Elastomer Solution Research Articles

Manufacturing Scalable Carbon Nanotube-Silicone/Kevlar Fabrics.

Carbon nanotube (CNT) hybrid composites were formed by combining a CNT and silicone elastomer solution with Kevlar yarn, Kevlar fabric, and Kevlar veil materials. The integration of a CNT-silicone matrix with Kevlar yarn and fabric materials produced a composite with moderate electrical and thermal conductivity due to CNT fabric combined with the strength of Kevlar fabric or yarn. In the material synthesis, a notable difficulty was that the CNT-silicone did not bond strongly to the Kevlar. The composites passed the Vertical Flame Test ASTM D6413 and the Forced Air Oven Test NFPA 1971. These hybrid composites can have multiple applications in areas requiring favorable conductivity, strength, and flame and heat resistance. The application areas include firefighter apparel, military equipment, conductive/smart structures, and flexible electronics. The synthesis process used to manufacture CNT-silicone/Kevlar composites yielded composite sheets with an area of 2250 cm2. The process is scalable and customizable for the synthesis of CNT composites with tailored properties. Improvements in the bonding of CNT-silicone to Kevlar are being investigated.

Highly Conductive and Compliant Silver Nanowire Nanocomposites by Direct Spray Deposition

The silver nanowire (Ag NW)/elastomer nanocomposite represents a prototypical form of a compliant conductor for flexible and stretchable electronic devices. The widespread implementations are currently hindered by the complicated procedures to effectively disperse Ag NWs into elastomer matrices. In this study, we report a facile and scalable coating process to create Ag NW nanocomposites on various flexible/stretchable substrates. As-synthesized Ag NWs from the high-yield polyol-reduction approach are homogeneously dispersed into a variety of dilute elastomer solutions, thereby enabling direct spray deposition into highly compliant conductors. The as-prepared nanocomposite exhibits excellent conductivity (∼11,000 S/cm) and high deformability to 100% strain. The stable electrical properties are largely retained under repetitive mechanical manipulations including stretching, bending, and folding. The patterned features of conductive nanocomposites are conveniently accessed using shadow masks or selective laser ablation. The practical suitability is demonstrated by the successful implementations of a stretchable sensing patch and a flexible light-emitting diode display.

Ultrasonic measurements of grouted tendon ducts in the concrete structure using Elop Insight Scanner

Infrastructures such as bridges, tunnels, dams, retaining walls, docks, parking garages and buildings are constructed from reinforced concrete. These structures deteriorate due to cyclic temperature and loading variations, aging, as well as physical causes such as accidents and aggressive chemical attack from the environment. Post tension tendon ducts commonly used in bridges are filled with grout and steel tendons. The voids in the grout inside the tendon ducts can occur due various reasons such as improper filling, material mixing, blockage due to tendons etc. The water can penetrate in these voids inside the tendon ducts which can initiate corrosion. It is therefore vital to detect voids/ unfilled or defective portions of the tendon ducts at an early stage of the construction phase to ensure the strength and safety of the structure. Different types of NDT (Non-Destructive Testing) methods are frequently used for monitoring such infrastructures during regular operation to prevent failure, increase life span and improve safety. One of these NDT techniques, ultrasonic testing, is relatively simple in operation and gives more accurate description of air pockets, voids, cracks, and delaminations in the concrete structures compared to other NDT methods. ELOP has developed a rolling ultrasonic scanner COBRI (COncrete and BRidge Inspection) together with a complete software solution for asset management of structures for faster and better inspection and monitoring of the internal condition of the concrete. It will provide asset owners with information about when, where and how to inspect, maintain and more accurately assess damages and overall condition of their structures. The COBRI scanner contains an array of transducers assembled in two separate rollers used in pitch-catch mode. It uses a patented elastomer solution to provide dry coupling to the concrete surface during scanner movement, without the need for any added fluid couplant. The system uses SAFT (Synthetic Aperture Focusing Technique) algorithm for image reconstruction to increase image quality and signal to noise ratio. It will provide users with improved tomographic (B, C and D-scan) image quality and 3D imaging. In the current work, we have used the COBRI scanner to explore its ability to image grouting defects inside tendon ducts used in concrete structures. The concrete specimen used in the evaluation has two tendon ducts positioned at 8 cm from the top surface with dimensions of 70 cm in length, 55 cm in width and 25 cm in thickness with average aggregate size of 22 mm. One of the tendon ducts is completely empty. The second one is half-length fully filled with grouting along the prestressed steel and other half only three quarters filled, leaving an air cavity on the top. The scanner is rolled approximately 50 cm over the concrete surface and the tomographic (B, C and D-scan) SAFT images are generated at different locations of the concrete specimen together with a 3D volume image. The results showed that the COBRI scanner is able to differentiate the filled and partially filled tendon ducts in the concrete structure. As COBRI is a rolling ultrasound scanner, it will help the bridge owners to scan and assess the grouting defects in the tendon ducts much more efficiently than other scanners available in the market.

