Zein as a basis of green plastic materials: Modifications, applications, and processing

A growing amount of corn (i.e., approximately 40 % of all corn produced) is being employed for bioethanol production, resulting in zein as a byproduct. Zein is a hydrophobic storage protein that represents 60-80 % of corn proteins and has been processed into several films, coatings and plastic materials. Common petroleum-derived plastics are being replaced by greener alternatives due to environmentally related issues caused by global plastic pollution. In this sense, materials based on zein benefit from their low production cost, biodegradability, biocompatibility, and hypoallergenicity. Moreover, the uniqueness of zein lies in its hydrophobicity and strong thermoplastic behaviour, which eases its processing compared with most proteins, which typically degrade or crosslink at similar temperature ranges. The present review discusses the main applications within the global plastic industry pursued for zein, mainly films, coatings, fibre mats, and adhesives for the food, pharmaceutical and medical fields. These plastic materials are obtained through different processing techniques, which are also reviewed, such as extrusion, injection moulding, electrospinning, solvent casting, or 3D printing. Already being used commercially in food and pharmaceutical coatings, films and binders for plastics, packaging and textile products, there are still some issues to solve related to their poor strength, high brittleness and instability. Overcoming these drawbacks remains a challenge for broadening the application of zein-based materials, supporting greater sustainability in the plastic industry.