Anisotropic compressive behavior of rigid PVC foam at strain rates up to 200 s−1

The elevated strain rate compressive response of closed-cell polyvinyl chloride (PVC) foam at various densities is investigated. Two loading directions, (i.e., parallel and perpendicular to foam rise direction) were considered to investigate structural anisotropy. The elevated strain rates tests (up to 200 s⁻¹) were performed using a customized drop tower device. Engineering stress/strain behavior, energy dissipation, and maximum stress capacity were obtained for each density and compared against each other. Except for the lowest density of 45 kg/m³, strain rate effects were clearly observed through increased compressive strength and plateau stress when loading in the foam rise direction. The strain rate effect is more evident at higher densities. However, no significant strain rate effect was observed when loading perpendicular to the foam rise direction. Scanning electron microscopy (SEM) analysis showed that plastic hinges are the primary deformation mechanism for PVC foam cells. An analytical model has been calibrated using the experimental results and successfully predicted the mechanical response of the foam. Shape anisotropy has been measured employing the SEM images. The analytical approach was also able to predict the foam's anisotropic mechanical response.     

A Study of Dynamic Interfacial Properties as Related to Foaming Properties of Sodium 2,5-dialkyl Benzene Sulfonates

In this article, foaming properties and dynamic interfacial properties of a series of sodium 2,5-dialkyl benzene sulfonates in aqueous solutions were carried out to elucidate the relationship between foaming properties and dynamic interfacial properties. The properties of foams generated from bubbling air through different surfactant solutions were measured using a modified Bikerman device. The dynamic surface tension and surface dilational elasticity were obtained from an image analysis technique based on the oscillating bubble method. The surfactants molecular adsorption at the air/water interface was introduced with Rosen empirical equation and the rate of adsorption was determined from measurements of the dynamic surface tension. The surfactant with the longest alkyl chain shows the lowest dynamic surface activity, which lead to the lowest foam volume. The short ortho straight alkyl chain has little effect on the arrangement of molecules at the interface and the foam stability changes a little with the changing of the ortho alkyl chain length. The foam stability is correlated with both the higher surface dilational elasticity and the larger surface monolayer strength.     

Porous cobalt hydroxide film electrodeposited on nickel foam with excellent electrochemical capacitive behavior

A new porous cobalt hydroxide film has been successfully electrodeposited on nickel foam from 0.1?M cobalt nitrate electrolyte at ?1.0?V vs. SCE without adding any surfactant. The microstructure and surface morphology of prepared cobalt hydroxide films were physically characterized by X-ray diffraction analysis and scanning electron microscopy. The results indicate that an interlaced network structure was obtained. The effects of electrodeposition time, deposition potential, and different substrates on the specific capacitance and microstructure of prepared porous ??-Co(OH)₂ thin film were systematically studied. The results indicate that the film deposited on nickel foam at ?1.0?V has excellent electrochemical properties. A maximum specific capacitance of 1473?F?g^?1 could be achieved at a current density of 2?A?g^?1.     

Permeability of Newtonian black foam films to gas

The gas permeability of Newtonian black foam films, formed on the top of a small bubble at the solution surface, was studied experimentally. The aqueous solutions contained sodium dodecylsulphate with concentrations in the range 1.5×10^–4 to 3×10^–3 mol/dm³ and sodium chloride (constant concentration of 0.5 mol/dm³). A dependence of the gas permeability coefficient on the surfactant concentration was obtained. The experimental results are discussed on the basis of a theory assuming the presence of clusters of molecule vacancies (holes) in the bilayer foam film, their number and size depending on the surfactant concentration. The experimental results are in agreement with this film structure and confirm the existence of flow through both the hole-free bilayer film and the holes. It was found that the holes of three molecule vacancies make the main contribution to gas permeability at low surfactant concentration. The diffusion coefficients through the hole-free film and through the three-vacancy holes are calculated.Dedicated to Professor Dr. Armin Weiss on the occassion of his 60th birthday.     

