Pore shape in the sodium chloride matrix of tablets after the addition of starch as a second component.

The present research aims to test the hypothesis that the addition of a minor component causes a change in pore shape in the matrix of the primary component, causing a decrease in mechanical strength. Tablets made of sodium chloride only and tablets made of a mixture of sodium chloride (97.5% v/v) and starch (2.5% v/v) were compared. Tablets were subjected to a heat treatment to remove the starch. The pore structure was evaluated with mercury porosimetry and image analysis on SEM images. At comparable porosities the tensile strength of the mixture tablets was significantly lower than that of the tablets made of NaCl only. Visual inspection of the images suggested a structure with less connectivity of the grains for the heat treated mixture tablets. This was confirmed by the results of the algorithm calculating the relative path length. Image analysis showed that the pore size distribution shifted towards larger pores after the addition of starch. It was thus concluded that the lower mechanical strength of the tablets made of the binary mixture was caused by the more open pore structure and more larger pores as could be detected with image analysis.