Study on lignin amination for lignin/SiO₂ nano-hybrids towards sustainable natural rubber composites

Lignin-based hybrid fillers are of increasing importance with regards to the valorization of low-value biomass and the requirement of sustainability in rubber industry, however, a facile lignin modification approach tuning the supramolecular interactions to favor the assembly of the hybrids is in demand. This study aimed to design a lignin/SiO₂ nano-hybrid via an in-situ assembly of diethylamine grafted lignin (DL) and SiO₂, and investigate its reinforcing effect on natural rubber (NR). DL was prepared through Mannich modification of lignin, and the grafted diethylamine can be clearly identified by FTIR, NMR and elemental analysis. The resultant hybrid (DLSi) displays as homogeneous nanospheres with well integrated DL and SiO₂ components as shown in the TEM images, and the hybrid (DLSi1) prepared with weight ratio of DL/SiO₂ = 1/2 shows a minimum particle size of 101.8 nm and significantly reduced polarity. Compared to the reference composite filled only with carbon black (CB), NR composites filled with DLSi/CB of 10/40 phr shows comparable mechanical properties and reduced rolling resistance, which is due to the low particle size, homogenous dispersion and strong rubber-filler interfacial affinity. Such remarkable performance suggests that the DLSi hybrid can be a promising versatile biobased filler for the application in gasoline-saving "green" tires.