Clean Manufacturing of Cellulose Nanopapers by Incorporating Lignin and Xylan as Sustainable Additives

In this work, we report for the first time the clean manufacturing of cellulose nanopapers by a green path of mixing nanocellulose suspension in water with lignin and xylan. The procedure involves grinding the old wastepaper, microfluidizing, casting, and water evaporation. The introduction of lignin and xylan with various loadings from 1 to 30 wt% showed that properties could be significantly tuned. Moreover, lignin and xylan loadings introduced into these nanopapers endow them with improved mechanical and structural properties, as evidenced by tensile tests and scanning electron microscopy analysis (SEM). Xylan strongly promotes the transparency of nanopapers. Even at low loadings, the addition of xylan and lignin enhanced specific strength by 1.3-fold, while specific elastic modulus was found to exhibit a a 2-fold enhancement. Mathematical modeling complemented the analysis of tensile properties. Thermogravimetric analysis testified that the wastepaper is made of highly purified cellulose. Furthermore, thermal properties analysis shows that the modified nanopapers have higher thermal conductivity and diffusivity than the unmodified ones. Thermal conductivity was found to improve 3.5-fold for compositions with 30 wt% loading of modifiers corresponding to the developed denser structure as revealed by SEM. The introduced crosscut and surface structure changes enable functional applications to obtain packaging, filtering, biomedical, and sensor materials.