Dynamic compression characteristics of flexible foams. II. Density variation

In Part I, a simple mathematical model was proposed, based on dimensional similarity parameters, to describe the characteristics of flexible plastic foams under impact conditions. The model assumes that the foam is a rate-dependent material. In the present part we extended the similarity model, by including the density of the foam parameter (for the same material and technological process). The density parameter is significant for systems cushioning with regard to weight and cost constraints. The behavior of flexible foams was studied with density as the variable parameter in a range of 100–240 kg/m³, with constant geometrical dimensions, for a wide range of drop heights and masses. We used the similarity parameters approach to predict the characteristics of the foams for various foam densities. The results show that for particular tested cases, the maximum deformation, the maximum deceleration, and the time pulse-period decrease as the foam density increases.     

Evaluation of cushioning properties of plastic foams from compressive measurements

Evaluation criteria for the cushioning properties of plastic foams were developed on the basis of their stress-strain curves. The energy-absorption efficiency and ideality parameters have maxima when plotted against stress. The maximum in the efficiency curve represents the strain range where maximum energy is absorbed by the foam at the corresponding stress; the higher and flatter this maximum, the better the cushioning properties of the foam. The maximum in the ideality curve represents the range where the foam transmits a constant force to the packaged product. Two flexible polyurethane foams and two semirigid bonded polyurethane chipfoams were evaluated by the proposed method.     

Pressure drop measurements and hydrodynamic model description of SiC foam composites decorated with SiC nanofiber

During the last decade there has been a growing interest in catalytic reactor engineering based on structured catalytic beds. Compared to traditional packed bed reactors, structured catalytic beds provide improved hydrodynamics and catalytic performance. In this context, silicon carbide (SiC) foam materials seems to be a good candidate for use as catalyst support due to their high geometrical surface area (m⁻¹) and open porosity leading to low pressure drop. However, foam structures have a relatively low specific surface area (m²/g) for performing good anchorage and dispersion of the active phase which is one of the crucial points in catalysis. This study proposes a new type of material which combined the advantage of foam (high porosity) with nanofiber of SiC (high specific surface (m²/g)). The knowledge of pressure drop characteristics of foam with nanofiber is necessary for the future process design. However, due to the complexity of the geometric shape of new foam materials, up to date, no general relationship exists for the calculation of the pressure drop through different foam matrix and generally, empirical equation with modified parameters of the Ergun's equation were needed to fit the data. This study show that a simple model can be used for the prediction of the pressure drop in the SiC foam with nanofiber through Ergun's equation without using any fitting in order to reconcile experimental data with theory.     

Open-cell flexible polyurethane foams: Comparison of static and dynamic compression properties

Dynamic stress–strain diagrams of polyurethane packaging foams have been obtained from free fall drop tests. The dynamic curves become higher as the deformation rates increase. An equation is proposed to describe the stress–strain dependence for different deformation rates. The model of filament buckling explains the form of the observed stress–strain dependence and phenomena related to repeated loading of the foam.     

Visco‐hyperelastic constitutive model for modeling the quasi‐static behavior of polyurethane foam in large deformation

Flexible polyurethane foam is widely used in numerous applications such as seats and mattresses, due to its low stiffness and its ability to absorb deformation energy. The main objective of this article is to model the quasi‐static mechanical behavior of three types of polyurethane foam in large deformation and to compare these three foams with three proposed models. The uniaxial compression/decompression tests at three different strain rates were performed. The test results show that the three foams present different plateau stresses, maximum stresses, and abilities to absorb energy. Moreover, polyurethane foam also presents a nonlinear hyperelastic behavior and a viscoelastic behavior in large deformation. Three visco‐hyperelastic models which include a hyperelastic component and a memory component are proposed to model these behaviors. Model parameters were identified using the experimental data and a proper identification method. These models were validated on these three types of foam with the aim to present comparison results. The comparison results show that Ogden's viscoelastic model best agrees with the experimental results. POLYM. ENG. SCI., 55:1795–1804, 2015. © 2014 Society of Plastics Engineers     

