Formamide and 2-hydroxy-N-[2-(2-hydroxy-propionylamino)-ethyl] propionamide (HPEP) as a mixed plasticizer for thermoplastic starch

As a plasticizer of starch, 2-hydroxy-N-[2-(2-hydroxy-propionylamino)-ethyl] propionamide (HPEP) is synthesized by the reaction of lactic acid and ethylenediamine. Melt extrusion processing is used to prepare thermoplastic starch by the mixed plasticizers of formamide and HPEP (FHTPS). Fourier Transform Infrared proves that the mixed plasticizers can form the interaction with CO group of starch in FHTPS. Scanning Electron Microscope shows that formamide and original water are necessary to from the homogeneous FHTPS containing formamide/HPEP/original water (20/10/10). X-ray diffraction exhibits that the mixture of formamide and HPEP can effectively suppress starch re-crystallization, and the original water has no effect on starch re-crystallization when FHTPS are stored at RH 50% for 50 days. Water absorption testing shows that the more HPEP is, the better water resistance of FHTPS is. With the increasing of HPEP ratios, the tensile strength of FHTPS is increased while the elongation is decreased at the whole range of water contents.