Classical and photopyroelectric studies of optical and thermophysical properties of starch sheets: dependence on water content and temperature

The optical and thermophysical parameters of starch films (obtained by extrusion) were determined in order to obtain input data for photothermal studies of water migration in such films. The optical spectra, sorption isotherm, and volume change were measured for samples equilibrated at different levels of relative humidities. The photopyroelectric method was used to measure thermal parameters as a function of water content and temperature. The thermal conductivity, thermal effusivity, and volume specific heat all increase with water content while the thermal diffusivity remains almost constant. The temperature behaviour of the thermal parameters in the -15+70 °C temperature range was measured for samples with different water contents. No phase transition was observed at 0 °C, which proves either that water in the starch matrix is not in a free form, or the fact that water dissolved other particles shifting the melting point to a lower temperature.