High improvement in the properties of exfoliated PU/clay nanocomposites by the alternative swelling process

In this work, a stable de-aggregated solvent-swollen organic modified clay, ALA-MMT, suspension is prepared by an efficient solvent swelling process using a home-made shaking mixer. It is found that the estimated average size of the as-prepared organoclay particles in the suspension is reduced to about 155 nm, which has not been reported before. The X-ray diffraction (XRD) patterns confirm that the d-spacing of the silicate layers of the solvent-swollen ALA-MMT expands from 1.4 nm to about 2.1 nm. The de-aggregated solvent-swollen ALA-MMT suspension is then used with polyurethane (PU) to prepare a series of highly exfoliated and high-organoclay-loading nanocomposites, PU/ALA-MMT. Both the XRD patterns and the TEM photographs of the as-prepared PU/ALA-MMT nanocomposites indicate that the organoclay is uniformly dispersed in the PU matrix with a highly exfoliated morphology structure of up to 7 wt% loading. Meanwhile, the TEM photographs give the first report for PU/clay nanocomposites which are almost completely exfoliated, and ∼1-nm thin silicate nanolayers are homogeneously dispersed in the polymer matrix with a high aspect ratio of 30-100. The thermal, mechanical, and anti-corrosion properties are all tremendously enhanced for the as-prepared nanocomposites. The results obtained for the PU nanocomposite with 7 wt% ALA-MMT loading (PUC7) reveal a 19 °C increment in T_g, a 48 °C increment in T_5%, a 248% increase in the tensile strength, and a 123% increase in the elongation. The stainless steel disk (SSD) coated with PUC7 shows the lowest corrosion rate of 2.01 × 10⁻⁶ mm/year, which is 469% lower than that of the SSD coated with pure PU. The reinforcements are much greater than the previously reported PU/clay nanocomposites with comparable clay loadings ascribed to the exceptional homogeneity of as-prepared nanocomposites, which are accredited largely to the stable de-aggregated solvent-swollen organoclay suspension generated by the efficient solvent swelling process.