Comparison of the viscoelastic properties of syndio‐ and isotactic polypropylenes

Abstract

++The viscoelastic properties of fourteen syndio-and isotactic polypropylenes (PPs) were measured in the molten state at several temperatures by means of oscillatory rheometry. Metallocene catalysis allows the control of molecular mass of both PP families and provides narrow molecular mass distributions (MMD) with a polydispersity of about 2. The validity of the Arrhenius and WLF equations for PP was checked. Syndio-and isotactic PP follow Arrhenius behavior but exhibit different activation energies of flow. From the dynamic shear moduli, viscoelastic parameters were determined and correlated with molecular mass. The dependence of the zero shear viscosity on the weight average molar mass exhibits the well-known scaling relation. Stereoregularity has an important effect on the viscoelestic behavior of PP melts.

Effect of stereoregularity of polypropylene on flow instability in capillary extrusion

“…These results correspond well with the literature. 4,5 Furthermore, it is confirmed that the modulus at the crossing point (G = G ) for sPP is significantly higher than that for iPP. This is attributed to the following two reasons; (1) molecular weight distribution, i.e., relaxation time distribution, of sPP is narrower than that of iPP as shown in Table I, and (2) rubbery plateau modulus of sPP is higher than that of iPP.…”

Rheology of nanocomposites based on layered silicates and polyamide-12

“…The slopes of pure PA-12 (PAB and PAA) are between 1.6 and 1.8. These slopes are in the range expected for polydisperse polymers [38]. NCLSAb-2 and NCLSAb-4 have the smallest slope.…”

Rheological and isothermal crystallization characteristics of neat and calcium carbonate‐filled syndiotactic polypropylene

“…Normally, the temperature dependence of a T can be expressed in terms of either an Arrhenius equation 18,19 …”

“…Studies related to rheological properties of s-PP are quite limited. In two related studies, Eckstein et al 18,19 studied oscillatory shear behavior of various s-PP samples in comparison with both i-PP and atactic polypropylene (a-PP) samples. The only available report on steady state shear behavior of neat and CaCO 3 -filled s-PP was by Supaphol et al, 15 who showed that, for a given shear rate, the steady-state shear viscosity increased with increasing CaCO 3 loading.…”

“…) and E a is the activation energy of flow, or the Williams-Landel-Ferry (WLF) equation: 18,19 log a T …”