Solution casting is a practical method for producing films at a laboratory scale and incorporating various additives into starch for food packaging. However, for industrial production, efficient and low-energy-consuming conventional polymer processing techniques like extrusion with slight modifications may be more beneficial for processing melted starch. The transformation of native starch granules to a uniform molten phase and the production of various product forms like films/sheets, foams, and shaped articles require thermal processing. The thermal phase transition of starch, which relates to its native multilevel structure, and the rheology of plasticized starch melts are essential factors that determine material performance and processibility.
The plasticization of starch requires a plasticizer that regulates its thermal phase transition. The amylose/amylopectin ratios and the type and structure of starch significantly affect its phase transition. During processing, shear treatment can break down starch granules and promote the melting of crystallites, impacting the phase transition. To study the thermal phase transition of starch, steps should be taken to prevent the loss of water, which is a commonly used plasticizer.
The rheological analysis of plasticized starch is a complex process due to the need to prevent moisture loss and apply thermomechanical input to ensure starch remelting prior to measurement. Moreover, it is necessary to consider macromolecular degradation, which is determined by the thermomechanical input, and has a significant effect on the rheological properties. Both viscous and elastic properties of plasticized starch are crucial in processing starch-based materials. Choosing the right extruder at different stages of starch processing is crucial because SSE and TSE have different advantages in processing. It is preferable to use a TSE in the first stage and an SSE in the latter stage. Premixing starch with a plasticizer before extrusion can enhance extrusion stability. Moreover, multiple extrusion runs are important for producing starch/biodegradable aliphatic polyester blend products with greater compatibility. The choice of die and subsequent drawing-out and collecting device(s) determines the specific product to be produced. Orientation is a crucial process for enhancing the mechanical properties of products during film/sheet production.
The future advancement of plasticized starch-based materials will depend on enhancing their processibility and material performance. Innovative extrusion-based processing techniques should be developed to produce plasticized starch with the maximum phase transition and minimal macromolecular shear degradation. It is also crucial to explore new plasticizers that can ensure the optimal plasticization of starch. Rheology, including both viscosity and elasticity, should receive greater emphasis in the processing of plasticized starch-based materials. Starch-based blends and (nano)composites will continue to be the main solutions for utilizing starch as a renewable resource to the fullest extent. However, the development of these materials must be integrated with the advancement of melt processing (typically extrusion) techniques for further industrialization. Currently, dispersion of nanoparticles may only be easily achieved with solution methods. Additionally, REX offers a promising method for producing high-performance starch-based blend and (nano)composite materials.