Micromorphology, phase behavior, and properties of environmental, multi-cross-linked polyurethane/polyacrylate microemulsions based on in situ surfactant-free polymerization.

The aqueous environmental polyurethane/polyacrylate (PUA) microemulsions were obtained through in situ surfactant-free emulsion polymerization exempt of any organic solvents. Hydroxyethyl acrylate (HEA) and pentaerythritol triacrylate (PETA) of different functionalities were adopted as cross-linker to connect polyurethane (PU) and polyacrylate (PA) to obtain PUAH and branched multi-cross-linking PUAP, respectively. It is interesting to note that PUA microemulsion was unstable if no connection was built between PU and PA when in situ surfactant-free emulsion polymerization was adopted, which is different from conventional seed emulsion polymerization. The particle size decreased from 75.27 to 51.24 nm and dispersibility index (DPI) decreased from 0.394 to 0.122 with the increase of vinyl content, and DPI was further decreased with the incorporation of PETA with three vinyl groups at the same vinyl content. Effects of HEA and PETA on the physicochemical properties of PUA films including micromorphology, gel content, surface composition, phase behavior, thermal stability, and water resistance were investigated. TEM and XPS analysis demonstrated that the micromorphology transferred from multi-morphology to single core-shell morphology with PA as the core and PU as the shell and then changed to uniform morphology with homogeneous distribution of PU and PA inside PUAP. High cross-linking density, together with uniform distribution of PU and PA inside PUA system, is beneficial to improve the PUA performance. In addition, the as-prepared microemulsions can be utilized as the surface sizing agent for cellulose fiber paper to greatly increase the physical strength and water resistance. [ABSTRACT FROM AUTHOR]