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In this study, a horizontal impact setup was used to measure the dynamic responses of specimens fixed on a reaction wall and subjected to repeated impacts generated by a large-tonnage impactor. The contact force, deformation process, energy absorption, and other properties of two specimens (a thin-walled steel tube and foam-filled steel tube) were thoroughly investigated. The results demonstrated that the thin-walled tube's properties were consistent with the four-phase and six-phase deformation models and that the foam-filled tube's properties were consistent with the two-phase deformation model. In the early stages of the experiment, the foam-filled and thin-walled tubes were similar in terms of the contact force and energy absorption. However, when the polyurethane (PU) strain reached 0.8, the PU significantly increased the support of the tubes, reduced the contact force (by extending the contact time), and increased the energy absorption capacity by 33.6-43.5%. The crush curves of the specimens were in agreement for cases involving multiple impacts, as well as for one impact with the same impact of kinetic energy. The crush curves can be used to assess the actual performance of crashworthy devices. Furthermore, after repeated impacts, the foam-filled tube exhibited a pseudo-shakedown behavior.

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Flexible polyurethane foams (PUF) are used in many consumer products. PUF may contain trace levels of aromatic diamine impurities that could represent a potential health risk. The risk associated with sleeping on a PUF mattress was evaluated. Toxicity benchmarks for sensitization and non-cancer endpoints were derived from the respective points-of-departure using standard assessment factors. For the cancer endpoints, toxicity benchmarks were derived from the 25th-percentile values of animal studies. Recently published emission and migration data allowed to link exposure with the CertiPURTM voluntary quality limits of ≤5 mg.kg-1 for 2,4-toluene diamine and 4,4'-methylene dianiline in PUF. Using conservative exposure scenarios, lifetime-average daily internal doses from the combined inhalation and dermal exposures were calculated. Margins of safety for non-cancer and sensitization endpoints were >104. The theoretical excess cancer risk was ≤1.5 × 10-7. It is concluded that sleeping on a mattress that satisfies the CertiPUR limit value does not pose undue risk to consumers.

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The discharge of crude petroleum oils and their derivatives poses serious environmental challenges, which can be mitigated through oil/water separation. In this study, polyurethane (PU)/polydopamine (PDA)/chitosan-graft (g)-octanal foam was prepared by immersing of PU foam in PDA and chitosan-g-octanal solutions. The fabricated PU foam exhibited thermal stability, flame retardancy, and hydrophobicity/superoleophilicity. The coated PU foam can selectively absorb heavy and light oils from dynamic and static oil/water mixtures. The maximum sorption capacity for olive oil was found to be as high as 41.48 g/g. PU/PDA/chitosan-g-octanal foam also demonstrated excellent flame retardancy and the ability to quickly extinguish fire, as confirmed by the limiting oxygen index (LOI) test.

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Polyurethanes are synthesized on industrial scale by the reaction of diisocyanates with diols in the presence of catalysts which are commonly based on tin complexes and amines. However, due to the toxicity and volatility of these tin catalysts and amines, there is the need to develop new catalysts that are more environmentally benign. Herein, we report the synthesis of O^N^O pincer-ligated Mn(III) and Fe(III) complexes that serve as suitable catalysts for urethane formation and are stable to hydrolysis as predicted by computations and observed experimentally. The O^N^O pincer scaffold is vital to the activity of these catalysts, simultaneously ensuring increased solubility in the reaction medium as well as providing a stable framework upon dissociation of co-ligands in the catalytic cycle. In silico mechanistic investigations for urethane formation show that the stabilization of active species in square-planar geometries enabled by these O^N^O ligands permit the simultaneous coordination of alcohol and isocyanate in suitable configuration at the metal center.

