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An experimental study of the kinetics of polymer crystallization during shear flow
Author(s) -
Lagasse R. R.,
Maxwell B.
Publication year - 1976
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760160312
Subject(s) - crystallization , materials science , shear rate , rheometer , shearing (physics) , rheology , crystallization of polymers , shear flow , shear (geology) , polymer , composite material , simple shear , thermodynamics , chemical engineering , physics , engineering
Some principles of rheology are applied to the study of the shear‐induced crystallization of molten polymers. A new technique is described for measuring crystallization kinetics during isothermal flow at constant shear rate in a parallel plate rheometer. The crystallization rate is characterized by the time elapsed from the start of shearing until the rise in melt viscosity due to crystallization. The measured‐viscosity and induction time for crystallization are shown to be independent of sample geometry. Kinetic data are presented for crystallization of three linear polyethylenes at shear rates of 0.03 – 30 sec −1 . It is shown that shear flow has a strong accelerating effect on crystallization when the deformation rate exceeds a critical value. Comparison of results for the different polyethylenes reveals that higher molecular weight materials crystallize faster at a given shear rate and temperature. Finally, shear‐induced crystallization of propylene polymers is shown to be unaffected by the presence of either a carbon black additive or a heterogeneous nucleating agent. It is concluded that the hydrodynamic origin of the shear‐induced crystallization is elastic chain extension due to entanglement couplings between molecules. Furthermore, it is suggested that transient orientation effects during the startup of shear flow may have a dominant influence on the observed phenomena.