Organic Foam Research Articles

Porous inorganic–organic shape memory polymers

Thermoresponsive shape memory polymers (SMPs) are a type of stimuli-sensitive materials that switch from a temporary shape back to their permanent shape upon exposure to heat. While the majority of SMPs have been fabricated in the solid form, porous SMP foams exhibit distinct properties and are better suited for certain applications, including some in the biomedical field. Like solid SMPs, SMP foams have been restricted to a limited group of organic polymer systems. In this study, we prepared inorganic–organic SMP foams based on the photochemical cure of a macromer comprised of inorganic polydimethylsiloxane (PDMS) segments and organic poly(ε-caprolactone) (PCL) segments, diacrylated PCL40-block-PDMS37-block-PCL40. To achieve tunable pore size with high interconnectivity, the SMP foams were prepared via a refined solvent-casting/particulate-leaching (SCPL) method. By varying design parameters such as degree of salt fusion, macromer concentration in the solvent and salt particle size, the SMP foams with excellent shape memory behavior and tunable pore size, pore morphology, and modulus were obtained.

Radiative properties of tannin-based, glasslike, carbon foams

This work deals with the measurement of radiative properties of lightweight rigid foams derived from tannins. Such cellular solids derived from renewable resources were investigated before and after carbonisation, the latter leading to glasslike carbon foams. Spectral quantities such as transmittance and reflectance were measured within the range of infrared wavelengths 1.5–12μm, from which optical thickness, albedo, scattering and absorption coefficients, and absorptance were deduced. Temperature dependence of emissivity of carbon foams was also derived from measurements and from calculated blackbody emissive power. Both organic and carbon foams were shown to be poor thermal conductors, whose radiative transfer properties increase when the porosity decreases, due to both bigger cells, and to thinner and to less pore walls and struts. The radiative conductivity of carbon foams was deduced from the measured overall conductivity and from a simple analytical model accounting for the conduction conductivity.

Preparation of low density carbon foams by foaming molten sucrose using an aluminium nitrate blowing agent

Low density carbon foams have been prepared by thermo-foaming of molten sucrose using aluminium nitrate as a blowing agent to produce solid organic foams followed by dehydration and carbonization. Gas bubbles are generated in the molten sucrose due to water vapour produced by the acid catalysed condensation between sucrose hydroxyl groups and NOx gases produced by the thermal decomposition of the aluminium nitrate. Higher melt viscosity achieved by cross-linking of the condensation products of sucrose through co-ordination of the aluminium ions with the hydroxyl groups stabilizes the bubbles against coalescence and rupture. The foam volume, foaming time and setting time depend on the aluminium nitrate concentrations. The carbon obtained by the pyrolysis of the solid organic foams has turbostratic graphite structure. The foams produced have an interconnected near-spherical cellular structure. The carbon foams prepared at aluminium nitrate concentrations in the range of 0.5–4wt.% have a density and average cell size in the ranges of 0.085–0.053g/cc and 1.55–0.83mm, respectively. The alumina (∼0.17–1.34wt.%) produced from the aluminium nitrate is concentrated more on the surface of cell walls, ligaments, and struts.

Influence of a density mismatch on TMPTMA shells nonconcentricity

AbstractSome laser target designs require low‐density organic foam shells to study fusion on the French high‐power laser laser mega joule. Low‐density trimethylolpropane trimethacrylate foam shells composed of C, H, and O, 2 mm diameter, 100‐μm wall thickness, and 250 mg cm−3 density are synthesized by a microencapsulation technique using a droplet generator. These shells have to reach a sphericity higher than 99.9% and a nonconcentricity (NC) lower than 1%. The wall thickness variation is one of the most difficult specifications to meet. An important factor in reducing this defect is the density matching between the three phases of the emulsion at polymerization temperature. The influence of a density mismatch between the internal water phase and the organic phase on the NC of TMPTMA foam shells was studied. The best NC results and yields of shells are obtained with a density gap between the internal water phase and the organic phase of 0.078 g cm−3 at 60°C, with an average NC around 2%. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Preparation of ultra-light magnetic nanocomposites using highly concentrated emulsions

