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Abstract
Research subject: In this research, epoxy modification was successfully performed by polyurethane and its effect on abrasion and adhesion properties have been investigated. The most important concern in the blending of these polymers was the formation of gels upon exposure of epoxy resin and isocyanate in polyurethane.
Research approach: One solution to overcome this problem is to control the chemical activity of Isocyanate. Therefore to reduce the chemical activity of isocyanate and prevent gel formation due to the combination of epoxy and polyurethane, first polyurethane prepolymer containing 3.58 wt.% NCO was prepared by mixing poly tetra methylene glycol 2000 (PTMG 2000) and toluene di isocyanate (2,4-TDI); and then by adding 20 wt.% of it to the epoxy resin, the curing process was completed by using dimethyl thio-toluene di amine (DMTDA) as a common curing agent and also specific heat treatment.
Main results: Fourier transformation infrared spectroscopy results showed that the modification process has been successful by elimination of the peaks related to epoxide and isocyanate groups in the prepared sample in addition to the formation of a broad peak related to secondary hydroxyl group (C-O) due to the opening of epoxide rings. Pull off tests also confirmed increasing adhesion to carbon steel substrate as a result of secondary hydroxyl generation through this blending. Although, the Persoz hardness of modified epoxy decreased by 5%, but with a 17-fold reduction of elastic modulus (as per tensile test result), abrasion resistance improved 6 times according to abrasion test. Finally, joining of the cavities to each other is introduced as the abrasion mechanism by considering the field emission- scanning electron microscope images.

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Research subject: In recent years, several studies have been performed for improving the adhesion properties of polyurethane and acrylic pressure-sensitive adhesives (PSAs). Generally, polyurethane PSAs are of higher shear strength, while acrylic PSAs have higher tack. This research is a feasibility study of exploiting the properties of both of these adhesives through a simple blending method, and the adhesion properties were evaluated.
Research approach: First, acrylic copolymer (Ac) consisting of 82 vol. % butyl acrylate and 18 vol. % methyl methacrylate was solution polymerized. On the other hand, a thermoplastic polyurethane (TPU) containing 17.5 wt. % hard segment was prepared by bulk polymerization. Blending of these two polymers was performed by solution mixing. Solutions of the pure polymers and their blends at different contents were cast on polyethylene terephthalate backing and dried at room temperature. Fourier transform infrared spectroscopy, gel permeation chromatography, and differential scanning calorimetry were used to identify TPU and Ac. Loop tack, static shear strength, dynamic mechanical behavior, contact angle of sessile drop, morphology, and haze of the PSAs were evaluated.
Main results: Tack of the acrylic PSA was higher than TPU PSA. Tack of the blend PSAs containing 20, 40, and 60 wt. % TPU was higher than the pure components and that of the blend containing 40 wt. % TPU was maximum. This blend demonstrated the lowest water contact angle compared to the other blends and the shortest relaxation time compared to the pure polymers, which resulted in better wetting and higher tack. The shear strength of the PSAs increased with increase in the content of TPU to higher than 40 wt. % in the blends compared to the acrylic PSA; so that the pure TPU showed the highest modulus at various frequencies and hence exhibited high-shear PSA characteristics in the Chang’s viscoelastic window and the highest adhesion strength. The immiscibility of the blends was confirmed by measuring the haze and calculating the Hansen solubility parameter.

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In this research, microcellular thermoplastic polyurethane foams are investigated as an absorbing material in the X-band                (8.2-12.4GHz) frequency range by means of numerical analysis and experiment. In the frame of this work, we aim at establishing relationships between the foams morphology including cell size and air volume fraction and their radar absorbing properties. We therefore first describe numerical method and modelling. Then numerical analysis of microcellular foams in various cell sizes and air volume fractions are explained. Then design basis and preparation of nanocomposite foams of various morphologies using supercritical carbon dioxide (scCO₂) as physical foaming agent are presented. After measuring the S-Parameters of the samples by VNA, numerical and experimental results are compared and finally we establish structure/properties relationships that are essential for further optimizations of the materials for the radar absorbing applications.  

