Numerical Study of the Effect of Thixotropy on Extrudate Swell.

The extrusion of highly filled elastomers is widely used in the automotive industry. In this paper, we numerically study the effect of thixotropy on 2D planar extrudate swell for constant and fluctuating flow rates, as well as the effect of thixotropy on the swell behavior of a 3D rectangular extrudate for a constant flowrate. To this end, we used the Finite Element Method.

Anomalous Terminal Shear Viscosity Behavior of Polycarbonate Nanocomposites Containing Grafted Nanosilica Particles.

Viscosity controls an important issue in polymer processing. This paper reports on the terminal viscosity behavior of a polymer melt containing grafted nanosilica particles. The melt viscosity behavior of the nanocomposites was found to depend on the interaction between the polymer matrix and the nanoparticle surface.

A filament stretching rheometer for in situ X-ray experiments: Combining rheology and crystalline morphology characterization.

We present a rheometer that combines the possibility to perform in situ X-ray experiments with a precise and locally controlled uniaxial extensional flow. It thus allows us to study the crystallization kinetics and morphology evolution combined with the rheological response to the applied flow field. A constant uniaxial deformation rate is ensured, thanks to a fast control scheme that drives the simultaneous movement of the top and bottom plates during a pulling experiment.

In Situ WAXD and SAXS during Tensile Deformation Of Moulded and Sintered Polyamide 12.

To provide knowledge to improve the mechanical performance of Polyamide 12 (PA12) sintered products, we have studied experimentally the mechanical response and structure development under constant strain rate of compression moulded and laser sintered PA12 by means of in situ small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) experiments. It is found that at low temperatures, i.e.

Effect of Thermal History and Shear on the Viscoelastic Response of PP Containing an Oxalamide-Based Organic Compound.

We report on the role of temperature and shear on the melt behavior of PP in the presence of the organic compound 1,1'-(propane-1,3-diyl)bis(2-hexyloxalamide) (). It is demonstrated that facilitates a viscosity suppression when it resides in the molten state. The viscosity suppression is attributed to the interaction of PP chains/subchains with molten nanoclusters.

Structure-Properties Relations for Polyamide 6, Part 2: Influence of Processing Conditions during Injection Moulding on Deformation and Failure Kinetics.

The effect of processing conditions during injection on the structure formation and mechanical properties of injection molded polyamide 6 samples was investigated in detail. A large effect of the mold temperature on the crystallographic properties was observed. Also the the effect of pressure and shear flow was taken in to consideration and analysed.

Structure⁻Properties Relations for Polyamide 6, Part 1: Influence of the Thermal History during Compression Moulding on Deformation and Failure Kinetics.

The deformation and failure kinetics of polyamide 6 samples prepared by several thermal histories were investigated by tests at different temperatures and relative humidities. PA6 samples were produced in quiescent condition and multiple cooling procedure. A characterization was performed to investigate the effect of the different thermal histories and the effect of hydration on both structures and glass transition temperature.

Effect of Self-Assembly of Oxalamide Based Organic Compounds on Melt Behavior, Nucleation, and Crystallization of Isotactic Polypropylene.

We report on the effect of an aliphatic oxalamide based nucleating agent () on the melt and crystallization behavior of isotactic polypropylene (PP) under defined shear conditions. Through polarized optical microscopy, we demonstrate that self-assembles from the PP melt into rhombic crystals whereas their size and distribution proved highly dependent on the employed cooling rates. The presence of 0.

Cross-Nucleation between Polymorphs: Quantitative Modeling of Kinetics and Morphology.

Cross-nucleation is defined as the nucleation of one polymorph on the surface of another polymorph of the same substance. Although the description of this particular form of heterogeneous nucleation is mainly phenomenological, recently dedicated quantitative studies are performed on several systems. In this work we propose a model framework that captures the phenomenon of cross-nucleation for a spherulitic seed-surface geometry, as well as the kinetic competition between the seed growth and the cross-nucleus formation, by the introduction of a tangential growth rate of the daughter polymorph.

Deformation-Induced Phase Transitions in iPP Polymorphs.

This detailed study reveals the relation between structural evolution and the mechanical response of α -, β - and γ -iPP. Uni-axial compression experiments, combined with in situ WAXD measurements, allowed for the identification of the evolution phenomena in terms of phase composition. Tensile experiments in combination with SAXS revealed orientation and voiding phenomena, as well as structural evolution in the thickness of the lamellae and amorphous layers.

Buffers Strongly Modulate Fibrin Self-Assembly into Fibrous Networks.

Fibrin is a plasma protein with a central role in blood clotting and wound repair. Upon vascular injury, fibrin forms resilient fibrillar networks (clots) via a multistep self-assembly process, from monomers, to double-stranded protofibrils, to a branched network of thick fibers. In vitro, fibrin self-assembly is sensitive to physicochemical conditions like the solution pH and ionic strength, which tune the strength of the noncovalent driving forces.

A constitutive model for developing blood clots with various compositions and their nonlinear viscoelastic behavior.

The mechanical properties determine to a large extent the functioning of a blood clot. These properties depend on the composition of the clot and have been related to many diseases. However, the various involved components and their complex interactions make it difficult at this stage to fully understand and predict properties as a function of the components.

