Shear degradation of polyisobutene
Article first published online: 9 MAR 2003
Copyright © 1976 John Wiley & Sons, Inc.
Journal of Applied Polymer Science
Volume 20, Issue 5, pages 1289–1300, May 1976
How to Cite
Abbås, K. B. and Porter, R. S. (1976), Shear degradation of polyisobutene. J. Appl. Polym. Sci., 20: 1289–1300. doi: 10.1002/app.1976.070200512
- Issue published online: 9 MAR 2003
- Article first published online: 9 MAR 2003
- Manuscript Revised: 14 AUG 1975
- Manuscript Received: 5 MAY 1975
A polyisobutene of M̄w 1.98 × 106, M̄w/M̄n 1.8, was extruded in an Instron capillary rheometer. Shear degradation occurred at high shear stresses, approaching melt fracture, and was more prominent at lower extrusion temperatures for tests at 60–140°C. The capillary was 2.0 in. long with a length/diameter ratio of 66.7 and a 90° entrance angle. Repetitive extrusions at constant shear rate caused a decrease in a molecular weight and a simultaneous narrowing of the molecular weight distribution. Extrudate expansion was measured after each successive capillary pass for tests at 80°C. Extrudate swelling correlated well with (M̄z+1) M̄z/M̄w, except for the two first passes, where melt fracture was pronounced. The correlation with equilibrium extrudate expansion was almost as good for (M̄z/M̄w)3.7 (Mill's correlation) and for M̄z+1 alone. The efficiency of bond rupture is low, with the energy required to rupture 1 mole of bonds being about 200,000 kcal at 80°C.