On the Post-Compaction Evolution of Tensile Strength of Sodium Chloride-Starch Mixture Tablets

This study focuses on the evolution of mechanical behavior of starch and sodium chloride (NaCl) mixture tablets after compaction. This type of mixture has attracted attention in the past because such tablets exhibit lower tensile strengths than the ones of its individual components. Here we demonstrate that the strengths of NaCl-starch mixtures and NaCl tablets evolve after compaction in an opposite way. When stored at relative humidity of 60%, NaCl tablets strengthen with time, whereas NaCl-starch mixtures weaken. To explain this behavior, we propose that in the NaCl-starch mixture, the presence of 2 materials with significantly different elastic moduli leads to creation of tensile stresses at the stiffer NaCl-NaCl contacts. Such tensile stresses lead to a reduction in strength of the compacted mixtures by negating a local dissolution-reprecipitation mechanism, which strengthens the NaCl-NaCl in pure NaCl tablet. This effect is proven by experimental results from NaCl specimens diametrically loaded during storage.