Fabrication of porous film based on poly(2,6-dimetyl-1,4-phenylene ether) block copolymer by supercritical carbon dioxide treatment
( 958-963) Reactive and Functional Polymers 71 #9 (2011)
Tsuchiya et al of the Tokyo University of Agriculture and Technology, Japan, prepared the block copolymer poly(2,6-dimethyl-1,4-phenylene ether)-b-polydimethylsiloxane (PPE-b-PDMS) via hydrosilylation between poly(2,6-dimethyl-1,4-phenylene ether) (PPE) and polydimethylsiloxane (PDMS) homopolymers.  The block copolymer films were treated by supercritical carbon dioxide (scCO2) at moderate temperatures under high pressure of 25 MPa for 2 h followed by depressurization.  The resulting films showed the microcellular structure by the formation of dense isolated pores, whereas few pores were observed in PPE homopolymer film after the same foaming process.  The size of the pores was able to be controlled by varying the processing temperature or the depressurization rate.  (RDC 8/4/2011)

Design of Bimodal PCL and PCL-HA Nanocomposite Scaffolds by Two Step Depressurization During Solid-state Supercritical CO2 Foaming
( 1150–1156)Macromolecular Rapid Communications 32 #15 (2011)
Salerno et al, Italy fabricated porous scaffolds of poly(ε-caprolactone) (PCL) and PCL loaded with hydroxyapatite (HA) nanoparticles with bimodal pore size distributions by a two step depressurization solid-state supercritical CO2 (scCO2) foaming process. Results show that the pore structure features of the scaffolds are strongly affected by the thermal history of the starting polymeric materials and by the depressurization profile. In particular, PCL and PCL-HA nanocomposite scaffolds with bimodal and uniform pore size distributions are fabricated by quenching molten samples in liquid N2, solubilizing the scCO2 at 37 °C and 20 MPa, and further releasing the blowing agent in two steps: (1) from 20 to 10 MPa at a slow depressurization rate, and (2) from 10 MPa to the ambient pressure at a fast depressurization rate. The biocompatibility of the bimodal scaffolds is finally evaluated by the in vitro culture of human mesenchymal stem cells (MSCs), in order to assess their potential for tissue engineering application.(RDC 7/27/2011)

Polymeric hydrogels and supercritical fluids: The mechanism of hydrogel foaming
(2819-2826) Polymer 52 #13 (2011)
Tsioptsias et al of the Aristotle University of Thessaloniki,, Greece, used hydrogel foaming to produce foams with supercritical carbon dioxide (CO2).  This method is applied to crystalline hydrophilic polymers that, practically, exhibit no phase transition (melting or glass transition) below thermal decomposition temperature and, due to their crystallinity, do not absorb CO2.  Such polymers are mainly natural (semi)-crystalline polymers (e.g. chitosan, cellulose, etc.) for which the classical polymer foaming method with supercritical carbon dioxide is not applicable.  The hydrogel foaming process (similar to classical polymer foaming) is applied to gelatin, chitosan, and gelatin/chitosan blend hydrogels that are physically crosslinked and may also be chemically crosslinked with glutaraldehyde vapour.  After the foaming process, water is removed from the gels by mild freeze-drying leading to porous materials.  Pore size control can be achieved by controlling different process parameters.  Gelatin exhibits solubility in water up to high concentrations and forms thermoreversible hydrogels, rendering it a suitable choice for the investigation of the process mechanism.  The sorption and Raman spectroscopy measurements suggest that, besides dissolution in water (of the hydrogel), extensive CO2 sorption by the polymer also occurs. (RDC 6/2/2011)

Wet and dry highly porous cellulose beads from cellulose–NaOH–water solutions: influence of the preparation conditions on beads shape and encapsulation of inorganic particles
 (759-765) Journal of Materials Science 46 #3 (2011)
Sescousse, Gavillon and Budtova developed highly porous (Aerocellulose) beads carrying encapsulated particles were made by drying coagulated cellulose under CO2 in supercritical conditions.  (RDC 1/12/2011)

Processing of nanocomposite foams in supercritical carbon dioxide. Part I: Effect of surfactant 
(3436-3444) Polymer 51 #15 (2010)
Van NGO et al showed the nucleation occurs primarily on physico-chemical nucleation sites that are the carbonyl group of the tethered copolymers synthesized on reactive clay and that present a strong affinity for CO2. The relaxation times determined by using solid-state NMR spectroscopy are consistent with the formation of the in situ copolymers.  (RDC 12/22/2010)

Batch foaming of SAN/clay nanocomposites with scCO2: A very tunable way of controlling the cellular morphology 
(3520-3531) Polymer 51 #15 (2010)
Urbanczyk et al of the University of Liege, Belgiumfound thatfoaming at low temperature (40 °C) leads to foams with the highest cell density (1012–1014 cells/cm3), the foam expansion is restricted (d0.7–0.8 g/cm3).  This drawback has been overcome with the use of the two-step foaming process, also called solid-state foaming, where foam expansion occurs during sample dipping in a hot oil bath (d0.1–0.5 g/cm3).  This result thus illustrates the huge flexibility of the supercritical CO2 batch foaming process for tuning the foam cellular morphology.  (RDC 12/22/2010)