Preparation of PU/GO hybrid wall microcapsules and their self-lubricating properties for epoxy composites

Polyurethane/graphene oxide (PU/GO) hybrid wall microcapsules were prepared by interfacial polymerization and electrostatic adsorption method. 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm]BF4)-loaded PU microcapsules were first fabricated in lignin-stable Pickering emulsion system. These PU microcapsules were treated with poly(ethyleneimine) (PEI) cross-linked polydopamine (PDA) to positively charge their outer surface, and then GO with negative charge was successfully attracted to the PDA-PEI modified PU microcapsules by electrostatic force. [BMIm]BF4-loaded PU/GO hybrid wall microcapsules with mean size of 82±26 μm were successfully prepared. Synthesized microcapsules have excellent permeability resistance and thermal stability, and the core content of microcapsules was 56.5±4.3wt.%. Epoxy composites containing microcapsules were fabricated and their tribological properties were investigated. GO can effectively improve the friction resistance of epoxy composites. The friction coefficient decreased from 0.610 (pure epoxy) to 0.265 (epoxy containing 15wt.% PU microcapsules) and 0.150 (epoxy containing 15wt.% PU/GO microcapsules). The wear rate decreased from 86.0×10−14 to 3.1×10−14 and 1.2×10−14 m3/Nm, respectively. The self-lubricating mechanism was described in detail. The GO and [BMIm]BF4 ionic liquid have the synergistic contribution to good self-lubricating performance of epoxy composites.