Methods of interconversion between linear viscoelastic material functions. Part I-a numerical method based on Prony series

The deformations and stresses during squeeze flows are evaluated for a wider class of materials than previously covered in articles on this subject. These include generalised Newtonian fluids, yield stress fluids, as well as elastic and viscoelastic materials. Wherever possible, results are given in a compact mathematical form. The effect of different boundary conditions (no slip, perfect slip and partial slip) and how these interact with different types of material behaviour to give a variety of macroscopic responses is also discussed. The significance of this in using squeeze flow as a rheometry method is highlighted and a state-of-the-art view of squeeze flow rheometry is given.

Squeeze flow theory and applications to rheometry: A review

Embodiments of the present invention relate to article comprising 1) a functionalized component, 2) tackifier, and 3) an olefin polymer comprising one or more C3 to C40 olefins, optionally one or more diolefins, and less than 5 mole % of ethylene having a Dot T-Peel of 1 Newton or more, a branching index (g′) of 0.95 or less measured at the Mz of the polymer; and an Mw of 100,000 or less; where the functional component is selected from the group consisting of functionalized polymers, functionalized oligomers and beta nucleating agents; and where the Gardner color of the adhesive does not change by more than 7 Gardner units when the adhesive has been heat aged at 180° C. for 48 hours as compared to the Gardner color of the unaged composition.

Polyolefin adhesive compositions and articles made therefrom

Effect of aging.

Branched polyesters: recent advances in synthesis and performance

The rheology of polymer melts depends strongly on temperature. Quantifying this temperature dependence is very important for fundamental, as well as practical, reasons. The purpose of this paper is to present a unified framework for handling the temperature dependence of rheological data. We considered the case (by far the most common in polymer melts) where all relaxation times (in the context of linear viscoelasticity) have the same temperature dependence (characterized by a “horizontal shift activation energy”) and all relaxation moduli have the same temperature dependence (characterized by a “vertical shift activation energy”). The horizontal and vertical activation energies were extracted from loss tangent vs. frequency and loss tangent vs. complex modulus data, respectively. This is the recommended method of calculation, as it allows independent estimation of the two activation energies (statistically uncorrelated). It was shown theoretically, and demonstrated experimentally, that neglect of the vertical shift leads to a stress (or modulus) dependent activation energy and necessitates different activation energies for the superposition of loss and storage modulus data. The long standing problem of a stress-dependent activation energy in long chain branched LDPE was identified as originating from the neglect of the vertical shift. The theory was applied successfully to many polyolefin melts, including HDPE, LLDPE, PP, EVOH, LDPE, and EVA. Linear polymers (HDPE, LLDPE, PP) and EVOH do not require a vertical shift, but long chain branched polymers do (LDPE, EVA). Steady-shear viscosity data can be superimposed using activation energies extracted from dynamic data.

Temperature dependence of polyolefin melt rheology

Low levels of long-chain branching (LCB) in an otherwise linear polyethylene, such as HDPE or LLDPE, are known to affect dramatically the polymer melt rheological properties. However, reliable techniques to detect and quantify LCB at these levels (i.e., ≪1 LCB/1000 C) have not been available. In this work, the long-chain-branching index (LCBI) is developed for essentially linear, polydisperse polyethylenes, which are those containing a small level of LCB, such that the measured intrinsic viscosity is the same, within experimental error, to that calculated from MWD data, assuming the resins are linear. The long-chain-branching index (LCBI) is fundamentally related to the viscosity enhancement due to long-chain branching, and it is independent of molecular weight (MW) and molecular weight distribution (MWD). It is given by the relation: LCBI = ηo0.179/4.8[η] − 1, where ηo (P) is the zero shear viscosity at 190 °C, and [η] (dL/g) is the intrinsic viscosity in trichlorobenzene at 135 °C. A suitable average mo...

Long-Chain-Branching Index for Essentially Linear Polyethylenes

Fountain flow is the phenomenon of deceleration and outward motion of fluid particles as they approach a slower moving interface. The use of a general purpose finite element program for the appropriate boundary conditions made possible the detailed flow description behind an advancing liquid front moving at constant speed inside two-dimensional channels and tubes. The results were qualitatively the same for both Newtonian and shear-thinning fluids.

Finite element simulation of fountain flow in injection molding

A complex molecular orientation distribution is observed in the injection molding of amorphous polymers. A major contribution is due to the flow‐induced deformation of the polymer molecules during mold filling and incomplete relaxation during cooling, after cessation of flow. In this work a numerical study is undertaken in an effort to resolve the impact of the fluid mechanics of mold filling on the molecular orientation of the final part, as reflected in available birefringence measurements. Viscoelasticity of the polymer melt is accounted for with the multimode Leonov model. A finite‐element solution of the fountain flow problem is obtained and the effect of the flow field on the deformation experienced by the fluid is elucidated. Frozen‐in stresses are calculated based only on material parameters and processing conditions. Predicted birefringence distributions agree well with published experimental results.

The Effect of Fountain Flow on Molecular Orientation in Injection Molding

Ethylene polymer composites and concentrates utilized for their preparation are provided. The composites of the invention have increased melt strength compared to the base resin and other improved physical characteristics. The composites contain an organically modified clay and may also contain a compatibilizng agent, depending on the base resin used.

Harilaos Mavridis

Papers

Temperature dependence of polyolefin melt rheology

Long-Chain-Branching Index for Essentially Linear Polyethylenes

Finite element simulation of fountain flow in injection molding

The Effect of Fountain Flow on Molecular Orientation in Injection Molding

Ethylene polymer compositions having improved melt strength