A Scalable Chemical Approach for the Synthesis of a Highly Tolerant and Efficient Oil Absorbent

In the past, bio‐inspired extreme water repellent property has been strategically embedded on commercially available sponges for developing selective oil absorbents. However, most of the reported materials lack physical and chemical durability, limiting their applicability at practically harsh settings. Herein, a stable dispersion of polymeric nanocomplexes was exploited to achieve a chemically reactive coating on the highly compressible melamine foam. A superhydrophobic melamine foam (SMF) was achieved after post‐covalent modification of the reactive coating through 1,4‐conjugate addition reaction at ambient conditions. The durability of the embedded extreme water repellent property in the as‐modified melamine foam has been elaborately demonstrated through exposing it to severe physical manipulations, chemically harsh aqueous media including pH 1, pH 12, surfactant contaminated water, river water, seawater and prolonged UV irradiation. Thus, the highly tolerant SMF was utilized as an efficient oil absorbent wherein oils of varying densities could be selectively recovered from an oil/water interface with high (e.g., 137 g g^?1 for chloroform and 83 g g^?1 for diesel) oil absorption capacity. Moreover, the selective oil absorption capacity of the as‐synthesized material remained unaffected at practically relevant severe chemical and physical settings, and the extreme water repellency of the material remained unaltered even after repetitive (at least 50 cycles) use for oil/water separation.     

Low density polyethylene,expanded polystyrene and expanded polypropylene: Strain rate and size effects on mechanical properties

Polymeric foam materials may be used as energy absorbing materials for protection in impact scenarios, and design with these materials requires the mechanical properties of foams across a range of deformation rates, where high deformation rate testing often requires small samples for testing. Owing to their cellular macrostructure, and the large deformations that occur during loading of foams, the measured stress-strain response of a foam material may be influenced by the sample size. In this study, the mechanical properties of three closed-cell polymeric foams (Low Density Polyethylene, Expanded Polystyrene and Expanded Polypropylene) at two different densities were investigated over a range of deformation rates from 0.01 s⁻¹ to 100 s⁻¹. For each foam material, three different nominal sample sizes (10 mm, 17 mm and 35 mm) were tested. On average, the polymeric foam materials exhibited increasing stress with increasing deformation rate, for a given amount of strain.Density variation was identified at the sample level, with smaller samples often exhibiting lower density. Expanded Polystyrene demonstrated the highest variability in sample density and corresponding variability in mechanical response, qualitatively supported by observed variations in the macrostructure of the foam. Expanded Polypropylene exhibited variability in density with sample size, and observable variability in the material macrostructure; however, the dependence of the measured mechanical properties on sample size was modest. Low Density Polyethylene was found to have a relatively consistent cell size at the macrostructure level, and the material density did not vary significantly with sample size. In a similar manner, the dependence of measured mechanical properties on sample size was modest. The effect of sample size was identified to be material specific, and it is recommended that this be assessed using sample-specific density measurements and considering different sized samples when testing foam materials.     

Ion flotation of nickel using ethylhexadecyldimethylammonium bromide

Nickel ions react with the surfactant ethylhexadecyldimethylammonium bromide (EHDABr) to foam a surface-active sublate which can be removed from aqueous chloride solutions by ion flotation. A typical ion-flotation procedure involves passing a fixed volume of air through a 250-ml solution containing 4.0 ppm nickel and 0.05 M KCl at a pH of 5 at a rate of 60 ml/min for 60 min. The method is simple and rapid with 87% removal of the nickel.     

多孔泡沫铜和硫脲协同作用构筑无枝晶锂负极

锂金属作为下一代储能电池的理想负极材料一直受到极大的关注,然而锂枝晶的不可控生长和负极副反应带来的低库伦效率问题严重限制了锂金属电池的发展。这里,我们提出了一种多孔泡沫铜和硫脲协同作用的策略,利用硫脲分子的超填充作用实现锂金属在多孔泡沫铜表面的均匀沉积。在电解液中添加0.02 mol·L^-1硫脲作为电解质添加剂,采用多孔泡沫铜的Li||Cu半电池在循环300圈以后,库伦效率仍保持在98%以上。此外,在5C的高倍率条件下,Li||Li FePO4全电池循环300圈以后仍有94%的容量保持率。本工作为锂金属负极保护提供了一种新的策略并且该策略也可以扩展到其他金属负极保护中,非常有利于下一代高能量密度储能电池的开发。     

Electrolysis of ammonia for hydrogen production catalyzed by Pt and Pt-Ir deposited on nickel foam

