N-(2-Hydroxypropyl)formamide and N-(2-hydroxyethyl)-N-methylformamide as two new plasticizers for thermoplastic starch

N-(2-Hydroxypropyl)formamide (HPF) and N-(2-hydroxyethyl)-N-methylformamide (HMF) were used independently as new plasticizers for corn starch to prepare thermoplastic starch (TPS). The hydrogen bond interaction between HPF (or HMF) and starch was proven by Fourier-transform infrared spectroscopy. By scanning electron microscopy, starch granules were shown to be completely disrupted and homogeneous materials were obtained. The crystallinity of corn starch, HPF-plasticized TPS (PTPS) and HMF-plasticized TPS (MTPS) was characterized by X-ray diffraction. The crystallinity of TPS was affected by the structure of plasticizer. The water resistance of PTPS was better than that of MTPS. At medium relative humidity (RH), both tensile strength and elongation at break of PTPS were higher than those of MTPS. At high RH, the elongation at break of PTPS was higher than that of MTPS, while the tensile strength of PTPS was close to that of MTPS.