Spatial glass transition temperature variations in polymer glass: application to a maltodextrin-water system

A model was developed to predict spatial glass transition temperature (T(g)) distributions in glassy maltodextrin particles during transient moisture sorption. The simulation employed a numerical mass transfer model with a concentration dependent apparent diffusion coefficient (D(app)) measured using Dynamic Vapor Sorption. The mass average moisture content increase and the associated decrease in T(g) were successfully modeled over time. Large spatial T(g) variations were predicted in the particle, resulting in a temporary broadening of the T(g) region. Temperature modulated differential scanning calorimetry confirmed that the variation in T(g) in nonequilibrated samples was larger than in equilibrated samples. This experimental broadening was characterized by an almost doubling of the T(g) breadth compared to the start of the experiment. Upon reaching equilibrium, both the experimental and predicted T(g) breadth contracted back to their initial value.