Electrolysis of ammonia in alkaline electrolyte solution was applied for the production of hydrogen. Both Pt-loaded Ni foam and Pt-Ir loaded Ni foam electrodes were prepared by electrodeposition and served as anode and cathode in ammonia electrolytic cell, respectively. The electrochemical behaviors of ammonia in KOH solution were individually investigated via cyclic voltammetry on three electrodes, i.e. bare Ni foam electrode, Pt-loaded Ni foam electrode and Pt-Ir loaded Ni foam electrode. The morphology and composition of the prepared Ni foam electrode were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Effects of the concentration of electrolyte solution and temperature of electrolytic cell on the electrolysis reaction were examined in order to enhance the efficiency of ammonia electrolysis. The competition of ammonia electrolysis and water electrolysis in the same alkaline solution was firstly proposed to explain the changes of cell voltage with the electrolysis proceeding. At varying current densities, different cell voltages could be obtained from galvanostatic curves. The low cell voltage of 0.58 V, which is less than the practical electrolysis voltage of water (1.6 V), can be obtained at a current density of 2.5 mA/cm². Based on some experimental parameters, such as the applied current, the resulting cell voltage and output of hydrogen gas, the power consumption per gram of H₂ produced can be estimated.     

Surfactant accumulation within the top foam layer due to rupture of external foam films

The analysis of processes taking place in a steady pneumatic (dynamic) foam shows the possibility of different modes of surfactant accumulation within the top layers of bubbles due to rupture of external foam films. An increasing surfactant concentration within the top layers promotes the stabilisation of bubbles and the foam as a whole. Considering the balance of surfactant and water during the bursting of films it is possible to estimate the accumulated surfactant loss caused by a downwards flow through the Plateau borders of the subsurface bubble layer. This effect depends on the particular conditions, especially on the surfactant activity and concentration of the surfactant, water volume fraction in the foam and size of foam bubbles. The process of surfactant accumulation in the top foam bubble layer can be complicated due to the removal of part of the accumulated surfactant through transport with droplets spread out during bubble bursting.     

Lightweight lignocellulosic foams for thermal insulation

Foams are mainly composed of dispersed gas trapped in a liquid or solid phase making them lightweight and thermally insulating materials. Additionally, they are applicable for large surfaces, which makes them attractive for thermal insulation. State-of-the-art thermally insulating foams are made of synthetic polymeric materials such as polystyrene. This work focuses on generating foam from surfactants and renewable lignocellulosic materials for thermally insulating stealth material. The effect of two surfactants (sodium dodecyl sulphate (SDS) and polysorbate (T80)), two cellulosic materials (bleached pulp and nanocellulose), and lignin on the foaming and stability of foam was investigated using experimental design and response surface methodology. The volume-optimized foams determined using experimental design were further studied with optical microscopy and infrared imaging. The results of experimental design, bubble structure of foams, and observations of their thermal conductivity showed that bleached pulp foam made using SDS as surfactant produced the highest foam volume, best stability, and good thermal insulation. Lignin did not improve the foaming or thermal insulation properties of the foam, but it was found to improve the structural stability of foam and brought natural brown color to the foam. Both wet and dry lignocellulosic foams provided thermal insulation comparable to dry polystyrene foam.

Graphical abstract

     

Charge reversal at the air/water interface as inferred from the thickness of foam films

Experiments are reported with foam films from aqueous solutions with increasing concentration of a cationic surfactant. A correlation is established between the foam film thickness and the possible variation of diffuse electric layer potential at the air/water interface from a negative value in absence of surfactant to positive values at higher surfactant concentrations. It is concluded that a charge reversal at the air/water interface is expected to occur under increasing concentration of cationic surfactants in aqueous solutions.     

Effects of preparation conditions on properties of rigid polyurethane foam composites based on liquefied bagasse and jute fibre

Rigid polyurethane foams based on liquefied bagasse and reinforced with jute fibre were prepared. The effects of preparation conditions were investigated using a paper cup with a small horizontal section area as a mould. They were reflected in the foam height, which acted as a sensitive indicator. Density gradient existed in the foam rise direction and decreased from the bottom to top. Although the amount of blowing agent water was fixed, the foam height increased with stirring time after the addition of diphenyl methane diisocyanate, the isocyanate index and the catalyst content. This was partly due to the released heat that also contributed to the foam expansion. The relative intensity of the C─N stretching band at 1510 cm⁻¹ and the N─H out-of-plane bending band at 1527 cm⁻¹ in the FTIR spectrum reflected isocyanate reactions, which had a close relationship with the crosslink density. The normalized compressive strength was essentially attributed to the combined effects of the crosslink density and the thickness of cell walls and struts. Jute fibre enhanced the compressive strength only slightly due to poor interfacial adhesion between some fibres and the matrix.     

