Polymer shear degradation

Hunston, D. L., Effects of molecular weight distribution in drag reduction and shear degradation, /. Polym. Sci. Polym. Chem. Ed, 14, 713-727 (1976). 

Other evidence for macroradical formation is the coreaction that occurs when two polymers are jointly subjected to mechanical action or when the polymerization of monomers is initiated by the presence of a shear-degraded polymer (see Chapter V). 

Dilute stream shear testing was performed on the EP injection skid, where Injectivity would not be Impaired. The sheared polymer solution was sampled at the wellhead, and numerous tests were performed to detect the changes in polymer solution quality. Viscosity, screen factor, concentration of polymer, core plug injectivity and filtration performance were measured to evaluate the shear degraded polymer solution. 

Molecular Weight. Measurement of intrinsic viscosity in water is the most commonly used method to determine the molecular weight of poly(ethylene oxide) resins. However, there are several problems associated with these measurements (86,87). The dissolved polymer is susceptible to oxidative and shear degradation, which is accelerated by filtration or dialysis. If the solution is purified by centrifiigation, precipitation of the highest molecular weight polymers can occur and the presence of residual catalyst by-products, which remain as dispersed, insoluble soHds, further compHcates purification. 

Aqueous Solution Viscosity. A special solution preparation method is used for one type of measurement of aqueous solution viscosity (96). The appropriate amount of poly(ethylene oxide) resin is dispersed in 125 mL of anhydrous isopropyl alcohol by vigorous stirring. Because the resin is insoluble in anhydrous isopropyl alcohol, a slurry forms and the alcohol wets the resin particles. An appropriate amount of water is added and stirring is slowed to about 100 rpm to avoid shear degradation of the polymer. In Table 4, the nominal resin concentration reported is based on the amount of water present and ignores the isopropyl alcohol. 

There are different reasons to discard a column a column can be damaged by irreversible adsorption of reactive polymer samples. Small amounts of styrene oligomers are known to permanently elute from styrene-divinylbenzene materials with tetrahydrofuran as the eluent, which means a continuous shear degradation of the separation material and consequently a decrease of the packing quality this observation is very important if fractions are collected and used for further analyses, e.g., for the determination of infrared (IR) spectra. One can presume that similar effects are present with other organic materials too. 

Compounding and palletizing of the latex blended material is sometimes done by melt mixing. In such cases precautions must be taken to avoid thermal and shear degradation of the blended polymer. 

Well before the advent of modern analytical instruments, it was demonstrated by chemical techniques that shear-induced polymer degradation occurred by homoly-tic bond scission. The presence of free radicals was detected photometrically after chemical reaction with a strong UV-absorbing radical scavenger like DPPH, or by analysis of the stable products formed from subsequent reactions of the generated radicals. The apparition of time-resolved ESR spectroscopy in the 1950s permitted identification of the structure of the macroradicals and elucidation of the kinetics and mechanisms of its formation and decay [15]. 

Chain scission is the ultimate fate of a stressed bond. At some value below the critical stress for chain rupture, bond angle deformation may result in an increase in reactivity. As stated in Sect. 3.1, mechanically activated hydrolysis of polymers containing ester groups can lead to the scission of the bond this concurrent reaction should be differentiated from homolytic chain scission, for example by looking at any pH-dependence as was found to be the case during shear degradation of DNA [84]. 

In the semi-dilute regime, the rate of shear degradation was found to decrease with the polymer concentration [132, 170]. By extrapolation to the dilute regime, it is frequently argued that chain scission should be nonexistent in the absence of entanglements under laminar conditions. No definite proof for this statement has been reported yet and the problem of isolated polymer chain degradation in simple shear flow remains open to further investigation. 

Pseudozan is an exopolysacchaiide produced by a Pseudomonas species. It has high viscosities at low concentrations in formation brines, forms stable solutions over a wide pH range, and is relatively stable at temperatures up to 65° C. The polymer is not shear degradable and has pseudoplastic behavior. The polymer has been proposed for enhanced oil-recovery processes for mobility control [1075]. 

McCormick, C.L., et al. "Development of Laboratory Screening Tests to Predict Polymer Performance in Enhanced Oil Recovery (I). Shear Degradation, Viscosity, and Electrolyte Studies," prepared for DOE under contract No. EF-77-S-05-5603, 1977. 

Chang, H.D., Darby, R. "Effect of Shear Degradation on the Rheological Properties of Dilute Drag Reducing Polymer Solutions," J. Rheol.. 1983, 27(1), 77-88. 

In the second section, improved column technology is emphasized. The effects of operational variables on the performance of the chromatographic system are considered. Some of the operational variable concerns are shear degradation of high molecular weight polymers, the use of mixed solvent systems, and the optimization of resolution for analysis of oligomers and small molecules. 

Shear Degradation of Very High Molecular Weight Polymers in Gel Permeation Chromatography... 

Experimentally it is difficult to detect the occurrence of polymer shear degradation since concentration effects, increased peak dispersion, and ultrafiltration of high molecular weight components may also distort the peak profile or shift the distribution towards the low molecular weight region. Furthermore,... 

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