Hybrid inorganic–organic ultra-light magnetic solid foams with iron oxide nanoparticles embedded in a divinylbenzene–polystyrene matrix were prepared using a highly concentrated emulsion polymerization method. Iron oxide nanoparticles with diameters of 3 and 10 nm were synthesized using two different methods. For comparison purposes, nanocomposites with magnetite nanoparticles dispersed in a non-porous polymeric matrix obtained by bulk polymerization were also investigated. Materials were characterized using several techniques such as dynamic light scattering (DLS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), small angle X-ray scattering (SAXS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and magnetization measurements. SEM and TEM images showed that solid foams are made of well-defined macro pores with nanoparticles embedded in the walls. The density of the solid foams was ca. 50–70 kg m −3, which is about 20 times lighter than the non-porous monoliths. The magnetic measurements show that both nanocomposites are superparamagnetic, and that there are differences regarding the interparticle interactions depending on matrix porosity. The synthesized materials may find applications in adsorbents, tissue reparation, enzyme supports, microreactors, or in water decontamination.

A simple and efficient method for manufacturing porous bioceramics

AbstractThe purpose of this study was to develop a simple and efficient method for manufacturing porous bioceramics, in which small organic foam spheres were taken as the poremaking reagent and green bodies were made by hot die-casting in moulds. The raw materials (small organic foam spheres, paraffin, oleic acid and β-TCP powder) were mixed into a slurry at 30–120ºC and moulded into green bodies using a hot die-casting machine at 30–90ºC; the green bodies were then sintered and the porous bioceramics obtained. The main characteristics (structure and size of pores, water permeability, apparent porosity and shrinkage) were tested. The results indicated that the apparent porosity was high and directly proportional to the mass ratio between the small organic foam spheres and the β-TCP powder. The pores connected with each other in three dimensions; the size, distribution of the shapes and structures of the pores were clearly related to the dimensions of the small organic foam spheres. The water permeability was proportional to the hot die-casting pressures and the shapes of the samples could easily be controlled by selecting different moulds. This study indicated that the method can be used to manufacture porous bioceramics with controlled pore structures and different shapes effectively and easily by adding different amounts and sizes of small organic foam spheres, mixing the raw materials evenly, and by selection of the hot die-casting pressure and by the use of different moulds.

Hybrid foams, colloids and beyond: From design to applications

Highly internal phase emulsion (polyHIPE) materials are promising macrocellular foams bearing versatile applications ranging from catalysis, optics, filtration, insulator and so forth. In this critical review water-in-oil HIPE, oil-in-water HIPE and Pickering-based HIPE are discussed. Also in each above-mentioned HIPE family, declination between the organic, inorganic or hybrid-organic foams chemical nature is proposed. The polyHIPE audience is thereby strongly interdisciplinary in nature crossing boundaries of physical chemistry, colloids, polymer science, sol-gel chemistry, hybrid materials, biology and beyond (114 references).

Apparent porosity of porous bioceramics prepared with small organic foam spheres as the pore-making reagent

AbstractThis study focuses on the main factors determining the apparent porosity of porous bioceramics prepared using small organic foam spheres as the pore-making reagent, in order to determine the best technical parameters for preparing porous bioceramics. In every experiment, only one of these factors (the time of heating, the sintering temperature, the mass ratio between small organic foam spheres and beta-tricalcium phosphate (β-TCP) powder, and the rate of the temperature rise) was changed, while the others were kept constant. In each case the apparent porosity was tested and the relation between the specific variable and apparent porosity was observed. Finally, the optimum technical parameters were deduced. The apparent porosity shows an inverse linear relation to the time of heating and the sintering temperature, and is approximately proportional to the mass ratio between the small organic foam spheres and the β-TCP powder and the rate of temperature rise. These factors have important influences on the apparent porosity. The optimum conditions were: heating time (soak time) 120 min, sintering temperature 850ºC, mass ratio 0.25, and a rate of temperature increase of 120ºC h–1.

