Influence of Composite Lay-Up and Cyclic Load Parameters on the Fatigue Behaviour of Flexible Composite Elements.

This work is dedicated to the design of flexible composite elements, specifically leaf springs. The design of these flexible composite elements took in consideration the technologies, materials and intermediate goods that are available and useable in laboratory manufacturing and the possibility for the transfer of gained knowledge to industrial practice. This work deals with individual types of materials and their processability and usability for the manufacturing of composite products exposed to cyclic stress. The impact of the designed lay-up diagrams and cyclic load boundary on the fatigue behaviour of manufactured specimens was used to evaluate the effect of cyclic stressing. Based on this assessment, a conclusion and recommendation were formulated for the serial manufacturing of flexible composite elements.

The Implementation of Neural Networks for Polymer Mold Surface Evaluation.

This paper presents the measurement and evaluation of the surfaces of molds produced using additive technologies. This is an emerging trend in mold production. The surfaces of such molds must be treated, usually using laser-based alternative machining methods. Regular evaluation is necessary because of the gradually deteriorating quality of the mold surface. However, owing to the difficulty in scanning the original surface of the injection mold, it is necessary to perform surface replication. Therefore, this study aims to describe the production of surface replicas for in-house developed polymer molds together with the determination of suitable descriptive parameters, the method of comparing variances, and the mean values for the surface evaluation. Overall, this study presents a new summary of the evaluation process of replicas of the surfaces of polymer molds. The nonlinear regression methodology provides the corresponding functional dependencies between the relevant parameters. The statistical significance of a neural network with two hidden layers based on the principle of Rosenblatt's perceptron has been proposed and verified. Additionally, machine learning was utilized to better compare the original surface and its replica.

Renewable whey-based hydrogel with polysaccharides and polyvinyl alcohol as a soil amendment for sustainable agricultural application.

This work describes the preparation of a novel biopolymer hydrogel based on acid whey, cellulose derivatives and polyvinyl alcohol (PVA). The hydrogel was prepared and characterized with the aim of producing an environmentally-friendly soil amendment to increase water retention capacity of the soil. The findings showed considerable swelling properties of the hydrogels depending on the PVA content and crosslinking density. The samples with PVA in a concentration 2.5 % and 5 % were more rigid, the gel fraction increased with a subsequently decrease in their swelling capacity. The hydrogels crosslinked with 15 % of citric acid demonstrated a constant swelling ratio (SR) of around 500 % within 10 swelling/drying cycles. The hydrogels crosslinked with 10 % citric acid and supplemented with 1 % of PVA showed SR of 1000-1400 % caused by less crosslinked polymer network and increased pore volume for water uptake. It was found that hydrogel with a higher gel fraction had a stable structure. Supplementing PVA at 5 % extended the period of decomposition of the hydrogel material by almost 60 % in the soil environment and soil humidity was maintained for longer. Applying 2 % of the hydrogel 5PVA to soil increased the water retention capacity by 19 %.

Flexible, ultrathin and light films from one-dimensional nanostructures of polypyrrole and cellulose nanofibers for high performance electromagnetic interference shielding.

Combining highly conducting one-dimensional nanostructures of polypyrrole with cellulose nanofibers (CNF) into flexible films with tailored electrical conductivity and mechanical properties presents a promising route towards the development of eco-friendly electromagnetic interference shielding devices. Herein, conducting films with a thickness of 140 µm were synthesized from polypyrrole nanotubes (PPy-NT) and CNF using two approaches, i.e., a new one-pot synthesis consisting of in situ polymerization of pyrrole in the presence of structure guiding agent and CNF, and a two-step synthesis, in which CNF and PPy-NT were physically blended. Films based on one-pot synthesis (PPy-NT/CNFin) exhibited higher conductivity than those processed by physical blending, which was further enhanced up to 14.51 S cm-1 after redoping using HCl post-treatment. PPy-NT/CNFin containing the lowest PPy-NT loading (40 wt%), thus the lowest conductivity (5.1 S cm-1), displayed the highest shielding effectiveness of -23.6 dB (>90 % attenuation), thanks to the good balance between its mechanical properties and electrical conductivity.

