Waste Coffee Silverskin as a potential filler in sustainable composites: Mechanical, thermal, and microstructural analysis

The over-exploitation of existing natural resources and increased environmental concerns have fueled a strong desire towards exploring novel ways of developing environment-friendly materials. Every year, an enormous amount of agro/industrial waste is disposed of in the environment. These waste materials can be easily utilized as reinforcement/fillers for the production of biocomposites. Coffee silverskin (CSS), the by-product derived from the roasting of green coffee beans, can be potentially used as a filler to develop biodegradable composites made of poly(lactic acid) (PLA) and bio-based poly(butylene succinate) (bio PBS) polymers. In the current research work, the original form of CSS was grounded and separated into two different sizes (150–212 µm and 212–425 µm) to make particulate composites with varying filler loading (10, 20, and 30 wt%). The developed composites were compared to pure PLA and bio PBS polymers in terms of their dynamic mechanical, thermal, morphological, and crystallization characteristics. The results indicate that CSS fillers can improve the mechanical properties of bio PBS composites. 10 wt% of filler content of smaller filler size has shown optimum tensile strength for bio PBS composites. The degree of crystallinity of PLA composites slightly increased with filler loading, while the crystallinity of bio PBS composites decreased due to the catalytic effect of metals present in the CSS. The incorporation of CSS fillers reduces the thermal stability of developed composites and substantially decreases their storage modulus and loss modulus values. Overall, bio PBS polymer composites fabricated with CSS fillers with lower filler size and loading have shown better thermal stability and mechanical properties along with good processability than PLA-based composites.