Microencapsulation of various reactive monomers by in situ polymerization

R. OLLIER; M. E. PENOFF; E. RODRIGUEZ; V. ÁLVAREZ

Gent

Congreso; Fourth International Conference on Self-Healing Materials ICSHM2013; 2013

Epoxy resins are reactive monomers and can be cured with wide variety of agents such as amines of differential functionalities and anhydrides at different temperatures. They are used in many applications such as coatings, adhesives, and laminates for composite materials due to excellent mechanical resistance of the cured products and good adhesion to many substrates. Thus, they may be used as healing agents for the fabrication of self-healing composites. The microencapsulation of epoxy resin has increasingly attracted researchers? interest due to the fact that the adhesion between the healing agent and the epoxy based composites is guaranteed. One of the key features for the effectiveness of the healing system is the first step of microcapsule design. The release properties depend on the wall materials, the microencapsulation method, the physico-chemical parameters of the process, the mean particle size and the shell thickness. In order to have a successful self-healing performance, it is important to synthesize microcapsules with rough surface morphology to assure a good adhesion with de polymer matrix, low core material permeability, appropriate diameter and core content, and adequate shell thickness. The aim of this work was to synthesize poly(urea-formaldehyde) microcapsules filled with an epoxy resin by in situ polymerization in oil-in-water emulsion and to select the best experimental conditions to optimize the subsequent healing efficiency. Many reaction conditions were analyzed: the rate of agitation, the organic/aqueous phase volume ratio, the concentration of surfactant and the viscosity of the encapsulated phase. As the commercial epoxy resins have high viscosity, they may not be used directly as healing agents, so the addition of reactive diluents to the sequestrated phase was evaluated as well. The improvement of the barrier property by the addition of nanodispersed clay along the shell was also studied. The final step of filtering and washing the obtained capsules with different solvents was analyzed showing interesting results.