Conducting and Magnetic Hybrid Polypyrrole/Nickel Composites and Their Application in Magnetorheology.

Hybrid organic/inorganic conducting and magnetic composites of core-shell type have been prepared by in-situ coating of nickel microparticles with polypyrrole. Three series of syntheses have been made. In the first, pyrrole was oxidised with ammonium peroxydisulfate in water in the presence of various amounts of nickel and the composites contained up to 83 wt% of this metal. The second series used 0.1 M sulfuric acid as a reaction medium. Finally, the composites with polypyrrole nanotubes were prepared in water in the presence of structure-guiding methyl orange dye. The nanotubes have always been accompanied by the globular morphology. FTIR and Raman spectroscopies confirmed the formation of polypyrrole. The resistivity of composite powders of the order of tens to hundreds Ω cm was monitored as a function of pressure up to 10 MPa. The resistivity of composites slightly increased with increasing content of nickel. This apparent paradox is explained by the coating of nickel particles with polypyrrole, which prevents their contact and subsequent generation of metallic conducting pathways. Electrical properties were practically independent of the way of composite preparation or nickel content and were controlled by the polypyrrole phase. On the contrary, magnetic properties were determined exclusively by nickel content. The composites were used as a solid phase to prepare a magnetorheological fluid. The test showed better performance when compared with a different nickel system reported earlier.

Iron-Sepiolite High-Performance Magnetorheological Polishing Fluid with Reduced Sedimentation.

A sedimentation-stable magnetorheological (MR) polishing slurry on the basis of ferrofluid, iron particles, Al2O3, and clay nanofiller in the form of sepiolite intended for MR polishing has been designed, prepared, and its polishing efficiency verified. Added clay substantially improved sedimentation stability of the slurry, decreasing its sedimentation rate to a quarter of its original value (1.8 to 0.45 mg s-1) while otherwise maintaining its good abrasive properties. The magnetisation curve measurement proved that designed slurry is soft magnetic material with no hysteresis, and its further suitability for MR polishing was confirmed by its magnetorheology namely in the quadratically increased yield stress due to the effect of applied magnetic field (0 to 600 kA m-1). The efficiency of the MR polishing process was tested on the flat samples of injection-moulded polyamide and verified by surface roughness/3D texture measurement. The resulting new composition of the MR polishing slurry exhibits a long-term stable system with a wide application window in the MR polishing process.

Natural Weathering Effects on the Mechanical, Rheological, and Morphological Properties of Magnetorheological Elastomer (MRE) in Tropical Climate.

Magnetorheological elastomer (MRE) materials have the potential to be used in a wide range of applications that require long-term service in hostile environments. These widespread applications will result in the emergence of MRE-specific durability issues, where durability refers to performance under in-service environmental conditions. In response, the outdoor tropical climatic environment, combined with the effects of weathering, will be the primary focus of this paper, specifically the photodegradation of the MRE. In this study, MRE made of silicone rubber (SR) and 70 wt% micron-sized carbonyl iron particles (CIP) were prepared and subjected to mechanical and rheological testing to evaluate the effects under natural weathering. Magnetorheological elastomer samples were exposed to the natural weathering conditions of a tropical climate in Kuala Lumpur, Malaysia, for 30 days. To obtain a comprehensive view of MRE degradation during natural weathering, mechanical testing, rheology, and morphological evaluation were all performed. The mechanical and rheological properties test results revealed that after 30 days of exposure and known meteorological parameters, Young's modulus and storage modulus increased, while elongation at break decreased. The degradation processes of MRE during weathering, which are responsible for their undesirable change, were given special attention. With the help of morphological evidence, the relationship between these phenomena and the viscoelastic properties of MRE was comprehensively defined and discussed.

Atom Transfer Radical Polymerization of Pyrrole-Bearing Methacrylate for Production of Carbonyl Iron Particles with Conducting Shell for Enhanced Electromagnetic Shielding.

