Processing of highly porous bioglass monoliths by hydrothermal hot pressing

Porous bioglass monoliths have been processed by hydrothermal hot pressing (HyHP) from sol-gel and melt-derived bioglass powders of composition (in mol %): SiO₂–CaO–P₂O₅ (55.0-40.0-5.0) and SiO₂–CaO–Na₂O–P₂O₅ (47.2-26.4-23.8-2.6), respectively. An open porosity of >70% ever reached in 3D structures is reported for monoliths issued from sol-gel powders. Dissolution studies were performed in simulated body fluid (SBF) for 1–30 days. The monoliths were analysed using X-Ray Diffraction (XRD), Fourier Transform Infra-Red (FTIR) spectroscopy and Scanning Electron Microscopy (SEM) to observe the formation of an apatite-like layer and elemental concentration of SBF was evaluated using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). A higher kinetics in the development of apatite layer was observed for sol-gel derived monoliths. This result is explained by the high surface areas of the nanosized sol-gel powders and the possibility of HyHP to create large porosity (mesoporous monoliths) and retain large surface areas. HyHP is also effective in processing 3D-bioglass structures with porosity gradient by co-sintering powders of different size.     

Preparation of highly porous ZrB2/ZrC/SiC composite monoliths using liquid precursors via direct drying process

We developed a simple liquid precursor method for the syntheses of porous ZrB₂/ZrC/SiC composite monoliths. Furfuryl alcohol (FA), zirconium n-butoxide, tetraethyl orthosilicate and boric acid are used as the raw materials. By combining the polymerization of FA and gelation of inorganic sols, porous hybrid monoliths are prepared by direct drying the wet gels. The inorganic and organic polymers possibly form interpenetrated network which provides the robustness for the wet gel to withstand the severe changes during dessication. When heat-treated at 1600 °C, hybrid gels are converted into porous ZrB₂/ZrC/SiC monoliths. The microstructure of the ZrB₂/ZrC/SiC monoliths can be easily tailored by controlling the synthesis conditions. The porosities of the ZrB₂/ZrC/SiC monoliths can be tuned around 74.3–81.6%, while the average pore diameters can be tuned ranging from 1.0 to 8.5 μm with pretty narrow distribution. The compressive strengths of such highly porous ceramics are in the range of 1.2–1.9 MPa.     

Production of porous polylactic acid monoliths via nonsolvent induced phase separation

Polylactic acid (PLA) is one of the most promising polymers for use as the matrix of a bone scaffold. In this work, porous PLA monoliths are fabricated via nonsolvent induced phase separation using dichloromethane as a solvent and hexane as a nonsolvent. The PLA-dichloromethane-hexane compositions which undergo liquid–liquid phase separation followed by gelation are shown to allow for the production of high quality foams. Solvent exchange with methanol after aging the gel is found to substantially reduce shrinkage during drying. Using this simple, versatile and template-free method we produced PLA foams with porosities as high as ∼90.8%, specific surface area up to 54.14 m²/g, crystallinity up to 62.6% and compressive modulus ranging from 1.8 to 57 MPa. Depending on ternary mixture concentration and standing temperature a range of mesoporous and combined meso/macroporous morphologies suitable for use as a bone scaffold are produced.     

Fabrication of highly porous biodegradable monoliths strengthened by graphene oxide and their adsorption of metal ions

Ordered porous chitosan–gelatin/graphene oxide (CGGO) monoliths with over 97% porosity were prepared by a unidirectional freeze-drying method and used as adsorbents for metal ions. They were characterized by X-ray diffraction, scanning electron microscopy and thermogravimetric analysis. In addition, their water absorption, wet-state stability and compressive strength were measured. The adsorption behavior of the CGGO monoliths and influencing factors such as pH, graphene oxide (GO) concentration, metal ion concentration as well as the effect of ethylenediaminetetraacetic acid (EDTA) were investigated. The incorporation of GO significantly increased the compressive strength of the CGGO monoliths in both their wet and dry states, and changed their porous structure. They exhibited an extremely high adsorbing ability for metal ions, which decreased at low pH, but increased from 20% to 88% upon the addition of EDTA at low pH. The CGGO monoliths have good stability and can be recycled several times with only a slight loss in adsorption ability. In addition, they are biodegradable, non-toxic, efficient and regenerable.     