Ni-Doping Alumina Foams for Fabricating MMCs by Pressureless Infiltration Using Fe Alloy

The preparation of Ni-doping alumina foams as precursors for MMCs (Metal Matrix Composites) fabrication was studied. Alumina foams were successfully adulterated with Ni using organic foam impregnation technique. Uniform Ni particles were distributed in alumina struts after they were sintered in a vacuum furnace. At the crucial infiltration step, an inducer such as elemental Ni melted so that interpenetrating channels were created in the ceramics. In contact with Fe melt, the metal matrix could spontaneously infiltrate in alumina foams struts. The influence of infiltration was subsequently investigated by SEM and EDS. Preliminary results showed that the interface between Ni-doping alumina foams and Fe metal matrix reached a full structural homogeneity and the use of Ni-doping alumina foams enhanced the capability of infiltration when processing continuous three-dimensional interconnected ceramics/metal networks MMCs by pressureless infiltration technique.

Effects of CeO<sub>2</sub>-Rich Mixed Rare Earth on the Mechanical Properties of Al<sub>2</sub>O<sub>3</sub>-Mullite Based Foam Ceramics

Using corundum, quartz, kaoline, etc, as base components and CeO2-rich mixed rare earth as modifier, foam ceramics were fabricated adopting the organic foam impregnation process. The mixed rare earth addition had much improving effects on the matrix mechanical properties owing to much glass phase and acerate mullite growing. While 3wt% was considered to be the optimal addition, in this case, homogeneous and compact ceramic microstructure with maximal glass condensation and minimal porosity formed, with the matrix compressive strength and the flexural strength at room temperature reached 0.87MPa and 0.66MPa respectively, which were 52.6% and 73.7% higher than the original samples respectively. As the mixed rare earth addition exceeded further, the compressive strength increased slowly and the flexural strength descended gradually. XRD and SEM were used to structure strengthening mechanism analysis.

Viscoelasticity of liquid organic foam: Relaxations, temporal dependence, and bubble loading effects on flow behavior

Liquid organic foams are prepared using a new blowing process based on the chemical generation of carbon dioxide. The foams are volumetrically stable for periods up to hours and can be fabricated with gas volume fractions ranging from 0.10 to 0.95. Both the "fresh" and temporal dependences of the linear viscoelastic response of these materials are evaluated. The organic foams exhibit rheological behavior characteristic of their aqueous counterparts: a weak dependence of the shear moduli over an extended frequency/time regime that is bounded by both a fast and slow relaxation. The onset of the fast mechanical response of the organic foams occurs at approximately the same frequency as in aqueous foams despite the continuous phase viscosity differing by orders of magnitude between the systems. This suggests that the viscosity does not affect the time scale of the "anomalous" viscous loss characteristic of these materials, which challenges currently proposed mechanisms for this dissipation and leaves the origin of the loss behavior unclear. The relative contribution of cell growth and bubble motion to the slow relaxation is also discerned by evaluating the relation between the transient and dynamic responses of the foam. Finally, the development of elasticity in the foam due to bubble interactions is analyzed and a bubble slip process is postulated to account for the lack of a true elastic response of the foam at intermediate time scales (between the fast and slow mechanical response) when gas fractions exceed 0.64.

Mechanical properties of tannin-based rigid foams undergoing compression

The mechanical properties of a new class of extremely lightweight tannin-based materials, namely organic foams and their carbonaceous counterparts are detailed. Scaling laws are shown to describe correctly the observed behaviour. Information about the mechanical characteristics of the elementary forces acting within these solids is derived. It is suggested that organic materials present a rather bending-dominated behaviour and are partly plastic. On the contrary, carbon foams obtained by pyrolysis of the former present a fracture-dominated behaviour and are purely brittle. These conclusions are supported by the differences in the exponent describing the change of Young's modulus as a function of relative density, while that describing compressive strength is unchanged. Features of the densification strain also support such conclusions. Carbon foams of very low density may absorb high energy when compressed, making them valuable materials for crash protection.

