Tailoring microwave absorption performance through foam density and filler localization in nickel-coated carbon filled polyurethane foams

In this paper, we present a kind of broadband absorbent material. The broadband absorbent material is designed based on topology optimization and tested. The optimizing of metamaterials with a genetic algorithm has become one of the most effective methods of designing metamaterials in recent years. An integral system with interactive simulation of MATLAB and CST Microwave Studio is developed, and the main program of genetic algorithm is written in MATLAB; with simulation and computation in CST the metamaterial is optimized by a genetic algorithm with power of global optimization. Vacuum assistant resin infusion process is a new cost-effective and high-performance process. The proposed radar absorbent material possesses a sandwich structure, which consists of transparent composite skin panel, resistive metasurface, polyurethane foam and reflective composite skin panel. The transparent composite skin panel is low-dielectric-constant glass fiber reinforced composite, which has excellent physical properties and weather resistant property. The core material is composed of low density polyurethane foam and metamaterials, which can well meet the requirements for weight reduction and the invisibility. The reflective composite skin panel is a low-resistance carbon fiber reinforced composite, which prevents the electromagnetic waves from transmitting and also provides electrical boundary conditions for metamaterial. Simulation and test results indicate that the reflectivity of the radar absorbent material is less than-12 dB in a range of 2-18 GHz. Because of the symmetrical structure design of the resistance film, the radar absorbent material is polarization-independent. We preliminarily produce a batch of radar absorbent materials and test their various performances. Such a radar absorbent material has a strong absorption and other properties such as light quality, high temperature resistance, low temperature resistance, humidity resistance and corrosion resistance. The radar absorbent material which has been widely used in the engineering field is easy to achieve the compatibility of absorption, mechanical properties and environmental performance. Compared with previous design method, the topology optimization design is simple in programming operation, good in generality, and short in design periode. The radar absorbent materials owns strong application value.

An environmentally friendly liquefaction of wood powder was prepared by atmospheric pressure liquefaction technology to replace the non-renewable petroleum polyols in the preparation of polyurethane foam composites. The liquefaction time varied from 0 min to 140 min. The composition of liquefied products and the effects of liquefaction time on the morphology, apparent density and mechanical properties of polyurethane foam composites were investigated. The results showed that the optimal process time for the preparation of wood powder liquefaction products, which could replace traditional petroleum polyols, was 110 min. At this time, polyether polyols are the main liquefaction products, with an average molecular weight in Mn reaching 237 and average molecular weight in Mw reaching 246. The functional group of the liquefied product consisted mainly of hydroxyl, with the highest content of 1042 mg KOH/g and the lowest acid number of 1.6 mg KOH/g. In addition, the surface of the polyurethane foam based on poplar wood is dominated by closed cell foam; thus its foam has good heat insulation and heat preservation properties. At 110 min liquefaction time, the apparent density of polyurethane foam is 0.164 g/cm3 and the compression strength is 850 kPa, which is higher than that of traditional polyurethane foam (768 kPa), which is without wood powder modification. Replacing petroleum polyol with renewable wood powder liquefaction products to prepare biomass-based polyurethane foam composite materials, researching complex chemical changes in different liquefaction stages, and finding the best liquefaction conditions are of great significance to optimize the performance of polyurethane, address the shortage of resources and reduce environmental pollution.

The study of energy absorbers is a main concern in various industries. In the automotive industry analyzing the energy absorbers is considered as a solution to minimize the consequences of traffic collision on occupants and enhance the automobile safety. Nowadays, thin-walled tubes have gained massive popularity as one of the most efficient energy absorption systems. In this research, the optimization of crashworthiness parameters in thin-walled grooved conical tubes was performed through computational experiments. Conical aluminum tube with grooves on the internal and external surfaces was simulated under quasi-static loading, while filled with polyurethane foam. Design of experiments method was applied along with validated finite element analysis for better performing and interpreting the results. The applied response surface methodology indicated that the thickness of the tube, foam density, the depth of the groove and the distance between the grooves are associated with energy absorption, respectively. Also, factors such as the density of the foam, the thickness of the tube, the distance between the grooves, groove depth and angle are related with crush force efficiency in that order. Finally, by analyzing all the design criteria, including absorbed energy of tube, mass of tube, the mean crushing force and the maximum crushing force, the optimal density of polyurethane foam and geometric parameters was obtained through both multi-objective optimization process and Pareto diagram. A comparison of results indicated the significance of grooves depth and thickness of tube as the most influential parameters.