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Heavy metal ions are toxic to humans, plants, and marine life, making it crucial to eliminate them from water. This study reports the development of a new nanocomposite material (Alg@Ag/PU) that involves modifying silver nanoparticles (Ag NPs) with alginate (Alg) and coating them onto a polyurethane sponge (PU) for removing heavy metal ions. The successful coating of Alg@Ag NPs onto PU due to their strong chemical binding was confirmed by morphology and size characterization. Batch experiments were conducted to evaluate the removal efficiency of heavy metal ions at high concentrations (∼100 mg/L). The maximum adsorption amount was achieved within 6 h, and the highest removal efficiency was obtained at pH values between 6 and 7. Furthermore, the Alg@Ag/PU nanocomposite demonstrated excellent recyclability for metal ion removal even after 5 cycles. In summary, this work developed a simple and cost-effective method for producing an environmentally-friendly nanocomposite material for the efficient removal of heavy metal ions.

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In this study, a novel hybrid metamaterial has been developed via fulfilling hyperbolic chiral lattice with polyurethane (PU) foam. Initially, both the hyperbolic and typical body-centered cubic (BCC) lattices are fabricated by 3D printing technique. These lattices are infiltrated in a thermoplastic polyurethane (TPU) solution dissolved in 1,4-Dioxane, and then freeze casting technique is applied to achieve the PU-foam-filling. Intermediate (IM) layers possessing irregular pores, are formed neighboring to the lattice-foam interface. While, the foam far from the lattice exhibits a multi-layered structure. The mechanical behavior of the hybrid lattice metamaterials has been investigated by monotonic and cyclic compressive tests. The experimental monotonic tests indicate that, the filling foam is able to soften the BCC lattice but to stiffen the hyperbolic one, further to raise the stress plateau and to accelerate the densification for both lattices. The foam hybridization also benefits the hyperbolic lattice to prohibit the property degradation under the cyclic compression. Furthermore, the failure modes of the hybrid hyperbolic lattice are identified as the interface splitting and foam collapse via microscopic analysis. Finally, a parametric study has been performed to reveal the effects of different parameters on the compressive properties of the hybrid hyperbolic lattice metamaterial.

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In this study, nonwoven fabrics, rigid polyurethane foam (RPUF), Basalt woven fabrics, and an aluminum foil film mold are used to produce multi-functional composite sheets with flame-retardant, sound-absorbing, and electromagnetic-shielding functions. The nonwoven layer is composed of Nomex fibers, flame-retardant PET fibers, and low-melting-point (LMPET) fibers via the needle rolling process. The optimal Nomex fiber/flame-retardant PET fiber/LMPET fiber (N/F/L) nonwoven fabrics are then combined with rigid polyurethane (PU) foam, Basalt woven fabric, and an aluminum foil film mold, thereby producing nonwoven/rigid polyurethane foam/Basalt woven fabric composite sheets that are wrapped in the aluminized foil film. The test results indicate that formed with a foaming density of 60 kg/m3 and 10 wt% of a flame retardant, the composite sheets exhibit electromagnetic interference shielding efficacy (EMI SE) that exceeds 40 dB and limiting oxygen index (LOI) that is greater than 26. The efficient and highly reproducible experimental design proposed in this study can produce multifunctional composite sheets that feature excellent combustion resistance, sound absorption, and EMI SE and are suitable for use in the transportation, industrial factories, and building wall fields.

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This study proposes the composites with a sandwich structure that is primarily made by the multi-step foaming process. The staple material is polyurethane (PU) foam that is combined with carbon fibers, followed by a Kevlar woven fabric. The composites are evaluated in terms of puncture resistance, buffer absorption, and electromagnetic wave shielding effectiveness (EMSE). The manufacturing process provides the composites with a stabilized structure efficiently. Serving the interlayer, a Kevlar woven fabric are sealed between a top and a bottom layer consisting of both PU foam and an aluminum film in order, thereby forming five-layered composites. Namely, the upper and lower surfaces of the five-layered sandwiches are aluminum films which is laminated on a purpose for the EMSE reinforcement. The test results indicate that the PU foam composites are well bonded and thus acquire multiple functions from the constituent materials, including buffer absorption, puncture resistance, and EMSE. There is much prospect that the PU foam composites can be used as a protective material in diverse fields owing to a flexible range of functions.

