Lysine‐Functionalized Gibbsite Nanoplatelet Dispersions for Nonisocyanate Polyhydroxyurethane Nanocomposites and Translucent Coatings

Abstract

AbstractThe lysine functionalization of ultrathin γ‐Al(OH)3 single‐crystal nanoplatelets (ly‐gibbsite) having an average thickness below 100 nm and a width ranging between 0.5 and 1.5 µm renders them organophilic and enables their agglomerate‐free dispersion in nonisocyanate polyhydroxyurethane (NIPU) thermosets prepared by amine cure of polyfunctional cyclic carbonates. Whereas most other nanoparticles drastically increase viscosity even at very low content, NIPU processing tolerates up to 40 wt% ly‐gibbsite without impairing its uniform dispersion. The amine groups of ly‐gibbsite can react with cyclic carbonate groups of NIPU to afford interfacial coupling. Contrary to the NIPU composites containing corundum and spherical gibbsite particles, ly‐gibbsite/NIPU nanocomposites exhibit substantially higher stiffness as reflected by high Young’s modulus up to 9500 MPa. Moreover, ly‐gibbsite/NIPU coatings remain translucent even at high ly‐gibbsite content when the nanoplatelet length is below 1 µm. As verified by transmission electron microscopic imaging of coatings, the ly‐gibbsite nanoplatelets are aligned parallel to the surface. At high ly‐gibbsite content, NIPU thermosets are rendered flame retardant in the absence of halogen and other flame retardants. The NIPU coatings tolerate the addition of aluminum flakes to produce metallic NIPU varnishes.