From loaded shell-core microcapsules to thermoplastic hybrid composites: a new pathway for the preparation of conductive and magnetic polyamide composites

Abstract

Polyamide microcapsules find various applications in biotechnology for protein and enzyme immobilization to produce drug delivery systems, in solid-phase diagnostics, biosensors, biocatalysts, extracorporeal therapy, and bio-separation. Also, they have direct and potential applications in fields of industrial materials for laser sintering, electro-conductive and magnetic composites, etc. This work presents an original one-pot synthesis of polyamide microcapsules containing in their cores finely dispersed carbon allotropes or metallic payloads. The microcapsules were synthesized by suspension anionic polymerization of ε-caprolactam in non-polar hydrocarbon solvents carried out in the presence of the payload of finely divided metals and carbon allotropes (carbon black, carbon nanotubes, graphite and carbon nanofibers). Various composite materials were prepared by compression molding of the resultant microcapsules. The morphology and crystalline structure of the microcapsules and that of the respective composites were studied by SEM, light microscopy and thermal analysis (DSC and TGA). The mechanical properties in tension of the composites were evaluated as well as their electromagnetic properties: volume conductivity, dielectric permeability and magnetic susceptibility. The results obtained suggest that loaded microcapsules can be obtained in high yields, with excellent dispersion of the conductive material and reaching electrical conductivities of semiconductors (in the case of carbon allotropes) or high dielectric constants (for metal loads) without any functionalization or compatibilization procedures. All this allows the conclusion about the significant application potential of the suggested pathway.