Rheological behavior of controlled‐rheology polypropylenes obtained by peroxide‐promoted degradation during extrusion: Comparison between homopolymer and copolymer

Abstract

International audienceIn the present work, experimental studies of the free-radical-initiated molecular weight degradation of polypropylene in a modular self-wiping corotating twin-screw extruder are investigated. The control of the molecular weight distribution of polypropylene resins by peroxide degradation is widely used in the polymer industry. It allows one to adjust the viscosity of these resins to the level required for processing applications. The purpose of this work was to characterize the influence of peroxide degradation on the rheological behavior of a polypropylene homopolymer and a block polypropylene/polyethylene copolymer, which includes an addition of a low percentage of polyethylene (around 7%). The homopolymer exhibits a classical behavior: When the peroxide amount is increased, we observe a decrease in the viscosity corresponding to a decreasing molecular weight and a pronounced shift toward more Newtonian behavior. The rheological behavior of the copolymer is influenced by the presence of the polyethylene phase which greatly modifies the viscoelastic properties and increases the viscosity when the polypropylene matrix is highly degraded

Grafting of maleic anhydride on polypropylene by reactive extrusion: effect of maleic anhydride and peroxide concentrations on reaction yield and products characteristics

“…Moreover, the behavior tends to become more and more Newtonian, except at high frequency, where a shear-thinning behavior may be detected. These results are classical for controlled rheology PP [33,34]. More interesting is the fact that, at constant peroxide content, the viscosity decreased when the amount of MA increased.…”

“…Figure 6 shows more precisely the change in M w with the percentage of introduced MA and peroxide. It is obvious that the increase of peroxide induced a strong decrease of molecular weight by β-scissions, as already observed for controlled rheology PP [33,34]. Concerning the effect of MA, the conclusions slightly differ from what could be observed for MFI in Figure 4.…”

Fracture toughness of controlled-rheology polypropylenes

“…Peroxide initiated scission reactions efficiently result in polymers with tailor made properties. The polypropylenes produced this way are termed "controlledrheology polypropylenes" (CRPP) and they have improved melt flow characteristics due to reduced MW and narrowing MWD [3][4][5][6][7][8][9].…”

Morphology and thermal behaviour of SAN/EPDM blends

“…To elucidate the extrusion process, reactions and interactions that are established [12][13][14][15][16], the separation of SAN/EPDM blends on its components was carried out by selective solvent extraction and the results are presented in Figure 1. Significant differences in the fractions of graft copolymer (EPDM-g-SAN), SAN polymer, EPDM polymer and gel were observed.…”