Porous polyurethane foam for use as a particle collection substrate in a nanoparticle respiratory deposition sampler

Porous polyurethane foam was evaluated to replace the eight nylon meshes used as a substrate to collect nanoparticles in the Nanoparticle Respiratory Deposition (NRD) sampler. Cylindrical (25 mm diameter by 40 mm deep) foam with 100 pores per inch was housed in a 25-mm-diameter conductive polypropylene cassette cowl compatible with the NRD sampler. Pristine foam and nylon meshes were evaluated for metals content via elemental analysis. The size-selective collection efficiency of the foam was evaluated using salt (NaCl) and metal fume aerosols in independent tests. Collection efficiencies were compared to the nanoparticulate matter (NPM) criterion and a semi-empirical model for foam. Changes in collection efficiency and pressure drop of the foam and nylon meshes were measured after loading with metal fume particles as measures of substrate performance. Substantially less titanium was found in the foam (0.173 µg sampler^?1) compared to the nylon mesh (125 µg sampler^?1), improving the detection capabilities of the NRD sampler for titanium dioxide particles. The foam collection efficiency was similar to that of the nylon meshes and the NPM criterion (R² = 0.98, for NaCl), although the semi-empirical model underestimated the experimental efficiency (R² = 0.38). The pressure drop across the foam was 8% that of the nylon meshes when pristine and changed minimally with metal fume loading (～19 mg). In contrast, the pores of the nylon meshes clogged after loading with ～1 mg metal fume. These results indicate that foam is a suitable substrate to collect metal (except for cadmium) nanoparticles in the NRD sampler.

Copyright © 2016 American Association for Aerosol Research     

Hydrodynamic and Mass Transfer Performances of a New SiC Foam Column Tray

The hydrodynamic performance of a novel SiC foam column tray (SFCT), made of thin slices of SiC foam material with a high specific surface area, is investigated. The performance parameters include pressure drop, entrainment, weeping, and clear liquid height. The tests are carried out with an air‐water system under atmospheric pressure. The mass transfer efficiency of the new SiC foam column tray is studied in a stainless‐steel plate column. The results provide some important parameters for the development of this innovative SiC foam tray.     

Relationship between the thermal degradation chemistry and flammability of commercial flexible polyurethane foams

In this article, we report the use of a variety of analytical methods, in particular, solid‐state ¹H‐NMR and ¹³C‐NMR to characterize the relationship between the condensed‐phase chemistry and burning behavior as determined by a series of combustion tests for two commercially derived flexible polyurethane foams, one combustion‐modified. The combustion tests showed that the foams met several regulatory requirements in terms of their fire performance, whether or not they were combustion‐modified. Both foams passed the MV SS 302 and CAL 117 small‐flame tests. The nonmodified foam failed the Crib 5 test, but this test had a much larger ignition source. The particular problem with the nonmodified foam was melt drip into the flame zone. This led to a steady maintenance of the fuel feed and a rapid escalation of the fire. In contrast, the combustion‐modified foam showed little melt drip and self‐extinguished. Thermal analysis data for the two foams showed that melamine acted in part as an endothermic heat sink. This alone did not account for the much reduced melt flow and drip of the combustion‐modified foam, but the solid‐state ¹H‐NMR data clearly showed that the molecular mobility of the combustion char from combustion‐modified foam was lower than the unmodified foam char, which indicated that the flame‐retardant formulation in the combustion‐modified foam acted by a condensed‐phase mechanism. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3024–3033, 2006     

Constitutive modeling and simulation of energy absorbing polyurethane foam under impact loading

The compressive-stress strain response of polyurethane foam under uniaxial compressive impact loading has been studied. The development of a uniaxial constitutive model from strain rate controlled compression tests is detailed. Density and temperature functions have been added to the integral power model proposed by Schwaber, Meincke, and Nagy. The model assumes that the effects of density, temperature, strain and strain rate on stress are separable functions. The model correlated well with actual static compression tests and was used successfully to predict the impact response of energy absorbing polyurethane foam under uniaxial compressive loading.     

