Effect of moisture content on the melting and subsequent physical aging of cornstarch
1992
Shogren, R.L.
Differential scanning calorimetry (DSC) and dynamic mechanical analysis were used to study low moisture (10-50%) gelatinized cornstarch in order to understand the severe embrittlement on ageing often seen in these systems. On ageing at 22°C, gelatinized starch having 11-20% moisture (glass transition temp. (Tg) = 112-30°C) developed endothermic DSC peaks characteristic of enthalpy changes due to structural relaxation. Increase in area (enthalpy) of these peaks with time correlated well with decreases in ultimate elongation as measured by tensile tests of extruded starch-water ribbons. Rates of increase of enthalpy and decrease in elongation with time increased with moisture content. At moisture contents of ≥25% (Tg < 15°C), high temp. endotherms characteristic of the melting of recrystallized amylopecton and amylose appeared. Data indicated that embrittlement of gelatinized starch can occur as a result of free vol. relaxation during sub-Tg ageing as well as a result of plasticizer (water) loss by evaporation.
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