Polypropylene/Layered Double Hydroxide (LDH) Nanocomposites: Influence of LDH Particle Size on the Crystallization Behavior of Polypropylene

Highly dispersed isotactic polypropylene (iPP) nanocomposites were prepared by incorporating two different sized Mg-Al LDH nanoparticles with different loadings from 1 to 10 wt % using a modified solvent mixing method. Larger sized LDH nanoparticles (similar to 3-4 mu m) were prepared from the gel form Of Mg-Al LDH, and the smaller sized nanoparticles (similar to 50-200 nm) were prepared by sonication of as-synthesized LDH particles. Such obtained LDH nanoparticles were carefully characterized using wide-angle X-ray diffraction (WAXD), transmission electron microscopy, and scanning electron microscopy. WAXD and atomic force microscopy results indicate that the LDH nanoparticles were highly dispersed in the [PP matrix. The influence of LDH nanoparticles size and concentration on the thermal stability, spherulitic morphology, melting behavior, isothermal crystallization kinetics, and lamellar structure of [PP were investigated. Incorporation of low loadings of sonicated LDH particles (e.g., 1-2.5 wt %) show substantial effect on thermal stability, spherulite size, crystallinity, and crystallization half-time and lamellar morphology of [PP compared to the pure iPP and that of nanocomposites with larger LDH particles with same loadings. The better nucleation ability of iPP in the presence of sonicated LDH can be attributed to the high surface area of LDH nanoparticles along with its better dispersibility within the polymer matrix. The incorporation of LDH nanoparticles does not change the crystallization growth mechanism and crystal structure of iPP.