Preparation and characterization of porous poly(vinyl ester) resin monoliths as separation media

Porous poly(vinyl ester) resin monolithic supports were first prepared by radical polymerization of the continuous phase of oil in water high‐internal‐phase emulsions. Vinyl ester (VE) resin was used as the monomer, ethylene glycol dimethacrylate was used as a crosslinker, and poloxamer 127 was used as the emulsifier in the emulsion polymerization. The prepared columns were evaluated by scanning electron microscopy, mercury intrusion porosimetry, and Fourier transform infrared spectroscopy to observe the morphological characteristics and confirm the absorbance based on the VE resin polymer. The obtained monolith showed not only higher column permeability but also lower back pressure and higher column efficiency. To investigate the absorption performance of the monolithic column, a maximum loading capacity experiment was also applied with lysozyme (Lys), and the results show that the maximum adsorption of the poly(vinyl ester) resin monolith was 1.579 mg/g. Moreover, the capabilities of separation on this column in conjunction with high‐performance liquid chromatography were investigated. Immunoglobulin could be separated from human plasma and chicken egg yolk with high resolution within 4 min. Additionally, fast separation of two mode proteins (interleukin‐18 and Lys) was achieved on the monolith within 2 min at the rate of 1445 cm/h, which demonstrated the potential of the poly(vinyl ester) resin monolith for the fast separation of proteins. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis of emulsion-templated porous polyacrylonitrile and its pyrolysis to porous carbon monoliths

PolyHIPEs are emulsion-templated polymers synthesized within high internal phase emulsions (HIPEs). The miscibility of acrylonitrile (AN) with water has made it difficult to synthesize PAN-based polyHIPEs. This paper describes the successful synthesis of PAN-based polyHIPEs by crosslinking through copolymerization with divinylbenzene (DVB), by stabilization with a polyglycerol polyricinoleate surfactant, and by initiation with both oil- and water-soluble initiators. The PAN-based polyHIPEs had porosities of over 86% and porous structures that were different from those of typical polyHIPEs. This paper also describes the production of porous carbon monoliths through the pyrolysis of these PAN-based polyHIPEs. Pyrolysis did not produce significant changes in the porous structures, which were quite similar to those of the original polyHIPEs. The porosities were around 95% and the carbon monoliths were largely macroporous and mesoporous, with some microporosity. These results indicate that PAN-based polyHIPE templates can be used for the a priori design of porous carbon monoliths.     

Preparation and characterisation aspects of carbon-coated monoliths

Carbon-coated monoliths have been prepared by dipcoating cordierite monoliths in a polymer solution and subsequent carbonisation. Parameters of preparation that were varied were viscosity of the dipcoating solution, carbon precursor and carbonisation temperature. Two different commercial polymers have been used as carbon precursors, Novolac and Furan resins. Also monoliths have been coated with slurry of such resins and a commercial mesoporous activated carbon (CP-97).

The features of the final carbon that have been optimised are carbon loading, carbon layer thickness, coverage and mesoporosity. Coverage has been tested by leaching test in acid media. Both coverage and mesoporosity are considerably enhanced when the dipcoating mixture was a slurry of Furan resin and a commercial activated carbon. These features makes carbon-coated monoliths very suitable for their use as catalyst support in three-phase reactions.     

Preparation and characterization of microcellular thin polycarbonate sheets

A new method was developed for the microcellular processing of polycarbonate (PC) thin sheets by compression molding above PC's glass‐transition temperature and below its melting temperature within a few minutes. The effects of the foaming time, foaming pressure, foaming temperature, and foaming agent active ratio on the cell size, cell density, and relative density were studied. The structures of the microcellular PC foam were controlled in the foaming process by carefully choosing the foaming parameters. In addition, the thermal, dynamic mechanical thermal, and electrical properties of the microcellular PC foam were investigated. A differential scanning calorimetry analysis showed that the microcellularly processed PC may have a plastication effect. The variation of the storage modulus, loss modulus, and tan δ under dynamic mechanical thermal analysis was in accord with the calorimetry analysis. The measurement of the electrical property demonstrated that the insulation ability of the microcellular PC thin sheet was obviously enhanced and the dielectric strength of the microcellular PC foam was decreased compared to the unfoamed PC. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1760–1766, 2006     

Preparation of highly purified concentrates of eicosapentaenoic acid and docosahexaenoic acid

Because of the complexity of marine lipids, polyunsaturated fatty acid (PUFA) derivatives in highly purified form are not easily prepared by any single fractionation technique. The products are usually prepared as the ethyl esters by esterification of the body oil of fat fish species and subsequent physicochemical purification processes, including short-path distillation, urea fractionation, and preparative chromatography. Lipase-catalyzed transesterification has been shown to be an excellent alternative to traditional esterification and short-path distillation for concentrating the combined PUFA-content in fish oils. At room temperature in the presence of Pseudomonas sp. lipase and a stoichiometric amount of ethanol without any solvent, efficient transesterification of fish oil was obtained. At 52% conversion, a concentrate of 46% eicosapentaenoic acid (EPA) plus docosahexaenoic acid (DHA) was obtained in excellent recovery as a mixture of mono-, di-, and triacylglycerols. The latter can be easily separated from the saturated and monounsaturated ethyl esters and converted into ethyl esters either by conventional chemical means or enzymatically by immobilized Candida antarctica lipase. Urea-fractionation of such an intermediary product can give an EPA+DHA content of approximately 85%.     

