Improving compatibility between coffee or black tea ground wastes and polymer matrix via silane treatment for production sustainable biofillers

The incorporation of bio-waste products into polymer materials as a fillers and colorants represents a highly significant approach for developing sustainable composites, aligning with the principles of a circular bioeconomy and contributing to reduced environmental impact. In this study, coffee grounds (CG) and black tea grounds (BTG), two mainstream food processing by-products, were employed as bio-fillers and pigments for ethylene-norbornene (EN) composites. The effects of hydrophobic treatment with (3-aminopropyl)triethoxysilane (APTS) on CG and BTG powders were compared to those of untreated bio-fillers with respect to dispersion, color characteristics, mechanical properties, and UV aging stability of the polymer composites subjected to 50, 100, 200 and 300 h of UV aging. Both the waste additives and the resulting composites were characterized through Fourier-transform infrared (FTIR) spectroscopy, tensile testing, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and spectrophotometric method. The obtained results demonstrated that the silanization of CG and BTG bio-fillers improved their dispersion within the EN matrix, consequently enhancing the UV aging resistance of the polymer composites. The EN/CG-APTS composite exhibited the best mechanical properties during the aging process, with the highest aging factor value of 0.6 after 300 h. On the other hand, the EN/BTG-APTS composite showed the smallest color change (ΔE = 7.8) after 300 h of aging. These findings indicate that improving the compatibility of bio-fillers with the polymer matrix can further increase their application potential in sustainable polymer materials technology.