Layered particle-based polymer composites for coatings: Part I. Evaluation of layered double hydroxides

Layered double hydroxides (LDH) suitable as fillers for the formulation of waterborne polyurethane (WPU) nanocomposites in coating applications are designed and characterized. Their elaboration follows a simple and reproducible process leading to samples without impurity. The attention is paid to the impact of the LDH nature (MxAl/CO32-, M = Mg and/or Zn, and x = 2, 3 and 4) on the structure characteristics, i.e. cell parameters and coherent domain dimensions. Focusing on two end-member phases M2Al/CO32-, M = Mg or Zn, the microstructural characterization performed from X-ray diffraction peak profile analyses permits to point out larger coherent domain sizes for Zn2Al species than for Mg2Al ones, and then to correlate with the "macroscopic" crystallinity of the samples. The evolution of LDH slurries over time is tentatively considered in a prediction interest. The stability of a chosen organic-inorganic hybrid, taken Mg2Al as inorganic host structure with anions of the 4-aminobenzene sulfonic acid (4-ABSA), is studied as function of its carbonate contamination in time. Finally, the dispersion of LDH fillers in WPU is scrutinized in terms of WPU/LDH structure revealed by indirect and direct observations, XRD and TEM, respectively. (C) 2008 Elsevier B.V. All rights reserved.