Void size distributions of wet-spun acrylic fibers were studied by means of mercury porosimetry, X-ray small angle scattering and combined measurement of surface area and density:
1. Measurements of the porosimetry revealed that first the void size distributions depend on the polymer compositions; the peaks of the distribution curve are at the radii of about 1000 A for fibers from acrylonitrile (AN) and methyl acrylate (MEA) copolymer, about 400 A for polyacrylonitrile fibers and fibers from AN, MEA and styrene sulfonate (SSS) terpolymer, about 100 A for fibers from AN and SSS or allyl sulfonate (SAS) copolymer, secondly the position of the peak shift to the small radius by stretching.
2. The results obtained from the X-ray small angle scattering based on Fankuchen's method are similar to that obtained by porosimetry.
3. Assuming that the frequency distribution of the void size takes gamma distribution, the mean radius (R_??_) and the number (N_??_) of the spherical voids are obtained by the following equations. where p is a parameter of gamma distribution function, d₁ is toluene density, d₂ is mercury density, A is surface area of fibers.
Using the relationship between gamma distribution and x² distribution, volume fraction of voids having radii larger than a certain value (Pr) can be estimated.
4. The results obtained from applying the analytical method mentioned at (3) are as follows; first, R_??_is nearly equal to the radius at which void size distribution curve from porosimetry takes a maximum value. Secondly logarithm of the number of voids having smaller radii than 1000 A is linearly related to the X-ray small angle scattering power.