Papers by Keyword: Polyurea

Abstract: In current days, sandwich structures have become popular due to their flexibility with design requirements and excellent performance under extreme loads, such as blast. There are different strategies for enhancing the blast resistance of such sandwich structures. Including an additional layer of polyurea and stiffeners are widely used techniques that may enhance the performance of the panels under high-rate loadings. In this study, the effects of polyurea and stiffeners on the protection of a steel and aluminum foam sandwich panels is studied. Effective configuration of the panels with both polyurea and stiffeners are investigated. Here, different configuration cases of the sandwich panels: (a) panel without polyurea and stiffeners, (b) with polyurea applied on the rear face, (c) with stiffeners applied on the rear face, and (d) with stiffeners and polyurea on the rear face are investigated and compared. The finite element models of sandwich panels are developed, where steel facesheets, steel stiffeners, and polyurea are modeled with shell elements, and aluminum foam core is modeled with solid elements. Elastic-plastic, crushing foam, and hyperelastic material behaviors are implemented for steel, aluminum, and polyurea layers of the sandwich panels, respectively. The performance of the different configurations of the panels are compared in terms of the response quantities, i.e., deformation, equivalent von-Mises stresses, and energy absorption. Moreover, the damage patterns with fragmentation effect are depicted for all the considered sandwich panels. The results of the study show that both polyurea and stiffeners are the most effective configurations in protecting the sandwich structures; however, with the same thickness of polyurea and stiffener, the stiffeners show better performance than polyurea against blast load. Furthermore, it is observed that the deflection values across the configurations follow a logarithmic decay pattern.

Abstract: The blast that caused from terrorist activities, explosion and weapons effect on not only the human life, but also the architectural structure. The development of materials used to protect them is needed. Polyurea is a one type of elastomer that derive from the reaction product of an isocyanate component and a synthetic resin blend component through step-growth polymerization. It is revealed that polyurea is a new entrant in the field of elastomer has received enormous attention in view of its excellent blast mitigation properties and ballistic protection. In this work, the microstructure and elemental composition of polyurea samples are studied using scanning electron microscope coupled with energy dispersive X-ray spectrometer (SEM-EDS). The main composition consisted of carbon, oxygen and silica approximately 63-75, 17-29, and 0.15-1.69 wt%, respectively. Sulfur and chlorine present as the chain extender. Titanium is added to modify its structure. Other elements present as the additives, fillers and pigments. Atomic force microscopy (AFM) is conducted to confirm nano-scale composition. Dynamic mechanical, thermal and tensile properties are also studied. It is shown that the modulus and loss factor increase as the increasing of the frequency and temperature. The elongation capacity is greater than 100%. Infrared spectroscopy based on synchrotron radiation (SR IR) shows the various constituents of the composition in the form of the functional groups along with the wave number.

Abstract: The effectiveness of preploymer and 1,6-Hexamethylene diamine encapsulated by double-walled microcapsules based polyurea (PUA) was explored for healing the cracks generated in epoxy coatings. Double-walled microcapsules were systhesized by interfacial polymerization at the interface between the prepolymer droplets and the 1,6-Hexamethylene diamine droplets to form the polyurea shell. The effect of synthetic stirring speed on the morphology of the microcapsules was observed by scanning electronmicroscopy (SEM) and optical microscopy (OM). The chemical structure as well as the thermal properties and the core content were characterized by Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric analyzer (TGA) respectively. Electrochemical impedance spectroscopy (EIS) studies of the artificial scratched area showed that the coating containing 2wt% and 5wt% microcapsules could effectively prevent further corrosion of the coating with high corrosion resistance efficiencies of 61.61% and 45.99% after immersing for 144h in seawater.

Abstract: A new fiber (x) reinforced Dynamic Covalent epoxy-polyurea Interface (x-DC_EPI) shows good mechanical energy transferability of impact and vibration forces. The bonding property of x-DC_EPI interface, engendered between curing, or reactive, epoxy and dynamic polyurea, is controlled by epoxy curing time (t_c). The reaction of curing epoxy, where t_c is a thermodynamic processing parameter, and fast-curing/ dynamic aliphatic polyurea, which lacks polyol in its resin chain extender, is linked to bulk mechanical energy transfer, quantified specifically via the loss modulus of x-DC_EPI. The parameter t_c effectuates designable chemical bond properties within x-DC_EPI. Using Generalized Maxwell models, viscoelastic properties of epoxy, polyurea, and x-DC_EPI are predicted, and results are verified using Dynamic Mechanical Analysis (DMA). The Maxwell models for x-DC_EPI, as a function of t_c, are used in a finite element analysis (ABAQUS) to control performance of dynamically loaded structures.

