Preparation of polypropylene/Mg–Al layered double hydroxides nanocomposites through wet pan-milling: formation of a second-staging structure in LDHs intercalates

Abstract

In this paper, polypropylene/MgAl-layered double hydroxide nanocomposites were in situ prepared by using a novel solid state shear milling (S³M) technology without use of any compatibilizer and any prior organic treatment of raw LDHs. The obtained composite powders and nanocomposites were characterized using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The results show that under the very strong shear force field of pan-milling, the anion-exchange reaction of CO₃²⁻-LDHs with sodium dodecyl sulfate (SDS) can be realized under non-acidic conditions. In addition, the in situ modification of LDHs with SDS and the co-intercalation of PP macromolecular chains into LDH interlayers were found to be completed in one process in aqueous medium. XRD results demonstrate that there are two types of layered structures in the prepared PP/LDHs co-powders and the occurrence of the transformation from layered structure I to II with increasing milling cycles and SDS loading. Staging is proposed to illustrate the anion-exchange reaction of intercalation of the SDS anion into CO₃²⁻-LDH layers and the corresponding transformation, showing the second stage intermediate corresponding to layered structure I and the first stage product corresponding to structure II. Both XRD analysis and TEM observation show the formation of exfoliated LDH layers at low LDH loading and concomitant intercalated/exfoliated LDH layers at high LDH loading in the prepared PP/LDHs nanocomposites. The dynamic mechanical properties and crystallization behavior of the obtained nanocomposites were also investigated using dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC), respectively.