Micropore Characterization of Mesocellular Foam and Hybrid Organic Functional Mesocellular Foam Materials

The micro- and mesoporous structures of microemulsion templated mesocellular foam (MCF) silica materials aged at different temperatures were investigated by using nitrogen sorption αs-comparison plots and positron annihilation lifetime spectroscopy (PALS). The impact of surface amino functionalization with (3-aminopropyl)triethoxysilane (APTES) on these structures was also studied. The nitrogen sorption αs-comparison plots show that the micropore volume of the MCF silica can be controlled by varying the synthesis aging temperature such that the higher the aging temperature, the smaller the micropore volume. The corresponding PALS data showed that this effect of temperature on micropore volume is a direct consequence of a temperature-dependent micropore population, with more micropores in the MCF material aged at lower temperature. After functionalization of the silica MCF materials with APTES, the BET surface area was seen to have reduced substantially, while maintaining the characteristic mesopore sizes....

Recent advances in development of materials for laser target

AbstractNearly ten years ago, a research program concerning materials and technologies was defined to develop the very complex cryogenic target for obtaining the combustion of a deuterium-tritium mixture by inertial confinement fusion in the laser megajoule facility. The CEA target fabrication project includes research and development on various organic polymers and materials for the cryogenic laser megajoule target assembly as well as for other targets that can be useful for the fusion program (pre and post-ignition). Recent advances have been accomplished concerning the development of specific organic materials for the fabrication of targets components, including the synthesis of polymers for the laser megajoule microshells and metal-doped organic foams for the elaboration of doped-foam microshells or for the micromachining of components.

A new technique for preparation of porous bioceramics with controllable macrostructures

AbstractThe purpose of this study was to develop a simple and economic method for the preparation of porous bioceramics with controllable macrostructure. Raw materials, including very small organic foam balls as the pore-creating reagent, wax (or paraffin) as the solvent, and oleic acid as the surface active agent, were selected along with bioactive materials such as β-TCP ceramic powder as the main component. The selected components were mixed into a slurry at 30–120ºC and shaped into a green body with a hot die-casting machine at 30–90ºC. The green body was then sintered and porous bioceramics were obtained. The main characteristics of porous bioceramics such as weight loss, compressive strength, connection and size of pores, percolation rate of water, apparent porosity and bulk density were measured. The results indicated that the apparent porosity and the specific surface area were large; the pores were connected in three dimensions and the compressive strength was >1.6 MPa. This study demonstrated that the methods used here are simple and effective in generating porous bioceramics with controllable macrostructures.

X-Ray Microtomography Studies of Tannin-Derived Organic and Carbon Foams

Tannin-based rigid foams of different bulk densities and their carbonized counterparts were investigated for the first time by X-ray microtomography. This method allowed acquisition of three-dimensional pictures of such highly porous materials. Through mathematical treatment of the images, extremely useful physical characteristics such as porosity, fraction of open cells, connectivity, tortuosity, and pore-size distribution were determined as a function of the foam's density. The obtained information was compared with independent data derived from pycnometry measurements and scanning electron microscope image analysis. The agreement was shown to be acceptable in the limit of the accuracy of the laboratory microtomograph (4 microm). Moreover, recalculating properties like permeability were shown to be quite possible based on the results of standard microtomography data.

