Interaction of moisture with sodium starch glycolate.

The relationship between the apparent moisture content and moisture sorption of modified starches was investigated. Samples of sodium starch glycolate (SSG), pregelatinized starch (PGS) and potato starch (PS) were stored for various times at 44% or 75% relative humidity (RH) to produce samples with moisture contents of up to 14%, as determined by loss on drying (LOD). Evaluation of LOD and mass gain data suggested that measured mass gain equated to predicted LOD values for PGS and PS. However, in SSG there was a nonstoichiometric relationship between mass gain and predicted LOD. In addition, samples of SSG displayed hysteresis during dynamic vapor sorption (DVS) cycling in that an apparent mass loss of about 2-3% was observed for two of the SSGs, with PS and PGS exhibiting reversibility. In some cases, SSG exhibited an apparent mass loss during the DVS cycle at with 50% RH. These observations suggest that one or more of the components of SSG "interact" with moisture. Because X-ray diffraction suggested there was no dramatic change in the crystallinity of SSG, an exchange of residual SSG solvent, alcohol, with moisture may, in part, explain the moisture sorption behavior of SSG.