Functionalization of black tea waste for application in bio-based natural rubber composites with enhanced properties

The use of biowaste as fillers of polymers represents an important step toward creating sustainable composites with reduced environmental footprint. Therefore, the aim of the study was the functionalization of plant-based biofiller, one of the mainstream food processing by-products, i.e. waste ground black tea leaves (BTG), using silanes and cationic surfactant to improve the dispersion of the biofiller in natural rubber (NR). The effect of biofiller modification on its dispersion in the elastomer matrix was investigated, as well as the influence of surface modification and filler dispersion on the curing behavior and properties of the elastomer composites, i.e., mechanical properties under static and dynamic conditions, hardness, crosslink density, and resistance to thermo-oxidative aging. Thermal analysis was applied to examine the impact of biofiller functionalization on the curing characteristics and thermal stability of the biocomposites. BTG waste improved the mechanical properties and resistance to thermo-oxidative aging of NR vulcanizates. However, agglomeration of the biofiller particles at higher loadings was observed. Functionalization of BTG with silanes and cationic surfactant efficiently increased the hydrophobicity of the biofiller surface and consequently improved its compatibility with non-polar rubber matrix. NR composites filled with functionalized BTG waste exhibited improved mechanical strength, thermal stability and thermo-oxidative aging resistance accompanied with good damping properties. • Black tea waste is valorized as a sustainable biofiller for natural rubber. • Silane and CTAB treatments improve biofiller hydrophobicity and matrix compatibility. • Polyphenols in tea waste improve thermo-oxidative aging resistance of composites. • Functionalization offsets thermal stability loss seen with unmodified filler.