Modified preparation of HDPE/clay nanocomposite by in situ polymerization using a metallocene catalyst

Abstract

In this study, preparation of high-density polyethylene (HDPE)/clay nanocomposite by in situ polymerization of ethylene using a zirconocene catalyst (bis-(cyclopentadienyl) zirconium dichloride (Cp2ZrCl2)) was investigated. To obtain higher efficiency, nanoclay particles (Na-montmorillonite) were modified by ammonia (NH3), NH3/methylaluminoxane (MAO), NH3/dodecylamine (DDA), and NH3/MAO/DDA systems. The results showed that the activity of the catalyst supported on the nanoclay particles modified by NH3/MAO (762 gp/mmol (Zr) t [atm]) was higher than that of the one supported on the unmodified nanoclay as well as the other prepared modified nanoclay-supported catalyst systems. The catalyst activities versus MAO concentration in NH3/MAO treatment system and versus DDA concentration in NH3/DDA system showed a maximum. Unexpectedly, a very low catalyst activity (180 gp/mmol(Zr) t [atm]) was obtained using NH3/MAO/DDA system. X-ray diffraction patterns showed that the HDPE/clay nanocomposites prepared by NH3/MAO/DDA treatment system had less intercalated structure. Fourier transform infrared (FTIR) spectroscopy confirmed that water molecules of the nanoclay particles were reduced by NH3 modification. DSC results revealed that crystallinity of the HDPE/clay nanocomposites increased with the modification of the nanoclay particles. The maximum degree of crystallinity of 80.8% was obtained for HDPE/clay nanocomposites prepared by the nanoclay modified by NH3. In addition, nanoclay modification with NH3, NH3/MAO, and NH3/DDA systems resulted in higher thermal decomposition temperature (~30 °C higher than 480 °C of the unmodified one). Such increase was not observed for the NH3/MAO/DDA treatment system. Dynamic mechanical analysis showed an increase in the elastic modulus of the nanocomposite samples prepared by modified nanoclay particles, as well. Meanwhile, modification of the nanoclay particles by NH3 led to the highest elastic behavior compared to the other modification systems. It was about 4.6 GPa which was 28% higher than the elastic modulus of the nanocomposite prepared by unmodified nanoclay particles.