Conductive and room-temperature self-healable polydimethylsiloxane-based elastomer film with ridge-like microstructure for piezoresistive pressure sensor

The fabrication of piezoresistive pressure sensor with self-healing function has attracted worldwide attention for its great prospects in intelligent robots, remote health monitoring and electronic skin. In this work, a conductive and self-healable elastomer (CSE) film with ridge-like microstructure was designed for flexible piezoresistive pressure sensor. Firstly, self-healable polydimethylsiloxane (PDMS)-based elastomer with ureido and imine groups was synthesized via a simple one-pot two-step polycondensation reaction with aminopropyl-terminated PDMS, isophorone diisocyanate and 1, 3, 5-triformylbenzene as monomers. Secondly, the synthesized PDMS-based elastomer solution was casted onto a sandpaper pre-sprayed with ureido pyrimidinone grafted carbon nanotubes/polyurea mixed solution, and the CSE film was obtained after drying and peeling off from the sandpaper. The piezoresistive pressure sensor fabricated with two single-electrode CSE films exhibited high sensitivity of 8.7 kPa−1 (0–6.1 kPa), low detection limit (50 Pa), fast response capability (response/relaxation time of 40/117 ms) and repeatability for 10,000 loading–unloading tests. Moreover, the sensor was able to fully recover to normal work after healing for 36 h at room temperature or even 200 s under the irradiation of near infrared (NIR) light. Importantly, the sensor was successfully applied for not only detecting human motions including radial pulse, speech recognitions and joint movements but also monitoring health status wirelessly through Bluetooth transmission. Our findings put forward a novel method to fabricate a high-performance self-healable piezoresistive sensor for wearable electronics, healthcare monitoring and electronic skin.

Particle organization versus volume fraction in magneto-active elastomer composites

Magneto-active elastomers (MAEs) are a subclass of smart materials that have the ability to actuate and alter their mechanical and magnetic response when subjected to an external magnetic field. Past research has shown that higher net magnetic remanence of an MAE is desirable to increase actuation and produce the most magnetic work. To create a magnetically aligned MAE, a hard magnetic material is mixed in an elastomer solution, then cured in a strong external magnetic field causing particle alignment. A high degree of alignment of magnetic particles is expected to result in improved remanence. However, in MAEs with soft magnetic particles cured in a field, past research has shown that the degree of alignment, vs. less ordered clustering, varies with particulate volume content. Consequently, it is important to study the degree to which volume content of magnetic material affects physical particle alignment, bulk magnetic properties, and the coupling between the two in MAEs with hard magnetic filler particles. In this study MAEs with a hard magnetic filer (barium ferrite) are investigated with varying volume content of magnetic material ranging from 5 to 30% by volume. Batches of MAEs were tested using X-ray diffraction and vibrating sample magnetometry to gain information on crystal structure and bulk magnetic properties. The results of the collected data suggested all poled samples had both higher physical particle orientation as well as a larger remanence than the unpoled counterparts. As volume fraction of magnetic filler was increased the net magnetic properties per volume of magnetic material remained fairly constant. However, the degree of physical particle orientation varied with a local minimum at medium volume fractions. Collected data was used to calculate two orientation parameters, the degree of preferred alignment parameter, η, and the orientation of distributions of magnetic domains parameter, σ. The two parameters were compared to show a relationship between physical particle alignment and net magnetic properties as volume of magnetic material increases. Based on the collected results, a hypothesis is presented on how particle interaction is speculated to evolve as volume fraction of magnetic material is increased.

