ISSN:
0032-3888
Keywords:
Chemistry
;
Chemical Engineering
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
Solutions of the random coiling polymers; polystyrene, poly (methylmethacrylate), and sodium polystyrene sulfonate (NaPSS), all at concentrations well below the critical value for entanglement, were subjected to transient, high, elongational strain rates by passage from a cylinder through an orifice into a gently diverging section, driven by a piston at constant, high velocity over a short stroke. It is shown that a critical orifice flow velocity Vc. exists for each polymer species, above which scission of polymer molecules occurs creating new molecules. By gel permeation chromatography, the number of additional polymer molecules created per initial polymer molecule, the scission index, was determined as Mn,0/Mn - 1 where Mn is the number average molecular weight, and Mn,0 is the initial value thereof. Vc is found to vary as approximately Mn-0.53. Above Vc the scission index was found to be proportional to Mn2.23, to the difference: orifice velocity V less Vc, and to the number of passes N of the polymer solution through the orifice. Expansion of NaPSS coils by reducing ionic strength of their aqueous solutions, at constant polymer molecular weight, decreases the scission index, The hypothesis is proposed that intramolecular entanglements are responsible for scission. The random coiling macromolecules in the solution cannot respond to the strain rate (imposed in ca, 100 microseconds) so as to avoid having internal sections, caught by loop entanglement, pulled to nearly full extension and thus broken.
Additional Material:
9 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pen.760200711
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