Macroporous foams

Liu, H., Nakagawa, K., Chaudhary, D., Asakuma, Y, and Tade, M.O., 2011. Freeze-dried macroporous foam prepared from chitosan/xanthan gum/montmoriUonite nanocomposites. Chemical Engineering Research and Design 89 2356-64. 

Macroporous foams based on PEEK were also produced (Figure 9.10). Particle-stabilized liquid foams provide a general route for producing low-density macroporous materials from either melt-processable or intractable thermoplastics. By varying the size, concentration, and wettability of the particles in the colloidal suspensions... 

Materials ivith Dual Mesa- and Macroporous Structure Templated in Macroporous Foams 295... 

Materials with Dual Meso- and Macroporous Stmcture Templated in Macroporous Foams Obtained From Highly Concentrated Emulsions... 

Advanced fabrication Fabrication in a variety of forms (i) Monoliths, films, and micromolded/ micropiinted structures accessible (ii) glasses, micro-/macroporous foams, flexible rabbets, and rigid plastics available (iii) microstructure and bulk properties can be engineered via precursor mix, hydrolysis and aging conditions, and templating methods. Full demonstration of advanced sol-gel biofabrication required... 

It is our intention to present strategies based on chemically induced phase separation (CIPS), which allow one to prepare porous thermosets with controlled size and distribution in the low pm-range. According to lUPAC nomenclature, porous materials with pore sizes greater than 50 nm should be termed macroporous [1]. Based on this terminology, porous materials with pore diameters lower than 2 nm are called microporous. The nomination mesoporous is reserved for materials with intermediate pore sizes. In this introductory section, we will classify and explain the different approaches to prepare porous polymers and to check their feasibility to achieve macroporous thermosets. A summary of the technologically most important techniques to prepare polymeric foams can be found in [2,3]. 

By far the most studied PolyHIPE system is the styrene/divinylbenzene (DVB) material. This was the main subject of Barby and Haq s patent to Unilever in 1982 [128], HIPEs of an aqueous phase in a mixture of styrene, DVB and nonionic surfactant were prepared. Both water-soluble (e.g. potassium persulphate) and oil-soluble (2,2 -azo-bis-isobutyronitrile, AIBN) initiators were employed, and polymerisation was carried out by heating the emulsion in a sealed plastic container, typically for 24 hours at 50°C. This yielded a solid, crosslinked, monolithic polymer material, with the aqueous dispersed phase retained inside the porous microstructure. On exhaustive extraction of the material in a Soxhlet with a lower alcohol, followed by drying in vacuo, a low-density polystyrene foam was produced, with a permanent, macroporous, open-cellular structure of very high porosity (Fig. 11). 

Microcellular foams can be produced by thermally induced phase separation (TIPS) [47, 74, 76], The induced spinodal decomposition can be optimized to generate, e.g., polylactide scaffolds with the porous morphology and physicomechanical characteristics of a foam. Interesting materials can be constructed in a simple process. These materials exhibited bundles of channels with a diameter of 400 pm. The internal walls of the tubular macropores have a porous substructure with pore diameters of " 10 pm. It appears to be remarkable that the channels have a preferential... 

Embryogenic rice calli tend to form larger clumps during cultivation. Therefore, immobilization of the calli has hardly been carried out until now. Porous supports such as polyurethane foam have often been used for the immobilization of mycelial cells [64, 65] and plant cells [66-68]. In almost all cases, effective production of biological materials by the immobilized cells has been reported. To avoid the damage due to the hydrodynamic stress, we proposed the immobilization culture of rice callus using a macroporous urethane foam support. A turbine-blade reactor (TBR), which has been developed for hairy root culture, was also used in the culture. In the culture space, polyurethane foam was added as an immobilization support. 

V. Maquet, S. Blacher, R. Pirard, J.-P. Pirard, M. N. Vyakamum, and R. Jerome, Preparation of macroporous biodegradable poly(L-lactic-co-e-caprolactone) foams and characterization by mercury intrusion porosimetry, image analysis and impedance spectroscopy, J. Biomed. Mater. Res. 66A, 199-213 (2003). 

Figures la-d shows typical cross-sections of isotropic PE foams and longitudinal and transverse sections of PLA foams. In the first case, image analysis characterization was used to determine the macropore size distribution. In the second case, a complete morphological description requires the determination of the density, size distribution, orientation and dispersion of the ultramacropores as well as the orientation and the size distribution of the macropores. The preliminary steps of the image quantification, i.e., gray level image transformations and binary image processing are detailed elsewhere [15].

Figure 1. Scanning electron micrograph of (a) isotropic PE foam at a x20 magnification (b,c) transverse sections of PLA foam at a xlO (b) and xlOO (c) magnification (d) longitudinal section of PLA foam at a xlOO magnification, (e-h) Extraction of ultramacropores (e, f), macropores (g) and pore orientations (h) of PE (e) and PLA (f-h) foams.

Figure 2. Size distribution of the ultramacropores in PE (a) and PLA (b) foams, (c) Area size distribution of macropores in PLA foams.

Those monoliths can be produced from a piece of structured foam polymer with macropores. The piece of polymer is soaked in a sol that will form a ceramic of the desired material after heat treatment. The sol-soaked structure is dried, and it is burned at a suitable temperature to remove the polymer. The remaining structure will be a ceramic one with macropores, permitting the wall-flow of gases. This technique is also used to produce heat plates and pipes with macroporous walls for gas separation purposes. The polymers used are often derived from polyurethanes [45-46]. 

Nam YS, Yoon JJ, Park TG. A novel fabrication method of macroporous biodegradable polymer scaffolds using gas foaming salt as a porogen additive. J Biomed Mater Res 2000 53. 

Porous materials can also be coated with zeolite films by direct synthesis. For example, microcellular SiOC ceramic foams in the form of monoliths were coated on their cell walls with thin films of silicalite-1 and ZSM-5 using a concentrated precursor solution for in situ hydrothermal growth (Fig. 9).[62] The zeolite-coated monoliths show a bimodal pore system and are thermally stable to at least 600 °C. A related strategy is based on the conversion of macroporous Vycor borosilicate glass beads, having pores of about 100 nm, to MFI-type zeolite-containing beads retaining the same macroscopic shape.[63] This conversion was achieved by hydrothermal treatment with an aluminium source and a template such as TPABr. 

Pores can also be classified on the basis of their state, either open or clo.sed. In order to identify the pores by gas adsorption (a method which has frequently been used for activated carbons), they must be exposed to the adsorbate gas. If some pores are too small to accept gas molecules they cannot be recognized as pores by the adsorbate gas molecules in other words, these pores are closed pores for the gas used. These pores are called latent pores and include closed pores. Closed pores are not necessarily in small size. Thus, when carbon foam was prepared by the impregnation of poly(imide) into a poly(uTethatie) foam followed by carbonization, large macropores, few millimeters in size, were formed in the center of a block of foam, which gave the advantage that the loam can float on water [2]. 

As viewed by the present review, the most distinctive feature of solvent-impregnated resins as solid sorbents is their macroporous structure, which differentiates them from all other types and/or sorts of solid sorbents used in separation chemistry which are compact (granular) or foams (polyurethane). 

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