A Deformable Linear Dielectric Elastomer Actuator

Dielectric elastomer actuator (DEA) is a compact device that consists of stretchable electrodes and elastomers. This device is energy efficient in performance and holds great promise in the development of soft actuators. DEAs performance relies significantly on the mechanical properties of its elastomers. This present study focuses on evaluating the soft material made of Sylgard 184 as the elastomers for DEAs. Sylgard 184 is a silicone elastomer that comes with two main parts (elastomers and its curing agent). A specific mixing ratio between elastomers and curing agent is essential to produce solid and reliable silicone elastomer. The recommended ratio for the elastomer solution was ten parts for the elastomers and one part for the curing agent (10:1). Producing softer elastomers was possible by reducing the curing agent. However, the performance of the material was unknown. We performed a series of cyclic tensile tests to understand the mechanical characteristic of the elastomer made of Sylgard 184. The result shows that reducing the curing agent did not have a significant effect on its cyclic performance. Furthermore, the use of a 30:1 ratio in the application of DEAs and deformable linear actuator indicates stable performance for both devices.

Solution Blow Spinning of Polymeric Nano-Composite Fibers for Personal Protective Equipment.

Light-weight, protective armor systems typically consist of high modulus (>109 MPa) and high-strength polymeric fibers held in place with an elastic resin material (binder) to form a non-woven, unidirectional laminate. While significant efforts have focused on improving the mechanical properties of the high-strength fibers, little work has been undertaken to improve the properties of the binder materials. To improve the performance of these elastomeric polymer binders, a relatively new and simple fabrication process, known as solution blow spinning, was used. This technique is capable of producing sheets or webs of fibers with average diameters ranging from the nanoscale to the microscale. To achieve this, a solution blow spinning (SBS) apparatus has been designed and built in the laboratory to fabricate non-woven fiber mats from polymer elastomer solutions. In this study, a commonly used binder material, a styrene-butadiene-styrene block-co-polymer dissolved in tetrahydrofuran, was used to produce nanocomposite fiber mats by adding metallic nanoparticles (NPs), such as iron oxide NPs, that were encapsulated with silicon oil and thus incorporated in the fibers formed via the SBS process. The protocol described in this work will discuss the effects of the various critical parameters involved in the SBS process, including the polymer molar mass, the selection of the thermodynamically appropriate solvent, the polymer concentration in solution, and the carrier gas pressure to assist others in performing similar experiments, as well as provide guidance to optimize the configuration of the experimental setup. The structural integrity and morphology of the resultant non-woven fiber mats were examined using scanning electron microscopy (SEM) and elemental X-ray analysis via energy-dispersive X-ray spectroscopy (EDS). The goal of this study is to evaluate the effects of the various experimental parameters and material selections to optimize the structure and morphology of the SBS fiber mats.

