Rheological properties and processing of thermally degraded polyolefins

Thermally degraded polypropylene and polybutene-1 were studied in a series of rheological and processing experiments.

The materials were rheological characterized in steady shear measurements which include steady shear viscosity measurements and the first normal stress difference measurements. The rheological properties in shear flow indicated not only a molecular weight lowering but a narrowing of the molecular weight distribution.

Studies of elongational flow indicated that the degraded melt could be drawn out into uniform filaments and gave elongational viscosities roughly three times the zero shear viscosity. The untreated and mildly degraded filaments developed defects and failed at small elongations.

Extrudate swell during isothermal extrusion was measured by a photographic method. Degradation reduces the swell at constant shear rate, shear stress and normal stress - shear stress ratio.

Diameter and velocity profile were measured during isothermal melt spinning and spinline elongational viscosity was estimated. Studies of instability in isothermal melt spinning indicated that thermal treatment stabilized the spinline.