The brittleness and water sensitivity of cellulose nanofibril (CNF) films have hindered their commercialization. Furthermore, residual lignin often deteriorates strength properties of CNF films. However, we demonstrate how colloidal lignin particles (CLPs) can not only enhance the ductility of CNF films, but also adds other advantageous properties to the composite material, like water resistance, and resistance against oxidation and protection from UV light. Unmodified CNF from bleached kraft pulp was obtained using disintegration with microfluidizer. The CLPs, with mean diameter around 100-200 nm, were obtained by dissolution of kraft lignin in organic solvent followed by spontaneous self-assembly into spherical lignin particles in water. The performance of cationic and anionic CLPs were systematically compared to bulk softwood Kraft lignin.<br/>We show that at optimal lignin concentration (10 wt-%), the nanocomposites demonstrate tougher film structure along with the highest strain at failure values reported thus far for all-lignocellulose films (Fig.1). The addition of CLPs furthermore rendered the films waterproof, provided antioxidant activity and UV-shielding with better visible light transmittance than obtained with irregular lignin aggregates. The fundamental reason behind the excellent performance is discussed. We conclude, based on electron microscopy, dynamic water sorption analysis, and tp-DSC that homogeneously distributed CLPs act as ball bearing lubricating and stress transferring agents in the CNF matrix. Achieving the aforementioned combination of properties using the two most abundant wood polymers presents new opportunities in the field of green bio-based nanocomposites. Other examples of novel materials with enhanced properties by combination of lignocellulosic nanoparticles will also be discussed. These materials may find applications in food packaging, water purification and biomedicine.

Combining nanocellulose and nanolignin for high-performance materials

2019 Spring National Meeting

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