PRESSURE SENSITIVITY OF THERMOPLASTIC POLYURETHANE

Mechanical material properties of polymers may change significantly when they are exposed to high pressures and/or temperatures. Within this paper the effect of hydrostatic pressure on shear relaxation modulus of three thermoplastic polyurethanes is presented. Results show that chemically identical materials may have significantly different hydrostatic pressure sensitivity. At pressure of 300 MPa, mechanical properties of two materials change “only” for a factor of 10, while for the third material, mechanical properties change 109 times

Needleless electrospinning of PA6 fibers: The effect of solution concentration and electrospinning voltage on fiber diameter

Needleless electrospinning is the process of forming thin material fibers from the open surface of its solution or melt in a strong electrostatic field. Electrospun non-woven materials are used in various applications that require specific fiber diameters and pore size distributions. Fiber diameter depends on the properties of the polymer solution and manufacturing conditions. A needleless electrospinning process using the Nanospider setup was investigated using the commonly used polyamide 6 (PA6) solution in a mixture of acetic and formic acids. Polymer solutions with different polymer concentrations were characterized by viscosity, surface tension and electrical conductivity. An increase in polymer content in the solution resulted in the exponential increase of the solution viscosity, polynomial increase of electrical conductivity and had almost no effect on surface tension. The effect of the polymer concentration in the solution, as well as electrospinning voltage on fiber diameter and diameter distribution, was investigated using scanning electron microscopy images. The average fiber diameter linearly increases with the increased polymer concentration and also demonstrates an increase with increased electrospinning voltage, although less pronounced. Therefore, a change in the PA6 solution concentration should be used for the robust adjustment of fiber diameter, while changes in electrospinning voltage are more appropriate for fine tuning the fiber diameter during the process of needleless electrospinning. © 2020 Journal of Mechanical Engineering.Slovenian Research AgencySlovenian Research Agency - Slovenia [L2-7550, P2-0264]; Fresenius Kabi Deutschland Gmb

A fi nding of invasive alien beetle species Acanthoscelides pallidipennis (Motschulsky, 1874) in pods of indigo bush (Amorpha fruticosa L.)

Plodovi čivitnjače (Amorpha fruticosa L.), invazivne biljne vrste, prikupljani su tijekom 2017. godine na području Pokupskog bazena i u Županji. Na plodovima žljezdastim mahunama uočeni su izletni otvori te je utvrđena prisutnost invazivne vrste kukca Acanthoscelides pallidipennis (Motschulsky, 1873). Ova je vrsta autohtona na području Sjeverne Amerike, a njezina rasprostranjenost usko je vezana uz staništa čivitnjače i puteve širenja ove invazivne biljne vrste. Na području Pokupskog bazena u prikupljenim su uzorcima zabilježene ukupno 554 infestirane mahune, dok su u Županji bile infestirane 434 mahune te nije utvrđena statistički značajna razlika između dvaju istraživanih područja. Rezultati ukazuju na to da je kukac A. pallidipennis raširen u sastojinama čivitnjače na obama područjima te da je potrebno pratiti potencijal njegova širenja kako bi se spriječila infestacija i drugih biljnih vrsta, posebice onih iz porodice Fabaceae koje učestalo napada.A pods of indigo bush (Amorpha fruticosa L.), an invasive plant species were collected during 2017. in the area of the Pokupski basin and in Županja. In the laboratory there were observed exit holes on pods, which determined the presence of the invasive beetle species Acanthoscelides pallidipennis (Motschulsky, 1873). This species is native to the territory of North America, and its distribution is closely related to the habitats of the indigo bush. In the area of Pokupski basin within the collected samples there were found 554 infested pods, moreover in Županja there were 434 infested pods. Therefore, statistically significant difference was not found within two study sites. The results indicate that the A. pallidipennis is widespread in amorphous stands in both study sites and thus it is necessary to monitor the potential of its spreading in order to prevent infestation of other plant species, especially those from the Fabaceae family that are frequently infested

An Intriguing Array of Extrudate Patterns in Long‐Chain Branched Polymers During Extrusion

The present study highlights a range of surface and volume extrudate patterns that can be detected during the extrusion flow of long-chain branched polymers. Thus, four linear low-density polyethylenes (LDPEs) have been extruded using a single-screw extruder coupled to an inline optical imaging system. The selected LDPEs are selected to outline the influence of molecular weight and long-chain branching on the types of melt flow extrusion instabilities (MFEI). Through the inline imaging system, space–time diagrams are constructed and analyzed via Fourier-transformation using a custom moving window procedure. Based on the number of characteristic frequencies, peak broadness, and whether they are surface or volume distortions, three main MFEI types, distinct from those typically observed in linear and short-chain branched polymers, are identified. The higher molecular weight, low long-chain branching LDPEs exhibited all three instability types, including a special type volume instability. Independently of the molecular weight, higher long-chain branching appeared to have a stabilizing effect on the transition sequences by suppressing volume extrudate distortions or limiting surface patters to a form of weak intensity type

Challenges in nano-structured fluid flows for assembly into hierarchical biomaterials

Hierarchical biomaterials have their place in the context of developing novel material systems particularly in the framework of sustainability. The key to their development is in controlling their assembly into hierarchical orders at various lengthscales. Thus, flow can be an asset in e.g. controlling orientation, however, resolving the hierarchical orientation dynamics of such systems remains a challenge. We focus here mainly on cellulose nanocrystals water-based suspensions, however, the outline is representative of numerous nanostructured fluids

