Tailoring of crystal size and significant enhancement of physical property, ductility and toughness in in-situ nano kraft lignin/nano-fibrillated cellulose biocomposite

An aqueous dispersion of nano-fibrillated cellulose (NFC) biocomposite solution with colloidal kraft lignin (CKL) particles ranging from 0 to 5 wt% was produced by preparing in-situ CKL in the aqueous dispersion of NFC. The CKL/NFC dispersions were vacuum filtered to remove excess water and then dried at 70 °C for 5 min using compression molding to obtain free-standing CKL/NFC composite films. The CKL particles remained homogeneously dispersed on the NFC fibril surfaces, forming hydrogen bonds with the hydroxyl groups of the NFC chain, which led to in-situ CKL-directed crystallization as well as nano-reinforcement. X-ray diffraction studies confirmed that the crystal size of the NFC molecules increased with the integration of in-situ CKL particles. Consequently, the CKL/NFC composite films demonstrated significant enhancement of tensile strength, elongation at break, and toughness. Additionally, CKL/NFC composite films exhibited outstanding thermal stability, UV-shielding, and antioxidant properties. These findings suggest that CKL/NFC biocomposite films could be suitable for structural and engineering composite materials, consumer products, and packaging applications.