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 extr usion) were determined in order to obtain input data for photothermal studi es of water migration in such films. The optical spectra, sorption isotherm , and volume change were measured for samples equilibrated at different lev els of relative humidities. The photopyroelectric method was used to measur e thermal parameters as a function of water content and temperature. The th ermal conductivity, thermal effusivity, and volume specific heat all increa se with water content while the thermal diffusivity remains almost constant . The temperature behaviour of the thermal parameters in the -15 + 70 degre esC temperature range was measured for samples with different water content s. No phase transition was observed at 0 degreesC, which proves either that water in the starch matrix is not in a free form, or the fact that water d issolved other particles shifting the melting point to a lower temperature.