Macroporous rubber gels as reusable sorbents for the removal of oil from surface waters

Macroporous organogels were prepared by solution crosslinking various rubbers in benzene at ?18 °C. Butyl rubber (PIB), cis-polybutadiene (CBR) and styrene–butadiene rubber (SBR) were used as the rubber components, while sulfur monochloride was the crosslinker in the gel preparation. The organogel networks consist of large pores of 10¹–10² μm in size caused by the benzene crystals acting as a template during gelation. The networks formed by CBR and SBR showed an aligned porous structure consisting of regular pores, whereas those derived from PIB had irregular pores with a broad pore size distribution due to the phase separation of PIB chains at low temperatures. All organogels were very tough and could be completely compressed without any crack development. Sorption tests showed that the organogels were efficient at removing crude oil, gasoline, diesel, fuel oil and olive oil. The organogels are reusable once they are squeezed, leading to continuous sorption capacities of CBR or SBR gels for crude oil and olive oil of 33–38 g/g and 24–27 g/g, respectively. These sorption capacities are two to three times the capacity of the gels derived from PIB.     

Porous rubber cryogels: effect of the gel preparation temperature

This paper examines the effect of the gel preparation temperature (T _prep) on the physical properties of the rubber-based macroporous organogels prepared by solution crosslinking in benzene at subzero temperatures. Cis-polybutadiene (CBR) and styrene-butadiene rubber (SBR) were used as the rubber components, while sulfur monochloride (S₂Cl₂) was the crosslinker in the gel preparation. It was shown that T _prep is an extremely important parameter to adjust the porous structure and thus, the cryogel properties. The networks formed by CBR and SBR showed an aligned porous structure with an exception of honey-comb structured porous SBR cryogels prepared at ?2 °C. 10¹- to 10²-μm sized regular pores of the networks caused by the benzene crystals act as a template during gelation, separated by 10–20 μm pore walls in thickness. They exhibit fast swelling and deswelling properties as well as reversible swelling–deswelling cycles in toluene and methanol, respectively. The ability of the organogels for the removal of petroleum products from aqueous solutions was also demonstrated using diesel and crude oil as model pollutants. In addition, the reusability of the organogels and their continuous sorption capacities were checked by repeated sorption–squeezing cycles. All the tests showed that the aligned porous organogels are suitable materials for the oil spill cleanup procedures.     

Porous hydroxyapatite ceramics by ice templating: Freezing characteristics and mechanical properties

Ice templating produces porous hydroxyapatite (HA) scaffolds with a lamellar morphology and aligned channels when using aqueous HA slurries. We investigated the freezing characteristics of HA slurries with regard to the pore structures of the porous HA scaffolds. We found that by increasing the cooling rate, the lamellar spacing decreased. The average lamellar spacing is about 785.7 μm at a cooling rate of 1.3 °C/min. The porous geometry changes from lamella and well aligned channels to a partial dendrite and partially aligned cavities with a decrease in the initial nucleation temperature and an increase in the degree of supercooling. Additionally, we determined the relationship between compressive strength and porosity. The compressive strength of the porous HA scaffolds reach 6.7 MPa at a porosity of 64% and the lamellar spacing is about 124 μm.     

Development of a new graded-porosity FeAl alloy by elemental reactive synthesis

A new graded-porosity FeAl alloy can be fabricated through Fe and Al elemental reactive synthesis. FeAl alloy with large connecting open pores and permeability were used as porous supports. The coating was obtained by spraying slurries consisting of mixtures of Fe powder and Al powder with 3-5 μm diameter onto porous FeAl support and then sintered at 1100 °C. The performances of the coating were compared in terms of thickness, pore diameter and permeability. With an increase in the coating thickness up to 200 μm, the changes of maximum pore size decreased from 23.6 μm to 5.9 μm and the permeability decreased from 184.2 m³ m^− 2 kPa^− 1 h^− 1 to 76.2 m³ m^− 2 kPa^− 1 h^− 1, respectively, for a sintering temperature equal to 1100 °C. The composite membranes have potential application for excellent filters in severe environments.     

