2.3.5. Determination of cell size and cell density
Both cell size and cell density are parameters frequently used to estimate the effectiveness of a blowing agent [19]. The average cell size was evaluated in accordance with ASTM D 3576 (procedure A)[20]. The cell size of foamed PVC/rice hull composites was determined by counting the number of cell wall intersections over a specified distance in micrographs obtained from scanning electron microscope (SEM). The cell population density per unit volume of the foamed composites (No) were determined from the SEM micrographs using Eqs. (1) and (2), and the average cell size, d, was also evaluated by using Eq. (3) [15,21].where A is the area of the micrograph, cm2, d is the average cell size,cm. No is the cell density, cells/cm3. M is the magnification factor for micrograph. n is the number of bubbles in the SEM micrograph, cells. Vf is the void fraction, %. q is the density of the rigid (unfoamed) composite, g/cm3. qf is the foam density, g/cm3. t is the average
cell chord length, mm