Viscoelastic behavior of flexible slabstock polyurethane foams: Dependence on temperature and relative humidity. I. Tensile and compression stress (load) relaxation

The relaxation behavior of the load in compression and the stress in tension was monitored at constant temperature and/or relatively humidity for a set of four slabstock foams with varying hard-segment content as well as two of the compression molded plaques of these foams. The majority of the compression relaxation tests were done at a 65% strain level in order to be consistent with the common ILD test. The tensile stress relaxation tests were performed at a 25% strain level. Over the 3-h testing period, a linear relationship between the log of compressive load or the log of tensile stress versus log time is observed for most testing conditions. For linear behavior, the values of the slope or the load/stress decay rate are comparable in both the tension and compression modes with the values being slightly higher in magnitude for the compression mode. These rates of decay are in the range of ?2.2 × 10 ^?2 to ?1.7 × 10 ^?2 for a 21 wt % hard-segment foam and ?3.2 × 10^?2 to ?2.4 × 10^?2 for a 34 wt % hard-segment foam. Increasing %RH at a given temperature does bring about a steady decrease in the initial load or initial stress as well as a slight increase in the rate of relaxation. The effect of temperature on the relaxation behavior is most significant at temperatures near 125°C and above. The FTIR thermal analysis of the plaques indicates that this significant increase is due to additional hydrogen bond disruption and possible chain scission taking place in the urea and urethane linkages that are principally present in the hard segment regions. The relaxation behavior in both tension and compression is believed to be mostly independent of the cellular texture of the foam at the strain levels given above. This conclusion is based on the similar relaxation behavior between the plaques and the foams. © 1994 John Wiley & Sons, Inc.     

COMPRESSION ANALYSIS OF DEHYDRATED AGRICULTURAL PRODUCTS

ABSTRACT

The textural properties of apple, banana, carrot and potato were experimentally determined by uniaxial compressive tests of cylindrical specimens at a constant deformation rate of 5mm/min. Compression tests were performed, following air drying, at various moisture contents ranging from 0.2 to 6 kg/kg db. The tests were performed using a universal texture testing machine and simple mathematical equations were used to correlate the maximum experimental stress and the corresponding strain to the moisture content. It was shown that the maximum stress decreases as the moisture content decreases, until a critical moisture content of 1.8 kg water/kg dry solids. Further removal of water tends to increase the maximum stress. The maximum experimental strain was found to increase as water was removed. The stress-strain data of compression test were modelled using a simple mathematical model, containing parameters such as the maximum stress (ow), the maximum strain (dim), the elastic parameter (E) and the viscoelastic exponent (p). The effect of the moisture content on the compressive behavior of dried materials was introduced through its effect on the model parameters. The shift in compression behavior at 1.8 kg water/kg solids leads to the conclusion that there is an important change of structure at this moisture content.     

基于相似理论的REAC出口弯管冲蚀瞬态特性

针对加氢REAC系统的频繁失效问题,研究流动与腐蚀耦合作用下REAC出口弯管的冲蚀破坏机理;在确定相似准则的基础上,结合具体的工艺特性运行数据,设计模型弯管,确定实验常数,并运用环道式多相流冲蚀实验装置,进行冲蚀瞬态特性测试,结合实验过程的CFD数值模拟获取模型弯管冲蚀瞬态特性参数。实验和仿真结果表明,模型弯管出现冲蚀瞬态特性时速度为7.93 m·s^-1,最大剪切应力为2.21 Pa;运用量纲分析法建立原型与模型冲蚀临界特性之间的数理方程,实现相似理论的求解,修正实验结果形成实际弯管的冲蚀瞬态特性参数,冲蚀剪切应力为1.79 Pa,结合工程测厚验证冲蚀瞬态特性测试实验和相似理论修正结果的可靠性和准确性;研究成果可为压力管道的多相流冲蚀预测提供科学的理论依据和实验方法。     

