Gel permeation chromatography is an elution chromatographic process depending on the permeation of the solute through a bed of gel particles. This process is used in the estimation of molecular weight distributions of polymers, since elution occurs in decreasing order of molecular size. The eluting species, however, are not perfectly fractionated, and apparent broadening of the distribution occurs. This broadening results from an axial (longitudinal) mixing of the eluting species. Consideration of the accessible bed volume for each species permits a correction to be made for this axial dispersion. The concept was applied to heterodisperse distributions by solving the resulting simultaneous equations. A least‐squares regression may be employed to utilize the experimental data most effectively. The experimental chromatogram can be described in terms of accessible bed volume and dispersion coefficient of each species together with flow rate, sample concentration, and chromatograph column geometry. The chromatogram corrected for the axial dispersion describes the molecular weight distribution more accurately than does the experimentally determined curve. The correction procedure was applied to a well‐characterized polystyrene; the results of the gel permeation chromatography show excellent confirmation of the results of fractionation and of other instrumental analyses.
Melt viscosity data were obtained for linear and branched ethylene polymers over temperatures of 150 to 250°C and shear rates of about one to 300 sec−1. A capillary rheometer was employed, and the appropriate corrections were made for the several sources of significant error in shear stress and shear rate. These corrected data were analyzed in terms of the Ree-Eyring inverse hyperbolic sine relationship for viscous flow. The molecular structure was determined by infrared absorption analyses and molecular weight determinations. The rheological character of these polyethylenes was found to depend on the weight-average length of the polymer backbone and on the branching. The major contribution to the viscosity depended on the length of the backbone and was associated with the longer relaxation times. An additional contribution to the viscosity depended on molecular segments about equal to the interbranch distance, and was associated with the shorter relaxation times. The temperature effect was found to depend on the number of the long-chain branches, as interpreted by the reduced variable procedure applied to the shear rate.
No abstract
SynopsisEight samples of high-density polyethylene with weight-average molecular weights ranging from 5.5 X lo4 to 17.3 X lo4 have been studied. In addition to GPC molecular weight characterization, the recoverable compliance, the shear viscosity, and the extrudate swell were determined a t temperatures between 138 and 200°C. The range of the maximum creep stresses ranged from 60 to 1840 dynes/cm2. The creep recovery response was in the linear or near-linear range. The results are interpreted in the light of the anomalous results of Mendelson and Finger.
Data are presented on the swelling of free and strained hair fibers in water and water vapor. The strained hair fibers were either under constant load or at constant elongation. In some cases rates of swelling are also shown. The swelling isotherms of the free fibers follow the volume changes predicted from density measurements (for wool) except at very high relative humidities. Straining the fiber may either increase or decrease the amount of swelling, depend ing on the type of experiment. An attempt to develop a statistical mechanical model to explain the equilibrium absorption and swelling behavior of a hair fiber is only partly successful. Finally, there seems to be evidence from the rates of swelling to indicate inhomogeneities in the hair with respect to its response to mechanical deformations.
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