Polyvinyl alcohol foams

Wongsuban, B., Muhammad, K., Ghazah, Z., Hashim, K., Hassan, M. A., The effect of electron beam irradiation on preparation of sago starch/polyvinyl alcohol foams. Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 2003,211(2), 244-250. 

Horton JA, Marano GD, Kerber CW et al. (1983) Polyvinyl alcohol foam-gelfoam for therapeutic embolization A synergistic mixture. Am J Neuroradiol 4 143-147... 

The size and extent of the tumor, the need to preserve any of the renal parenchyma, and the overall goal of embolization should be considered in planning embolotherapy of renal tumors. Historically, the choice of embolic agents depended on the experience and preference of the operator. Although more than twenty embolic agents have been used (Table 16.2), it is most worthwhile to consider three classes of embolic agents currently used for embolizations of renal tumors liquid agents (the prototype of which is absolute ethanol), particulate materials (the prototype of which is polyvinyl alcohol foam), and metallic coils. 

Wright KC, Anderson JH, Gianturco C, WaUace S, Chuang VP (1982) Partial splenic embolization using polyvinyl alcohol foam, dextran, polystyrene, or silicone. An experimental study in dogs. Radiology 142 351-354... 

Among the nonabsorbable embolic materials. Polyvinyl Alcohol particle (PVA) is one of the most widely used. This consists of a water-soluble, biocompatible material made by a reaction of polyvinyl alcohol foam with formaldehyde. When it is moisturized, it expands its volume up to 20% more... 

Berenstein A,Graeb D (1982) Convenient preparation of ready-to-use polyvinyl alcohol foam suspension for embolization. Radiology 145 846-850... 

Work at the EPA Gulf Breeze Laboratory has demonstrated the potential usefulness of encapsulation in the bioremediation of PAHs. A model system has been developed in which a pure culture capable of degrading fluoranthene (strain EPA505) has been successfully encapsulated in polyurethane foam and polyvinyl alcohol (Baker et al., 1988). The capsules can be stored for several months at 4 °C with only minimal loss of viability. Upon addition of the capsules to moist soil, fluoranthene mineralization commenced in approximately the same way as observed when fresh bacterial cells were added to the soil. These results are shown in Figure 5.7a. Since the same inoculation size was used in all flasks during this experiment, the results suggest that the immobilization process does not significantly affect microbial activity. 

Quite similar results have been reported by van Vliet [226]. He found that the equilibrium thickness of foam films from aqueous solutions of polyvinyl alcohol at low pressure is much larger than twice the adsorption layer thickness measured by ellipsometry. The core thickness is again several times the radius of gyration of the polymer molecules in... 

The shape of the experimental isotherm (Fig. 3.38) is qualitatively similar to that found by van Vliet [226] with foam films from aqueous solutions of polyvinyl alcohol. It is also characteristic of the interaction energy as a function of the distance between two mica surfaces bearing grafted polymer brushes in good solvent as determined with Surface Force Apparatus (SFA) [e.g. 242],... 

A direct relation between the polymer foams density (respectively, the expansion ratio) and the oligomer content in it has been established [114], Addition of water soluble polymers (polyvinyl alcohol, carboxymethyl cellulose, etc.) led to a reduction in resin consumption without deteriorating the quality of the solid foam obtained. Polymer foams of density 5-7 kg m3 were produced when the oligomer consumption was not more than 15-20% with respect to the solution volume. 

The materials employed for making hollow microspheres include inorganic materials such as glass and silica, and polymeric materials such as epoxy resin, unsaturated polyester resin, silicone resin, phenolics, polyvinyl alcohol, polyvinyl chloride, polyjM-opylene and polystyrene, among others, commercial jx oducts available are glass, silica, phenolics, epoxy resin, silicones, etc. Table 36 shows low-density hollow spheres. Table 37 shows physical properties of glass microspheres, and Table 38 shows comparison of some fillers on the physical properties of resulting foams (10). 

Madders. Phenolic polymers are known to have high rigidity, and this property extends to phenolic foams, which are highly friable. In order to reduce friabUity and permit some flexibUity and toughness, various kinds of modifiers are sometimes used. Reactive modifiers are used in the course of resol-resin preparation, and they become integral parts of the polymer structure. Examples include PVA (polyvinyl alcohol), PVA-PVC (polyvinyl alcohol-polyvinyl chloride-copolymer), resorcinol, o-cresol, furfuryl alcohol, and other various types of polyols. 

Waste Disposal. All processes must include some form of washing step to remove impurities from the bottles. If the adhesive, poly(vinylacetate), PVA, is to be separated through dissolution or hydrolysis to poly(vinyl alcohol), the waste stream will contain PVA and/or dissolved polyvinyl alcohol in addition to the other contaminants which must be removed. Paper fibers are another major source of impurities. For a lOMM Ib/yr plant about 75,(XX) Ib/yr PVA will be removed via the effluent. Environmental regulations probably require that this problem be addressed, especially since polyvinyl alcohol is an excellent foaming agent. 

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