Spent coffee grounds utilization for green ultraviolet filter and nanocomposite fabrication

Spent coffee grounds (SCGs), the main by-product in the coffee industry, were proposed as a starting material to fabricate both ultraviolet (UV) shielding material and nanocomposite based on polyvinyl alcohol (PVA). The extract using low SCGs concentration (0.25 wt%) contains a significant amount of UV-absorbing substances. The UV shielding film from 5 wt% PVA solution and SCGs extract (1 g SCGs/200 ml water) could shield most of the radiation in UV-B and UV-C regions and maintain 63% transmittance at 550 nm. The SCGs after washing were ball milled and the ultrasonic liquid processor was applied to synthesize SCGs nanoparticle. The effects of ultrasonic amplitude and hexadecyltrimethylammonium bromide (CTAB) on the particle's hydrodynamic diameter were investigated. The particle's size of 148 nm was obtained with 50% ultrasonic amplitude. Fourier-transformed infrared spectroscopy (FTIR) results confirmed the presence of hydroxyl groups (-OH) on the SCGs-based nanoparticle's surface. The tensile strength of PVA-SCGs nanocomposite was significantly improved. However, the presence of CTAB in the nano solution could not show a better tensile result. The organic compounds contained in the SCGs extract and even in the nano SCGs solution could enhance thermal oxidation stability for both UV shielding films and nanocomposites.