Fabrication of Low-Density Foam Shells from Resorcinol-Formaldehyde Aerogel
Resorcinol-formaldehyde (RF) aerogel chemistry has been used with encapsulation techniques to fabricate low-density, transparent, foam shells. To accomplish this, the gelation time was reduced from several hours to several minutes by the addition of acid following base-catalyzed RF particle growth. However, additional "annealing" of the gel for at least 20 h was needed to maximize crosslinking and minimize swelling in exchange solvents. Increasing the molar ratio of formaldehyde to resorcinol from 2 to 3 also helped to increase crosslinking. Densification of the foam shells due to dehydration during curing was greatly reduced by judicious choice of immiscible oil phases and by saturating the exterior oil phase during the annealing stage. Shells have been produced with diameters of about 2 mm, wall thicknesses ranging from 100 to 200 μm and foam densities approaching 50 mg/cc.
S. M. Lambert et al., "Fabrication of Low-Density Foam Shells from Resorcinol-Formaldehyde Aerogel," Journal of Applied Polymer Science, vol. 65, no. 11, Jan 1997.
The definitive version is available at http://dx.doi.org/10.1002/(SICI)1097-4628(19970912)65:11<2111::AID-APP7>3.0.CO;2-K
Keywords and Phrases
Annealing; Crosslinking; Curing; Dehydration; Densification; Density (specific gravity); Encapsulation; Formaldehyde; Gelation; Gels; Solvents; Swelling, Aerogels; Resorcinol, Foamed plastics
International Standard Serial Number (ISSN)
Article - Journal