Hierarchically porous monoliths of carbon and metal oxides with ordered mesopores

Hierarchically porous carbon and metal oxide materials offer great benefits in separations, catalysis and renewable energy. We have here used hierarchically porous silica monoliths with ordered mesopores as hard templates to produce nanocast carbon, Co₃O₄, and NiO monoliths with similar structures. Besides providing the materials with more well-defined physicochemical properties, the ordered mesopore structure also offers an excellent model system for investigating the nanocasting process in detail. The mesopores of the silica monoliths were first infiltrated with furfuryl alcohol or metal nitrate precursor solutions, which subsequently could be thermally converted to carbon or the corresponding metal oxides. After the silica scaffolds have been removed by etching in base solutions, the resulting replica monoliths display macroscopic morphology and macropore structure similar to the original silica template. However, while the carbon and Co₃O₄ materials both display a well-organized nanowire structure, giving rise to high surface area and narrow pore size distribution, the NiO monoliths exhibit a significantly lower surface area and less well-defined mesopore structure implying that only part of the silica mesopores has been replicated. We believe this apparent difference between the two metal oxides is a consequence of differences in mass transport.     

Hierarchically porous sulfur-containing activated carbon monoliths via ice-templating and one-step pyrolysis

Hierarchically porous sulfur-containing activated carbons were prepared by ice-templating from an aqueous sodium poly(4-styrenesulfonate) (Na-PSS) solution followed by a single 800 °C pyrolysis step. This thermal treatment induced crosslinking, with the in-situ generation of Na₂SO₄ (activating agent), before carbonization and activation. The thermal treatment also resulted in the formation of sulfur salts, which could be converted to elemental sulfur upon a simple HCl acid wash. The sulfur content in the monoliths measured by microanalysis could be increased from 17.07 wt. % to 39.74 wt. % by incorporating additional Na₂SO₄ into the monoliths prior to pyrolysis. The sulfur was uniformly dispersed within the micropores of the carbon, and could be selectively removed by degassing (heating under vacuum) at different temperatures, revealing specific surface areas of up to 1051 m² g⁻¹. The materials were characterized by various techniques and were also evaluated for their potential as cathode materials for the lithium–sulfur battery. This work may open up new and facile routes to prepare sulfur-containing porous carbons for applications where its presence is beneficial.     

Preparation of ZrC/SiC porous self-supporting monoliths via sol-gel process using polyethylene glycol as phase separation inducer

We present a straightforward method via sol-gel process using polyethylene glycol (PEG) as phase separation inducer to prepare zirconium carbide/silicon carbide (ZrC/SiC) porous monoliths. Organic/inorganic hybrid gels are prepared using zirconium oxychloride, furfuryl alcohol, and tetraethyl orthosilicate as major starting materials. In the presence of PEG, crack-free hybrid monoliths are obtained by drying the wet gels under ambient pressure, whereas in the absence of PEG, the wet gels break into pieces as expected. PEG plays a key role in maintaining the macroscopic shape of the monoliths. After ceramization at 1300–1500?°C, ZrC/SiC porous monoliths are obtained. SEM and mercury intrusion porosimetry data show that PEG also has strong influence on the microstructures of the monoliths. The compressive strengths of the ceramic monoliths are in the range of 0.3 to 0.7?MPa. And their compressive behavior starts to differ due to the changes in their microstructures, especially the pore structure.     

Preparation and characterisation of carbon-coated monoliths for catalyst supports

Carbon coated monoliths have been prepared by dipcoating cordierite monoliths in a polymer mixture and subsequent carbonisation and activation. Preparation parameters that were varied were viscosity of the dipcoating mixture, carbon precursor and carbonisation temperature. Two different polymers have been used as carbon precursors, Novolac and Furan resins. Also monoliths have been coated with slurry of these resins and a commercial activated carbon, CP-97. The features of the final carbon that have been optimised are carbon loading, carbon layer thickness, coverage and mesoporosity. Coverage has been tested by leaching tests in acid media and SEM analysis. Both coverage and mesoporosity are considerably enhanced when the dipcoating mixture was a slurry of Furan resin and activated carbon. Leaching of the cordierite was considerably reduced but not completely eliminated. The morphology of the activated carbon could be transferred to the coating layer.     

