Orientation development in tubular film extrusion of polyethylene and polystyrene

Date Issued
August 1, 1980
Author(s)
Choi, Kyung Ju
Advisor(s)
Joseph E. Spruiell
Additional Advisor(s)
J L White
E S Clark
Permanent URI
Abstract
Orientation in tubular film extrusion of atactic polystyrene and high density polyethylene were studied as a function of the stresses in the melt at the point of vitrification (polystyrene) or crystallization (polyethylene). The film forming conditions were varied over a wide range so that the orientation could be varied from essentially uniaxial orientation to approximately equal biaxial orientation. In the polystyrene samples the orientation was determined from measurements of the in-plane and out-of-plane birefringence. Both birefringence and wide angle x-ray pole figures were used for studying orientation in polyethylene. Small angle x-ray scattering patterns were used to help further characterize the morphology of the' polyethylene as a function of the kinematics (drawdown, blow-up ratio) and applied tensions and bubble pressures.

Both polystyrene and polyethylene experimental results are interpreted in terms of White and Spruiell's biaxial orientation factors.

The data for the amorphous polymer, polystyrene, can be correlated by comparing the birefringences with the stresses acting in the film at the position of vitrification. These data compare quantitatively with the Rheo-Optical Law and with Oda, White and Clark's correlation developed for the birefringence of sanples vitrified during shear and uniaxial extensional flow.

The polyethylene films showed much higher levels of crystalline orientation from WAXS than would be expected from the Rheo-Optical Law due to oriented nucleation and growth of crystals. The morphological changes of polyethylene with processing conditions are described. With uniaxial state, row structure first described by Keller is favored. A biaxially oriented sample exhibited a morphology which could be interpreted in terms of the superposition of two row structure components with one component having lamellae stacked along the machine direction and one component having lamellae stacked along the transverse direction.

Degree
Master of Science
Major
Polymer Engineering
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