ISSN:
0022-3832
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The effects of molecular weight distribution and branching on the viscosity of polyethylene melts were studied by making mixtures of paraffin wax with 0 to 100% of various types of high and low density polyethylenes of known weight-average molecular weights, M̄w and measuring their Newtonian melt viscosity at 150°C. The range of molecular weights from about 400 to 106 gave about a billionfold range in the viscosities (10-2 to 10+7 poises). The results showed that the melt viscosity did not vary with M̄w3.4, since samples with the same M̄w might differ by up to 100,000-fold in viscosity. An analysis of the flow process in melts suggested that the viscosity-average molecular weight M̄v might be more significant than the M̄w. Within the accuracy of our knowledge of the initial molecular weight, the viscosities of all mixtures having viscosities above about 10 poises fit the equation \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {\log \eta = - 12.3 + 3.45\log (w_1 M_1^\alpha + w_2 M_2^\alpha)^{1/\alpha}} \\ {= - 12.3 + 3.45\log \bar M_v} \\\end{array} $$\end{document} where w1 and w2 are the weight fractions, and M1 and M2 are the molecular weights of the paraffin and polyethylene, respectively, and M̄v is a viscosity-average molecular weight of the mixture. Theory and experiment show that the value of α may be obtained without any knowledge of the initial molecular weight, from the slope of the curve for log η0 versus log concentration at small concentrations of wax. Polyethylenes with large amounts of long-chain branching had low values of α (down to about 0.25), while polymers with relatively little long-chain branching had values of α up to about 0.8. Where the comparisons could be made, the value of α determined from a polymer melt was surprisingly close (∼ +0.15) to the value of α in the intrinsic viscosity equation for the same polyethylene dissolved in paraffin wax.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1962.1205816604
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