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Keywords:

  • chain polymerization;
  • epoxy;
  • impact strength;
  • organic fibers;
  • polymer composites

Abstract

A two-component healing agent, consisting of epoxy-loaded microcapsules and an extremely active catalyst (boron trifluoride diethyl etherate, (C2H5)2O · BF3)), is incorporated into epoxy composites to provide the latter with rapid self-healing capability. To avoid deactivation of the catalyst during composite manufacturing, (C2H5)2O · BF3 is firstly absorbed by fibrous carriers (i.e., short sisal fibers), and then the fibers are coated with polystyrene and embedded in the epoxy matrix together with the encapsulated epoxy monomer. Because of gradual diffusion of the absorbed (C2H5)2O · BF3 from the sisal into the surrounding matrix, the catalyst is eventually distributed throughout the composites and acts as a latent hardener. Upon cracking of the composites, the epoxy monomer is released from the broken capsules, spreading over the cracked planes. As a result, polymerization, triggered by the dispersed (C2H5)2O · BF3, takes place and the damaged sites are rebonded. Since the epoxy–BF3 cure belongs to a cationic chain polymerization, the exact stoichiometric ratio of the reaction components required by other healing chemistries is no longer necessary. Only a small amount of (C2H5)2O · BF3 is sufficient to initiate very fast healing (e.g., a 76% recovery of impact strength is observed within 30 min at 20 °C).