Mechanical Degradation of Polypropylene Flowing under Large Pressure Drops

MARTINI, RAQUEL; BRIGNOLE, ESTEBAN; BARBOSA, SILVIA

JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS

Año: 2007 vol. 45 p. 455 - 465

0887-6266

The degradation of Polypropylene (PP), dissolved in n-alkanes at high temperatures and pressures, during the solution discharge to ambient conditions was experimentally studied. Molecular weight distributions (MWD) of the solubilized polypropylene were measured by gel permeation chromatography. The MWD curves of PP obtained after discharge of the polymer solution shift to the low molecular weight side of the distribution and the polydispersity is reduced. In this work, a systematic study on the discharge products was performed, to elucidate the degradation mechanism and the effects of temperature and concentration on this phenomenon. Initially, pure polymers (PP and PS) were studied varying the solution temperature. In a second stage, the effect of polymer concentration on chain scission was assessed using experiments on physical blends of PP/PS. In all cases, thermal and oxidative degradation were previously analyzed. Mechanical degradation was found to be the main chain scission mechanism. A negative linear functionality of the chain scission was found with both temperature and polymer concentration. To analyze the relationship between polymer degradation and molecular weight, the chain scission distribution function was calculated. On this basis, a critical molecular weight for the beginning of chain scission was obtained. This value is a function of temperature but remains constant with concentration.