Low Transition Temperature Mixtures (LTTM) Containing Sugars as Potato Starch Plasticizers

For the first time, low transition temperature mixtures - LTTM based on sugars: fructose (Fruc), glucose (Gluc) or sucrose (Suc), and glycerol (G) are prepared, characterized by DSC and applied as potato starch plasticizers. Sugar-based LTTM exhibits good plasticizing activity leading to homogenous transparent, flexible thermoplastic starch (TPS) materials. Mechanical, dynamic mechanical (DMA), X-ray diffractometry (XRD), and FTIR analysis of obtained TPS/LTTM films are performed for their relative comparison. For TPS/Fruc:G films, tensile strength (TS) and Young's modulus (YM) decreases and elongation at break (EB) increases with increase of G. However, for TPS/Gluc:G molar ratio of Gluc to G did not affect significantly on films mechanical properties. Comparing two monosugars, i.e., Gluc and Fruc, TPS/Gluc:G materials exhibit slightly higher TS (4.8-5.8 MPa) but lower EB (44-61%) in comparison with TPS/Fruc:G films (TS 3.2-5.0 MPa; EB 90-115%) at 25 degrees C, RH 50%. LTTM as whole mixture of components led to TPS products with not only higher TS, YM but even EB in comparison with films where sugars and G were added separately into starch. Mutual interaction between sugar, polyol and starch is confirmed by DMA. XRD reveals that starch with LTTM undergone amorphization and TPS/Suc:G 1:6 is the most amorphous among investigated TPS films.