Lactic acid–magnesium oxide nanocrystal interactions: how nanoparticle size and shape affect chemistry and template oligomerization

Abstract

L-Lactic acid was allowed to react with small amounts of commercial MgO, Nanoactive®, and Nanoactive Magnesium Oxide Plus® particles, each of which differs in surface area, shape, and reactivity. The reactions were carried out by refluxing the nanoparticles in a solvent suspension of methanol or propanol. Upon addition of the lactic acid monomer, at reflux temperature, two reactions competed with each other: (1) acid–base to yield magnesium lactate salt, and (2) oligomerization to yield a nanocomposite prepolymer. The products were characterized for thermal, chemical, and morphological properties. Additionally, titrations were performed to determine how much MgO was consumed by the acid, and how this changed with nanoparticle size and shape. Polymerization appears to initiate on the surface of the magnesium oxide particles, the results of which are physically unique composites of lactic acid and magnesium oxide, and final properties depend on MgO nanoparticle characteristics. One of the most interesting results was the finding that larger, less reactive MgO favored the acid–base neutralization reaction, while smaller, more reactive MgO particles favored the MgO induced oligomerization pathway.