A constitutive model for the time-dependent, nonlinear stress response of fibrin networks.

Blood clot formation is important to prevent blood loss in case of a vascular injury but disastrous when it occludes the vessel. As the mechanical properties of the clot are reported to be related to many diseases, it is important to have a good understanding of their characteristics. In this study, a constitutive model is presented that describes the nonlinear viscoelastic properties of the fibrin network, the main structural component of blood clots.

Self-regulation in flow-induced structure formation of polypropylene.

Flow-induced structure formation is investigated with in situ wide-angle X-ray diffraction with high acquisition rate (30 Hz) using isotactic polypropylene in a piston-driven slit flow with high wall shear rates (up to ≈900 s(-1) ). We focus on crystallization within the shear layers that form in the high shear rate regions near the walls. Remarkably, the kinetics of the crystallization process show no dependence on either flow rate or flow time; the crystallization progresses identically regardless.

A constitutive model for a maturing fibrin network.

Blood clot formation is crucial to maintain normal physiological conditions but at the same time involved in many diseases. The mechanical properties of the blood clot are important for its functioning but complicated due to the many processes involved. The main structural component of the blood clot is fibrin, a fibrous network that forms within the blood clot, thereby increasing its mechanical rigidity.

Cheetahs, Acinonyx jubatus, balance turn capacity with pace when chasing prey.

Predator-prey interactions are fundamental in the evolution and structure of ecological communities. Our understanding, however, of the strategies used in pursuit and evasion remains limited. Here, we report on the hunting dynamics of the world's fastest land animal, the cheetah, Acinonyx jubatus.

Mechanically induced chemiluminescence from polymers incorporating a 1,2-dioxetane unit in the main chain.

Nature uses mechanochemical transduction processes to achieve diverse and vital functions, such as hearing, cellular adhesion and gating of ion channels. One fascinating example of biological mechanotransduction is the emission of light on mechanical stimulation. However, molecular-level transduction of force into luminescence in a synthetic system remains a challenge.

Oriented Gamma Phase in Isotactic Polypropylene Homopolymer.

The presence of γ-phase in isotactic polypropylene is well-known but, up until now, could only be induced by specific processing conditions or material modifications. Typically, for Ziegler-Natta (ZN) iPPs pressures of 2000 bar are required, otherwise, metallocene (M) iPPs and copolymerization using olefin-type counits should be used. Here we show that crystallization under the unique combination of moderate pressure ( ≥ 900 bar) and strong shear flow oriented specimens with high contents of γ-phase are created in ZN-iPPs.

Linear shear response of the upper skin layers.

This study presents an in vitro experimental method to determine shear properties of the epidermis. Shear tests were performed with a parallel plate rheometer on samples of stratum corneum and the viable epidermis. The method was validated on very thin silicon sheets.

In vitro indentation to determine the mechanical properties of epidermis.

The lack of understanding of the mechanical behavior of the human skin layers makes the development of drug delivery using microneedles or microjets a challenging task. In particular, the key mechanical properties of the epidermis composed of stratum corneum and viable epidermis should be better understood. Micro-indentation experiments were applied, using a spherical tip with a large diameter to the sample thickness ratio.

Does subcutaneous adipose tissue behave as an (anti-)thixotropic material?

Although subcutaneous adipose tissue undergoes large deformations on a daily basis, there is no adequate mechanical model to describe the transfer of mechanical load from the skin throughout the tissue to deeper layers. In order to develop such a non-linear model, a set of experimental data is required. Accordingly, this study examines the long term behavior of adipose tissue under small strain and its response to various large strain profiles.

Linear viscoelastic behavior of subcutaneous adipose tissue.

Subcutaneous adipose tissue contributes to the overall mechanical behavior of the skin. Until today, however, no thorough constitutive model is available for this layer of tissue. As a start to the development of such a model, the objective of this study was to measure and describe the linear viscoelastic behavior of subcutaneous adipose tissue.

Crystallization and dissolution of flow-induced precursors.

We make use of a specially synthesized linear high density polyethylene with a bimodal molecular weight distribution (MWD) to demonstrate that it is possible to produce a suspension of extended-chain (shish) crystals only. Such a suspension can be generated at high temperatures, above but close to the equilibrium melting temperature of the unconstrained extended-chain crystals (T(m)(0)=141.2 degrees C) and requires stretch of the longest chains of the MWD.

Non-linear viscoelastic behavior of abdominal aortic aneurysm thrombus.

The objective of this work was to determine the linear and non-linear viscoelastic behavior of abdominal aortic aneurysm thrombus and to study the changes in mechanical properties throughout the thickness of the thrombus. Samples are gathered from thrombi of seven patients. Linear viscoelastic data from oscillatory shear experiments show that the change of properties throughout the thrombus is different for each thrombus.

Determination of linear viscoelastic behavior of abdominal aortic aneurysm thrombus.

The objective of this study is to determine whether the linear viscoelastic properties of an abdominal aortic aneurysm thrombus can be determined by rheometry. Although large strains occur in the in vivo situation, in this work only linear behavior is studied to show the applicability of the described methods. A thrombus exists of several layers that vary in composition, structure and mechanical properties.