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In this study, the numerical and experimental study of energy absorption and deformation of thinwalled tubes with square geometry and circular cross under impact loading is studied. The purpose of this study was to investigate the effect of geometry on the energy absorption of aluminum tubes and the effect of foam filled tubes to absorb more energy under transverse impact. In the experimental part, the tubes of aluminum in form of hollow and filled with solid polyurethane foam prepared and then the quasi-static tests with static and dynamic loading rates by drop hammer have been performed on samples with different energy and the acceleration-time diagrams in each test is obtained. In the last part of this study simulation of the phenomenon of transverse impact on thin sections was carried out with the ABAQUS software. The discussion and conclusions of this study, the results of experimental tests carried out by the author of the thesis has been compared with the results of numerical analysis show a good agreement(difference below twenty percent). Finally, it was concluded that with regard to material of structure, at high energies square tubes have 50 percent specific energy absorbed higher than circular tubes and filled tubes have 20 percent specific energy absorbed higher than hollowone's. And transverse displacement of the hollow tube and circular tube is always higher than the filled tube and square tube.

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This article investigates energy absorption capacity and plastic deformation of lateral flattening process on an aluminum profile with special cross-section under the lateral compressive loading in the quasi-static condition by experimental method. The profile section is a circular tube with two symmetric longitudinal grooves. Different samples with various lengths and outer diameters in three different filling conditions consist of empty, core-filled and full-filled by polyurethane foam were prepared. Some specimens with the same geometry and filling condition but, with different loading angles of 0, 30, 45, 60 and 90o respect to symmetric line of two longitudinal grooves, were laterally compressed. Effects of various parameters such as profile length, outer diameter, three different filling conditions, and loading angle are investigated on lateral loading and specific absorbed energy. Experimental results show that specific absorbed energy is independent of specimen length. At the same displacement, when diameter of samples increases compressive loading decreases. Also, in zero loading angle, presence of the filler enhances lateral load; and consequently, increases specific absorbed energy by the structure. In viewpoint of the design of an energy absorber design, optimum specimen is full-filled profile under a loading angle equal to zero. However, if due to some design limitations, assembling the special profile with loading angle of zero is impossible, assembling the structure in empty condition with loading angle of 90o can be the next suggestion. Experiments show that the highest specific absorbed energy occurs in the profile with different diameters under loading angles of zero and 90o.

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It is inevitable to replace the tissues and organs that were disrupted due to trauma or various diseases. One of the methods that can help to speed up the regeneration of wounds is to improve the technology of wound dressings. In the current research, by using the properties of polyurethane nanofibers and improving their properties with additives including graphene oxide, selenium nanoparticles, and henna plant extract, it was aimed to improve the performance of wound dressings. After finding the optimal concentration for the electrospinning machine, DMSO solution containing 12 wt.% polyurethane was used to produce wound dressing nanofibers. The images from scanning electron microscope (SEM) confirmed the production of uniform scaffolds composed of polyurethane nanofibers. Antibacterial properties and mechanical properties of the fabric were studied to check the performance of the manufactured fabric as a wound dressing. For the PU-GO-Se-Henna composite sample, the antibacterial activity against two bacteria, S.aureus and E.coli, was 3.26 and 2.85, respectively, which indicates the very attractive antibacterial properties. This sample reached a tensile strength of 92 MPa in the tensile test, which showed a 104% increase in strength compared to the pure polyurethane sample.
 