Investigating relative density effects on quasi-static response of high-density Rigid Polyurethane Foam (RPUF)

<div class="htmlview paragraph">Polyurethane foam has been used in automotive seating for over twenty years. The use of high resilience (HR) foam provides design flexibility, comfort, and cost-effectiveness, all of which make it the material of choice for seat cushioning applications.</div> <div class="htmlview paragraph">There has been a trend recently towards thinner seat cushions to allow for more head room and to lower vehicle weight. To maintain good support and prevent “bottoming out”, these thinner foams must be made firmer.</div> <div class="htmlview paragraph">This paper discusses the consequences of the different approaches to making firmer, thin seat cushions. Several factors including foam thickness, density, and formulation were investigated. The results show that thinner seats can be produced which provide good support, durability, and physical properties. This result is possible as long as foam density and resilience are maximized.</div>

In this article, the effects of polyurethane foam (PUF) density and skin materials, namely, e-glass/epoxy and e-glass/polyester on the damping behavior of PUF sandwich structures were investigated in the temperature range 20 to 100 C using Rheovibron dynamic mechanical analyzer. Three types of specimens, viz. Epoxy/Glass-PUF-Epoxy/Glass (EPE), Polyester/Glass-PUF-Polyester/Glass (PPP) and Epoxy/Glass-PUF-Polyester/Glass (EPP) with three foam densities (0.6, 0.65 and 0.7 gm/cc) were considered. The effects of the skin material, the density of foam, the interface bonding between the skin, and the foam and the operating temperature on the damping mechanism of the sandwich structures are discussed. The experimental results showed the maximum peak damping capacity at 0 C in case of PPP specimens for a foam density 0.6 gm/cc. The damping capacity initially increased in the temperature range 20 to 0 C, attained peak value at 0 C, further decreased marginally up to 60 C and finally, drastically decreased in the temperature range 60-100 C.

A dry starch–oil composite was blended with each of three glycols; ethylene, polyethylene, and propylene, and then reacted with isocyanate to produce polyurethane foams. The liquid glycols permitted the dry composite to blend well with the other ingredients in the foam formulations. Infrared spectra confirmed the presence of urethane structures in the composite–glycol foams. Polyethylene glycol provided a slightly less dense foam than the other glycols in the composite–glycol products. Microscopy showed a greater number of larger cells in the composite–polyurethane glycol foams. Infrared spectra indicated essentially no qualitative differences in the composite–glycol foams with the three glycols. By prestaining starch with toluidene blue and oil with sudan red, the location of the starch and oil components of the milled composite were observed in the composite–propylene glycol foam. Intact flakes of the composite were observed in the foam. An apparent loss of mobility of oil in the composite–polyurethane foam, as evidenced by NMR analysis, is probably due to crosslinking by isocyanate diffusing into the flakes. Both the cell structure and uniformity of blending were improved by using these glycols rather than the polyester polyol described previously. J Appl Polym Sci 69: 957–964, 1998. Published 1998 John Wiley & Sons, Inc.

A dry starch–oil composite was blended with each of three glycols; ethylene, polyethylene, and propylene, and then reacted with isocyanate to produce polyurethane foams. The liquid glycols permitted the dry composite to blend well with the other ingredients in the foam formulations. Infrared spectra confirmed the presence of urethane structures in the composite–glycol foams. Polyethylene glycol provided a slightly less dense foam than the other glycols in the composite–glycol products. Microscopy showed a greater number of larger cells in the composite–polyurethane glycol foams. Infrared spectra indicated essentially no qualitative differences in the composite–glycol foams with the three glycols. By prestaining starch with toluidene blue and oil with sudan red, the location of the starch and oil components of the milled composite were observed in the composite–propylene glycol foam. Intact flakes of the composite were observed in the foam. An apparent loss of mobility of oil in the composite–polyurethane foam, as evidenced by NMR analysis, is probably due to crosslinking by isocyanate diffusing into the flakes. Both the cell structure and uniformity of blending were improved by using these glycols rather than the polyester polyol described previously. J Appl Polym Sci 69: 957–964, 1998. Published 1998 John Wiley & Sons, Inc.

Although the preparation of polyurethane foam (PUF) composites for oil absorption have attracted increasing research attention, the preparation process of PUF composites are still a thorny problem due to the nonrenewable raw materials. Proposed herein is an environmentally friendly method to prepare the biomass carbon/PUF composites. In this proposal, the biomass carbon with superhydrophobicity was prepared by using the cellulose of bamboo as precursors. Then, the biomass carbon/PUF composites were synthesized using one step foaming technology using the biomass carbon as modifier. This facile synthesis technique has the advantages of scalable fabrication of porous PUF composite for versatile water–oil separation. The PUF composites are mainly composed of hollow microspheres with holes on their surfaces. The PUF composite show very high efficiency in oil separation and quickly absorb edible oil from the glass surface and heavy oils under water. The resulting PUF composites exhibited high oil absorption capacities in the range from 8.59 to 37.10 times of their own weight for various organic solvents. Importantly, recovery oils absorption for PUF composites was obtained for 5 consecutive cycles without a significant decrease in the oil absorption properties. This study suggests potential environmental advantage in using biomass materials in improving the oil absorption properties of oil-absorbing resin for recovering oils from oily wastewater.

Vermiculite and perlite fillers were incorporated into polyurethane (PU) foam to improve sound absorbing, thermal insulating and rebound resilience properties. This article investigated effects of fillers content and foam density on sound absorbing, thermal insulating and rebound resilience properties of resultant PU foam composites. The result indicates that, after vermiculite and perlite fillers addition, sound absorption peak shifted to lower frequency, thermal insulation and rebound resilience improved simultaneously. Sound absorption and thermal insulation improved with foam density and vermiculites content. Comparatively, smaller vermiculites and bigger perlites in PU foam displayed better sound absorbing and thermal insulating property. The resultant PU foam composite possessed 0.87 absorption coefficients at 1000 Hz, 0.054 W/mK thermal conductivity, and 40 % rebound resilience rate, after addition of 5 wt% vermiculites in diameter of 0.71–2.00 mm and foaming at 50 kg/m3.

