Modeling of the rheological properties of multinanolayer films in the presence of compatibilized interphase

heological behavior of nanolayered films of polyethylene/polyamide 6 (PE/PA6) compatibilized in situ during the coextrusion process has been studied at a temperature between the melting temperatures of PE and PA6. Thanks to the high number of interfaces, a drastic increase in dynamic moduli has been measured when increasing the interphase volume fraction in the films, and a solid-like behavior for the interphase was identified. Different models are compared to capture the complex viscosity of nanolayered films as a function of angular frequency. A model considering interphase and bulk viscosities and a single fitting parameter, namely, the thickness over which the viscosity decreases linearly from the interphase to the bulk one, captures the complex viscosity of all samples. This thickness is comparable to the PE layer thickness up to values about 1 μm before a significant bulk region has to be added to capture the behavior for thicker layers. This suggests that the melt rheology is impacted by the presence of a nanometric interphase over very large (micronic) length scales

Assessing the shear viscous behavior of continuous carbon fiber reinforced PEKK composites with squeeze flow measurements

Out-of-autoclave processes of carbon fiber thermoplastic composites are gaining interest as they can drastically reduce the economic cost. To optimize consolidation, the flow behavior of these highly filled composites has to be characterized. Here, we propose to measure viscosity of carbon fiber/polyetherketoneketone through squeeze flow experiments in a rheometer. A modified Stefan's law assuming a power law fluid behavior with full anisotropy is developed for square and circular geometries to model the data. Values of the power law parameters K and n are obtained, on the order of 15,000 Pa.sn and 0.02 at 1 bar. Though as expected independent of the samples' geometry and tapes' stacking, K and n depend on the applied pressure and plate size. This is due to localized shear which results in a shear-banding-like phenomenon. Finally, squeeze flow is compared to dynamic measurements and invalidate the Cox-Merz rule for such materials

Polymer microlenses for quantifying cell sheet mechanics

Mechanical interactions between individual cells and their substrate have been studied extensively over the past decade; however, understanding how these interactions change as cells interact with neighboring cells in the development of a cell sheet, or early stage tissue, is less developed. We use a recently developed experimental technique for quantifying the mechanics of confluent cell sheets. Living cells are cultured on a thin film of polystyrene [PS], which is attached to a patterned substrate of crosslinked poly(dimethyl siloxane) [PDMS] microwells. As cells attach to the substrate and begin to form a sheet, they apply sufficient contractile force to buckle the PS film over individual microwells to form a microlens array. The curvature for each microlens is measured by confocal microscopy and can be related to the strain and stress applied by the cell sheet using simple mechanical analysis for the buckling of thin films. We demonstrate that this technique can provide insight into the important materials properties and length scales that govern cell sheet responses, especially the role of stiffness of the substrate. We show that intercellular forces can lead to significantly different behaviors than the ones observed for individual cells, where focal adhesion is the relevant parameter

Combined compatibilization and plasticization effect of low molecular weight poly(Lactic acid) in poly(lactic acid)/poly(3-hydroxybutyrate-co-3-hydroxyvalerate) blends

Improving overall properties of poly(lactic acid) (PLA) by blending it with another biobased polymer has been a strong field of research over the last years. In this study we demonstrate the synergetic effect of a small amount (between 0.1 and 1 wt%) of oligomer-like PLA (oLA) on the thermal, mechanical and gas barrier properties of the widely studied PLA-poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) blends (90–10 wt%). Films of PLA/PHBV/oLA blends were prepared via single-screw extrusion. oLA being miscible with both PLA and PHBV, its compatibilizing effect was demon- strated by a decrease of the interfacial tension, a slight shift in the Tgs of both polymers, and an increase in the elongation at break. It was also showed that oLA had a plasticizing effect on the PHBV dispersed phase, increasing its crystallinity rate. This resulted in a decrease in the permeability of the films while improving Young’s modulus

Effect of fibre concentration on the mechanical properties of welded reinforced polypropylene

International audienceThe effects of fibre concentration on the mechanical response of welded glass-fibre-reinforced polypropylene (GF-PP) were studied in-depth. Experimental observations during tensile tests of unwelded and welded GF-PP have shown a weld ratio reduction – ratio between the strength of the welded material and that of the bulk material – as high as 60%. For all conditions studied, no significant change in the polymer matrix was observed. Increasing the fibre content on the welded material was additionally associated with a decrease in the stress at break and the strain at the maximum stress, respectively 68 and 84% for 50 wt% GF-PP. The DIC technique was used to retrieve the local response in the welded zone, showing local strain as high as 19.5 times the macroscopic strain. Using X-ray microtomography, the strain magnification could be explained by the significant increase of the fibre density at the welded zone. It was also shown that at least 2/3 of the fibres were orientated within the weld plane limiting the transverse strain, favouring void nucleation and embrittlement of the material. As a consequence, the rupture can be explained by the amplification of the strain linked with the fibre concentration and orientation of the welded material

Confinement effect in PC/MXD6 multilayer films: Impact of the nanolayered structure on gas barrier properties of MXD6

International audienc

Confinement effect in PC/MXD6 multilayer films: Impact of the nanolayered structure on gas barrier properties of MXD6

International audienc