Preparation and properties of long chain branched high-density polyethylene based on nano-SiO₂ grafted glycidyl...

A compounded nanoparticle with multiple double bonds (C[double bond, length as m-dash]C) was prepared by grafting glycidyl methacrylate (GMA) onto the surface of nano-SiO₂. Then gel-free long chain branched polyethylene (LCBPE) was prepared by melt branching reaction in a Haake torque rheometer in the presence of initiator peroxide and GMA grafted nano-SiO₂ (SiO₂-g-GMA). The sampling time corresponded to the summit of the reaction peak in the torque curve. Fourier transform infrared results indicated that SiO₂-g-GMA had been grafted onto the HDPE backbone via radical reaction. The reaction mechanism and the topological structure of the PE products are also discussed. Rheological results showed that the relaxation time and molecular weight distribution of modified PE were increased owing to the introduction of LCB structure, and the more SiO₂-g-GMA was added, the more apparent variation could be observed. Compared with linear HDPE, both the melt strength and mechanical properties of LCBPE were improved obviously. From the differential scanning calorimetry and polarized optical microscopy results, smaller crystal size and lower growth rate were observed compared with linear HDPE, which are ascribed to the nucleation and restriction of long branching chains in the system. Well distributed nano-SiO₂ without any agglomeration in the PE matrix was observed in the scanning electron microscope images when the SiO₂-g-GMA content was less than 3 phr.