Influence of starch content on the properties of low-cost microfiltration ceramic membranes

Abstract

The use of starch as pore former is frequent in the fabrication of porous ceramic membranes, since starches are cheap, innocuous and environmentally friendly. A study has been conducted to evaluate the influence of potato starch content (0–30 wt%) and sintering temperature (1100 and 1400 °C) on low-cost ceramic microfiltration membranes. The raw materials were a mixture of kaolin, alumina and starch, from which membrane specimens were shaped by uniaxial dry pressing.

The results indicated that the percentage of potato starch did affect the properties of the membrane. Thus, an increase of starch content provoked a reduction of bulk density (an increase of porosity) a rise of water permeability and a substantial modification (coarsening) of the pore size distribution. This effect deals with the role as pore former of starch, which burns out when fired. More interestingly, it was experimentally observed that the effect of starch was particularly effective for starch percentages higher than 10 wt% once a connected coarse pore network is developed. On the other hand, an increase in sintering temperature from 1100 to 1400 °C also influenced membranes׳ characteristics but the effect was much less significant than that of starch content.

A percolation analysis based on the Effective Medium Approximation (EMA) contact model allowed to conclude that the critical porosity calculated corresponds to a starch content of 10.2 wt%, which agrees quite well with the estimation from experimental results. Finally, tortuosity was calculated with a simple model derived from the Hagen–Poiseuille equation. The obtained data showed that tortuosity factor decreased as the starch content or sintering temperature increased. These findings are consistent with SEM analysis and pore size determination.