Horizontal extensional rheometry (HER) for low viscosity polymer melts

Modeling of nonlinear extensional and shear rheology of low‐viscosity polymer melts

“…The extensional viscosity of two samples of LCB LDPE, Lupolen LDPE 1840H (BASF SE) and LDPE 2426 k (Sinopec Daqing), as well as of the linear poly‐(ethylene‐co‐α‐butene), PEB A‐780090 (Tafmer), were measured with extended region of low viscosity limits using the HER by Li et al [ 33 ] LDPE 1840H and LDPE 2426 k have a melting index of 1.5 g/10 min and 4 g/10 min at 190°C/2.16 kg, respectively. LDPE 1840H and LDPE 2426 k have a density of 918 and 923 kg/m 3 at 25°C, respectively, and zero‐shear viscosities of 36,604 Pas at 150°C (LDPE 1840H), and of 7502 Pas at 175°C and 1471 Pas at 230°C (LDPE 2426 k).…”

“…PEB A‐780090 has a zero‐shear viscosity of 455 Pas at 160°C. Details for the rheological measurements of the polymers examined here can be found in Li et al [ 33 ]…”

“…Li et al [ 33 ] developed a horizontal extensional rheometer (HER) that greatly extended the lower limit of elongational viscosity measurements for polymer melts as compared to existing rheometers. HER combines the qualities of SER and RME: HER adopts the scheme of RME to address the inherent gravitational sagging complication faced by SER while retaining the windup technique, which has the benefits of uniform flow and true applied strain rate.…”

“…With the new design of HER, the rheometer was able to measure a wide viscosity range from 441 Pas to 3.8 × 10 4 Pas for long‐chain branched (LCB) low‐density polyethylene (LDPE) and linear polymer poly‐(ethylene‐co‐α‐butene) (PEB). [ 33 ] Numerical simulation of polymer processes needs more than just a wide range of rheological data, as it also requires a reliable rheological constitutive equation with as few free parameters as possible while still retaining its accuracy at reproducing the experimental results measured for a broad variety of polymer melts in different types of deformations. [ 34 ] Moreover, a simple while realistic constitutive equation can improve the stability of flow simulation to achieve convergent and precise solutions.…”

“…[ 34 ] Moreover, a simple while realistic constitutive equation can improve the stability of flow simulation to achieve convergent and precise solutions. [ 35,36 ] Li et al [ 33 ] used the multimode differential Pom‐Pom model [ 37,38 ] to model the transient extensional viscosity growth results of LDPE 2426 k from Sinopec Daqing and PEB A‐780090 from Tafmer. A generalized Maxwell model was used to fit the dynamic moduli by a discrete relaxation spectrum when the transient shear viscosity of the polymers was used to determine the nonlinear parameters of the Pom‐Pom model.…”