Graphene–Polyurethane Coatings for Deformable Conductors and Electromagnetic Interference Shielding

AbstractElectrically conductive, polymeric materials that maintain their conductivity even when under significant mechanical deformation are needed for actuator electrodes, conformable electromagnetic shielding, stretchable tactile sensors, and flexible energy storage. The challenge for these materials is that the percolated, electrically conductive networks tend to separate even at low strains, leading to significant piezoresistance. Herein, deformable conductors are fabricated by spray‐coating a nitrile substrate with a graphene–elastomer solution. The electrical resistance of the coatings shows a decrease after thousands of bending cycles and a slight increase after repeated folding‐unfolding events. The deformable conductors double their electrical resistance at 12% strain and are washable without changing their electrical properties. The conductivity–strain behavior is modeled by considering the nanofiller separation upon deformation. To boost the conductivity at higher strains, the production process is adapted by stretching the nitrile substrate before spraying, after which it is released. This adaption meant that the electrical resistance doubles at 25% strain. The electrical resistance is found sufficiently low to give a 1.9 dB µm−1 shielding in the 8–12 GHz electromagnetic band. The physical and electrical properties, including the electro magnetic screening, of the flexible conductors, are found to deteriorate upon cycling but can be recovered through reheating the coating.

Superhydrophobic and high-flashover-strength coating for HVDC insulating system

In high voltage power equipment especially those for outdoor applications, the surface of dielectrics suffers from various problems such as flashover, raining, contamination, and ultraviolet illumination, which becomes the weak link in the whole insulating system. However, a high-throughput, flexible, and low-cost approach to simultaneously improve these properties of surface insulation was not reported yet. Here, a “binding polymer + nanofillers” based multifunctional nanocoating was fabricated by spray-coating of ZnO particles and multiwalled carbon nanotubes (MWCNT) dispersed in a poly(dimethylsiloxane) (PDMS) elastomer solution. The ZnO/MWCNT/PDMS coating plays multiple roles including inhibiting charge injection from electrodes due to the introduced deep interfacial traps, accelerating charge dissipation for the enhanced surface conductivity, and forming a micro-nanoscale hierarchical surface structure. As a result, the coatings endowed various dielectric materials such as epoxy resin, polymethyl methacrylate and silicone rubber with multifunctionality of high DC flashover strength (maximum 54% flashover voltage increase), superhydrophobic surface (water contact angle >150°), self-cleaning capability, good abrasive resistance, ultraviolet-resistance, and anti-icing performances. The ZnO/MWCNT/PDMS coating is well suitable for the surface modification of dielectrics in both indoor and outdoor HVDC insulating system. The present approach provides a new insight for simultaneously improving the multiple surface properties of dielectric insulation.

Superhydrophobic Cellulose Paper‐Based Triboelectric Nanogenerator for Water Drop Energy Harvesting

AbstractThe high‐efficiency conversion of water drop mechanical energy into electrical energy has always been an urgent issue in the development and utilization of raindrop energy. In this work, a novel drum‐like triboelectric nanogenerator (D‐TENG) with robust self‐cleaning superhydrophobic features is developed to harvest water drop energy. An elastic superhydrophobic cellulose paper is created by spray‐coating nanofumed silica dispersed in a thermoplastic elastomer solution, followed by treatment with triethoxy‐1H,1H,2H,2H‐tridecafluoro‐n‐octylsilane. When raindrops hit the D‐TENG surface, the superhydrophobic cellulose paper will vibrate and periodic contact and separation with polytetrafluoroethylene will occur to generate electricity. The results demonstrate that when a 6 mm water drop falls from a height of 2.5 m and hits the D‐TENG, the generated voltage output can reach a peak of 21.6 V and charge transfer of 10 nC. The output power of the D‐TENG can reach 16 µW per droplet, which is more than 13.3 times that generated from the previous TENGs based on the electrostatic induction of water droplets. These results indicate that the superhydrophobic cellulose paper‐based D‐TENG is potentially a strong candidate for harvesting energy from raindrops, thereby making it a promising sustainable energy source for next‐generation electronics.

