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Molecular weight universal

T. I. Obiaga, "Lignin Molecular Weight and Molecular Weight Distribution during Alkaline Pulping of Wood," Ph.D. thesis. University of Toronto, Canada, 1972. [Pg.146]

There are no universally accepted wet analytical methods for the characteri2ation of quaternary ammonium compounds. The American Oil Chemists Society (AOCS) has estabhshed, however, a number of appHcable tests (180). These include sampling, color, moisture, amine value, ash, iodine value, average molecular weight, pH, and flash point. [Pg.378]

The appearance of n as the index of jc in Eq. (3.28) needs to be Justified. Combustion in gas turbines usually involves substantial excess air and the molecular weight of the mixed products is little changed from that of the air supplied, since nitrogen is the main component gas for both air and products. Thus the mean gas constant (universal gas constant divided by mean molecular weight) is virtually unchanged by the combustion. It then follows that... [Pg.40]

Universal SEC calibration reflects differences in the excluded volume of polymer molecules with identical molecular weight caused by varying coil conformation, coil geometry, and interactive propenies. Intrinsic viscosity, in the notation of Staudinger/ Mark/Houwink power law ([77]=fC.M ), summarizes these phenom-... [Pg.463]

Electrostatic and adsorption effects conspire to make aqueous GPC more likely to be nonideal than organic solvent GPC. Thus, universal calibration is often not obeyed in aqueous systems. Elence, it is much more critical that the standard chosen for calibration share with the polymer being analyzed chemical characteristics that affect these interactions. Because standards that meet this criterion are often not available, it is prudent to include in each analysis set a sample of a secondary standard of the same composition and molecular weight as the sample. Thus, changes in the chromatography of the analyte relative to the standards will be detected. [Pg.557]

In SEC, universal calibration is often utilized to characterize a molecular weight distribution. For a universal calibration curve, one must determine the product of log(intrinsic viscosity molecular weight), or log([7j] M). The universal calibration method originally described by Benoit et al. (9) employs the hydro-dynamic radius or volume, the product of [tj] M as the separation parameter. The calibration curves for a variety of polymers will converge toward a single curve when plotted as log([7j] M) versus elution volume (VJ, rather than plotted the conventional way as log(M) versus V, (5). Universal calibration behavior is highly dependent on the absence of any secondary separation effects. Most failures of universal calibration are normally due to the absence of a pure size exclusion mechanism. [Pg.565]

Durihg recent years a considerable amount of re-.search has been undertaken to understand what in the makeup of a polymer affects the processability. In the late 1980s, the Rubber Manufacturers Association in the United States undertook a research project with the Department of Polymer Engineering at the University of Akron to evaluate the laboratory equipment available using specially made butadiene-acrylonitrile polymers with different acrylonitrile levels, molecular weights, and molecular weight distributions. The results from the study confirmed that, from the processing variables viewpoint, the major factors are frequency (shear rate), temperature (temperature), and deformation (strain). [Pg.452]

In this very useful form, Rg is known as the universal gas constant, has a value of 1545 and is the same for all gases. The specific gas constant (i i) for any gas can be obtained by dividing 1545 by the molecular weight. Rg is only equal to 1545 when gas pressure (p) is in PSIA volume (y) is expressed as cubic feet per pound mole and temperature (T) is in Rankine or absolute, i.e. °F + 460. [Pg.634]

The situation becomes most complicated in multicomponent systems, for example, if we speak about filling of plasticized polymers and solutions. The viscosity of a dispersion medium may vary here due to different reasons, namely a change in the nature of the solvent, concentration of the solution, molecular weight of the polymer. Naturally, here the interaction between the liquid and the filler changes, for one, a distinct adsorption layer, which modifies the surface and hence the activity (net-formation ability) of the filler, arises. Therefore in such multicomponent systems in the general case we can hardly expect universal values of yield stress, depending only on the concentration of the filler. Experimental data also confirm this conclusion [13],... [Pg.80]

The most widely used molecular weight characterization method has been GPC, which separates compounds based on hydrodynamic volume. State-of-the-art GPC instruments are equipped with a concentration detector (e.g., differential refractometer, UV, and/or IR) in combination with viscosity or light scattering. A viscosity detector provides in-line solution viscosity data at each elution volume, which in combination with a concentration measurement can be converted to specific viscosity. Since the polymer concentration at each elution volume is quite dilute, the specific viscosity is considered a reasonable approximation for the dilute solution s intrinsic viscosity. The plot of log[r]]M versus elution volume (where [) ] is the intrinsic viscosity) provides a universal calibration curve from which absolute molecular weights of a variety of polymers can be obtained. Unfortunately, many reported analyses for phenolic oligomers and resins are simply based on polystyrene standards and only provide relative molecular weights instead of absolute numbers. [Pg.385]

Note Like sulfuric acid (q.v.) ort/io-phosphoric add is a universal reagent, with which almost all classes of substance can be detected at high temperatures (150-180 °C) by charring e.g. high molecular weight hydrocarbons (mineral oils) [20]. The colors and fluorescences produced at lower temperatures (<120°C) and their intensities are very dependent on the temperature and period of heating. It is not possible to use meta- or pyrophosphoric acid in place of or/Ao-phosphoric add, since, for instance, amanita toxins react well with alcoholic phosphoric add only weakly with aqueous phosphoric add and not at all with meta- or pyrophosphoric acid [17]. [Pg.180]

Industrial Engineering Chemistry Research 37, No.7, July 1998, p.2582-91 POLYETHYLENE PYROLYSIS THEORY AND EXPERIMENTS FOR MOLECULAR WEIGHT DISTRIBUTION KINETICS Sezgi N A Cha W S Smith J M McCoy B J California,University... [Pg.63]

In these equations x and y denote independent spatial coordinates T, the temperature Tib, the mass fraction of the species p, the pressure u and v the tangential and the transverse components of the velocity, respectively p, the mass density Wk, the molecular weight of the species W, the mean molecular weight of the mixture R, the universal gas constant A, the thermal conductivity of the mixture Cp, the constant pressure heat capacity of the mixture Cp, the constant pressure heat capacity of the species Wk, the molar rate of production of the k species per unit volume hk, the speciflc enthalpy of the species p the viscosity of the mixture and the diffusion velocity of the A species in the y direction. The free stream tangential and transverse velocities at the edge of the boundaiy layer are given by = ax and Vg = —ay, respectively, where a is the strain rate. The strain rate is a measure of the stretch in the flame due to the imposed flow. The form of the chemical production rates and the diffusion velocities can be found in (7-8). [Pg.406]


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See also in sourсe #XX -- [ Pg.184 , Pg.185 , Pg.189 ]




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