Valorization of Spent Lignocellulosic Substrate of Edible Mushrooms into Cellulose Nanofibers for Bionanocomposites Production

At the present, the spent Pleurotus substrate (SPS), which is a lignocellulosic waste from the industrial production of mushrooms, is poorly valorized and mostly landfilled. Considering the large amount of SPS that is required to produce one kilo of mushrooms and its hazard to the environment if not properly disposed of, finding means to valorize this waste is of utmost importance. This work proposes the valorization of SPS through the extraction of cellulose nanofibers (NC-SPS), by applying several bleaching and alkaline hydrolysis treatments followed by microfluidization. Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction (XRD), and thermogravimetric analysis (TGA) of NC-SPS showed that most of the lignin, hemicelluloses, and other impurities were removed after the treatments of SPS. The transmission electron microscopy analysis of NC-SPS showed the presence of nanofibers with an average width of 24.5 ± 14.9 nm, XRD indicated an increase in crystallinity from 60% for SPS to 71% for NC-SPS, while TGA showed that the onset degradation temperature increased with about 43 °C after the treatments. The new NC-SPS are similar to the nanocellulose extracted from wood and can replace it in various applications. In this work, NC-SPS were tested as modifiers for poly(lactic acid) (PLA) leading to an increase in its crystallinity, Young’s modulus (of up to 57%), and storage modulus, while preserving its thermal stability and transparency. These results showed that NC-SPS acted as good reinforcing agents for PLA, and more applications are foreseen.