Agro-food waste as fillers in polymer composites for sustainable valorization

This Master’s thesis focuses on the valorisation of agro-food waste through its incorporation into bio-based and compostable polymers and on the other hand fusel-based conventional polymer matrices for the production of reusable and sector-specific products. Brewer’s spent grain and corn silage waste were selected as lignocellulosic fillers, while low-density polyethylene (LDPE), high-density polyethylene (HDPE), polybutylene succinate (PBS), and polylactic acid (PLA) were used as polymer matrices. The final goal is the development of massive, reusable objects such as fruit crates, beer packaging, and plant pots, intended for use within the same sectors generating the waste. Polymer–filler composites were prepared at different filler contents (15 wt% and 30 wt%) through drying, dry blending, extrusion, and injection moulding. PLA composites were produced exclusively with spent grain due to thermal stability limitations of the corn silage waste. Standard specimens were manufactured for material characterization and analysed in terms of chemical, thermal, and mechanical properties using FTIR spectroscopy, DSC, TGA, DMA, tensile, flexural, and Izod impact tests. In parallel, different methodologies were developed to estimate unknown filler content within the polymer matrix, based on DSC crystallinity variation and two different approaches using TGA and its first derivative. Results show that filler incorporation is feasible for both bio-based and compostable polymers and on the other hand fusel-based conventional polymers, with better processability and mechanical property retention observed in more ductile matrices such as LDPE and PBS, even at higher filler contents. In addition, the developed analytical methods proved effective in estimating filler loading within the composites. Future developments include the production of durable reusable components based on LDPE, as well as compostable single-use items solutions based on PBS, supporting circular economy strategies in food and agricultural sectors.