Injection moldable, self-healable, and recyclable rubber-bonded NdFeB magnets with the magnetic particulates content up to 90 wt%

To apply the facile injection molding technique commonly used in thermoplastics processing to rubber-bonded magnets, typical highly filled thermosetting composites, an approach based on Diels-Alder (DA) chemistry is proposed by the authors. In the proof-of-concept experiments, the oligomers of hydroxyl-terminated polybutadiene rubber are successively functionalized by furyl and trifluoromethyl, and the magnetic NdFeB particles are modified by maleimide. By taking advantage of the reversible DA reaction, cross-linkages are established among the treated polybutadiene oligomers and NdFeB particles. The composite exhibits very low viscosity due to de-cross-linking when heated to retro-DA reaction temperature, which provides the highly filled system with necessary thermal processibility. In addition, the fluorine groups of the rubber phase are aggregated surrounding the particulate fillers allowing for well separation of the latter in the melt state. During the subsequent cooling, the DA bonds are re-built up in the rubber and at the particles/rubber interface, respectively, offering the robustness of traditional thermosets. As a result, the polybutadiene-bonded magnets with NdFeB content up to 90 wt% can be injection molded and possess rather high magnetic properties, mechanical properties, self-healability, and recyclability. The present work combines the merits of thermoplastics and thermosets and satisfies the contradictory requirements of high filling, efficient manufacturing, and balanced performance of functional polymer composites.

Automated summary

The authors propose an approach based on Diels-Alder (DA) chemistry to apply the injection molding technique to rubber-bonded magnets. By functionalizing the oligomers of hydroxyl-terminated polybutadiene rubber and modifying the magnetic NdFeB particles, cross-linkages are established using the reversible DA reaction. The resulting composite exhibits low viscosity and good separation of fillers in the melt state, and retains the robustness of traditional thermosets. The polybutadiene-bonded magnets can be injection molded with high magnetic and mechanical properties, self-healability, and recyclability.