Effects of the cell density on the total water uptake
The relationship between the foam cell density per unit volume and the final water absorption at the soaking time of 90 days was exhibited in Table 1. The data evidently show an increment of the water uptake when the cell density increased. The greater cell density implied that there were more of the pore sites at which the absorbed water could be accommodated and retained. Microscopic observation on the skin surfaces of the foamed PVC/rice hull composites revealed abundant surface openings depicting the passages of water diffused into the PVC/rice hull foamed structures, as illustrated in Fig. 3.