Controlling the Melt Resistance to Flow as a Possibility of Improving the Miscibility and the Time Behavior of Some Blends Based on Starch

Doina Dimonie,Miruna Musat,Eugeniu Vasile,Liliana Anton,Roxana Trusca,Sanda Maria Doncea,Celina Maria Damian,Maria Râpă

doi:10.1155/2015/582901

Abstract

The paper proves that the miscibility of some blends based on starch can be improved by finding for each of them the melt resistance to flow at which the nonstationary flow and the melt degradation are avoided and the developed shear rate homogenizes optimally the material composition. The obtained results show that, for process sensitive materials like starches, the border between good and less miscibility is so narrow that the window of melt processing conditions and the best formulation must be found for each of them. The improving of miscibility by controlling the melt resistance to flow proves to be a good method to prevent retrogradation and plasticizer leaching and so to handle the new compounds behavior during usage.

Highlights

Physical modification of starch is a common practice to diminish its limitations such as poor processability, brittleness, hydrophilicity, and low compatibility [1] and involves the obtaining of multicomponent, multiphase materials [2,3,4]
The shear rate of the low (Figure 1(a)), medium (Figure 1(b)), and high (Figure 1(c)) plasticized blends at low load rises on the entire temperature range from 145∘ C to 175∘ C, from approximately 10 s−1 to about s−1 and, respectively, to 50 s−1
The increase of the shear rates is biggest at higher plasticizer content and great load almost on the entire temperature range, mainly from 155∘ C

Summary

Introduction

Physical modification of starch is a common practice to diminish its limitations such as poor processability, brittleness, hydrophilicity, and low compatibility [1] and involves the obtaining of multicomponent, multiphase materials [2,3,4]. The free flow without degradation of the macromolecules of each polymer (destruction under shear) and the creation of new interactions, this time, between the chains of PVOH and those of starch are hard to be reached simultaneously [8, 12,13,14]. These difficulties lead to undesired blends behavior during usage as retrogradation and plasticizer leaching [14, 18], phenomena which diminish severely the quality of goods achieved from the new materials. The paper aim was to study the possibility of improving the miscibility of some blends based on starch by controlling the melt dynamic viscosity to avoid the nonstationary flow of the melt and the retrogradation and the plasticizer leaching in the solid state and so to handle the time behavior during usage of new obtained amorphous materials designed for goods with short life

Experimental

Melt Rheology

Blends Miscibility

XRD-Retrogradation

Conclusions