Abstract: Polyurea coatings are very reactive and fast curing even at very low temperatures with exceptional mechanical properties, chemical resistance and durability. Polyurea spray coating technology is used to overcome the initial problems in surface coating such as substrate wetting,mixing and surface finish. The study deals with the analysis of morphology and tensile properties of polyurea coating. The polyurea sample is characterized by using SEM, FTIR and XRD in addition to EDAX to determine the microstructure and chemical composition. Finally Tensile Test was carried out to examine the ultimate tensile strength and young’s modulus of Polyurea using UTM.

Abstract: In recent years, polyurea has been successfully applied as a coating material for increasing the survivability of structures and components subjected to critical impact loading conditions. It was also shown that if a polyurea coating is reinforced with ceramic particles or short glass fibers, an enhanced benefit on the overall impact resistance due to the increased dissipation properties of the material can be observed. Notwithstanding the use of polyureas as coating materials for structures protection, other applications where control and damping of vibrations is of concern would benefit from the high dissipation characteristics of the reinforced elastomer. Nevertheless, there are well known drawbacks in the use of the reinforced elastomers which can be identified in their pronounced nonlinear behavior under cyclic loads and the softening of their mechanical properties. In order to investigate such a phenomenon, in this manuscript we present an experimental investigation conducted on the effects of different volume fractions of the same filler on the response of a polyurea elastomer at varying amplitudes of the applied strain. The characterization of the materials was conducted by using a dynamic mechanical analyzer (DMA). From our preliminary results we observed that in the case of polyurea reinforced with short glass fibers, the nonlinear response of the polymer at varying strain amplitudes becomes evident for fillers volume contents of 10%. Furthermore, the nonlinearity of the response of the material due to the Payne effect seems to be associated with the complex fibers-matrix interaction rather than the disruption of the agglomeration of the fillers under load.

Abstract: In this paper, paraffin/polyurea (PU) phase change microencapsules were prepared through an interfacial polymerization method using composite paraffin with solid/liquid mass ratio 3:7 as core materials, 2,4 toluene diisocyanate (TDI) and ethylenediamine (EDA) as monomers, NP-10 as an emulsifier. It was explored the effect of the monomer mass ratio m_EDA: m_TDI on the yield of hollow PU microcapsules, and the effect of core/shell ratio on the particle size and coating efficiency and storage-energy performance of paraffin/PU phase change microencapsules. The experimental results showed the PU yield is increasing with the increasing of EDA:TDI mass ratio until 0.5:1,then keeps the constant. Paraffin/PU phase change microencapsules prepared with the core-shell ratio of 2:1 have better performance: the melting point of 28.1°C, the enthalpy of 58.4KJ/Kg, encapsulation efficiency of 87.5%, the average particle size of 4.32μm, and the uniform particle size distribution.

Abstract: The polyurea was modified by adding different amounts of nanometer ZnO. The corrosion behavior of polyurea/primer composite coating system in wet-dry cyclic environment of 3.5% NaCl solution was studied by using the Electrochemical Impedance Spectroscopy (EIS) measurement and adhesion test technology. The experimental result showed that, different mass fractions of nanometer ZnO had different influences on the corrosion resistance property of coating. When the mass fraction of nanometer ZnO was 5%, the composite coating had the largest protective action. The corrosion resistance property of nanometer ZnO can be improved by increasing the density of polyurea coating, however, the corrosion resistance property of polyurea coating will be weakened in case of exceeding the critical adding amount.

Abstract: The corrosion mechanism of organic silicon modified polyurea composite coating under different CO₂ partial pressures was studied using high-temperature autoclave, combined with scanning electron microscopy (SEM), adhesion tests and electrochemical impedance spectroscopy (EIS) technology. The experimental results showed that: there was no corrosion product formed on the surface of coating sample after high-temperature high-pressure corrosion test, and with the increasing of CO₂ partial pressure, the coating adhesion and impedance values decline increases. Moreover CO₂ partial pressure increases accelerated the failure process of polyurea composite coating system.

Abstract: In this paper, Microencapsulated paraffin/polyurea (PU) phase change materials were prepared through an interfacial polymerization method using composite paraffin with solid/liquid mass ratio 3:7 as core materials, 2,4 toluene diisocyanate and ethylenediamine as monomers, NP-10 as an emulsifier. It was investigated the effects of emulsion speed, the amount of emulsifier and polymerization temperature on the particle size and coating efficiency and storage-energy performance of microencapsulated paraffin / PU phase change materials. The results showed when the emulsion speed is 2000r/min and the amount of emulsifier to core material is 6% and the polymerization temperature is 70°C, Microencapsulated paraffin / PU phase change materials have better performance: the melting point of 28.1°C, the enthalpy of 58.4KJ/Kg, coating efficiency of 87.5%, the average particle size of 3~4μm, and the uniform particle size distribution.