The Role of Citric acid/Glycerol Ratio on Viscoelastic Behavior of Melt Processed Thermoplastic Starch

In this work, the effect of citric acid/glycerol ratio on plasticization of starch and its influence in determining the melt viscoelastic behavior of resulting thermoplastic starch was investigated by means of a combination of rheology and XRD and thermal analysis. It was shown that the melt rheology can be utilized as a complementary technique with XRD to study the plasticization as well as the melt process ability of TPS. In this context, the complex viscosity (η*) and/or storage modulus (G’) of the samples at low frequency range were considered as a measure of the extent of gel formation and therefore the process ability of TPS. The effect of citric acid on reducing the complex viscosity through chain scission mechanism was found to be much greater compared to that induced by glycerol plasticization. From these results and the results of XRD and thermal analysis (DMTA) it was shown that the TPS sample plasticized by citric acid/glycerol ratio of 1:9 could have more reasonable combination of process ability and physical performance compared to other TPS samples