Green Composite of Instant Coffee and Poly(vinyl alcohol): An Excellent Transparent UV-Shielding Material with Superior Thermal-Oxidative Stability

Producing ultraviolet-light-shielding (UV-shielding) materials via green chemistry has been attracting researchers' attention. Herein, a polymer composite produced by hybridizing instant coffee with poly(vinyl alcohol) (PVA) is reported. It has been shown that adding coffee extract can significantly improve the UV-shielding property of the PVA material in the wavelength range between 200 and 400 nm, and the polymer composite remains largely transparent in the visible region. The UV-shielding performance of the composite can be maintained under the accelerated aging condition with a UV light dose of 40 MJ/m(2) for 68 h (approximately equivalent to a 45-day outdoor exposure in Miami, Florida). In addition, enhanced thermal-oxidative stability has been observed for the composite, as indicated in the thermal gravimetric analysis (TGA). The composite material can be used in the form of polymer films processed by solution casting or be served as a protection layer by dip coating. The mechanisms of UV shielding and thermal-oxidative stability are discussed based on effective components such as melanoidin, caffeine, and chlorogenic acid. The work demonstrates yet another route toward fabricating biocompatible and environment-friendly UV-shielding materials with sound overall performance.