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Biobased materials offer a good alternative to the widespread use of fossil-based plastic. Foamed plastics used in various industries such as packaging, automotive, marine, and aerospace may result in sea, soil, and air pollution due to insufficient waste management systems. One of the most abundant biobased materials is starch derived from natural sources such as potatoes, tapioca, and corn. This class of materials can be handled as a thermoplastic material and employed in the foaming extrusion process by using plasticizers (such as water and glycerol) and other additives. Starch foams as a biobased and biodegradable product could be a promising alternative to expandable polystyrene (EPS) or expanded polypropylene (EPP). Their application remains, however, difficult due to issues related to moisture content and irregular swelling at the die exit, both of which affect the final product properties and well-defined shape of an extrudate. Typically, to obtain the required shape of the extrudate, a die with an approximate shape is created and iteratively adjusted based on the quality of the extrusion until the shape matches the desired one, which is still considered an art. This work aims to develop and validate a fluid dynamics model for starch-based mixtures flowing in a die and relate the shape of the foamed extrudate cross-section with the predicted die geometry and estimated flow conditions to reduce trial and error iterations. The calculated pressure drop and velocity profile are compared to experimental data. Also, the die swell phenomenon (or Barrus effect) is investigated by numerical simulation to predict the final shape of the extrudate. [ABSTRACT FROM AUTHOR]

Polymer foams with complex cross-sectional shapes are used in a multitude of different applications (including transportation, construction, packaging, food, extraction and separation) thanks to their low mass allowing efficient energy transport, optimal acoustic absorption, catalytic, impact, and cushioning properties. Dimensional accuracy of the final foamed product, obtained through a die, is one of the biggest challenges for the engineering of a stable foam extrusion process. Nowadays, the design of dies is considered an art and, usually, it involves several experimental runs, wherein a die with an approximate shape is manufactured and iteratively modified based on the quality of the extrudate. This method is time and money consuming. Herein, the design is tackled using Computational Fluids Dynamics (CFD) reducing the trial-and-error process. We present the modelling of the rheological behavior of starch-based mixtures and the results of the CFD simulations on the slit die geometry. [ABSTRACT FROM AUTHOR]