Preparation of polybenzoxazine foam and its transformation to carbon foam

An organic foam derived from a new type of phenolic resin, namely polybenzoxazine, was successfully prepared with a noncomplex and economical foaming method by using azodicarbonamide (AZD) as a foaming agent. The influence of foam density on the physical and mechanical properties of the foams was studied. All resulting polybenzoxazine foams and carbon foams exhibit a tailorable uniform microstructure. Polybenzoxazine foams showed a density in the range of 273–407 kg/m 3, and a compressive strength and a compressive modulus in the range of 5.2–12.4 MPa and 268–681 MPa, respectively. The foam density not only affects the physical and mechanical properties, but also affects the deformation response of the foam. In addition, the polybenzoxazine foam was further transformed into carbon foam by carbonization at 800 °C under an inert atmosphere, and its properties were examined.

Microwave‐Sensitive Foamable Poly(ionic liquids) Bearing tert‐Butyl Ester Groups: Influence of Counterions on the Ester Pyrolysis

Several poly(ionic liquids) have been synthesized based on poly(1-vinyl-3-tert-butoxycarbonylmethylene imidazolium) salts with different counterions to investigate the tert-butyl ester pyrolysis of these compounds. It is found that the counterions strongly influence the temperature of the pyrolysis. The pyrolysis temperature shifts to higher or lower temperatures depending on the nature of the counterions. The use of microwave irradiation was employed to accelerate the gas release because of the high dipolar interaction of amorphous salts with microwaves. The result of these reactions is the formation of organic foams that could be of industrial interest.

Preparation of Ni–Cr alloy foams by electrodeposition technique

Metallic foams have many applications in industry and are made using various methods. However, no suitable method for heating Ni–Cr alloy foam has been available. A method of preparing Ni–Cr alloy foam by an electrodeposition technique is described in the present paper. The method includes the following steps: establishing electrical conductivity of organic foam; electroplating of a Ni layer; electroplating of a Cr layer; eliminating the organic matrix and a homogenisation heat treatment. The plating solutions and process parameters of electrodeposition are introduced in detail. Homogenisation of the samples was carried out in a sealed quartz tube at 1100°C and the homogenisation time was determined by experiment and calculation. Experimental results are shown indicating that the Ni–Cr alloy foam made by this electrodeposition technique had a three-dimensional reticulated structure and formed a single phase Ni based solid solution. Also, the apparent resistivity was measured and it is demonstrated that the higher resistivity of the foam gave it good electrical heating properties.

Technical note: Thermal insulations for hot water cylinders: a review and a conceptual evaluation

This paper presents a review and evaluation of thermal insulation materials for application in hot water storage cylinders. A range of thermal insulation materials including organic foams, inorganic insulations, composite insulations and vacuum insulation panels have been evaluated. The evaluation addressed parameters such as effects of insulation thickness on the energy saving and system cost. Vacuum insulation panels offered the best results in terms of energy saving and annualised system cost, given that the vacuum could be maintained at a desirable level throughout system lifetime. The overall evaluation indicates that polyisocyanurate (PIR) foam is the best overall single insulation material that could be applied for hot water storage cylinders when all the parameters including cost, thermophysical properties and environmental impact are taken into account. Microporous silica aerogel is more expensive than any other single insulation material that could be applied for hot water storage cylinders, but offers excellent performance in terms of reduced thickness and weight. When used in conjunction with PIR in a composite form, the combination offers a competitive performance in comparison with some of the conventional insulation materials, e.g. EPS, PU and glass fibre. Practical applications: The paper provides a comprehensive and compact summary and information on a range of thermal insulation materials for application in hot water storage cylinders. Although, the discussion is confined to hot water storage, the information is useful for a wide range of industries including construction industry, domestic appliance industry, technicians working in the above two industries and more importantly to R&D institutions. R&D institutions could directly benefit from the information provided in this paper, where the basic information and data are required to short list materials that should be given attention for further investigation for a given research area. Trade names normally dominate the industry with regards to material use; the paper provides basic scientific background on the origin of the thermal insulation materials, which are commonly known only by trade names within the industry, manufacturing processes, relative cost, their properties and related environmental impact. The paper provides awareness of other alternative insulation materials; that could be considered for a given application.