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Today, most commercial polyols used to make polyurethane (PU) foam are produced from petrochemicals. A renewable resource, castor oil (CO), was employed in this study to alleviate concerns about environmental contamination. This study intends to fabricate a bio-based and low-density EMI-defending material for communication, aerospace, electronics, and military appliances. The mechanical stirrer produces the flexible bio-based polyurethane foam and combines it with nanoparticles using absorption and hydrothermal reduction processes. The nanoparticles used in this research are graphite nanoplates (GNP), zirconium oxide (ZrO2), and bamboo charcoal (BC). Following fabrication, the samples underwent EMI testing using an EMI test setup with model number N5230A PNA-L. The EMI experimental results were compared with computational simulation using COMSOL Multiphysics 5.4 and an optimization tool using response surface methodology. A statistical design of the experimental approach is used to design and evaluate the experiments systematically. An experimental study reveals that a 0.3 weight percentage of GNP, a 0.3 weight percentage of ZrO2, and a 2.5 weight percentage of BC depict a maximum EMI SE of 28.03 dB in the 8-12 GHz frequency band.

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The present paper illustrates a comparison of open-cell aluminum foams. The foams were fabricated by two different methods: spark plasma sintering and replication on a polyurethane template. The influence of pressure, temperature, and diameter of space holding material on foam obtained by the spark plasma sintering method was investigated. Additionally, the aluminum powder content in slurry and atmosphere during thermal processing of foam prepared by the replication technique were studied. The morphology and structure of obtained samples were analyzed by scanning electron microscopy and X-ray diffraction analysis. Supplementarily, mechanical properties and electrical conductivity were studied. The porosity of obtained samples was 83% for the SPS sample and 85% for the replication sample. The results of the studies carried out gave us an understanding that the SPS method is more promising for using the obtained foams as cathode current collectors in lithium-ion batteries due to excessive aluminum oxidation during sintering in the furnace.

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Development of green, efficient and profitable recycling processes for plastic material will contribute to reduce the expanding plastic pollution and microplastics accumulation in the environment. Polyurethanes (PU) are versatile polymers with a large range of chemical compositions and structures. This variability increases the complexity of PU waste management. Biological recycling researchers have recently demonstrated great interest in polyethylene terephthalate. The adaptation of this route towards producing polyurethanes requires the discovery of enzymes that are able to depolymerize a large variety of PU. A laccase mediated system (LMS) was tested on four representative PU models, with different structures (foams and thermoplastics), and chemical compositions (polyester- and polyether-based PU). Size exclusion chromatography was performed on the thermoplastics and this revealed a significant reduction in the molar masses after 18 days of incubation at 37 °C. Degradation of foams under the same conditions was demonstrated by microscopy and compression assay for both polyester- and polyether-based PU. This study represents a major breakthrough in PU degradation, as it is the first time that enzymatic degradation has been clearly demonstrated on a polyether-based PU foam. This work is a step forward in the development of a sustainable recycling pathway, adapted to a large variety of PU materials.

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Pedicle bone screws are one of the most critical materials used in spinal orthopaedic operations. Screw loosening and pull-out (PO) are basic complications encountered during or after surgery. Pull-out Strength (POS) of the bone is one of the significant parameters to understand the mechanical behaviour of a screw fixed to poor quality or osteoporotic bone. This study investigates how the POS of a pedicle screw is affected by the factors of the screw diameter and the polyurethane (PU) foam density by experimental analysis. In the experiments, two different diameter (5.5 and 6.5 mm) of conical pedicle screws and five different density (0.08, 0.16, 0.24, 0.32 and 0.48 g·cm-3) PU foams were used. According to the force-displacement curves obtained from experimental results, the POS increased with the increases in screw diameter and PU foam density.

