Molecular weight CMC

Different water-soluble cellulose derivatives have been used for the determination of endocellulase activities. Carboxymethylcellulose (CMC) has been proposed as substrate and recently Almin et al. (3) have improved their method for the calculation of endocellulase activities, using a medium-molecular-weight CMC (Mv = 299,000 and Mw = 142,000) with well-defined physicochemical properties. No corrections... 

When selecting CMC for level 8, a low-molecular-weight CMC (viscosity 100-500 mPa s at 1 wt%) is recommended for graphite requiring a solid content of 60 wt% on the other hand, high-molecular-weight CMC (viscosity 1,000-2,000 mPa-s at 1 wt%) is advisable for a solid content <60 wt%. 

Sodium carboxymethyl cellulose [9004-32-4] (CMC) and hydroxyethyl cellulose [9004-62-0] (HEC) are the ceUulosics most widely used in drilling fluids (43). CMC is manufactured by carboxymethylation of cellulose which changes the water-insoluble cellulose into the water-soluble CMC (44). Hydroxyethyl cellulose and carboxymethyl hydroxyethyl cellulose (CMHEC) are made by a similar process. The viscosity grade of the material is determined by the degree of substitution and the molecular weight of the finished product. 

The logarithm of the micellar molecular weight (M) and consequently the aggregation number of sodium dodecyl sulfate at 25°C in aqueous sodium chloride solutions is linearly related to the logarithm of the CMC plus the concentration of salt (Cs), both expressed in molar units, through two equations [116]. Below 0.45 M NaCl micelles are spherical or globular, and Eq. (18) applies ... 

From the data in Table 5 it can be seen that the CMC depends on the type of surfactant and, within a series of similar or homologous compounds, on the chain length, i.e., molecular weight of the compound. For the three AOS compounds it is seen that the CMC of the lowest molecular weight product is about twice the value of the other two products. The CMC values of the commer-... 

CMCs of LAS-AOS mixtures in water that contained no calcium or magnesium ions were determined by Suri et al. [3] by means of the surface tension method. The purpose of this work was to study the advantage of LAS-AOS synergism in prototype phosphate-free carbonate-built formulations for use in the Indian market. The authors have used a commercial C10-C14 LAS sample with an average molecular weight of 343 and a commercial C16-C18 AOS sample with an average molecular weight of 350. 

For example, for alkyl (8-16) glycoside (Plantacare 818 UP) non-ionic surfactant solution of molecular weight 390 g/mol, an increase in surfactant concentration up to 300 ppm (CMC concentration) leads to a significant decrease in surface tension. In the range 300 < C < 1,200 ppm the surface tension was almost independent of concentration. In all cases an increase in liquid temperature leads to a decrease in surface tension. This surface tension relaxation is a diffusion rate-dependent process, which typically depends on the type of surfactant, its diffusion/absorption kinetics, micellar dynamics, and bulk concentration levels. As the CMC is approached the absorption becomes independent of the bulk concentration, and the surfactant... 

Calf thymus (CT) DNA was first fragmented by sonication, then purified by a standard procedure. Agarose gel electrophoresis for the sonicated CT DNA revealed a distribution in molecular weight ranging from 30 kDa to 260 kDa which is equivalent in base pairs (bp) from 40 to 400 (1 bp = 660 Da). The DNA fragments were reacted with HEDS in the presence of l-cyclohexyl-3-(2-morpholinoethyl) carbodi-imide metho-p-toluenesulfonate (CMC/jTs). Finally, the reaction mixture was gel-filtered and the macro-molecular fractions, when displayed the characteristic absorption of 260 nm of the nucleic bases, were collected. 

Utilization of a microfabricated rf coil and gradient set for viscosity measurements has recently been demonstrated [49]. Shown in Figure 4.7.9 is the apparent viscosity of aqueous CMC (carboxymethyl cellulose, sodium salt) solutions with different concentrations and polymer molecular weights as a function of shear rate. These viscosity measurements were made using a microfabricated rf coil and a tube with id = 1.02 mm. The shear stress gradient, established with the flow rate of 1.99 0.03 pL s-1 was sufficient to observe shear thinning behavior of the fluids. 

Fluid loss additives such as solid particles and water-thickening polymers may be added to the drilling mud to reduce fluid loss from the well bore to the formation. Insoluble and partially soluble fluid loss additives include bentonite and other clays, starch from various sources, crushed walnut hulls, lignite treated with caustic or amines, resins of various types, gilsonite, benzoic acid flakes, and carefully sized particles of calcium borate, sodium borate, and mica. Soluble fluid loss additives include carboxymethyl cellulose (CMC), low molecular weight hydroxyethyl cellulose (HEC), carboxy-methYlhydroxyethyl cellulose (CMHEC), and sodium acrylate. A large number of water-soluble vinyl copolymers and terpolymers have been described as fluid loss additives for drilling and completion fluids in the patent literature. However, relatively few appear to be used in field operations. 

Laboratory and pilot plant studies [14] on the Stillwater ore showed that the molecular weight of the CMC affected both PGM grade and recovery. Figure 18.3 shows the effect of molecular weight of CMC on PGM grade-recovery relationship. 

The best results were obtained using CMC with an average 300,000 molecular weight, corresponding to a viscosity of over 3000 cps. 

Figure 18.3 Effect of CMC molecular weight on PGM grade-recovery relationship.

Estimation is easier and less time-consuming because use is made of empirical relationships between the BCF and physicochemical properties of the compound, such as water solubility (S) [42-48], Km, (solid organic carbon/water partition coefficient) [48], Kmw (membrane water partition coefficient), iipw (liposome water partition coefficient) [49], critical micelle concentration (CMC) [45], steric factors, molecular weight [47,48], and others. The most common regression method is the estimation of BCF from the octanol-water partition coefficient (Kovl) [18,42,44-48,50,51],... 

The least abundant moieties, LCCs 1 and 2, were relatively high molecular weight species having lower cmc values than the more abundant, smaller LCCs 3 and 4, which exhibited about 10-fold higher cmc values. 

Elution profiles of purified and enzyme treated LCCs 1,3, and 4 appear in Figures 6, 7, and 8, respectively. For each treated LCC, independent of the enzyme(s) used, elution profiles were qualitatively identical. In enzyme digests of LCCs 1 and 3, while there was loss of congruence of A2go and carbohydrate content, there was little evidence for the production of significant amounts of low molecular weight material. Enzyme treatment of LCC 1 = 0.1, cmc = 20 -... 

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