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The increasing importance of environmental sustainability has led to the development of new materials that are environmentally friendly, functional, and cost-effective. Lignin-containing cellulose nanomaterials are a common example of these. The advantages of lignocelluloses include their renewability, sustainability, and functionality combined with molecular rigidity and enhanced hydrophobicity. In order to valorize these beneficial traits from lignin-containing nanocellulose, various approaches have been examined in industrial applications. However, the safety of these materials has not been tested or validated in humans. In this study, we tested 21 wt% lignin-containing nanocellulose (L-MFC) in vitro using the human lung and kidney cell lines, H460 and HEK293 cells, respectively. The cytotoxicity of cellulose, L-MFC, and lignin was compared using the water-soluble tetrazolium salt assays. In addition, the gene expressions of HSP70 and HSP90 as cellular stress markers treated with cellulose, L-MFC, and lignin were quantified using real-time polymerase chain reaction (PCR) and Western blotting. Our data indicated little cytotoxicity for cellulose and significant cytotoxicity for lignin and a relatively low level of cytotoxicity for L-MFC, providing the lethal median concentration (LC50) values of L-MFC and lignin. The gene expression of HSP70 and HSP90 was little affected by moderate concentrations of L-MFC. Interestingly, the lignin contained in L-MFC influenced the cell viability and the gene expression of HSP70 and HSP90 less than the same amount of lignin alone. These results indicate that L-MFC displays cell-type-dependent sensitivity and suggest that L-MFC could serve as a new eco-friendly material that is relatively safe for humans.

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This study explores the effects of using lignin-rich microfibers as a reinforcing material to enhance paper strength. The microfibers prepared by alkaline kneading of organosolv pulp for 1 to 3 hours were characterized in terms of fiber dimensions, residual lignin content, freeness, and water retention value. Longer alkaline kneading times were more effective for improved fiber micronization. In addition, freeness decreased and water retention value increased as a result of the kneading treatment. The microfibers were added at increasing amounts (1%, 3%, and 5% based on oven-dry weight) to commercial bleached kraft pulp to evaluate the effect of microfiber content on handsheet strength. The results showed that microfibers at a level of 5% increased the tensile index of the handsheet by up to 8%, indicating that lignin-rich microfibers have a high potential for use as paper strength additives.