Halloysite nanotubes as a stabilizer: fabrication of thermally expandable microcapsules via Pickering suspension polymerization

Core-shell thermally expandable microcapsules were prepared via Pickering suspension polymerization. Acrylonitrile (AN) and methyl methacrylate (MMA) were used as the comonomers and the halloysite nanotubes (HNTs) were used as the Pickering emulsifier. The influence of the HNT concentration, AN/MMA ratio, and types of hydrocarbon was investigated. When the HNT concentration was 0.6 wt%, the microcapsules exhibited a core-shell morphology that contained approximately 35 wt% of the blowing agents with an average particle size of 232.0 μm. Increasing the MMA contents resulted in a larger particle size and lower thermal stability. Core-shell microcapsules could be synthesized using iso-hexane, iso-octane, and n-octane, but microcapsules could not be fabricated with n-pentane. At 1 and 3 bar, the contents of the encapsulated blowing agents were 10 %, whereas the contents of the encapsulated blowing agents were approximately 35 and 60 % at 1.5 and 2 bar, respectively.