Microporous foams

Figure 1 Formulation of controlled drug delivery systems using the supercritical fluid-derived RESS process (A) films, (B) microparticles/nanoparticles/ liposomes, (C) coated products including microcapsules, and (D) microporous foams.

Another conceptual design deals with end-grafting a PPl with e-caprolac-tone or /-lactide in the presence of a minor amount of a second monomer to produce absorbable crystalline polymers for use as bone sealants, barrier membranes, or films that can form a continuous cell microporous foam, respectively. 

This category of treatments is devoted to improving still further the fabric s filtration efficiency and cake release characteristics. In this respect, there are basically two types of treatment (1) attachment of a more efficient membrane, for example biaxi-ally stretched PTFE (Fig. 3.9) in a lamination operation and (2) the application of a low-density microporous foam (Fig. 3.10). 

Just as microporous foams present better properties than conventional foams, it is expected that nanoporous foams will present enhanced properties because of their lower pore size. For instance, they could have better mechanical properties, such as better toughness, higher impact energies, and strain to failure [26], In addition, they could present an improved thermal insulation behavior because of the Knudsen effect [27], More details about the expected properties of nanoporous polymer foams will be provided in the last section of this chapter. 

Although it is commonly expected that nanoporous polymer foams will present improved properties over conventional or microporous foams, there are just a few experimental evidences about this behavior. The main limitation to characterize several properties of nanoporous foams is the production of sufficiently large samples that can be subjected to standard test protocols (with most of the results reported previously obtained in the form of thin films). 

A recent aproach to microporous foams involves the polymerization of high internal-phase water in oil emulsions (130). These flexible, hydrophilic open-celled foams are suitable for absorption of aqueous fluids and are being... 

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