BIOPLASTICS BASED ON POTATO AND COFFEE BY-PRODUCTS FOR ACTIVE CARDBOARD COATING

The increasing generation of agri-food by-products has intensified the need for effective valorisation strategies within circular economy frameworks. Coffee silverskin (CS), a by-product of coffee roasting rich in lignocellulosic components and phenolic compounds, shows high potential as a functional additive in bio-based materials. Cardboard is widely used due to its biodegradability and recyclability; however, its hydrophilic and porous structure limits barrier performance and mechanical stability under humid conditions, while conventional coatings reduce sustainability. This work aims to develop biodegradable and active coatings for cardboard by incorporating CS into bio-based matrices. Thermoplastic starch (TPS) derived from potato washing slurries was used as matrix, and coatings were produced by thermomechanical processing and applied by hot pressing, comparing TPS and TPS/CS formulations. A pilot-scale proof of concept was performed by incorporating CS into a commercially available bioplastic formulation, followed by extrusion and film blowing. Compared to neat cardboard, TPS and TPS/CS-coated samples improved water resistance, with contact angle values increasing up to 95°, depending on formulation and coating side. TPS and TPS/CS coatings also showed moderate, time-dependent antioxidant activity. Pilot-scale processing enabled the production of thin films and natural brownish pigmentation. These results demonstrate that CS can be effectively valorised as a functional additive, supporting scalable and sustainable paper-based packaging solutions.

Acknowledgements: This work was developed within the scope of the project CICECO Aveiro Institute of Materials, UID/50011/2025 (DOI 10.54499/UID/50011/2025) & LA/P/0006/2020 (DOI 10.54499/LA/P/0006/2020), financed by national funds through the FCT/MCTES (PIDDAC). IG acknowledges FCT funding. The authors also acknowledge the BIOCOATING project (COMPETE2030-FEDER-00590400), funded by Compete 2030, Portugal 2030 and the European Union, as well as A Saloinha and FEB Cafés for providing agri-food by-products.