Effect of solvent on polymer degradation in turbulent flow

The molecular degradation of polysiobutylene (PIB) was investigated at high Reynolds number in different quality solvents. Cyclohexane was used as the "good" solvent and toluene as the "poor" solvent. Drag reduction and degradation studies were carried out using 100 and 20 ppm PIB solutions in capillary tubes of 1.54mm internal diameter. Results indicated that the drag reduction effectiveness of PIB increased with increasing Reynolds number until a "critical" value. Beyond this value, the drag reduction effectiveness of PIB deteriorated. The cause of this phenomenon was examined by molecular weight distribution measurements, utilizing a gel permeation chromatography technique. It was found that in turbulent flow, PIB degraded more in a poor solvent at low Reynolds numbers, whereas an opposite effect was observed at high Re. Results also showed that mid-point scission is approached in both good and poor solvents; however, the approach occurs at lower Reynolds numbers for the former solvents. This difference was attributed to the existence of two possible sources: polymer stretching and intramolecular entanglements.