Hydrogen bond of thermoplastic starch and effects on its properties

The hydrogen bond played an important role in the properties of thermoplastic starch. In this paper, we analyzed the hydrogen bond interaction between plasticizer and starch in glycerol plasticized thermoplastic starch (GPTPS) and formamide plasticized thermoplastic starch (FPTPS), and thought formamide could form more stable hydrogen bond with starch than glycerol. Fourier transform infrared (FT-IR) spectroscopy revealed that the oxygen of C-O-C group participated in the hydrogen bond with plasticizers, and the hydrogen of C-O-H group in starch formed the hydrogen bond with plasticizers rather than the oxygen of C-O-H group. The excessive plasticizers would form hydrogen bond within each other and weaken the interaction between plasticizers and starch. The effect of plasticizers on the properties of thermoplastic starch (TPS) was also investigated. Because the hydrogen bond between plasticizer and starch in FPTPS was stronger than the interaction in GPTPS, the properties of two TPSs were very different. At three relative humidities (RH = 0%, 50%, 100%), the effect of hydrogen bond on the retrogradation of two TPSs was studied by X-ray diffraction. Formamide could effectively restrain the starch retrogradation. Dynamic mechanical thermal analysis (DMTA) illustrated that the stronger hydrogen bond decreased more the T-g of FPTPS. Mechanical testing showed that compared with GPTPS the tensile strength and Youngs modulus of FPTPS were lower while elongation at break and energy break were higher.