It is well known that radar absorbing potentiality of existing magneto-dielectric composites can be significantly enhanced by the application of frequency selective surface (FSS) and cascaded electromagnetic (EM) structures. But the optimization of such complex EM structures and validation of the adopted optimization strategy is still a very challenging task for the researchers. Therefore, in this study, an effective effort has been made for the optimization and the corresponding validation for Single Square FSS (SS-FSS) impinged and cascaded radar wave absorbers using advanced computational EM software’s like FEldberechnung fur Korper mit beliebiger Oberflache – a German acronym (FEKO) and high frequency structure simulator (HFSS). In addition, a critical analysis of dielectric constant (ε′) has been carried out to select the best combination of composites for the development of efficient radar wave absorbers. A comparison between optimized and simulated results have been carried out to examine the effect of advanced EM approaches over reflection loss (RL) characteristics of composite radar absorbing materials (CRAMs). A rapid change in radar absorption properties of composites has been observed after the application of SSFSS and cascading. A SS-FSS impinged composite has been found to provide a wide absorption bandwidth of 3.6 GHz at X-band. A cascaded absorber having layer thickness 1.8 mm provides a peak RL of −42.6 dB at 10.6 GHz with an absorption bandwidth of 2.5 GHz. The strong agreement between mathematical model, HFSS and FEKO results clearly reflects the efficiency of adopted approach for distinct practical EM applications.

Experimental investigation of pull-out performance of pedicle screws at different polyurethane (PU) foam densities.

Development of electroless (Ni-P)/BaNi0.4Ti0.4Fe11.2O19 nanocomposite powder for enhanced microwave absorption

If the diffusion behaviour in a polyurethane (PUR) foam is known for all cell gases, it is possible to predict the change in gas composition and consequently the change in thermal conductivity over time for any configuration or dimension of insulating foam [1,2]. Carbon dioxide, which is always present, diffuses much faster out of the foam than e.g. cyclopentane. A simultaneous inward diffusion of air reduces the insulating capacity of the foam [3,4]. Calculation of heat loss presupposes knowledge of the initial partial pressures of the cell gases in the foam and their diffusion coefficients at operational temperatures. One application of PUR foam is in district heating pipes, transmitting hot water (80–100°C) for space heating purposes. The pipes consist of a PUR insulated steel pipe with a polyethylene casing. The temperature gradient over the foam cross-section influences the cell gas pressure and thus the diffusion properties. Use of cyclopentane as blowing agent in rigid PUR foam insulation has increased during the last decade, especially in Europe and Japan. In the foam, cyclopentane is present as a gas in the cells and dissolved in the polymer matrix. Due to concentration and temperature, cyclopentane may also be present as a condensed liquid in the cells. This reservoir of cyclopentane can compensate for losses of the gas due to diffusion [5,6]. Thus it keeps up the concentration of cyclopentane in the gas phase in the cells of the foam, which is beneficial for the long-term thermal performance The diffusion coefficients of oxygen, nitrogen, carbon dioxide and cyclopentane in PUR foam were determined in the temperature range 20–60°C. Samples were taken from district heating pipes: carbon dioxide-blown foam (density 71 kg·m−3) and cyclopentane blown foam (density 61 kg·mm−3). The cell gas concentrations were determined after grinding the foam sample and analysis of the released cell gases by gas chromatography [7]. The effective diffusion coefficients in the PUR foam were evaluated by a curve fitting procedure from the change of the partial pressures of the cell gases over time [1,6]. See Table 1. Very different activation energies of the cell gases, as in our study (See Table 1.), means that the insulating performance determined at a certain time and temperature cannot easily be extrapolated. Thus, the diffusion rates of these gases must be affected by temperature to a different extent, which is in agreement with die effective diffusion showed in Table 1. Table 1 Effective diffusion coefficients and activation energies for samples of PUR foam taken from district heating pipes (densities 61–71 kgm−3). Gas Effective diffusion coefficient Deff(·10−13m2·s−1) Activation energy ED (J-mole−1) 20°C 40°C 60°C Nitrogen 25 220 44–103 Oxygen 150 650 30–103 Carbon dioxide 500 1300 19–103 Cyclopentane 0.6* 4 7 59.103 * Determined at 23° 610PUR foams exposed to elevated temperatures get darker and become more brittle. This is probably due to oxidation of the polymer. In an unpublished study we observed that the amount of oxygen in PUR foams stored at 100°C was less than in foams stored at 80°C. Hence, oxygen must have been consumed in an oxidation process. This means that oxygen diffusion coefficients based on studies of cell gas concentrations at high temperature may be underestimated.

Energy absorption performance of steel plate-polyurethane foam composite protective structures