Comparative study of bleached and lignin-containing cellulose nanofibrils as reinforcements in epoxy composites

This comparative study explores the influence of incorporating cellulose nanofibrils (CNFs) obtained from bleached and lignin-containing cellulose pulp as reinforcements in an epoxy matrix. The research aims to identify optimal nanocellulose loading levels for improved mechanical properties of corresponding composites. Bleached CNF (BCNF) and lignin-containing CNF (LCNF) were introduced at different weight percentages (0.5, 0.75, and 1%) using high-energy mechanical mixing and the composites were characterized through mechanical, morphological, chemical, and thermal analyses. The results indicated that BCNF exhibited superior performance compared to LCNF in improving the mechanical properties of the epoxy composites. Specifically, a 0.75% BCNF loading significantly enhanced the composite’s toughness (41% increase) and elastic modulus (79% increase) while reducing brittleness, making the material stronger and more ductile. In contrast, LCNF composites displayed lower mechanical performance and reduced ductility. The interaction between BCNF and the epoxy matrix was more pronounced, as confirmed by QCM-D and FTIR analysis, suggesting better compatibility. Thermal analysis showed that both BCNF and LCNF reduced the thermal stability of the epoxy matrix, but LCNF, with lignin, provided some protection. Lignin’s aromatic and antioxidant structure helped maintain thermal resistance, making LCNF composites at 1% loading thermally comparable to neat epoxy. However, higher BCNF loading (1%) led to decreased mechanical properties, likely due to nanocellulose aggregation. This research highlights the potential of optimizing nanocellulose content for tailored performance in bio-based composite materials.