Scanning force microscopy as a tool to investigate the properties of polyglycerol ester foams

Foamed products are a popular class of food products. The mechanism of stabilization of the air bubbles is often only partially understood. The current study aims at better understanding the stabilization of air-water interfaces through the low molecular weight surfactant polyglycerol ester (PGE). We chose PGE films as an exemplary case for a non-equilibrium situation at an air-water interface--a situation that requires the development of new experimental techniques. Several different film preparation and transfer methods onto solid substrates have been tested. The films were then investigated by scanning force microscopy, and structural artifacts associated to the sample preparation were identified and discussed. In addition to the study of Langmuir monolayers and Gibbs adsorption layers, we have proposed a new approach to investigate the skins of foam bubbles. We thereby were able to determine that PGE indeed covers bubbles by a multilayer structure and that the pH plays a role in the structuring of the films. We show that a combination of different film preparation methods allows us to get an insight into the aggregation behavior of PGE at the air-water interface and thereby better understand the stabilization mechanism of this particular surfactant.     

Synergism and foaming properties in mixed nonionic/fatty acid soap surfactant systems

The synergism and foaming behavior of a mixed surfactant system consisting of a nonionic surfactant (polyethoxylated alkyl ether C(n)E(m)) and a fatty acid soap (sodium oleate) were studied. The micellar interaction parameter (the beta-parameter) was determined from the cmc following the approach of Rubingh's regular solution theory. For both the C(12)E(6)/sodium oleate and the C(14)E(6)/sodium oleate mixtures, the results indicate a fairly strong attractive interaction (negative beta-values), which were in agreement with previous data reported for other nonionic/anionic surfactant systems. The characteristics of the foam produced from the surfactants were evaluated using a glass column equipped with a series of electrodes measuring the conductance of the foam, which enabled the water content of the foam to be determined. From these measurements, since the total foam volume was almost the same for all concentrations and surfactants, we compared the amount of liquid in the foam produced under dynamic foaming and the ability of the foam to entrain the liquid after the airflow was switched-off (static foam stability). The amount of liquid in the foam 100 s after the air was switched-off followed the order NaOl > C(12)E(6) > C(14)E(6). Also, the mixtures had the same foam volumes as the pure surfactants at the same concentration. However, both mixtures had higher concentrations of liquid in the foam when the mole fraction of the nonionic surfactant in the mixed surfactant system was greater than about >0.3 in the solution.     

Foam Countercurrent Chromatography Based on Dual Counter-Current System

Abstract

A novel method of performing foam separation is described. The method utilizes a gas-liquid dual countercurrent flow through a helical column subjected to a particular type of synchronous planetary motion. Samples introduced at the middle portion of the column, in either batch or continuous mode, are separated according to the foam affinity. Any material having an affinity to the foam is quickly carried with the foaming stream and eluted through one end of the column whereas other materials are carried with the liquid stream in the opposite direction and eluted out through the other end of the column. Capability of this foam countercurrent chromatographic method is demonstrated on separations of rhodamine B and Evans blue with an anionic surfactant, SDS, as a collector of rhodamine B. Successful preliminary separation of protein samples, BSA and sheep hemoglobin, indicates that the present method may be effectively applied to separation and purification of various biological samples such as enzymes, membrane receptors, etc.     

Enhancing the effectiveness of a laccase–TEMPO treatment has a biorefining effect on sisal cellulose fibres

Enhancing the effectiveness of a laccase–TEMPO treatment on sisal pulp by increasing pulp consistency was for the first time found to increase the biorefining potential of this enzyme–mediator system. The operating conditions used were those previously found to maximize oxidative functionalization and paper strength. Prior to the enzyme treatment, the pulp was refined at a variable intensity (0, 3,000 and 4,500 revolutions) in order to ascertain whether the increased surface area would lead to enhanced functionalization and boost the refining effect as a result. Increasing pulp consistency increased the contents in aldehyde and carboxyl groups by 130% and 94%, respectively. Also, it resulted in more marked reduction of pulp viscosity during the enzyme treatment, especially at a high refining intensity; this had a detrimental effect on fibre strength and significantly reduced tear strength in the refined pulp. Oxidized pulp exhibited a considerably increased water retention value with respect to the initial pulp, particularly after refining. Dry tensile index was increased by 21, 18 and 12%, and burst index by 23, 16 and 13% at 0, 3,000 and 4,500 rev, respectively, by the laccase–TEMPO treatment as a result of increased inter-fibre hydrogen bonding offsetting the loss of fibre strength, an effect that can provide substantial savings in refining energy. Based on the results, a laccase–TEMPO treatment is an enzymatic booster of mechanical refining with the added advantages of providing unaltered drainability and increased air permeability. The most salient effect of the laccase–TEMPO treatment was an increase in wet tensile strength (by 160, 553 and 588% at 0, 3,000 and 4,500 rev, respectively) that can be ascribed to inter-fibre covalent bonding through hemiacetal linkages promoted by aldehyde groups. The improvement was much greater than that obtained at a lower consistency under identical conditions.     