The technique of automated applying of polymer coatings used for repair of tractor parts

Restoration of case parts of machines significantly reduces the cost of their repairing. The present paper proposes a method for restoring case parts using the repair size method. Depending on wear degree, the fitment holes are bored to three repair sizes. The prepared hole is inserted with a new bearing, the outer ring of which is covered with a polymeric coating of the appropriate thickness ensuring the fixity of the joint. As a result of theoretical studies, the model was obtained for the formation of a uniform polymer coating on the outer surface of a rotating cylindrical part. The facility and technological equipment were developed for applying a polymer coating of F-40C elastomer solution onto the outer surface of the rotating bearing. The facility includes screwing lathe 1K62, centering drift pin, bath and magnetic holder MV-V. The holder is designed for mounting a bath filled with polymer solution and its plunging movement when rolling bearings are immersed in polymer solution. The drift pin serves for centering and assembling bearings. The assembled drift pin is inserted into the chuck of the machine rotating the pin when applying polymer coating. The screwing lathe 1K62 is equipped with an INNOVERT frequency converter of H3400A05D5K type, which allows adjusting infinitely the spindle speed from 0 min-1. The paper presents the results of experimental studies on the F-40C elastomer shrinkage, the parameters of the mode of immersing parts into its solution, the dependence of the geometric parameters of the formed polymer coating on the components of application and adhesion modes for polymer coatings based on F-40C elastomer solutions of different viscosity. The acceptable thickness of the polymer coating of elastomer F-40C on the bearing 209, ensuring the non-failure operation of the restored seating with a cyclic radial load of 20 kN is 0.1 mm.

Coaxial Printing of Silicone Elastomer Composite Fibers for Stretchable and Wearable Piezoresistive Sensors.

Despite the tremendous efforts dedicated to developing various wearable piezoresistive sensors with sufficient stretchability and high sensitivity, challenges remain pertaining to fabrication scalability, cost, and efficiency. In this study, a facile, scalable, and low-cost coaxial printing strategy is employed to fabricate stretchable and flexible fibers with a core–sheath structure for wearable strain sensors. The highly viscous silica-modified silicone elastomer solution is used to print the insulating sheath layer, and the silicone elastomer solutions containing multi-walled carbon nanotubes (CNTs) are used as the core inks to print the conductive inner layer. With the addition of silica powders as viscosifiers, silica-filled silicone ink (sheath ink) converts to printable ink. The dimensions of the printed coaxial fibers can be flexibly controlled via adjusting the extrusion pressure of the inks. In addition, the electro-mechanical responses of the fiber-shaped strain sensors are investigated. The printed stretchable and wearable fiber-like CNT-based strain sensor exhibits outstanding sensitivities with gauge factors (GFs) of 1.4 to 2.5 × 106, a large stretchability of 150%, and excellent waterproof performance. Furthermore, the sensor can detect a strain of 0.1% and showed stable responses for over 15,000 cycles (high durability). The printed fiber-shaped sensor demonstrated capabilities of detecting and differentiating human joint movements and monitoring balloon inflation. These results obtained demonstrate that the one-step printed fiber-like strain sensors have potential applications in wearable devices, soft robotics, and electronic skins.

Use of coffee grind with cocoa shell as the basis for a filter to reduce lead from contaminated water from a river, Peru

The purpose of this research was to evaluate the efficiency of coffee grind residues with cocoa shell as the basis for a filter to reduce lead from the contaminated water of the Chirino River, San Ignacio - Cajamarca, 2018. Providing a method of low cost and without the use of large-scale technologies, by taking advantage of the organic waste mentioned above, thus improving its final disposal. The experimentation was carried out in a conventional design system, where the placed filter presented a spongy structure containing 60% of coffee borage with cocoa shell applied in three different doses (15g coffee grind with 15 g cocoa shell, 10g coffee grind with 20g cocoa shell and 20g coffee grind with 10 g cocoa shell) and 40% of sugar in silicone elastomer solution; having bioadsorbent properties to reduce metals. The sampling point and the amount of sample in liters was for convenience, evaluating the concentration of Lead present in the water of the river Chírinos in the stages of pre-treatment and post treatment. The results obtained with respect to the efficiency to reduce Lead of the three doses applied coded with T-1, T-2 and T-3 were 77.1%, 98.53% and 87.36% respectively; being the most efficient T-2 contiendo the dose of 10g coffee grind with 20g cocoa shell, without the need to add a chemical activator, making the application friendly with the environment.