The conducting polymer poly(2-(1H-pyrrole-1-yl)ethyl methacrylate (PPEMA) was synthesized by conventional atom transfer radical polymerization for the first time from free as well as surface-bonded alkyl bromide initiator. When grafted from the surface of carbonyl iron (CI) a substantial conducting shell on the magnetic core was obtained. Synthesis of the monomer as well as its polymer was confirmed using proton spectrum nuclear magnetic resonance (1H NMR). Polymers with various molar masses and low dispersity showed the variability of this approach, providing a system with a tailorable structure and brush-like morphology. Successful grafting from the CI surface was elucidate by transmission electron microscopy and Fourier-transform infrared spectroscopy. Very importantly, thanks to the targeted nanometer-scale shell thickness of the PPEMA coating, the magnetization properties of the particles were negligibly affected, as confirmed using vibration sample magnetometry. Smart elastomers (SE) consisting of bare CI or CI grafted with PPEMA chains (CI-PPEMA) and silicone elastomer were prepared and dynamic mechanical properties as well as interference shielding ones were investigated. It was found that short polymer chains grafted to the CI particles exhibited the plasticizing effect, which might be interesting from the magnetorheological point of view, and more interestingly, in comparison to the neat CI-based sample, it provided enhanced electromagnetic shielding of nearly 30 dB in thickness of 500 µm. Thus, SE containing the newly synthesized CI-PPEMA hybrid particles also exhibited considerably enhanced damping factor and proper mechanical performance, which make the material highly promising from various practical application points of view.

Loss Factor Behavior of Thermally Aged Magnetorheological Elastomers.

Polymer composites have been widely used as damping materials in various applications due to the ability of reducing the vibrations. However, the environmental and surrounding thermal exposure towards polymer composites have affected their mechanical properties and lifecycle. Therefore, this paper presents the effect of material-temperature dependence on the loss factor and phase shift angle characteristics. Two types of unageing and aging silicone-rubber-based magnetorheological elastomer (SR-MRE) with different concentrations of carbonyl iron particles (CIPs), 30 and 60 wt%, are utilized in this study. The morphological, magnetic, and rheological properties related to the loss factor and phase shift angle are characterized using a low-vacuum scanning electron microscopy, and vibrating sample magnetometer and rheometer, respectively. The morphological analysis of SR-MRE consisting of 30 wt% CIPs revealed a smoother surface area when compared to 60 wt% CIPs after thermal aging due to the improvement of CIPs dispersion in the presence of heat. Nevertheless, the rheological analysis demonstrated inimitable rheological properties due to different in-rubber structures, shear deformation condition, as well as the influence of magnetic field. No significant changes of loss factor occurred at a low CIPs concentration, whilst the loss factor increased at a higher CIPs concentration. On that basis, it has been determined that the proposed changes of the polymer chain network due to the long-term temperature exposure of different concentrations of CIPs might explain the unique rheological properties of the unaged and aged SR-MRE.

Polymer Processing and Surfaces.

Polymer processing and surfaces are considered key parameters for developing unique materials for various applications [...].

Sensitivities of Rheological Properties of Magnetoactive Foam for Soft Sensor Technology.

Magnetoactive (MA) foam, with its tunable mechanical properties and magnetostriction, has the potential to be used for the development of soft sensor technology. However, researchers have found that its mechanical properties and magnetostriction are morphologically dependent, thereby limiting its capabilities for dexterous manipulation. Thus, in this work, MA foam was developed with additional capabilities for controlling its magnetostriction, normal force, storage modulus, shear stress and torque by manipulating the concentration of carbonyl iron particles (CIPs) and the magnetic field with regard to morphological changes. MA foams were prepared with three weight percentages of CIPs, namely, 35 wt.%, 55 wt.% and 75 wt.%, and three different modes, namely, zero shear, constant shear and various shears. The results showed that the MA foam with 75 wt.% of CIPs enhanced the normal force sensitivity and positive magnetostriction sensitivity by up to 97% and 85%, respectively. Moreover, the sensitivities of the storage modulus, torque and shear stress were 8.97 Pa/mT, 0.021 µN/mT, and 0.0096 Pa/mT, respectively. Meanwhile, the magnetic dipolar interaction between the CIPs was capable of changing the property of MA foam from a positive to a negative magnetostriction under various shear strains with a low loss of energy. Therefore, it is believed that this kind of highly sensitive MA foam can potentially be implemented in future soft sensor systems.