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The non-selective property of conventional polyurethane (PU) foam tends to lower its oil absorption efficiency. To address this issue, we modified the surface properties of PU foam using a rapid solvent-free surface functionalization approach based on the chemical vapor deposition (CVD) method to establish an extremely thin yet uniform coating layer to improve foam performance. The PU foam was respectively functionalized using different monomers, i.e., perfluorodecyl acrylate (PFDA), 2,2,3,4,4,4-hexafluorobutyl acrylate (HFBA), and hexamethyldisiloxane (HMDSO), and the effect of deposition times (1, 5 and 10 min) on the properties of foam was investigated. The results showed that all the modified foams demonstrated a much higher water contact angle (i.e., greater hydrophobicity) and greater absorption capacities compared to the control PU foam. This is due to the presence of specific functional groups, e.g., fluorine (F) and silane (Si) in the modified PU foams. Of all, the PU/PHFBAi foam exhibited the highest absorption capacities, recording 66.68, 58.15, 53.70, and 58.38 g/g for chloroform, acetone, cyclohexane, and edible oil, respectively. These values were 39.19-119.31% higher than that of control foam. The promising performance of the PU/PHFBAi foam is due to the improved surface hydrophobicity attributed to the original perfluoroalkyl moieties of the HFBA monomer. The PU/PHFBAi foam also demonstrated a much more stable absorption performance compared to the control foam when both samples were reused for up to 10 cycles. This clearly indicates the positive impact of the proposed functionalization method in improving PU properties for oil absorption processes.

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Polyurethane foam (PU foam) is a new material which is being used in producing both macro-anatomical and micro-anatomical specimens. PU foam is simple to use, without need for special equipment. The present study was carried out to evaluate morphology of coronary sinus and its tributaries. During the study, we encountered few problems in carrying out injections. Coronary sinus and its tributaries were difficult to cannulate since the coronary sinus lacks a vascular stem, around which ligature can be tied before injection so that the cannula can be held in place. In contrast, in majority of the organs it is easy to inject since they possess tubular vascular stem to hold the cannula in place. A new device was developed which could be used to cannulate coronary sinus orifice to inject the casting media. The second problem we faced was saponification of adipose tissue. This made corrosion of the soft tissue difficult. Hence in this study, we describe the device we have developed to place in the coronary sinus orifice, and how saponified adipose tissue was taken care during the actual maceration step.

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Polyurethane foam (PU foam) is a new material which is being used in producing both macro-anatomical and micro-anatomical specimens. PU foam is simple to use, without need for special equipment. The present study was carried out to evaluate morphology of coronary sinus and its tributaries. During the study, we encountered few problems in carrying out injections. Coronary sinus and its tributaries were difficult to cannulate since the coronary sinus lacks a vascular stem, around which ligature can be tied before injection so that the cannula can be held in place. In contrast, in majority of the organs it is easy to inject since they possess tubular vascular stem to hold the cannula in place. A new device was developed which could be used to cannulate coronary sinus orifice to inject the casting media. The second problem we faced was saponification of adipose tissue. This made corrosion of the soft tissue difficult. Hence in this study, we describe the device we have developed to place in the coronary sinus orifice, and how saponified adipose tissue was taken care during the actual maceration step.

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Developing novel oil sorbents with both superhydrophobicity and flame resistance reveals an enticing prospect for oil/water separation. In this study, superhydrophobic foam with superior flame retardancy and sorption capability is reported through a simple one-step fabrication route in alkaline water/ethanol system containing dopamine, fly ash (FA) and dodecanethiol (DT). The introduction of FA endows the foam with excellent flame retardancy, and the as-prepared foam reveals improved flame resistance compared with original and polydopamine (PDA) coated foams, The obtained foams can quickly absorb various types of oils up to 34-47 times of their own weight, and the absorbed oils can be repeatedly recovered by a simple vacuum filtration process. The foams can also maintain their high hydrophobicity after long term immersion in different corrosive solutions and oils, and are able to be used for removing the oils from corrosive high-temperature water. More importantly, the foams with FA coating can effectively separate a broad range of oil-in-water emulsions with high efficiency (>93.0%). The outstanding separation property of the as-prepared foams and their eco-friendly, low-energy, and inexpensive fabrication process imply the great potential for oily wastewater treatment and oil spill cleanup.

