A three-phase microstructural model to explain the mechanical relaxations of branched polyethylene: a DSC, WAXD and DMTA combined study

Modeling Sorption of Hydrocarbons in Polyethylene with the SAFT-γ Mie Approach Combined with a Statistical-Mechanical Model to Describe Semicrystalline Polymers

A recently developed statistical-mechanical model is applied systematically to estimate the fraction of tie-molecules (polymer chains linking different crystals directly or via entanglements) in semicrystalline polyethylene (PE) samples. The amorphous domains of the polymer are divided into constrained interlamellar domains and "free" outer-lamellar domains. A set of model parameters is assigned to each sample by correlating previous experimental measurements and minimizing the difference between the predicted solubility of pure hydrocarbons in the sample and the experimental values. We show that the sorption isotherms of multiple pure fluids in each sample can be described by a single parameter set, proving that the polymer-solute interactions (described accurately by the SAFT-γ Mie EoS) are decoupled from the sample-specific properties of the polymer. We find that ∼30% of the crystalline stems in the lamellae of PE are connected to tie-molecules, within the bounds suggested by previous theoretical and computational work. The transferability of the sample-specific parameters is assessed by predicting cosolubility effects and solubility at different temperatures, leading to good agreement with experimental data.

Two-photon microscopy as a visual tool for polymer compatibilization monitoring: the PE-EVOH case

In this study, we present two-photon microscopy (2PM) as an original technique to investigate the compatibilization between PE-HEMA and EVOH at the sub-micrometer level, both on the surface and in the bulk. 2PM is a nonlinear fluorescence imaging technique commonly exploited for thick biological tissue analysis. Here, we use 2PM to visualize polymer blending through 3D images of the obtained films. Compatibilization was performed in solution, upon functionalization of PE-HEMA with 1.4% molar of ODIN, a fluorescent molecule able to form multiple hydrogen bonds with EVOH and to act as a fluorescent probe. Different blends were synthesized, and the obtained films were analyzed by 2PM. For all compositions, it was demonstrated that ODIN is evenly distributed both on the surface and in the bulk. 2PM analysis of the thermally reprocessed specimen revealed that repeated reprocessing allows the reformation of ODIN dimers as the most stable H-bonding array in the solid state, partially reversing the compatibilization.

Comparative experimental and modelling study of the thermal and thermo-mechanical properties of LLDPE/wax blends

The interactions and morphology of molecules in a polymer blend influence the physical properties of the blend. However, little is known about the influence of molecular interaction and morphology on the thermal and mechanical properties of LLDPE/wax blends. Although cooling rate can be used to investigate blends' thermal and mechanical properties, it is inadequate to determine interactions between the molecules in the LLDPE/wax blends. However, since the morphology is related to the thermal and mechanical properties of polymer blends and could be related to the cooling rate, LLDPE/wax samples prepared by melt mixing were cooled at different rates. The thermal and mechanical properties of the LLDPE/wax blends were modelled through molecular dynamic simulations. The modelled transitions were compared to experimentally determined mechanical relaxations of LLDPE/wax blends to investigate the effect of wax addition on the blend crystallinity. The crystallization behaviour of the blends was studied by differential scanning calorimetry, dynamic mechanical behaviour by dynamic mechanical analysis, and differences in crystallinity by X-ray diffraction. There were no significant differences between the results for the slow- and quench-cooled samples, confirming the rapid crystallization of both the LLDPE and the wax. Experiments and molecular dynamics simulations confirmed the cocrystallization of wax with LLDPE.

Physically cross-linked polyethylene via reactive extrusion

Ureidopyrimidinone (UPy) is introduced into various polyethylenes (PEs) bearing hydroxyl groups by solution grafting, affording physically cross-linked PE via multiple H-bonding.

Understanding and Control of High Temperature Oxidation Flaws of Low-Density Poly(ethylene) with Raman Spectroscopy

Studies of high temperature oxidation of polyethylene are not much present in the literature though it can really be a problem especially in polymer production and processing. This study aims to detect oxidation flaws in polyethylene and to determine their impact on polymer structure and properties. Besides, we suggest a method via PLS-regression to determine the degree of flaws that can occur during polymer processing due to oxidation. Several kinds of oxidation flaws were reproduced in laboratory at 150°C in an oven operating in air and Raman spectroscopy analysis was performed on each sample. Using statistical tools as chemometrics on these spectra, we have built a Partial Least Square (PLS) model able to predict the oxidation degree of flaws. Interpretation of the model construction and further characterization tests show that oxidation can be followed with the evolution of the crystalline carbon group and of the created carbonyl functions. Finally we suggest possible mechanisms which can explain the high temperature oxidation process in LPDE, and we link them to the modification of the material properties.