Advances in Elastomers.

Elastomer materials are characteristic for their high elongation and (entropy) elasticity, which makes them indispensable for widespread applications in various engineering areas, medical applications or consumer goods [...].

Magnetorheological fluids based on core-shell carbonyl iron particles modified by various organosilanes: synthesis, stability and performance.

Although smart materials, specifically magnetorheological (MR) fluids, have shown remarkable practical importance, their drawbacks such as an aggregation of magnetic fillers, insufficient compatibility with the carrier liquid, low resistance to corrosion and poor sedimentation stability still cause severe limitations for their broader utilization. To address this challenge, our study presents a facile concept for the coating of magnetic particles, leading to their enhanced utility properties and sufficient MR performance. This concentrates on the coating of magnetic carbonyl iron (CI) particles with a thin modifying layer as a surface shell utilizing four organosilanes; tetraethoxysilane, (3-aminopropyl)triethoxysilane, bis[3(trimethoxysilyl)propyl]amine and vinyltrimethoxysilane. Characterization of the modified particles and their suspensions was examined using various methods. XPS analysis confirmed the successful particle modification, while the surface free energy was evaluated by tensiometric measurements reflecting the better compatibility of particles with the dispersing medium. The lowest surface free energy possessed particles modified with (3-aminopropyl)triethoxysilane. The magnetization of the modified core-shell particles was not negatively affected by the organosilanes layer present on the particles resulting in comparable MR performance of the systems based on pure CI particles and their modified analogues as was proved by the fitting of the corresponding flow curves by the Robertson-Stiff model. Moreover, the modification of the particles improved their thermo-oxidation stability and chemical stability investigated via thermogravimetric analysis and acidic tests, respectively. Finally, the sedimentation stability of the modified particle-based systems expressed as a weight gain measured using a tensiometer device was enhanced in comparison with the pure CI particle-based system, which can be very positive in the intended applications.

One-Dimensional Nanostructures of Polypyrrole for Shielding of Electromagnetic Interference in the Microwave Region.

Polypyrrole one-dimensional nanostructures (nanotubes, nanobelts and nanofibers) were prepared using three various dyes (Methyl Orange, Methylene Blue and Eriochrome Black T). Their high electrical conductivity (from 17.1 to 60.9 S cm-1), good thermal stability (in the range from 25 to 150 °C) and resistivity against ageing (half-time of electrical conductivity around 80 days and better) were used in preparation of lightweight and flexible composites with silicone for electromagnetic interference shielding in the C-band region (5.85-8.2 GHz). The nanostructures' morphology and chemical structure were characterized by scanning electron microscopy, Brunauer-Emmett-Teller specific surface measurement and attenuated total reflection Fourier-transform infrared spectroscopy. DC electrical conductivity was measured using the Van der Pauw method. Complex permittivity and AC electrical conductivity of respective silicone composites were calculated from the measured scattering parameters. The relationships between structure, electrical properties and shielding efficiency were studied. It was found that 2 mm-thick silicone composites of polypyrrole nanotubes and nanobelts shield almost 80% of incident radiation in the C-band at very low loading of conductive filler in the silicone (5% w/w). Resulting lightweight and flexible polypyrrole composites exhibit promising properties for shielding of electromagnetic interference in sensitive biological and electronic systems.

Ethylene-Octene-Copolymer with Embedded Carbon and Organic Conductive Nanostructures for Thermoelectric Applications.

