Ultra-broad molecular weight distribution effects on viscoelastic properties of linear multimodal PE

Abstract

Rheological investigation of polyethylene (PE) blends with a significant amount (up to 50 wt. %) of ultrahigh molecular weight PE (UHMWPE, with weight average molecular weight Mw > 106 g/mol) was not accessible so far. The development of special Enders catalysts allows the synthesis of such homogeneous PE reactor blends (RBs). In this paper, by melt blending of RBs with high-density PE polymer matrix, multimodal PE blends were prepared and their rheological properties were investigated. The analysis grants access to better understand how notably high amount of UHMWPE and ultra-broad molecular weight distribution displaying extremely high polydispersity, Ð ∼ 1000, influence the linear viscoelasticity. Moreover, taking advantage of the opportunities offered by molecular models, applying the tube-based time-marching algorithm, the “rheological” molecular weight distribution (MWD) of multimodal PE blends was determined, overcoming drawbacks of high-temperature size exclusion chromatography. Analyzing the zero-shear viscosity, η 0, versus Mw scaling relation for blends of any MWD, a correction scheme was developed which allows to take into account the Ð effects on η 0 properly. The analysis revealed that in a double logarithmic plot versus Mw, corrected η 0 shows a unique linear dependency with a slope of 3.6 if Mw is smaller than the reptation molecular weight (Mr). If Mw > Mr, the slope of this linear dependency turns into 3. The analysis of transition zone between the two linear dependencies allowed the experimental determination of PEs Mr.