Online Research on Plasticizing Process of Starch Under Superimposed Vibration Field

摘要

A novel testing machine, integrating plastic vibration processing with molding, based on a multipass rheometer, was used to investigate the effect of the complex force field on plasticization of taro and wheat thermoplastic starch (TPS) melts. Various kinds of continuous vibration fields could be tested by controlling the movement of pistons. A superimposed vibration field, combining the effects of vibration and shear, was obtained by adding a high-frequency low-amplitude oscillation on a low-frequency high-amplitude oscillation. The rheological properties of starch were directly monitored during and after the plasticization process without removing the starch melts out of the testing machine. The apparent viscosity of the TPS melts were obtained for different high-frequency oscillation conditions by monitoring the pressure difference in the cavity. The plasticization preparation time was used to characterize the benefit provided by the superimposed vibration field. The results showed the decrease of the percentage of the average plasticizing preparation time for taro starch was 3.4%, while that for wheat starch was 1.6% compared to single, low-frequency, high-amplitude oscillation. Comparison of the plasticizing preparation time under different vibration frequencies showed that the plasticization was promoted by applying the superposed vibration field, and the effective degree was related to the vibration frequency and starch type. Both TPS exhibited shear-thinning behavior after the plasticization, and samples of both types of starch which were plasticized under higher vibration frequency presented lower apparent viscosities at certain shear rates.