Synthesis of a dual-microcapsule system comprising 2-ethyl hexyl acrylate monomer and benzoyl peroxide initiator and study of their application in capsular adhesives

Adhesives containing microcapsules filled with active resin materials are considered intelligent and promising systems. In this work, dual-component polyurethane/urea-formaldehyde (PU/UF) microcapsules comprising 2ethyl hexyl acrylate monomer (EHA) and benzoyl peroxide (BPO)-filled gelatin-gum-Arabic/polyureaformaldehyde (Gel-GA/PUF) microcapsules were synthesized. PU/UF-microcapsules containing EHA were made in an oil-in-water emulsion via in-situ and interfacial polymerizations at 1000 and 1200 rpm agitation speeds and with core-to-shell ratios of 75:25 and 85:15. The Gel-GA/PUF microcapsules were prepared in the presence of a mixture of sodium dodecyl sulfate and polyvinyl alcohol (SDS/PVA), or polyethylene maleic anhydride (EMA) at stirring rates of 500 and 700 rpm with core-to-shell ratios of 55:45 and 65:35 via consecutive complex coacervation and in-situ polymerization. The results showed that the BPO-filled Gel-GA/PUF-microcapsules synthesized at stirring speeds of 1000 and 1200 rpm were spherical with no inter-adherence and with an average diameter (dm) of 135 and 94 mu m, respectively. Similarly, EHA-filled PU/UF-microcapsules synthesized in the presence of SDS/PVA at stirring speeds of 500 and 700 rpm formed free-flow powders consisting of spherical particles with a dm of 242 and 165 mu m, respectively. Furthermore, adhesive formulations containing neat and microencapsulated EHA with 2.0 wt% BPO showed the best shear strength of 2.23 MPa and 1.95 MPa, respec-tively. These results reveal the efficacy of the EHA and BPO filled dual-component microcapsules in a capsular adhesive formulation.