Combustion behaviour of polyurethane flexible foams under Cone Calorimetry test conditions

The first part of this study focuses on the effect of cone calorimeter test variables on polyurethane flexible foam properties such as ignitability, heat release rate, effective heat of combustion and mass loss. Three of the main commercial foam types were used, i.e. conventional slabstock foams, high-resilience slabstock foams and all-MDI (methylene diphenyldiisocyanate) moulded foams. A decrease in heat flux (down to 40%) with increasing distance from the conical heater was measured. As a consequence, results were found to depend to a large extent on the thickness and the melting behaviour of the foam samples. To achieve a sufficiently constant and uniform heat flux exposure, sample thickness had to be limited to 25 mm. In addition, repeatability was found to be good under various conditions, with percentage standard deviations for effective heat of combustion, peak rate of heat release and mass loss below 10%. Levels of radiant flux above 25 kW m^?2 were found to be very severe to test flexible polyurethane foams. Under such conditions, foams that show large differences in combustion performance in small-scale flammability tests performed almost identically in the cone calorimeter. In the second part of this study the effects of foam variables, such as foam type, density and melamine content, are defined. These effects were clearly pronounced at radiant flux levels of 15–25 kWm^?2. Density was found to be the key variable in controlling ignition resistance. In addition, high-resilience slabstock foams and all-MDI moulded foams performed better than conventional slabstock foams of the same density. Melamine addition resulted in a delay of ignition for all three foam types and an incomplete combustion, decreased heat release and effective heat of combustion in HR-slabstock and all MDI moulded foams. However, melamine is not effective as a heat sink in conventional slabstock foams. The different performance of the foam types under study can be explained by a different melting behaviour.     

Role of two stage pyrolysis in fire growth on flexible polyurethane foam slabs

A series of experiments designed to characterize fire behavior on flat 1.2 m × 1.2 m samples of commercial non‐fire‐retarded flexible polyurethane foam were performed. Time‐resolved heat release and mass loss rates were measured. Experimental parameters varied, including foam thickness (5.1 and 10.2 cm) and burning angle (+25°, +12.5°, 0°, ?12.5°, and ?25°). Polyurethane foam is typically produced by reacting a multifunctional isocyanate with a polyol. The foam used here was formed by reacting toluene diisocyanate and a polyol based on a condensed polyether of polypropylene oxide. Earlier cone calorimeter studies of this foam had revealed a clear two stage pyrolysis behavior in which the heated foam first released a gaseous fuel derived from the isocyanate component, while leaving behind a liquid produced primarily from the polyol, which only gasified and burned following additional heating. The subsequent burning behavior of the polyol‐derived liquid is shown in this work to play a crucial role in the maximum heat release rate and total heat released by the fires spreading across the foam slabs. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

Nickel foam and carbon felt applications for sodium polysulfide/bromine redox flow battery electrodes

The first use of nickel foam (NF) as electrocatalytic negative electrode in a polysulfide/bromine battery (PSB) is described. The performance of a PSB employing NF and polyacrylonitrile (PAN)-based carbon felt (CF) as negative and positive electrode materials, respectively, was evaluated by constant current charge-discharge tests in a single cell. Charge/discharge curves of the cell, positive and negative electrodes show that the rapid fall in cell voltage is due to the drop of positive potential caused by depletion of Br₂ dissolved in the catholyte at the end of discharge. Cell voltage efficiency was limited by the relatively high internal ohmic resistance drop (iR drop). Polarization curves indicated that both NF and CF have excellent catalytic activity for the positive and negative redox reactions of PSB. The average energy efficiency of the single cell designed in this work could be as high as 77.2% at 40 mA cm⁻² during 48 charge-discharge cycles.     

