Design of a Lignin-Based Versatile Bioreinforcement for High-Performance Natural Rubber Composites

This work designed a lignin-based reinforcing agent for reinforcing natural rubber (NR) via building up an integrated interfacial network. A facile lignin modification approach was developed using a cyclic anhydride with a long alkene chain, (2-dodecen-1-yl)succinic anhydride. The grafting of the modifiers preferentially takes place at the aliphatic −OH sites as indicated by 2D heteronuclear single-quantum coherence and 31P NMR spectra. The amount of grafted modifier was estimated via TGA, being 27.1 and 48.8 wt % for the two modified lignin samples. The high degree of modification results in an elevated molecular weight, reduced Tg, and improved hydrophobicity. The NR composites show comparable mechanical properties when 30 wt % of carbon black was replaced with modified lignin. The modification of lignin generates more −COOH groups, which facilitates coordination interactions, and the introduction of zinc dimethacrylate imparts further improved mechanical properties beyond the counterpart with carbon black, especially for the stress at low deformation. Stress relaxation and cyclic tensile tests reveal that these composites are able to largely keep and recover the network structure due to the coordination interaction. This work provides a versatile lignin-based reinforcement for more sustainable and higher-performance NR composites.