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Barium titanate/nitrile butadiene rubber (BT/NBR) and polyurethane (PU) foam were combined to prepare a sound-absorbing material with an alternating multilayered structure. The effects of the cell size of PU foam and the alternating unit number on the sound absorption property of the material were investigated. The results show that the sound absorption efficiency at a low frequency increased when decreasing the cell size of PU foam layer. With the increasing of the alternating unit number, the material shows the sound absorption effect in a wider bandwidth of frequency. The BT/NBR-PU foam composites with alternating multilayered structure have an excellent sound absorption property at low frequency due to the organic combination of airflow resistivity, resonance absorption, and interface dissipation.

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The fabrication of pressure sensors based on reduced graphene oxide (rGO) as the sensing material is challenging due to the intrinsic hydrophobic behavior of graphene oxide inks as well as the agglomeration of graphene oxide flakes after reduction. Hydrazine (a reducing agent) and a dual-component additive comprising benzisothiazolinone and methylisothiazolinone in appropriate proportion were used to synthesize a rGO ink with a hydrophilic nature. Utilizing this hydrophilic rGO ink mixed with multiwalled carbon nanotubes (MWNTs), a very simple, low-cost approach is demonstrated for the fabrication of a pressure sensor based on polyurethane (PU) foam coated with the MWNT-rGO ink (MWNT-rGO@PU foam). The MWNT-rGO@PU foam-based devices are shown to be versatile pressure sensors with the potential to detect both small-scale and large-scale movements. At low pressure (below 2.7 kPa, 50% strain), the formation of microcracks that scatter electrical charges results in a detectable increase in resistance suitable for detecting small-scale motion. At a higher pressure, the compressive contact of the coated faces of the PU foam results in a sharp decrease in resistance suitable for monitoring of large-scale motion. Moreover, these sensors exhibit good flexibility and reproducibility over 5000 cycles. The versatility of this sensor has been demonstrated in a wide range of applications, such as speech recognition, health monitoring, and body motion detection. The significant advantages of this sensor are that its cost is low, it is easy to fabricate, and it has a versatility that renders it favorable to health-monitoring applications.

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Sound absorbing composites with stratified structures, including double-layer and sandwich structures, were prepared through the combination of nitrile butadiene rubber (NBR) and polyurethane foam (PUFM). The effects of the thickness ratio of layers, different stratified structures and the variety of fillers on the sound absorption performance of the NBR-PUFM composites and the sound absorption mechanism were studied. The results show that the NBR-PUFM composite with a sandwich structure and thickness ratio of 1:8:1 displays good sound absorption, which could be improved further by adding fillers. Because the airflow resistivity, resonance absorption, interface dissipation and interface reflection were combined organically in the sandwich structure, the composites show excellent low-frequency sound absorption performance. Moreover, the composite also has advantages in cost and functionalization aspects.

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Pressure ulcers influence people with limited mobility who must spend a long time lying or sitting because these positions create high interfacial pressure between the body and supporting materials. Supporting materials, such as mattresses and cushions, are designed to prevent pressure ulcers by increasing the contact area, reducing the interfacial pressure or reducing the contact time. Foam is the most common supporting material for relieving pressure because it is cheap and easy to change its shape to fit the contour of the body. Past studies showed that BMI, body position and supporting material properties have an impact on relieving pressure; however, there is no study of the main and cross-over effects among these parameters. This study aims to investigate the main and cross-over effects among BMI, body position and supporting material properties on pressure relieving performance using univariate ANOVA and correlation analysis. It was found that body position and foam density were the main effect and BMI and body position, and body position and foam density were the cross-over effects on pressure relief. It was also found that low density Polyurethane (PU) foam of less than 4 cm in thickness as well as the appropriate K2 and K3 moduli are best suited for pressure relief. The actual value of foam thickness and the appropriate K2 and K3 moduli are subject to BMI values and body position. The significance of the outcomes from this study is that it will aid in optimizing the design of supporting materials with varied BMI values and body positions to greatly reduce pressure ulcers for ailing patients.

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