Importance of coupling between specific energy and viscosity in the modeling of twin screw extrusion of starchy products

Abstract

During the twin extrusion process, starch basic structure is modified and it is very important to be able to predict the changes experienced by the product. To model the transformation of starch during twin screw extrusion, it is thus necessary to take into account the strong coupling between viscosity and thermomechanical treatment. It is the purpose of the present work. We have used the software Ludovic ª to calculate the flow of a molten starch along a twin screw extruder. We have assumed that the degradation reaction (viscosity decrease) was linked to the specific mechanical energy received during the flow. We have compared extrusion cases with and without viscosity/energy coupling, and we show that it is important to take it into account to correctly predict the parameters of the extrusion process (torque, energy, product temperature, etc.) and the level of starch transformation.

Rheology to understand and optimize processibility, structures and properties of starch polymeric materials

“…Based on the previously proposed principle by Springer et al [125], an in-line rheometer called "Rheopac" has been developed by Vergnes et al [120] and used in the rheological studies of starch polymer melts [58,[126][127][128][129]. A schematic representation of this rheometer is shown in Fig.…”

“…According to the literature [93,126,129], when a TSE is used, higher screw speed (N), lower feed rate (Q), or higher N/Q can lead to higher SME. Besides, screw profile can also have impact on SME.…”

Glycol based plasticisers for salt modified starch

“…6 Thus, twin screw extrusion is generally preferred in order to ne tune the thermomechanical history of the material and efficient modelling soware have been developed to optimise the process. 7 Nevertheless, remaining issues associated with the thermoplastic starch (TPS) materials obtained with conventional plasticisers are that they are not particularly strong and they exhibit a tendency to recrystallise with time and become brittle.…”

Tough thermoplastic starch modified with polyurethane microparticles by reactive extrusion

“…Compared with CS, the viscosity of TPS decreased and was steady as the temperature increased. This was due to the high temperatures and mechanical stresses during extruder processing which destroyed the chains of amylose and amylopectin, reduced the M w of starch and thus lowered the viscosity [32]. After adding 5 wt% content of PUP, the viscosity of CP5 decreased and proved to be lower than that of TPS.…”