The time, temperature and shear dependence of the viscosity of polypropylene and its influence upon the extrusion process

Mathematical model of a single-screw plasticating extruder

“…As a result, the power-law parameters, m0, k and n can change in the course of the extrusion process, particularly for degradable types of polymers. In such cases the D Z, MZ and MCZ calculations with constant power-law parameters can cause significant discrepancies between experimental and theoretical results [21], in particular for the axial pressure profile. This is the reason for requiring that the power-law parameters be expressed as a function of quantities such as temperature, shear rate, residence time, see figures 15, 17, 18 and Appendix A.…”

“…The parameters m0, k and n can be given as a function of temperature, shear rate and varying properties of the melt due, for example, to its degradation [21].…”

Thermal degradation of polypropylene reprocessed in a co-rotating twin-screw extruder: kinetic model and relationship between Melt Flow Index and Molecular weight

“…Abrupt changes in polymer properties at degradation temperatures ∼ 280°C have also been reported by other authors. For instance, Závadský et al studied the effective viscosity of PP extruded between 190°C and 310°C, and found that only the data for PP extruded below 280°C could be fit into a single curve (Závadský et al, 1982). In addition, da Costa et al reported a sharp decrease in the apparent viscosity of PP extruded at 270°C, in comparison 240°C (da Costa et al, 2005), and a sharp decrease in the break properties of PP processed multiple times at 260°C or 270°C, compared to 240°C or 250°C (da Costa et al, 2007).…”