Starch-based films have gained popularity due to their biodegradability, renewability, and wide range of applications. One of the most common methods of producing these films is through solution casting. In this article, we will explore the process of solution casting in detail, including its advantages, limitations, and applications.
The Solution Casting Process
Solution casting is a four-step process that involves solution preparation, gelatinization, casting, and drying. Firstly, the process involves mixing starch and plasticizers to about 3%–10% solid concentration in water, creating a film-forming solution. The solution is then heated up to a temperature that allows the starch to become fully gelatinized while being constantly shaken and/or stirred. After gelatinization, the solution is poured onto a flat Teflon or acrylic plate and left to dry for about 24 hours in an oven at about 40–75°C to a constant weight. The final thickness of cast films is typically 0.02–0.10mm, which is controlled by calculating the quantity of starch suspension poured onto the plate.
Advantages and Limitations of Solution Casting
One advantage of solution casting is that the low viscosity of the solution makes it suitable for preparing starch-based nanocomposites through solution casting. The low starch concentration and low viscosity ensure a good dispersion of nanoparticles. Additionally, plasticizers play an important role in processing and improving the mechanical properties of starch-based films. Plasticizers can increase film flexibility by reducing the hydrogen bonding between separate polymer chains, leading to an increase of intermolecular space. However, a limitation of solution casting is that it can result in brittle films that may limit their use in some applications. High-amylose starch has been found to have better film-forming and mechanical properties than other types of starch.
Applications of Starch-Based Films
Starch-based films have a wide range of applications in the food industry and beyond. Edible hydrophilic starch-based films have excellent oxygen-barrier characteristics, making them suitable for food protection. The use of starch-based films has the potential to significantly reduce the environmental impact of packaging materials, particularly in the food industry where traditional plastics are widely used.
Electrospraying Method for Preparing Starch Films
Another method for preparing starch films is electrospraying. This method involves gelatinizing 5% starch in deionized water, adding small quantities of dispersant and ethanol, and employing ultrasonic disruption to make a stable modified starch solution. The solution is then electrosprayed in a cone-jet mode, and films of varying thicknesses are obtained by varying the electrospraying time. This method results in instantaneous films due to the solvent evaporating quickly.
Solution casting is a simple and cost-effective method for producing starch-based films and sheets, with a wide range of potential applications in the food industry and beyond. As research into the properties and processing of starch-based films continues, new and innovative applications are likely to be discovered. The development of sustainable packaging materials such as starch-based films is an important step towards a more sustainable and environmentally conscious future.