Polyethylene Based Ionomers as High Voltage Insulation Materials

Polyethylene based ionomers are demonstrated to feature a thermo-mechanical and dielectric property portfolio that is comparable to cross-linked polyethylene (XLPE), which may enable the design of more sustainable high voltage direct-current (HVDC) power cables, a crucial component of future electricity grids that seamlessly integrate renewable sources of energy. A new type of ionomer is obtained via high-pressure/high-temperature free radical copolymerization of ethylene in the presence of small amounts of ion-pair comonomers comprising amine terminated methacrylates and methacrylic acid. The synthesized ionomers feature a crystallinity, melting temperature, rubber plateau modulus and thermal conductivity like XLPE but remain melt-processable. Moreover, the preparation of the ionomers is free of byproducts, which readily yields a highly insulating material with a low dielectric loss tangent and a low direct-current (DC) electrical conductivity of 1 to 6\ub710−14\ua0S\ua0m−1 at 70\ua0\ub0C and an electric field of 30\ua0kV\ua0mm−1. Evidently, the investigated ionomers represent a promising alternative to XLPE-based high voltage insulation, which may permit to ease the production as well as end-of-use recycling of HVDC power cables by combining the advantages of thermoset and thermoplastic materials while avoiding the formation of byproducts

Neural networks for predicting the temperature-dependent viscoelastic response of PEEK under constant stress rate loading

High-performance polymer composites are used in demanding applications in civil and aerospace engineering. Often, structures made from such composites are monitored using structural health monitoring systems. This investigation aims to use a multilayer perceptron neural network to model polymer response to a non-standard excitation under different temperature conditions. Model could be implemented into health monitoring systems. Specifically, the neural network was used to model PEEK material\u27s creep behavior under constant shear stress rate excitation at different temperatures. Optimal neural network topology, the effect of the amount of training data and its distribution in a temperature range on prediction quality were investigated. The results showed that based on the proposed optimization criterion, a properly trained neural network can predict polymeric material behavior within the experimental error. The neural network also enabled good prediction at temperatures where stress-strain behavior was not experimentally determined

PRESSURE OPTIMISED VISCOELASTIC VIBRATION AND IMPACT INSULATION

Within this contribution we present recently published findings [1] on the new way of utilizing polymeric materials for vibration damping. We present and demonstrate patented dissipative bulk and granular systems technology [2], based on which we have developed granular damping elements (GDE). The damping elements consist of granular viscoelastic material encapsulated and pressurized within a woven container made of basalt, carbon, and/or glass fibres. The hydrostatic pressure changes material properties and consequently the performance of the vibration isolation. Within this contribution, properties of three TPU materials in solid state are investigated, which after granulation are potential candidates for producing new GDE damping elements. We have demonstrated that for the case of TPU materials the stiffness and energy absorption capability of insulation may be increased between 10 to 100 times

Brezigelno elektropredenje vlaken PA6: vpliv koncentracije raztopine in električne napetosti na premer vlaken

Needleless electrospinning is the process of forming thin material fibers from the open surface of its solution or melt in a strong electrostatic field. Electrospun non-woven materials are used in various applications that require specific fiber diameters and pore size distributions. Fiber diameter depends on the properties of the polymer solution and manufacturing conditions. A needleless electrospinning process using the Nanospider setup was investigated using the commonly used polyamide 6 (PA6) solution in a mixture of acetic and formic acids. Polymer solutions with different polymer concentrations were characterized by viscosity, surface tension and electrical conductivity. An increase in polymer content in the solution resulted in the exponential increase of the solution viscosity, polynomial increase of electrical conductivity and had almost no effect on surface tension. The effect of the polymer concentration in the solution, as well as electrospinning voltage on fiber diameter and diameter distribution, was investigated using scanning electron microscopy images. The average fiber diameter linearly increases with the increased polymer concentration and also demonstrates an increase with increased electrospinning voltage, although less pronounced. Therefore, a change in the PA6 solution concentration should be used for the robust adjustment of fiber diameter, while changes in electrospinning voltage are more appropriate for fine tuning the fiber diameter during the process of needleless electrospinning

Viscoelasticity of new generation thermoplastic polyurethane vibration isolators

This paper presents the analysis of pressure dependence of three thermoplastic polyurethane (TPU) materials on vibration isolation. The three TPU Elastollan materials are 1190A, 1175A, and 1195D. The aim of this investigation was to analyze how much the performance of isolation can be enhanced using patented Dissipative bulk and granular systems technology . The technology uses granular polymeric materials to enhance materials properties (without changing its chemical or molecular composition) by exposing them to "self-pressurization," which shifts material energy absorption maxima toward lower frequencies, to match the excitation frequency of dynamic loading to which a mechanical system is exposed. Relaxation experiments on materials were performed at different iso- baric and isothermal states to construct mastercurves, the time-temperature-pressure interrelation was modeled using the Fillers-Moonan-Tschoegl model. Dynamic material functions, related to isolation stiffness and energy absorption, were determined with the Schwarzl approximation. An increase in stiffness and energy absorption at selected hydrostatic pressure, compared to its stiffness and energy absorption at ambient conditions, is represented with K_k(p, [omega]), defining the increase in stiffness and K_d (p, [omega]), defining the increase in energy absorption. The study showed that close to the glassy state, moduli of 1190A and 1195D are about 6-9 times higher compared to 1175A, whereas their properties at ambient conditions are, for all practical purposes, the same. TPU 1190A turns out to be most sen- sitive to pressure: at 300 MPa its properties are shifted for 5.5 decades, while for 1195D and 1175A this shift is only 3.5 and 1.5 decades, respectively. In conclusion, the stiffness and energy absorption of isolation may be increased with pressure for about 100 times for 1190A and 1195D and for about 10 times for 1175A. Published by AIP Publishing