Water-assisted Extrusion as a Novel Processing Route to Prepare Polypropylene Nanocomposites Based on Natural Halloysite Nanotubes: Structural and Thermal Behaviour

摘要

In the last two decades, polymer nanocomposites based on inorganic clay minerals have attracted a great deal of attention. In the field of polyolefin nanocomposites, most of the research was focused on spherical (e.g. silica) and platelet-like shape (e.g. montmorillonite) nanoparticles [1]. However, a third shape of clay combining the geometry of nanotubes and the chemistry of kaolinite begins to attract much interest for the fabrication of polymer nanocomposites. Halloysite is a naturally occurring aluminosilicate (Al2Si2O5(OH)4.2H2O) with a predominantly hollow tubular structure and exhibits unique surface chemical property with only a few hydroxyl groups located at the surface of the nanotubes [2]. As compared to layered silicates, these halloysite nanotubes (HNTs) can thus be more easily dispersed in hydrophobic matrix like polypropylene (PP) due to the weak secondary interactions among the nanotubes by hydrogen bonds and van der Waals forces. Recently, an increasing number of publications have reported the fabrication and characterization of polymer/HNTs nanocomposites [3-6]. However, the dispersion of unmodified HNTs in PP stays relatively limited due the huge polarity difference between the polyolefin matrix and the clay [7]. The water-assisted extrusion process was first used to prepare polyamide/untreated clay nanocomposites [8]. Liquid water is injected into the polymer/clay blend during the melt-compounding and then degassed. In this work, PP/HNTs nanocomposites are obtained using similar water-assisted extrusion process. The influence of compatibilizer and water injection on the structure and thermal properties of PP/HNTs nanocomposites is presented.