The increasing consumption of single-use plastics in packaging raises environmental concerns due to fossil fuel depletion and alarming plastic waste production and accumulation. Sustainable alternatives, such as biobased and biodegradable materials, are urgently needed. The pasteurized milk in Italy has a short shelf-life (6 days) after which it cannot re-enter the human food chain and it has to be destroyed or utilized elsewhere: for animal feeding, composting, production of biogas or fertilizers. The aim of our research is to find an application for expired milk in order to mitigate the biowaste and to increase its value by upcycling it into biodegradable packaging material.

Casein was extracted from expired milk using different methods yielding casein-based powders with varying structure and behaviour. These powders were further used for the preparation of dispersions under a variety of conditions (solvent, pH, concentration). Rheological properties were assessed through small amplitude oscillatory shear measurements, carried out at 25 °C. The analyses provided the evaluation of rheological behaviour based on the type of powder, solvent and pH of the dispersion. Moreover, the preliminary structural and thermal characterizations were performed using FTIR and TGA analyses, respectively. Based on the results, the most suitable dispersions were suggested to be utilized as 3D printing material for biobased food packaging.

Our approach not only reduces milk waste but also offers a sustainable alternative to petroleum-based plastics. Future experiments will be focused on the optimisation of printing conditions and mechanical characterisation of the materials.