Fabrication of porous SiC ceramics having pores shaped with Si grain templates

SiC porous ceramics were prepared by heating mixtures of Si powder and carbon black at 900 °C for 24 h in Na vapor. The grains of the Si powder were not only the source of Si for SiC but also served as templates for the pores in the SiC porous ceramics. Angular-shaped pores with sizes of 2-10, 10-150 and 50-150 μm were formed by angular Si grains with sizes of ≤10, ≤50 and ≤150 μm, respectively. The porosity of the SiC porous ceramics was around 55-59%. Spherical pores were also formed when spherical Si grains were used. A bending strength of 14 MPa was measured for the SiC porous ceramics prepared with the Si grains (≤50 μm).     

Macroporous hydrogel beads of high toughness and superfast responsivity

Macroporous hydrogel beads based on the monomers acrylamide and 2-acrylamido-2-methylpropane sulfonic acid sodium salt were prepared by dropwise addition of the monomer solution into the paraffin oil as the continuous phase at subzero temperatures. The beads prepared between ?15 and ?20 °C have irregular large pores of 1–10 μm in diameter, typical for macroporous networks created by the cryogelation technique, while nonporous hydrogels were obtained at room temperature. Swelling measurements show that the low temperature beads swell within seconds to attain their equilibrium states in water. The beads formed at subzero temperatures were very tough and can be compressed up to 94% strain without any crack development while those formed at room temperature were fragile and broke at a strain of about 40%. The results indicate that the tough hydrogel beads formed at subzero temperatures can be used in separation processes in which the separated compounds can easily be recovered by compression of the beads under a piston.     

Fabrication of CaSiO3 bioceramics with open and unidirectional macro-channels using an ice/fiber-templated method

Porous CaSiO₃ bioceramics with open and unidirectional macro-channels of pore size more than 200 μm are of particular interest for biomedical applications. An ice/fiber-templated method was employed for the fabrication of CaSiO₃ bioceramics with interconnected lamellar pores and macro-channels of pore size more than 200 μm. The pores formed by ice crystals transformed from cellular to lamellar, while the pores formed by fibers were aligned macro-channels, which were also in alignment with the lamellar pores. Keeping the initial slurry concentration constant and increasing the packing density of fibers, the volume fraction of macro-channels and open porosity increased, and the compressive strength decreased. Maintaining the packing density of fibers and increasing the initial slurry concentration, the pore sizes of lamellar pores and open porosity decreased, and the compressive strength increased. The results indicated that it was possible to manufacture porous CaSiO₃ bioceramics with the macro-channels of 250–350 μm, lamellae spacing of 50–100 μm, open porosity of 71.12–83.94% and compressive strength of 0.87–3.59 MPa, indicating the suitability for tissue engineering.     

Filling of mesoporous silicon with copper by electrodeposition from an aqueous solution

Copper filling into mesopores formed in highly doped p-type silicon was investigated. When the copper electrodeposition was carried out at a very small constant current density (−6.4 μA cm⁻²), the mesopores with 4 μm depth were filled with copper continuously from the bottom to the opening. When the electrodeposition current was set at an absolute value twice as large as in the above condition, the isolated particles were electrodeposited in the mesopores. The depth also affected the filling behavior. The pores with 8 μm in depth were not continuously filled with copper even in the condition at which the pores of 4 μm in length were completely filled. Electrodeposition behavior in mesopores was also simulated using a simple model. The numerical simulation suggested that the diffusion-limited electrodeposition could be achieved in mesopores at a very small current, at which the diffusion-limited condition had never been realized on a planar electrode.     

Porous mullite templated from hard mullite beads

Porous mullite bodies were developed by spark plasma sintering (SPS) amorphous mullite beads of about ∼30 μm in diameter at two temperatures, 950 and 1300 °C. Materials showed a close random stacking of solid spheres that retained their original packing but slightly flattened at the contacts in some cases. Depending on the thermal history, the beads were partially or fully crystallized. The thermal conductivity of the different porous mullite materials was analyzed as a function of the microstructure. Owing to the particular porous network, high gas permeability and very low thermal conductivities (1-2 W m⁻¹ K⁻¹) were achieved, among the lowest reported for sintered mullite materials.     

