Preparation of graphene oxide and alkali lignin nanohybrids and its application to reinforcing polymer

Lignin has been widely used as an eco-friendly and sustainable filler in polymer composites, which is a promising reuse of lignin waste. However, it suffers from a dissatisfactory reinforcing effect for polymers due to the many surface functional groups of lignin. In this work, a small quantity of graphene oxide (GO) nanosheets was employed to help form a network of alkali lignin (AL) nanoparticles to improve their hardness. The morphologies and structures of GO–AL hybrids were characterized by transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis (TGA) and Raman spectra. Taking poly(vinyl alcohol) (PVA) as a model polymer, the reinforcing effect of GO–AL hybrids was examined. Dynamic mechanical analysis results showed that the storage modulus of PVA was improved more by GO–AL hybrids than AL, especially in the high-temperature region (50–120 °C). By contrast, the tensile strength and the Young’s modulus of PVA containing 4 wt% GO–AL (1:4) were increased by 84.4% and 335.3%, respectively. TGA analysis indicated that the thermal stability of the PVA nanocomposites was improved after incorporation of nanofillers. The main observation presented here could serve as the basis for the design and preparation of lignin and other biomass-based polymer nanocomposites.