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Reduction of unwanted noises is an important issue in the current societies regarding their potential negative impact on the mental and physical health of the peoples. Researchers are trying to find a new method to reduce the damage of this unwanted sound. Accordingly, the use of sound absorbing materials with appropriate acoustic properties has increased in the recent years. In this article, the production of polyurethane foam explained first and sound absorption coefficient of pure PUF has been measured. In order to improve the mechanical and acoustical properties of polyurethane foam, various quantities of Nano-Alumina powder is added to the structure of the foam. The effects of this additive material on the acoustic and mechanical properties of the foam are then measured. In this work, for the first time, the mechanical, physical and acoustical properties of the polyurethane foam improved by Nano-Alumina are studied. Finally, the change of the sound absorption coefficient of the produced composite material is analyzed based on the mechanical and physical experimental results. The sound absorption coefficient of this foam is then measured using two microphone method with Impedance tubes.

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In this paper, concentrated and distributed compressive loading quasi-static tests were conducted on sandwich structures with empty and foam filled honeycomb core. The sandwich structure used in this research were formed by aluminum plate and aluminum 5052 honeycomb structure. Foam used to fill the honeycomb structure was polyurethane foam with a density of 137.13 kg / m3.Concentrated loading quasi-static tests were performed by flat ended penetrator with a diameter of 10 mm and universal machine. Also distributed loading quasi-static tests were carried out by universal machine. In distributed loading, force is applied uniformly to the entire structure surface. Displacement rate was 2 mm/min for both types of loading. The purpose of this paper was to study the filler material effect on energy absorption and destruction shape of sandwich structure, as well as comparison of the two types of loading in unfilled and foam filled honeycomb core sandwich panels. The results of quasi-static tests showed that filler material has positive effects on increasing energy absorption in both concentrated and distributed loading. Polyurethane foam as filler material of honeycomb structure used in sandwich panel core increase specific absorbed energy of sandwich panel with foam filled core proportion to empty honeycomb core sandwich panel structure in concentrated and distributed loading by 6% and 29% respectively.

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Objective: In order to improve the water solubility and bioavailability of curcumin in cancer therapy, we prepared and tested a novel waterborne cationic polyurethane (PU) as a nano-carrier for curcumin loading (CU-PU). We studied the effect of this prepared nano-drug on melanoma (F10B16) and fibroblasts cells (L929). Methods: Morphology, size and cell internalization ability of the prepared nanoparticles were analyzed by zetasizer, SEM, AFM and fluorescent microscopy, respectively. We anticipated that curcumin was loaded in the hydrophobic core of the PU carrier. Next, the suitable dose and therapeutic effects of CU-PU for both skin cancer and normal cell lines were evaluated by the MTT assay and real-time PCR. Results: The average diameters and polydispersity of the nanoparticles were 62.37 ± 1.7 nm and 0.080 ± 2.1 at 25 ̊C, respectively. The drug encapsulation efficiency was 87 ± 0.2%. The morphological analysis confirmed both a spherical shape and good dispersion without remarkable aggregation. The MTT assay results showed that the IC50 at 24 hours was 36.2 µM, whereas it was 25.4 µM at 48 hours. Real-time PCR results indicated that the CU-PU significantly decreased mRNA expressions of VEGF, Bcl-2, MMP-9 and COX-2 genes. An increase in mRNA expression of the BAX gene was also observed. Conclusion: Our result provided acceptable evidence for cell proliferation inhibition and the apoptotic effect of CU-PU on skin cancer cells. There were no adverse effects detected for normal cells.

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This article investigates energy absorption capacity and plastic deformation trend of lateral flattening of an aluminum profile with H-shaped cross section under the quasi-static lateral loading by experimental, numerical and theoretical methods. Samples were prepared with different lengths and three different filling conditions including empty, core-filled and perfectly-filled by polyurethane foam. In addition, samples with the same geometry and filling conditions were laterally compressed with loading angles of 0 and 90 degree. Effect of some parameters such as length, three different filling conditions and loading angle were experimentally investigated on lateral force and specific absorbed energy (SAE). The results show that SAE is independent of samples length. At the loading angle of 90 degree, presence of the filler causes increment of SAE by the structure. Using the perfectly-filled profile under the loading angle of 90 degree is the most optimum condition. Based on two different energy absorption mechanisms, a theoretical equation was derived to estimate total absorbed energy (TAE) by empty sample with loading angle of zero; and predicted results were compared with the experimental samples. Due to present limitations in preparing the samples with different geometrical dimensions, nonlinear ABAQUS software was employed. Some samples with different wall thicknesses were modeled and influence of thickness was investigated on TAE. TAE is directly correlated to the second power of wall thickness; and this relationship can be clearly understood from the theoretical equation and numerical results. High correlation of experimental, numerical and theoretical results indicates precision and accuracy of the performed research.

