Casein proteins as building blocks for making ion-conductive bioplastics

Abstract

Plastic items are an indispensable part of our society, but due to the high carbon footprint and limited degradability of many of the petrochemical-based plastics, they raise an immense ecological concern on our planet. One approach to replacing current plastics is switching to bioderived plastics (bioplastics), which are based on the use of biological materials for the making of bioplastics. While most bioplastics to date focused on replacing common thermoplastics, we show here the use of abundant biological materials for the making of the first ion-conductive bioplastic, for which we use the most commonly available casein protein in a one-pot process. We show that sulfonating the casein chains results in an enhanced ionic conductivity of the bioplastic. The final bioplastic shows attractive tunable mechanical (Young's modulus of 2–200 MPa) and electrical (0.01–0.4 mS cm⁻¹) properties, and owing to the protein-based nature, the bioplastic is degradable upon disposal. Due to the abundance of the raw starting material and the lack of any purification stage, the final casein bioplastic has a low price tag of below 0.01 USD cm⁻².