A Superhydrophobic Smart Coating for Flexible and Wearable Sensing Electronics.

Superhydrophobic surfaces have shown versatile applications in waterproofing, self-cleaning, drag reduction, selective absorption, etc. The most convenient and universally applicable approach to forming superhydrophobic surfaces is by coating; however, currently, superhydrophobic, smart coatings with flexibility and multiple functions for wearable sensing electronics are not yet reported. Here, a highly flexible multifunctional smart coating is fabricated by spray-coating multiwalled carbon nanotubes dispersed in a thermoplastic elastomer solution, followed by treatment with ethanol. The coatings not only endow various substrate materials with superhydrophobic surfaces, but can also respond to stretching, bending, and torsion-a property useful for flexible sensor applications. The coatings show superior sensitivity (gauge factor of 5.4-80), high resolution (1° of bending), a fast response time (<8 ms), a stable response over 5000 stretching-relaxing cycles, and wide sensing ranges (stretching: over 76%, bending: 0°-140°, torsion: 0-350 rad m-1 ). Moreover, multifunctional coatings with thicknesses of only 1 µm can be directly applied to clothing for full-range and real-time detection of human motions, which also show extreme repellency to water, acid, and alkali, which helps the sensors to work under wet and corrosive conditions.

Production technology of metallopolymer rolling bearings

Results of experimental studies of applying modes and mechanical treatment of coatings from F-40S elastomer solution on rolling bearings are considered. The experimental data confirm the correctness of the coating formation model from elastomer solution on the outer rotary ring of a bearing. A technology of mechanized applying of coatings from F-40S elastomer solution on rolling bearings developed by generalizing the research materials is presented.

Theoretical aspects of polymer coatings formation from elastomer solutions when infrared drying

The great scientific and practical interest has the study of infrared processing of polymer coating from elastomer solutions in order to reduce porosity and improve the quality of coatings. This paper proposes a method of infrared drying of polymer coatings from elastomer solutions on the holes in housing part. Literature analysis allowed making the choice of optimal wavelength and finding the most suitable type of transducer. The efficiency of the two-stage heat treatment comparing to tradi-tional single-stage is shown.

Fabrication of a model continuously graded co-electrospun mesh for regeneration of the ligament–bone interface

Current scaffolds for the regeneration of anterior cruciate ligament injuries are unable to capture intricate mechanical and chemical gradients present in the natural ligament–bone interface. As a result, stress concentrations can develop at the scaffold–bone interface, leading to poor osseointegration. Hence, scaffolds that possess appropriate mechano-chemical gradients would help establish normal loading properties at the interface, while promoting scaffold integration with bone. With the long-term goal of investigating regeneration of the ligament–bone interface, this feasibility study aimed to fabricate a continuously graded mesh. Specifically, graded meshes were fabricated by co-electrospinning nanohydroxyapatite/polycaprolactone (nHAP-PCL) and poly(ester urethane) urea elastomer solutions from offset spinnerets. Next, mineral crystallites were selectively deposited on the nHAP-PCL fibers by treatment with a 5× simulated body fluid (5× SBF). X-ray diffraction and energy-dispersive spectroscopy indicated calcium-deficient hydroxyapatite-like mineral crystallites with an average Ca/P ratio of 1.48. Tensile testing demonstrated the presence of a mechanical gradient, which became more pronounced upon treatment with 5× SBF. Finally, biocompatibility of the graded meshes was verified using an MC3T3-E1 osteoprogenitor cell line. The study demonstrates that graded meshes, for potential application in interfacial tissue engineering, can be fabricated by co-electrospinning.

