, with phosphatase activity regenerated before ATPase activity.51 It seems evident that the lipid will affect the conformation of the enzyme and determine membrane fluidity, which is relevant to conformational change. 

As mentioned above, the binder/filler ratio determines the fluidity and hence the process technology for a given syntactic composition. The solid line in Fig. 1 shows how the apparent density depends on the relative microsphere concentration in syntactic compounds, provided there are no air inclusions. The lower limit of apparent density is at the concentration at which the filler is most densily packed at this point the material has its highest specific strength (strength per unit apparent density). Experience has shown that the closest packing of the spheres within the binder is obtained when the material is mixed and cast or molded under vacuum 8 10). 

Frequently used single-point viscosity tests in the starch plant are orifice pipettes,56 orifice funnels,57 the Hot Scott viscometer, and various methods to determine alkaline fluidity.58 For absolute measurements of the rheological properties, rotating viscometers with coaxial cylinders are used.59 The paper industry uses mainly the Brookfield viscometer and the Hercules viscometer for determining shear-dependent viscosity, pseudoplasticity, and thixotropy. Oscillatory and capillary viscometers are used for more detailed viscosity characterization, such as yield value, elastic properties, and viscoelasticity.60... 

These points respectively define the temperature at which, on reheating, a cooled or quenched pyrolysis residue begins to soften and develop fluidity and the temperature at which the liquid residue begins to change its chemical composition, i.e., when pyrolysis recommences. This latter point is more ambiguous since it is determined from a thermogravimetric experiment which is subject to the effects of experimental procedure, as discussed earlier. Therefore, it is essential to use a fixed heating rate, etc., in the determination of the decomposition temperature. The volatile content can be determined in the same experiment. 

Then, DI of the coke produced by adding residual oil in an amount equal to that of the replacement coal in the manner described above was determined, and the reflectance of the residual oil was determined from the regression line given in Figure 6. The reflectance thus determined is herein defined as the effective reflectance, Rog. After determination of RoE, DI is determined on the coke produced from a blend of coal and residual coil in the fluidity control region. 

Blending Limit of Petroleum Coke, The blending limit of petroleum coke is considered to be about 5% as already mentioned above. This can be explained from the current average value of MF of about 200 to 500 DDPM for coal blends in the Japanese coking industry. Figure 13 shows limit quantities of added petroleum coke for various values of fluidity for the base coals. In the determination of these limit quantities, the quantity of added petroleum coke with which the fluidity of the coal blend decreased to below 200 DDPM under the effect of this blending was deemed as the limit. 

Various process steps were used to determine their Influence on the morphological nature of liquid crystalline copolyester films. Compression molding was used to form quiescent films, while extenslonal deformation above and below the onset of fluidity, as well as shear deformation above the onset of fluidity was used to make non-quies-cent films. It Is a basic result that molecular orientation can only be achieved when the deformation is done while the polymer is In a liquid crystalline melt state. Experimental details are given In the subsection Materials and Processing, while an interpretation is offered in the discussion in the subsection Morphological and Process Consideration. ... 

Essential fatty acids (EFAs) are essential for the survival of humans and other mammals they cannot be synthesized in the body and, hence, have to be obtained in our diet and, thus, are essential (1-4). EFAs are an important constituent of cell membranes and confer on membranes properties of fluidity thus, they determine and influence the behavior of membrane-bound enzymes and receptors. Two types of naturally occurring EFAs exist in the body the oo-6 series derived from linoleic acid (LA, 18 2) and the oo-3 series derived from a-linolenic acid (ALA, 18 3). Both the 00-6 and the oo-3 series are metabolized by the same set of enzymes to their respective long-chain metabohtes. Although some functions of EFAs require their conversion to eicosanoids and other products, in most instances the fatty acids themselves are active. The longer-chain metabolites of LA and ALA regulate membrane function and are of major importance in the brain, retina, liver, kidney, adrenal glands, and gonads. 

First, we tried to determine the gel point precisely. Figure 1 shows the graph for determination of the gel point in the bulk polymerization of DAP as a typical example [33]. The gel point was estimated as the conversion at the time when the gel starts to be formed. The gel point was determined as 22.3%, being somewhat lower than the 25% stated by Simpson [31]. This author estimated the gel point from the extrapolation of the conversion-time curve obtained in the early stage of polymerization to the time at which the fluidity of the reaction mixture was lost by gelation. 

There may be several arguments to explain this observation. First, the D-97 calls for determining the PP at either —24°C or —27°C, i.e., the actual loss of fluidity may occur at the temperature which is closer to —27°C than —24°C, but it still qualihes as a PP of —24°C, rather than —27°C. 

Therefore, the study of rheological properties, the determination of the activation energy of viscous flow, composition-fluidity relationships, and key factor effects of the lubricity-promoting additive on the fluidity of oligoethylsiloxane-based compositions were of interest. 

This presentation, based solely on pure film studies, shows that the validity of fluidity and polarity profiles as determined from spin-label probes, is questionable. More important, however, is the fascinating insight into the unique surface chemistry of these compounds. 

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