Low-density, salt-loaded foams. [RbF] Page: 4 of 11
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Examples of these two types of foam cell structures are shown in Fig. 1.
Figure la is a photograph of the cross section of a foam cylinder, showing
the large linear cells produced by extruding a 3 wt% solution of PAN (Aldrich
Chemical Co. #18, 131-5) dissolved in N,N-dimethylacetamide (DMA) into room
temperature water. The foam shown in Fig. lb was r-oduced from the same 3 wt%
solution of PAN in DMA to which about 5 to 10% acetone had been added. Ths
addition of the acetone, a nonsolvent for PAN, reduc u the solvent power )l'
DMA and changes the polymer solidification process from nucleation and growth
to spinoidal decomposition.
Several variables can be adjusted to vary the foam cell size; the addition
of acetone appears to he the most effective. The temperature of the water bath
(or methanol/water bath) into which the polymer solution is extruded also
affects the foam cell size. Uniform, submicrometer-sized cells can be produced
by extruding the PAN/DMA/acetone solution into 00C water.
A 3 to 3.5 wt% solution of PAN in DMA/acetone yields foams with densities
of 0.05 to 0.06 g/cm3. Solutions of 2 wt% PAN are too low in viscosity to
extrude well. Solutions of b and 5 wt% PAN are too viscous, making it diffi-
cult to prepare uniform solutions. At the higher PAN concentrations, dimethyl
formamide is a better solvent because it yields less viscous solutions.
To prepare a 3 wt% solution of PAN in DMA/acetone, we used the following
procedure. The polymer is dissolved in the DMA, with stirring, by heating
(a} {b)
Y0 J m - 1001m
Fig. 1. Photomicrographs of polyacrylonitrile (PAN) foam: (a) foam formed
by nucleation and growth (density = 0.06 g/cm3), note the columnar
cell structure; (b) foam formed by spinoidal decomposition (density
= 0.065 g/cm3), note the -10-um diameter isotropic cells.
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Rinde, J.A. Low-density, salt-loaded foams. [RbF], report, January 10, 1979; Livermore, California. (https://digital.library.unt.edu/ark:/67531/metadc1208676/m1/4/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.