Internal stress effect induced by drying in starch-based composite films

[Display omitted] •Tm of paraffin is shifted to high temperature when encapsulated in starch films.•Level of shift of Tm depends on the humidity during drying.•The shift is due to internal stress developed by the shrinkage of starch matrix. Starch films containing eicosane droplets with diameters of 3–5 μm homogeneously distributed over the thickness were prepared using the casting method. The films also contain a quantity of water (4–22%) depending on the relative humidity during conditioning (from 7% to 90%, respectively). The calorimetric behavior of dispersed eicosane droplets, studied by Differential Scanning Calorimetry, shows a shift in the melting temperature (Tm) of about 12 °C above the Tm of pure eicosane, which is 35.8 °C. This shift depends on the relative humidity during the conditioning of glassy starch films. The shift is also revealed by dynamic mechanical analysis and temperature-controlled X-ray analysis. The diffractogram did not show crystal structure changes associated with temperature shift. Based on the Pressure–Temperature phase diagram of eicosane, the temperature shift can be attributed to an internal pressure of up to 50 MPa on eicosane droplets, applied during starch drying.