SU‐FF‐I‐127: Patient Specific Angiography Phantoms for Investigating New Endovascular Image‐Guided Interventional (EIGI) Devices

Purpose: To provide patient‐specific phantoms for investigating new endovascular image‐guided interventional (EIGI) devices such as stents. Methods and Materials: A human cerebral/saccular aneurysm phantom was constructed from a patient's segmented CT‐scan data. The CT‐derived vascular lumen was converted to a standard stereolithography (STL) computer file which was used, through a rapid‐prototyping process, to make a plastic resin (Accura 25) mold of the vessel with the aneurysm. In this process, an ultraviolet laser is used to selectively cure a liquid plastic layer by layer resulting in a highly accurate and very detailed positive model. RTV silicone is placed around this plastic aneurysm, allowed to cure, and then cut in half to create a mold with a cavity in the shape of the aneurysm. This mold is used to make a wax replica of the human aneurysm. The wax replica is then immersed in a silicone elastomer solution, the bubbles removed via vacuum, and the elastomer allowed to cure. The wax is then dissolved using boiling water. Results: The finished product is a clear elastomer model with a patient‐specific aneurysm cavity that may be used in both x‐ray and optical flow experiments. Multiple identical elastomer phantoms can be generated from one mold so that new EIGI devices such as an asymmetric stent with a low porosity patch region to occlude aneurysmal flow can be variously deployed under fluoroscopic guidance and evaluated angiographically. Additionally, the effects of contrast media can be studied by comparisons with optical flow studies. Comparisons of angiographic and optical time‐density curves for an anterior cerebral artery with multi‐lobular aneurysm will be presented. Conclusions: We have developed a unique system for the creation of realistic patient‐specific phantoms which enable the evaluation of detailed vascular flow and experimental EIGI treatment techniques for clinically representative pathology.(Support: NIH R01‐NS43924, R01‐EB002873, Toshiba Corp.).

Organoclay–natural rubber nanocomposites synthesized by mechanical and solution mixing methods

AbstractThis investigation describes two methods to obtain rubber composites based on natural rubber (NR) and organophilic layered silicates. In order to improve the exfoliation and compatibilization of the organoclays with the rubber matrix, a new approach which involves swelling of the organoclays with an elastomer solution prior to compounding has been used. The effect of the addition during swelling of a coupling agent, namely bis(trietoxysilylpropyl)tetrasulfan (TESPT), on the behaviour of the composites was also investigated. The results show that a low amount of organoclay (10 phr) significantly improves the properties of natural rubber. This suggests a strong rubber–organoclay interaction which is attributed to a high degree of rubber intercalation into the nanosilicate galleries, as was confirmed from X‐ray diffraction. In addition, an ulterior improvement in the properties of the nanocomposites prepared by solution mixing is clearly observed, due to the better filler–rubber compatibility. An even further increase in the properties is observed by treating the silicate with a silane coupling agent. The silane functional groups modify the clay surface, thus reducing the surface energy, and consequently improving the compatibility with the rubber matrix. Copyright © 2004 Society of Chemical Industry

Evaluation of rheological behaviour of some thermoplastic polyurethane solutions

In this paper some rheological properties of two type of thermoplastic polyurethane elastomer solutions are presented. For preparation of these solutions we utilized dimethylformamide as solvent. The concentration values and temperature of the polyurethane solutions was ranged between 7% and 15%, and respectively 30–60°C. Rheological measurements were effectuated with a rotating viscosimeter (Rheotest-2, Germany). Processing of experimental results give off the material constant value (k) and the extremities viscosity ( η 0 and η ∞). These values were verified with some rheological models. Interpretation of rheological properties by Cross model proof that the solutions belong to the pseudoplastic category (viscosity decreasing with increasing shearing rate).