Study of anodizing process on aluminium foam to improve the corrosion behavior

Aluminium foam is obtained by the production of air into metallic melt. This material shows a very low density together with good mechanical properties, high impact energy absorption, and fire resistance. Different production ways to obtain metallic foam are possible. Considering the cost, the Alporas process is particularly interesting. By means of this production method, a block of metallic foam with close cells is obtained. By slicing, foam panels are obtained. The mechanical cut promotes the formation of an open cells texture on the surface. In this last case, the complex morphology of aluminium foam could be a critical point considering the corrosion behavior in aggressive environments, where localized corrosion phenomena, as pitting or crevice corrosion, are likely to occur. The anodizing treatment is one of the most used methods to improve the corrosion resistance of aluminium and aluminium alloys. The aim of this paper is to perform an anodization treatment to enhance the corrosion resistance of aluminium foam. Constant voltage anodization (12 V for 60 min) and pulsed current anodization (0.04 A/cm² for 60 seconds and 0.01 A/cm² for 15 seconds, repeated for 15 cycles) have been carried out in 15 wt% H₂SO₄ at 20°C. The anodized samples are observed in cross section by optical and electronic microscopes to investigate the structure of the anodic oxide layer and the presence of defects and to measure the thickness of the layer. The corrosion protection performance and the compactness of layers are evaluated using acetic salt spray test and electrochemical impedance spectroscopy.     

Thermodynamic studies on thin liquid films. III: Miscibility in adsorbed films at film interfaces

Thermodynamic treatment of surfactant mixture was developed for the adsorption at interfaces of thin liquid films and applied to the study of the foam film stabilized by decyl methyl sulfoxide (DeMS) in the presence of NaCl. The total surface density of NaCl and DeMS and the mole fraction of DeMS in the adsorbed film at the film surface were numerically evaluated by applying thermodynamic equations to the film tension as a function of the total molality of NaCl and DeMS and the mole fraction of DeMS in the mixture. Miscibility of NaCl and DeMS at the film surface was clarified by a phase diagram of adsorption and compared with that at the meniscus adjacent to the foam film. Judging from a phase diagram of phase transition, the transition in the DeMS foam film between common black and Newton black films, observed in part II, is a negative azeotropic transformation caused by the attractive interaction between the head group of DeMS molecule and Na⁺ or Cl^– in the adsorbed film.     

Re-Emerging Field of Lignocellulosic Fiber – Polymer Composites and Ionizing Radiation Technology in their Formulation

Natural cellulose-based fibers offer low cost, low density composite reinforcement with good strength and stiffness. Because of their annual renewability and biodegradability, natural fibers have materialized as environmentally-friendly alternatives to synthetic fibers in the last two decades. They are replacing synthetic materials in some traditional composites in industrial manufacturing sectors such as automotive, construction, furniture, and other consumer goods. In this work, the use of lignocellulosic fibers in green materials engineering, particularly their application as polymeric composite reinforcement and surface treatment via ionizing radiation are reviewed. Because these cellulose-based materials are intrinsically hydrophilic, they require surface modification to improve their affinity for hydrophobic polymeric matrices, which enhances the strength, durability, and service lifetime of the resulting lignocellulosic fiber-polymer composites. In spite of a long history of using chemical methods in the modification of material surfaces, including the surface of lignocellulosic fibers, recent research leans instead towards application of ionizing radiation. Ionizing radiation methods are considered superior to chemical methods, as they are viewed as clean, energy saving, and environmentally friendly. Recent applications of controlled ionizing radiation doses in the formulation of natural fiber –reinforced polymeric composites resulted in products with enhanced fiber-polymer interfacial bonding without affecting the inner structure of lignocellulosic fibers. These applications are critically reviewed in this contribution.