Superfast responsive ionic hydrogels with controllable pore size

A series of strong polyelectrolyte hydrogels was prepared from the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) as the monomer and N,N′-methylene(bis)acrylamide (BAAm) as a crosslinker in aqueous solutions. The gel preparation temperature (T_prep) was varied between −22 and 25 °C. It was found that the swelling properties and the elastic behavior of the hydrogels drastically change at T_prep=−8 °C. The hydrogels prepared below −8 °C exhibit a discontinuous morphology consisting of polyhedral pores of sizes 30-50 μm, while those formed at higher temperatures have a non-porous structure. The pore size of the networks increased by decreasing the charge density of the hydrogels, while addition of low molecular weight salts into the gelation system reduced the size of the pores. Calculations based on the equilibrium between the ice and unfrozen gel phases in the reaction system at low temperatures explain the results of observations. It was also shown that the hydrogels formed below −8 °C exhibit superfast swelling properties as well as reversible swelling-deswelling cycles in water and acetone.     

Manufacture and characterization of ultra and microfiltration ceramic membranes by isostatic pressing

This paper describes the manufacture of tubular UF and MF porous and supported ceramic membranes to oil/water emulsions demulsification. For such a purpose, a rigorous control was realized over the distribution and size of pores. Suspensions at 30 vol.% of solids (zirconia or alumina powder and sucrose) and 70 vol.% of liquids (isopropyl alcohol and PVB) were prepared in a jar mill varying the milling time of the sucrose particles, according to the pores size expected. The membranes were prepared by isostatic pressing method and structurally characterized by SEM, porosimetry by mercury intrusion and measurements of weight by immersion. The morphological characterization of the membranes identified the formation of porous zirconia and alumina membranes and supported membranes. The results of porosimetry analysis by mercury intrusion presented an average pore size of 1.8 μm for the microfiltration porous membranes and for the ultrafiltration supported membranes, pores with average size of 0.01-0.03 μm in the top-layer and 1.8 μm in the support. By means of the manufacture method applied, it was possible to produce ultra and microfiltration membranes with high potential to be applied to the separation of oil/water emulsions.     

Foaming strategies for bioabsorbable polymers in supercritical fluid mixtures. Part II. Foaming of poly(?-caprolactone-co-lactide) in carbon dioxide and carbon dioxide + acetone fluid mixtures and formation of tubular foams via solution extrusion

This paper reports on the foaming of poly(?-caprolactone-co-lactide) in carbon dioxide and carbon dioxide + acetone mixtures. Experiments were carried out in specially designed molds with porous metal surfaces and fluid circulation features to generate foams with uniform dimensions at 60, 70 and 80 °C at pressures in the range 7-28 MPa. Depending upon the conditions, foams with pores in the range from 5 to 200 μm were generated. Adding acetone to carbon dioxide improved the uniformity of the pores compared to foams formed by carbon dioxide alone. In addition, a unique high-pressure solution extrusion system was designed and used to form porous tubular constructs by piston-extrusion of a solution from a high-pressure dissolution chamber through an annular die into a second chamber maintained at controlled pressure/temperature and fluid conditions. Long uniform porous tubular constructs with 6 mm ID and 1 mm wall thickness were generated with glassy polymers like poly(methyl methacrylate) by extruding solutions composed of 50 wt% polymer + 50 wt% acetone, or 25 wt% polymer + 10% acetone + 65% carbon dioxide at 70 °C and 28 MPa. Pores were in the 50 μm range. The feasibility of forming similar tubular constructs were demonstrated with poly(?-caprolactone-co-lactide) as well. Tubular foams of the copolymer with interconnected pores with pore sizes in the 50 μm range were generated by extrusion of the copolymer solution composed of 25 wt% polymer + 10 wt% acetone + 65 wt% carbon dioxide at 70 °C and 28 MPa. Reducing the acetone content in the solution led to a reduction of pore sizes. Comparisons with the foaming behavior of the homopolymer poly(?-caprolactone) that were carried out in the molds with porous metal plates show that the foaming behavior of the copolymer is more akin to the foaming behavior of the caprolactone homopolymer component.     