Preparation of hierarchically porous spinel CoMn2O4 monoliths via sol–gel process accompanied by phase separation

Cobalt manganite-based hierarchically porous monoliths (HPMs) with three-dimensionally (3D) interconnected macropores and open nanopores have been prepared via the sol–gel process accompanied by phase separation. The controlled hydrolysis and polycondensation of the brominated metal alkoxides, which are generated from an incomplete reaction between epichlorohydrin and MBr₂ (M = Co and Mn) in N,N-dimethylformamide (DMF), form a monolithic gel based on the two divalent metal cations. The dual-polymer strategy using polyvinylpyrrolidone (PVP) and poly(ethylene oxide) (PEO) effectively induces the spinodal decomposition, where PVP and PEO are preferentially distributed to the gel phase and fluid phase, respectively, resulting in a porous gel characterized by the co-continuous structure. The effects of DMF and PVP on the porous morphology derived from the phase separation have been systematically studied. Calcination of the as-dried gels allows for the crystallization into the spinel phase yielding hierarchically porous CoMn₂O₄ monoliths, which have been examined in detail by the structural and compositional analyses.     

Preparation of highly porous Al2O3 aerogel by one-step solvent-exchange and ambient-pressure drying

This work presents the preparation of alumina aerogel via sol-gel route utilizing ambient-pressure drying. A novel and efficient solvent-exchange process has been utilized as an alternative to conventional solvent-exchange processes by directly boiling the hydro-gel in solvent. High emphasis has been given in the selection of solvent based on polarity, boiling point, and specific gravity compared with water to facilitate efficient solvent-exchange and reuse of the solvent. The ambient-pressure-dried alumina aerogel was thermally treated at temperature from 300°C-1200°C to study the change in density, porosity, specific surface area, and microstructure along with crystalline properties. The ambient-pressure-dried alumina aerogel showed lower tapped density 0.108 g/cm³, specific surface area 519 m²/g, and total weight loss of 36.94% at 900°C. The degree of crystalline structure from amorphous was observed to increase with increase in thermal treatment temperature above 300°C, dominant above 700°C, whereas the transformation of bayerite γ-Al(OH)₃ to boehmite γ-AlO₂H was observed at 150°C-300°C and to γ-Al₂O₃ phase was observed at temperature of 300°C-1200°C.     

Preparation and characteristics of highly porous BN-Si3N4 composite ceramics by combustion synthesis

Nitride based ceramics are considered as a kind of promising material for structural and functional integration due to their robust structure, extreme environmental resistance and electromagnetically transparency. It is still challenging to prepare nitride based ceramics with homogeneous and controllable microstructure because of their low self-diffusion coefficient and difficulty in sintering. Here, we developed a gelcasting-SHS process by combining gelcasting forming and self-propagating high temperature synthesis (SHS) for the preparation of porous BN-Si₃N₄ composite ceramics. First, carbon residue problem in the gelcasting -SHS process was studied. Based on the result, porous BN-Si₃N₄ composite ceramics with high porosity (69.42 ~ 86.48%), high strength (21.7 ~ 81.0 MPa) and low dielectric constants (1.42 ~ 2.87) were synthesized. In addition, the thermal shock resistance of porous BN-Si₃N₄ composite ceramics until 1000 ℃ was evaluated.     

Preparation of microcellular poly(ethylene terephthalate) and its properties

Engineering plastics poly(ethylene terephthalate) (PET) is relatively difficult to process microcellularly compared to general thermal plastics because of its low melting viscosity. A new method was developed to microcellularly process PET in this study with a general hydraulic press above PET's crystallization temperature and below its melting temperature within times of a few minutes. A processing window existed in which to prepare microcellular PET under certain foaming time, pressure, temperature, and foaming reagent content scope. The effects of foaming time, temperature, pressure, and foaming reagent content on the thermal, mechanical, and dynamic mechanical thermal properties of microcellular PET foam were investigated. Differential scanning calorimetry (DSC) analysis showed that the transition temperature and crystallinity of microcellular PET had small changes with increasing foaming time. Under some processing conditions used in this study, the tensile strength and breaking extension of microcellular PET foam were both increased at the same time, indicating strengthening and toughening effects. The variation of storage modulus, loss modulus, and tan δ under dynamic mechanical thermal analysis was in accord with DSC analysis and mechanical measurements. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1956–1962, 2003     

混合脂肪酸选择性加氢制高纯度油酸

高纯度油酸是重要的精细化工产品。混合脂肪酸选择性加氢在化学工业中是一个非常重要的环节,同时也是生产高纯度油酸的合理途径。以雷尼镍作催化剂对混合脂肪酸进行选择性加氢正交试验和单因素水平试验,对所得产品进行凝固点测定和韦氏法碘值测定后得出最佳反应条件：在温度200℃、压力0．6MPa、时间1h、催化剂ω（B）=0．6％、搅拌250r／min的条件下可使混和脂肪酸碘值从120．84降到100左右,反应前后凝固点变化不大,提高了油酸的纯度。