SORPTION BEHAVIOR OF NATIVE AND THERMOPLASTIC STARCH

Because of the interest in their possible application as biologically degradable polymers, the isotherms of sorption of water vapour by native and thermoplastic starch were measured. The thermomechanical treatment of starch and the insertion of glycerol as softener lead to the disappearance of the hysteresis and to the transition from a Type II to a Type III isotherm. A theory, describing the sorption behaviour of swellable sorbents, is introduced and its statements are discussed by means of experimental results. The theory allows to draw conclusions on the molecular behaviour during sorption.