Biodegradation of phenol at high concentration by a novel bacterium: Gulosibacter sp. YZ4

BACKGROUND: A novel bacterial strain, Gulosibacter sp. YZ4, has been isolated from activated sludge. Its application potential for phenol biodegradation has not yet been reported, therefore, in this study, biodegradation tests using strain YZ4 were executed under different conditions. RESULTS: The strain was identified as a new member of the genus Gulosibacter and nominated as Gulosibacter sp. YZ4. Phenol biodegradation tests showed that strain YZ4 could thoroughly biodegrade 1000 mg L^?1 phenol across a wide temperature range from 10 to 42 °C and pH range 5 to 11. Degradation of 1000 mg L^?1 phenol was not inhibited by the coexistence of p‐cresol or quinoline. During phenol degradation, strain YZ4 excreted both phenol hydroxylase and catechol 1,2‐dioxygenase to efficiently metabolize phenol. At 36 °C, pH 7.5, strain YZ4 could effectively degrade phenol at concentrations as high as 2000 mg L^?1 within 76 h. Haldane's model with the parameters obtained from the experiments could successfully describe the behavior of the phenol biodegradation by the strain YZ4. CONCLUSIONS: The strain YZ4 has a high potential for applications in phenol wastewater treatment in view of its adaptability to temperature and pH fluctuations and great tolerance to other coexistent toxics. Copyright © 2011 Society of Chemical Industry     

A predictive model based on tortuosity for pressure drop estimation in ‘slim’ and ‘fat’ foams

The use of porous structures with high external surface area represents an important breakthrough in several industrial applications. Foam structures have received an increasing scientific and industrial interest since the last decade. Knowledge of pressure drop induced by these foam structures is thus essential for successful design and operation of high performance industrial systems. In this context, an analytical investigation was conducted for the determination of the permeability and the inertial coefficient in foams. The theoretical model is based on modified cubic lattice, which allows to take into account the presence of matter at the junction of struts. The existing model developed in the literature is then modified to incorporate this geometrical approach for determining the tortuosity of the foam. Finally, the permeability and inertial coefficient analysis are performed in order to derive the pressure drop on foams. The modeling procedure is based only on physical principles and geometrical considerations with no adjustable parameters in order to reconcile the theoretical work with the experimental data of the literature. Finally, this model is validated for two marginal cases (i.e. ‘slim’ and ‘fat’ foams).     

Ignition resistant upholstery by coating PU flexible foam with vinylidene chloride copolymers

A method is described by which the UK Upholstered Furniture (Safety) Regulations of 1980 may be complied with. By coating the surface of flexible polyurethane foam with vinylidene chloride copolymer latex, a fire retardant surface is obtained. This enables most fabric/foam combinations to pass both the cigarette and the match tests as laid down in BS5852. The coating process can be carried out with a brush, a roller or by spraying. Drying can be at room temperature or by using heat and/or a forced draught. Using about 350 gm^?2 only certain deep-pile fabrics fail, and even hen additionally back-coating them with PVDC can ensure compliance. The presence of thin wadding or stockingette makes no difference, but thick wadding will burn with the fabric for more than the mandatory two minutes without setting fire to the PU foam. Fabrics successfully tested with the coated PU foam include cottons, polypropylene, acrylic, polyester and ‘Dralon’. After 80 000 indentations in a standard test the coating was still effective, as it was also after heating in a detergent for 4h.     

Nano-Mg(OH)2 platelets coated flexible polyurethane foam for fast and environment-friendly removal of Cu2+ from aqueous solution

In this study, flexible polyurethane foam (FPUF) was successfully coated with nano-Mg(OH)₂ platelets. Due to the strong interaction between chitosan and nano-Mg(OH)₂, it was possible to yield modified foam with a weight-gain of up to 15 wt% by depositing one chitosan layer and one nano-Mg(OH)₂ layer. Meanwhile, the adsorption isotherms of Cu²⁺ on FPUF covered with 10 wt% coating (FPUF-10) shows the Langmuir behavior. It was found that for the FPUF-10, the removal % for Cu²⁺ after 30 min and 50 min treatment were 86% and 90%, respectively. Moreover, the maximum removal % could reach up to 95%.