Sodium Humate Functionalized Graphene and Its Unique Reinforcement Effects for Rubber

Sodium humate (SH), a cost-effective and environmentally friendly humic substance, was employed to noncovalently functionalize graphene. The functionalized graphene (SHG) could stably and individually be dispersed in water at very high concentration (up to 30 mg/mL). The stabilization mechanism of SHG colloid was revealed to be π–π interaction and hydrogen bonding between SH and graphene layer. SHG was incorporated into carboxylated nitrile rubber (XNBR) through latex co-coagulation to form XNBR/SHG composites. The composites were cured with sulfur and magnesium oxide (MgO). A unique reinforcement effect of SHG toward XNBR was found. For instance, with the incorporation of 1 phr SHG, the fracture energy of the composite was doubled and the extensibility was improved, while the modulus was practically unchanged. The unique combination of high fracture energy, high extensibility, and low modulus was correlated with the interactions between SHG and MgO which pronouncedly affected the cross-linking of the rubber.