Production of porous calcium phosphate (CaP) ceramics with highly elongated pores using carbon-coated polymeric templates

This study reports a new way of enhancing the compressive strength of porous calcium phosphate (CaP) ceramics by creating highly elongated pores. These elongated pores were produced by casting a CaP/camphene slurry into stretched polymeric sponges with a thick carbon coating layer used as a template. The sample produced after sintering at 1250 °C for 3 h showed a highly elongated porous structure with a porosity of 38 ± 1.2 vol%, where elongated pores with a size of 512 ± 96 μm were formed as a replica of the template. In addition, CaP walls with a thickness of 841 ± 239 μm were fully densified without any noticeable defects due to the high CaP content of 40 vol% in the CaP/camphene slurry. The compressive strength of the sample was as high as 21 ± 4.9 MPa when tested parallel to the direction of pore elongation, which is much higher than that (12 ± 2.4 MPa) of the sample tested normal to the direction of pore elongation. The sample also showed good biocompatibility, as assessed by the in vitro cell test using a pre-osteoblast cell line.     

Freeze-dried macroporous foam prepared from chitosan/xanthan gum/montmorillonite nanocomposites

Freeze-dried macroporous foams were prepared from an aqueous colloidal suspension of chitosan/xanthan gum/Na⁺-montmorillonite nanoclay (MMT). The suspension formed gel structure as a consequence of freezing, named cryogel. Cryogel is defined as a gel formed due to the concentration increase of the substrates caused by the ice formation during freezing. This obtained cryogel was subsequently dried under vacuum condition to produce porous foam materials. Two freezing methods were employed in the present work in order to investigate the influence of the processing on sample characteristics, namely; contact freezing with a heat exchanger and immersion freezing in a cryo-bath. Based on the SEM observation, in the case of contact freezing; rapid freezing (−2 °C/min) resulted in randomly aligned pores as compared to the pore alignment obtained in the case of slow freezing (−0.25 °C/min); the mean pore size for rapid freezing and slowing freezing were 40 μm and 68 μm, respectively. However, in immersion freezing samples, aligned and bamboo-like straight structures with pore layer spacing of 22 μm were observed. The different microstructures significantly influenced the mechanical hardness of the prepared foams nanocomposites. The MMT dispersion within the bionanocomposites was found to be characteristically exfoliated from X-ray diffraction and electron microscopy analysis. Small angle X-ray diffraction data indicated that the polymeric networks were modified by the exfoliated MMT and the MMT also improved the hardness of the prepared foams.     

A porous hydroxyapatite scaffold for bone tissue engineering: Physico-mechanical and biological evaluations

Polymer sponge replication method was used in this study to prepare the macroporous hydroxyapatite scaffolds with interconnected oval shaped pores of 100-300 μm with pore wall thickness of ∼50 μm. The compression strength of 60 wt.% HA loaded scaffold was 1.3 MPa. The biological response of the scaffold was investigated using human osteoblast like SaOS2 cells. The results showed that SaOS2 cells were able to adhere, proliferate and migrate into pores of scaffold. Furthermore, the cell viability was found to increase on porous scaffold compared to dense HA. The expression of alkaline phosphate, a differentiation marker for SaOS2 cells was enhanced as compared to nonporous HA disc with respect to number of days of culture. The enhanced cellular functionality and the ability to support osteoblast differentiation for porous scaffolds in comparison to dense HA has been explained in terms of higher protein absorption on porous scaffold.     

Pore size and shape in mortar by thermoporometry

The pore structure of mortar (w/c = 0.55) was examined using thermoporometry (TPM), nitrogen adsorption/desorption (NAD), and mercury intrusion porosimetry (MIP). The TPM measurements were calibrated by comparison to NAD and MIP measurements on porous glass; similar comparisons were made on dried and resaturated mortars. For undried mortars, TPM provides the size of pore entries (from the freezing cycle) and interiors (from the melting cycle). In keeping with previous studies, we find that there is an unfrozen layer of water between the ice and the pore wall in porous glass that is about 0.8 nm thick; when lime-saturated water is used, the thickness of that layer increases by about 10%. In mortar, the unfrozen layer is about 1.0-1.2 nm thick, so no freezing occurs in pores with diameters ≤ 4.5 nm, at least down to − 40 °C (where the radius of the crystal/liquid interface is ∼ 1.5 nm). Based on the hysteresis in the freezing and melting curves, the larger mesopores in mortar were found to be rather spheroidal, while the smaller ones were more cylindrical.     