Hybrid thermoelectric composites consisting of organic ethylene-octene-copolymer matrices (EOC) and embedded inorganic pristine and functionalized multiwalled carbon nanotubes, carbon nanofibers or organic polyaniline and polypyrrole particles were used to form conductive nanostructures with thermoelectric properties, which at the same time had sufficient strength, elasticity, and stability. Oxygen doping of carbon nanotubes increased the concentration of carboxyl and C-O functional groups on the nanotube surfaces and enhanced the thermoelectric power of the respective composites by up to 150%. A thermocouple assembled from EOC composites generated electric current by heat supplied with a mere short touch of the finger. A practical application of this thermocouple was provided by a self-powered vapor sensor, for operation of which an electric current in the range of microvolts sufficed, and was readily induced by (waste) heat. The heat-induced energy ensured the functioning of this novel sensor device, which converted chemical signals elicited by the presence of heptane vapors to the electrical domain through the resistance changes of the comprising EOC composites.

Effect of Structure of Polymers Grafted from Graphene Oxide on the Compatibility of Particles with a Silicone-Based Environment and the Stimuli-Responsive Capabilities of Their Composites.

This study reports the utilization of controlled radical polymerization as a tool for controlling the stimuli-responsive capabilities of graphene oxide (GO) based hybrid systems. Various polymer brushes with controlled molecular weight and narrow molecular weight distribution were grafted from the GO surface by surface-initiated atom transfer radical polymerization (SI-ATRP). The modification of GO with poly(n-butyl methacrylate) (PBMA), poly(glycidyl methacrylate) (PGMA), poly(trimethylsilyloxyethyl methacrylate) (PHEMATMS) and poly(methyl methacrylate) (PMMA) was confirmed by thermogravimetric analysis (TGA) coupled with online Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Various grafting densities of GO-based materials were investigated, and conductivity was elucidated using a four-point probe method. Raman shift and XPS were used to confirm the reduction of surface properties of the GO particles during SI-ATRP. The contact angle measurements indicated the changes in the compatibility of GOs with silicone oil, depending on the structure of the grafted polymer chains. The compatibility of the GOs with poly(dimethylsiloxane) was also investigated using steady shear rheology. The tunability of the electrorheological, as well as the photo-actuation capability, was investigated. It was shown that in addition to the modification of conductivity, the dipole moment of the pendant groups of the grafted polymer chains also plays an important role in the electrorheological (ER) performance. The compatibility of the particles with the polymer matrix, and thus proper particles dispersibility, is the most important factor for the photo-actuation efficiency. The plasticizing effect of the GO-polymer hybrid filler also has a crucial impact on the matrix stiffness and thus the ability to reversibly respond to the external light stimulation.

Poly(2-oxazoline)-based magnetic hydrogels: Synthesis, performance and cytotoxicity.

Research on the subject of smart biomaterials has become a cornerstone of tissue engineering and regenerative medicine. Herein, the authors report on developing magnetic hydrogels that combine high biocompatibility and remarkable activity in magnetic fields. We fabricated magnetic hydrogels based on poly(2-ethyl-2-oxazoline) (POx) via living ring-opening cationic polymerization with in-situ embedding of the carbonyl iron (CI) particles. Investigation was made as to the effect exerted by the concentration of CI on magnetic, viscoelastic/magnetorheological properties, the degree of equilibrium swelling, and cytotoxicity. The hydrogels exhibited an open pore structure, as evidenced by computed tomography (CT) imaging. Susceptibility measurements revealed the concentration-dependent field-induced particle restructuration indicating elongation/contraction of the material, thereby determining the potential for magneto-mechanical stimulation of the cells. The POx-based magnetic hydrogels were amphiphilic in character, showing decrease in their capability to hold liquid alongside increase in CI concentration. Viscoelastic measurements suggested that interaction occurred between the particles and matrix based on inconsistency between the experimental storage modulus and the Krieger-Dougherty model. The synthesized materials exhibited excellent biocompatibility toward the 3T3 fibroblast cell line in tests of extract toxicity and direct contact cytotoxicity (ISO standards). The unique combination of properties exhibited by the material - magneto-mechanical activity and biocompatibility - could prove favorable in fields such as biomedicine and biomechanics.