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In this research, influence of foam filling technique in sandwich beams with expanded metal sheet as core by using lightweight rigid polyurethane foam is investigation. Relationships between the force and displacement at the midspan of the sandwich beams are obtained from the experiments. Three types of Steel lattice cores both bare and foam-filled were subjected to quasi-static. The performance of sandwich structures with expanded metal sheets as core were studied under transverse bending. In the following, by studying the orientation of the core layers to evaluation the impact parameters, including Specific Energy Absorption (SEA) as discussed testing purposes. the energy absorbing system can be used in the aerospace industry, shipbuilding, automotive, railway industry and elevators to absorb impact energy. experimental results showed that foam filling technique can significantly increase specific absorbed energy. Results of three point bending crushing tests showed that the SEA of foam-filled sandwich beam increased by 74 %, comparing to the hollow beam. Also, appropriate orientation of core in the sandwich beam caused to increase the specific energy absorption by 66.5%. Finally, appropriate geometric parameters and the best examples of criteria considered with respect to the objectives, are introduced.

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In this paper, experimental investigation and regression analysis on plastic deformation of polyurethane composite sandwich panels reinforced with nanoclay under blast loading is investigated. For this purpose, polyurethane sandwich panels with different percentages of nanoclay and in different densities were prepared. The mechanical properties of nanoclay-reinforced foams were studied by tensile-compression test. Explosive shock tube device and C4 explosive material were used for explosive loading. Then, in order to investigate the effect of significant parameters such as the percentage of nanoclay and density of polyurethane foam on the displacement of composite sandwich panels and optimizing them for minimum deformation, the response surface methodology was used. The results obtained from the regression model at 95% confidence level indicate a very good agreement between the experimental results and the values ​​predicted by the model. The high value of the correlation coefficient between the studied parameters and the amount of plastic deformation of the sandwich panel (R² = 99%) indicate that the proposed model has a higher accuracy. Finally, the optimal conditions for achieving the minimum displacement of composite sandwich panels were determined as 1.57% nanoclay content and foam density of 130 kg/m³.

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Metal faced Polyurethane/Polyisocyanurate sandwich panels are used in construction sites and temporary accommodation especially after destructive events such as flooding and earthquake, that a clear example was the temporary settlement of earthquake victims after earthquake occurrence in the Kermanshah province at November 2017. However, flammability of polyurethane foam core of these panels and the higher risk of fire in these types of buildings, highlight the importance of assessing fire performance of these panels.In this study, fire performance of several types of metal faced sandwich panels with PUR/PIR foam core produced in the country, was evaluated by reaction to fire and fire resistance tests. The reaction to fire behavior of foams was also evaluated separately. The results showed that the polyurethane foam was not fire retarded and met reaction to fire class F; but the poly-isocyanurate foam depicted a better fire behavior and met fire class E. Fire resistance tests were performed on common types of sandwich panels in the temporary buildings with two different execution details including a steel sheet fixed to the joint position in the panels and the other, fireproof paint and their fire performance was compared to unprotected panel. According to the results, deformation of the joint in sandwich panel is the main disadvantage and it is very critical in real fire due to flame spread through the joints which is critical in a real fire incident, when evacuating the occupants and acting fire brigades. Hence, protection of the joints by insertion of a protective sheet, increases fire resistance and improves the integrity by increasing the time by 40 minutes compared to the unprotected panel. Finally, fire safety recommendations were provided for the safe use of these panels in temporary buildings.
 

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