Rheological characterization and constitutive modeling of two LDPE melts

V této praci byly analyzovány experimentální reologické data dvou tavenin LDPE pomocí MSF modelu. Bylo zjištěno, že pro kvantitativní modelování obou toků bylo nutné použít pouze tři nelineární viskoelastické materiálové parametry.Experimental data of two low-density polyethylene (LDPE) melts at 200 degrees C for both shear flow (transient and steady shear viscosity as well as steady first normal stress coefficient) and elongational flow (transient and steady-state elongational viscosity) as published by Pivokonsky et al. [1] were analyzed by use of the Molecular Stress Function (MSF) model for broadly distributed, randomly branched molecular structures. For quantitative modeling of melt rheology in both types of flow and in a very wide range of deformation rates, only three nonlinear viscoelastic material parameters are needed: While the rotational parameter, a(2), and the structural parameter, beta, are found to be equal for the two melts considered, the melts differ in the parameter f(max)(2), describing maximum stretch of the polymer chains.SIP-IPN [20082971]; Mexico, by Grant Agency of the Czech Republic [A200600703]; Ministry of Education of the Czech Republic [MSM 7088352101]; German Science Foundation (DFG

Reologická charakterizace LDPE materiálů pomocí diferenciálních konstitučních rovnic

For rheological description of branched LDPE melts (Escorene LD165BW1 a Bralen RB0323) the following differential constitutive equations were used: eXtended Pom-Pom, Phan Thien-Tanner-XPP, and modified Leonov models. There was carried out quantitative and qualitative comparison of efficiency of the predictions determined by these models with the experimental data measured at 200oC. For both materials there were measured linear viscoelastic properties, shear and uniaxial extensional viscosities

Vliv reakčního vytlačování na reologické vlastnosti metalocénových polypropylénů

Constitutive equations represent a powerful tool for analysis and description of linear and branched polymer materials (even for polydisperse ones). Predictive/fitting capabilities of three constitutive models (eXtended Pom-Pom, PTT-XPP, and modified Leonov models) were examined using four standard industrial PE materials (two linear and two branched). All the materials were tested in both shear and uniaxial extensional flows (steady and transient)

On the predictive/fitting capabilities of the advanced differential constitutive equations for branched LDPE melts

Prediktivní schopnosti XPP, PTT-XPP a modifikovaného Leonovova modelu byly posouzeny v ustálených i přechodových smykových a elongačníc tocích pro dva typy rozvětvených LDPE (Escorene LD165BW1 and Bralen RB0323).Predictive/fitting capabilities of the XPP, PTT-XPP and modified Leonov constitutive equations are compared in both steady as well as transient shear and uniaxial elongational flows using two, highly branched LDPE materials (Escorene LD165BW1 and Bralen RB0323). It has been found that even if all three tested models exhibit very good fitting capability for steady uniaxial extensional viscosity curve, their predicting capabilities may differ significantly for shear viscosity as well as first and second normal stress coefficients

On the predictive/fitting capabilities of the advanced differential constitutive equations for linear polyethylene melts

V této práci je provedena detailní analýza reologického chování tří typů diferenciálních konstitutivních rovnic (XPP, PTT-XPP, modifikovaný Leonovův model) pro lineární polyolefiny s ohledem na ustálené a časově závislé smykové a elongační toky.This contribution examines the capabilities of three differential constitutive models (XPP, PTT-XPP, and modified Leonov) in predicting rheological properties of two virtually linear polyethylene materials (HDPE Tipelin FS 450-26, mLLDPE Exact 0201) with specific attention to both steady as well as transient shear and uniaxial elongational flow situations. For each situation the (dis)advantages of the individual models are discussed and both, qualitative and quantitative model efficiency evaluation has been carried out

Rheological characterization and modeling of linear and branched metallocene polypropylenes prepared by reactive processing

V této práci je srovnáno reologické chování tří různých typů metalocenových PP připravených reakčním vytlačováním jejichž molekulární struktura je následně charakterizována pomocí XPP a PTT-XPP modelů.The aim of this contribution is to compare rheological behavior of three different samples of metallocene catalyzed polypropylene [virgin (linear) metallocene polypropylene (mPP), and (branched) mPPs prepared through reactive processing with (0.01 wt.%) and without peroxide]. For their theological description in different flow situations (shear and elongational) the extended Pom-Pom (XPP) and PTT-XPP models were used. A rotational rheometer (ARES 2000) with the SER Universal Testing Platform was used for the measurement of dynamic data (storage G' and loss G '' moduli) and uniaxial extensional viscosity. It was shown that both processed (branched) mPPs (with and without peroxide) exhibit distinct behavior in uniaxial extensional viscosity (appearance of strain hardening) in comparison to the virgin (linear) mPP. The XPP and PTT-XPP models proved their usefulness for a branching level quantification based on the measurements of steady shear and elongational viscosities. On the other hand, poorer models' predictions of the transient extensional viscosity indicate absence of an H branching for the processed mPPs. Based on the activation energy data it has been suggested that processed mPPs may have star-branched structure

Rheological characterization and modeling of metallocene based polypropylenes prepared by reactive extrusion process

The aim of this contribution is to compare rheological behavior of three different samples of metallocene catalyzed polypropylene [virgin (linear) metallocene polypropylene (mPP), and (branched) mPPs prepared through reactive processing with (0.01 wt %) and without peroxide]. For their rheological description in different flow situations (shear and elongational) the eXtended Pom-Pom (XPP) and PTT-XPP models were used. A rotational rheometer (ARES 2000) with the SER Universal Testing Platform were used for the measurement of dynamic data (storage G' and loss G'' moduli) and uniaxial extensional viscosity. It was shown that both processed (branched) mPPs (with and without peroxide) exhibit distinct behavior in uniaxial extensional viscosity (appearance of strain hardening) in comparison to the virgin (linear) mPP. The XPP and PTT-XPP models proved their usefulness for a branching level quantification based on the measurements of steady shear and elongational viscosities. On the other hand, poorer models predictions of the transient extensional viscosity indicate absence of an H branching for the processed mPPs

Applicability of advanced constitutive equations for coextrusion flows of polyolefin melts

The fitting/predictive capabilities of three models (extended Pom-Pom, PTT-XPP and modified Leonov model) are tested for both, steady as well as transient shear and uniaxial extensions flows of mLLDPE and HDPE. The applicability of these constitutive equations has been investigated from the coextrusion flow modeling point of view. Finally, the FEM and modified Leonov model has been employed for the stress analysis in the coextrusion flow domain and predicted stress fields have been compared with the stress measurements from the flow coextrusion visualization cell

Polymer Melt Viscosity and Free Volume Interconnection: Comparison Study

Viscosity and pressure-volume-temperature (PVT) measurements were carried out on selected polymeric materials. Analytical approximation of Simha-Somcynsky equation of state (SSeos) was used to compute free volume parameter from PVT dependencies. Pressure and temperature dependent SSeos free volume parameter was connected with shear viscosity data of polymer melts at appropriate pressure and temperature. Two approach of interconnection of pressure-temperature-dependent viscosity and free volume behaviour were compared. The results indicate similarities of both methods used

Investigation of advanced constitutive equations under different flow conditions

The predictive capabilities of three models (eXtended Pom-Pom, PTT- XPP and modified Leonov model) are tested for both, steady as well as transient shear and uniaxial extensional flows of LDPE. In the second part of the paper, the modified Leonov model is employed in FEM modeling of the abrupt contraction flow and predicted stress fields are compared with the stress measurements from the flow visualization cell