Enhanced and Tunable Electrorheological Capability using Surface Initiated Atom Transfer Radical Polymerization Modification with Simultaneous Reduction of the Graphene Oxide by Silyl-Based Polymer Grafting.

In this study, a verified process of the "grafting from" approach using surface initiated atom transfer radical polymerization was applied for the modification of a graphene oxide (GO) surface. This approach provides simultaneous grafting of poly(2-(trimethylsilyloxy)ethyl methacrylate) (PHEMATMS) chains and a controllable reduction of the GO surface. This allows the fine tuning of its electrical conductivity, which is a crucial parameter for applications of such hybrid composite particles in electrorheological (ER) suspensions. The successful coating was confirmed by transmission electron microscopy and Fourier-transform infrared spectroscopy. The molecular characteristics of PHEMATMS were characterized by gel permeation chromatography. ER performance was elucidated using a rotational rheometer under various electric field strengths and a dielectric spectroscopy to demonstrate the direct impact of both the relaxation time and dielectric relaxation strength on the ER effectivity. Enhanced compatibility between the silicone oil and polymer-modified GO particles was investigated using contact angle measurements and visual sedimentation stability determination. It was clearly proven that the modification of the GO surface improved the ER capability of the system due to the tunable conductivity during the surface-initiated atom transfer radical polymerization (SI-ATRP) process and the enhanced compatibility of the GO particles, modified by polymer containing silyl structures, with silicone oil. These unique ER properties of this system appear very promising for future applications in the design of ER suspensions.

Polyglobalide-Based Porous Networks Containing Poly(ethylene glycol) Structures Prepared by Photoinitiated Thiol-Ene Coupling.

The high interest in polymers from natural resources prompted us to investigate the use of enzymatically synthesized polyglobalide (PGL) in the preparation of polymer networks with potential applications as biomaterials for drug delivery devices. Polymer networks were obtained under mild conditions by photoinitiated thiol-ene coupling between PGL and a poly(ethylene glycol- co-thiomalate) (PEG-SH) copolymer obtained by polycondensation. The obtained polymer networks were thoroughly characterized by Raman spectroscopy, scanning electron microscopy, titration of thiol groups and elemental analysis. Our study took into consideration the synthesis parameters for the polymer networks, such as the total polymer concentration and the SH/C=C functionality molar ratio. Swelling in both THF and water was assessed, and the potential of the materials for drug delivery was determined. The scanning electron microscopy images showed that the prepared polymer networks may have different morphologies ranging from homogeneous polymer materials to macroporous structures. Additionally, the prepared materials were found to be suitable from a cytotoxicity point of view, enabling their application as biomaterials for drug delivery devices.

Reversible Actuation Ability upon Light Stimulation of the Smart Systems with Controllably Grafted Graphene Oxide with Poly (Glycidyl Methacrylate) and PDMS Elastomer: Effect of Compatibility and Graphene Oxide Reduction on the Photo-Actuation Performance.

This study is focused on the controllable reduction of the graphene oxide (GO) during the surface-initiated atom transfer radical polymerization technique of glycidyl methacrylate (GMA). The successful modification was confirmed using TGA-FTIR analysis and TEM microscopy observation of the polymer shell. The simultaneous reduction of the GO particles was confirmed indirectly via TGA and directly via Raman spectroscopy and electrical conductivity investigations. Enhanced compatibility of the GO-PGMA particles with a polydimethylsiloxane (PDMS) elastomeric matrix was proven using contact angle measurements. Prepared composites were further investigated through the dielectric spectroscopy to provide information about the polymer chain mobility through the activation energy. Dynamic mechanical properties investigation showed an excellent mechanical response on the dynamic stimulation at a broad temperature range. Thermal conductivity evaluation also confirmed the further photo-actuation capability properties at light stimulation of various intensities and proved that composite material consisting of GO-PGMA particles provide systems with a significantly enhanced capability in comparison with neat GO as well as neat PDMS matrix.