Constrained sintering kinetics of 3YSZ films

3YSZ green layers approximately 10 μm thick were screen-printed onto 3YSZ substrates and their constrained sintering kinetics were measured at 1100-1350 °C using an optical dilatometer. The densification rates of the same powder in the form of pellets and free-standing films were also measured. The constrained densification rate was greatly retarded compared with the free densification rate at a given temperature and density. The retardation increased with increasing density and temperature and could not be properly accounted for by existing theories of constrained sintering. As a result the apparent activation energy is much lower for constrained sintering (135 ± 20 kJ mol⁻¹) than for free sintering (660 ± 30 kJ mol⁻¹). It is proposed that this is because the constrained microstructure exhibits larger and more widely separated pores at the higher temperatures.     

Polyvinylpyrrolidone-assisted synthesis of microscale C-LiFePO4 with high tap density as positive electrode materials for lithium batteries

Carbon-coated LiFePO₄ (C-LiFePO₄) with micron particle size (6 μm) and high tap density (1.6 g cm⁻³) was prepared from spherical FePO₄·2H₂O powder via the co-precipitation method. The C-LiFePO₄ powder was calcined at temperatures between 650 and 800 °C. The 6 μm C-LiFePO₄ prepared at 800 °C exhibited an excellent rate capability, delivering 150 mAh g⁻¹ on discharge at the 0.1 C-rate and 108 mAh g⁻¹ at the 5 C-rate. The volumetric capacity of the 6 μm C-LiFePO₄ corresponded to 225 mAh cm⁻³, since the large secondary particles (6 μm) C-LiFePO₄ sufficiently allowed tight packing of the particles. The 6 μm C-LiFePO₄ powder with high tap density makes an attractive positive electrode candidate for lithium-ion batteries designed for high energy density.     

Electroplating synthesis and electrochemical properties of macroporous Sn-Cu alloy electrode for lithium-ion batteries

Macroporous material of Sn-Cu alloy of different pore sizes designated as anode in lithium-ion batteries were fabricated through colloidal crystal template method. The structure and electrochemical properties of the macroporous Sn-Cu alloy electrodes were examined by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and galvanostatic cycling. The results demonstrated that the electrodes of macroporous Sn-Cu alloy with pore size respectively of 180 and 500 nm can deliver reversible capacity of 350 and 270 mAh g⁻¹ up to 70th cycles of charge/discharge. The cycle performance of the macroporous Sn-Cu alloy of 180 nm in pore size is better than that of the macroporous Sn-Cu alloy with 500-nm-diameter pores. It has revealed that the porous structure of the macroporous Sn-Cu alloy material is of importance to strengthen mechanically the electrode and to reduce significantly the effect of volume expansion during cycling.     

Porous alumina ceramics with highly aligned pores by heat-treating extruded alumina/camphene body at temperature near its solidification point

This study reports a novel way of increasing the pore size of highly aligned porous alumina ceramics by heat-treating an extruded alumina/camphene body at a temperature near its solidification point. The pore size obtained increased remarkably from 51 ± 8 to 125 ± 27 μm with increasing heat-treatment time from 1 to 24 h, due to the continuative overgrowth of the camphene dendrites during heat-treatment, while a highly aligned porous structure was preserved. In addition, interestingly, this heat-treatment enabled alumina walls to be densified quite well, whereas porous walls were observed in the sample produced without heat-treatment, which led to a considerable increase in compressive strength. The sample produced with a heat-treatment time of 12 h showed a high compressive strength of 11.6 ± 1.2 MPa at a porosity of approximately 84 vol%, which was much higher than that (0.28 ± 0.1 MPa) of the sample produced without heat-treatment.