Organophilic Layered Silicate Modified Vinylester-Urethane Hybrid Resins: Structure and Properties

Abstract

A commercial vinylester-urethane (VEUH) hybrid resin was modified with organophilic layered silicates (OLS), incorporated in various amounts (0.1 to 5 wt.%). As organophilic intercalants of the layered silicate (synthetic fluorohectorite) trimethyl dodecylamine (TMDA) and octadecylamine - N,N-bis[allyl(2-hydroxypropyl)ether] (OAE) served. The latter quaternary amine was expected to support the intercalation/exfoliation of the silicate by participating in the crosslinking reactions. Both OLS types became intercalated based on X-ray diffractograms (XRD). Dynamic-mechanical thermal analysis (DMTA) displayed a slight increase in the stiffness by adding OLS up to 2.5 wt.%. However, at 5wt% OLS content the stiffness of the nanocomposites was below that of the unfilled hybrid resin. The glass transition temperature (Tg) did not change practically with the OLS type and content. Fracture mechanical tests were performed on compact tension (CT) specimens. The fracture toughness (Kc) increased slightly, while the fracture energy (Gc) markedly with increasing OLS content. Unexpectedly, TMDA proved to be a more suitable intercalant than OAE. The failure mode of the specimens was studied in a scanning electron microscope (SEM) and discussed. In addition, the water sorption behavior of the OLS modified VEUHs was determined and the diffusion coefficients (D) deduced.