SPECIAL ISSUE CONTRIBUTIONS L. Pietrzak, E. Piorkowska * , A. Galeski, J. Bojda, P. Sowinski Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Lodz, Poland Modification of Syndiotactic Polypropylene with Nano-Calcium Carbonate and Halloysite Composites of syndiotactic polypropylene (sPP) with 5 to 17 vol.% of halloysite and 2.5 to 7.5 vol.% of stearic acid modified nano-calcium carbonate, having an average grain size of 80 nm, were prepared and examined. The effect of fil- lers on thermal properties of sPP was different; halloysite in- creased markedly peak crystallization temperature. The com- posites with the highest filler contents, 7.5 vol.% of calcium carbonate and 17 vol.% of halloysite, exhibited a solid-like behavior at 170 8C, with the storage modulus exceeding the loss modulus in the entire frequency range, that is 512 to 0.1 rad s –1 . The composites with halloysite exhibited de- creased Izod impact strength compared to neat sPP. On the contrary, 2.7 fold improvement of the impact strength was found for the composites with nano-calcium carbonate. More- over, nano-calcium carbonate did not worsen the drawability of the materials during uniaxial drawing. It was found that debonding at calcium carbonate/sPP interface occurred both during the impact test and tensile drawing facilitating the plastic deformation of the polymer. 1 Introduction Polymer composites are long known and used as they offer many advantages over plain polymers like higher modulus, higher impact resistance, modified barrier properties, reduced flammability, lower cost, etc. It is well known that the large surface area of nanoparticle/polymer interface permits to achieve modification of properties at relatively low loading levels, often a few percent. For instance, it has been found that low contents of nano-powders dispersed in isotactic polypro- pylene (iPP) can improve its mechanical performance, for ex- ample tensile strength and ductility (Bikiaris et al., 2006; Chan et al., 2002; Ma et al., 2005; Tjong, 2006; Wu et al., 2002; Zu- browska et al., 2015). Calcium carbonate (CaCO 3 ) is often applied as a filler be- cause of high chemical purity, high degree of whiteness, low abrasiveness, good dispersability. Bartczak et al. (1999) re- ported dramatic many-fold increase of toughness of high den- sity polyethylene filled with calcium stearate-treated calcium carbonate when the mean interparticle ligament thickness of the matrix decreased below 0.6 lm. Toughening of iPP was achieved by incorporation of submicron (Zuiderduin et al., 2003) or nano-sized calcium carbonate particles, but in the lat- ter only after surface treatment improving adhesion (Fu et al., 2008; Guo et al., 2005; Levita et al., 1989). Levita et al. (1989) analyzed the fracture energy in terms of the crack pinning model but due to the very small size of particles the pinning contribution proved to be negligible. Lin et al. (2010) described the synergic effect of the high-molecular weight iPP and the monolayer-coated nanoparticles producing nanocom- posites with high impact strength, which was much greater than that of the neat polymer. Also a biodegradable polymer – polylactide was recently toughened with nano-calcium carbo- nate (Jiang et al., 2007; Piekarska et al., 2016; 2017); separa- tion of the particles from the matrix resulted in crazing, sufi- ciently intense to impart ductility of the amorphous matrix. Syndiotactic polypropylene (sPP) exhibits interesting fea- tures such as high ductility, flexibility and high optical clarity, although the sPP physical properties depend on the crystalliza- tion behavior, which is strongly related to stereoregularity (De Rosa and Auriemma, 2006). Recently, Pietrzak et al. (2016) demonstrated that filling sPP with calcium carbonate having 0.85 lm average grain size, allowed to achieve nearly 4.5 fold increase in the Izod impact strength at 17 vol.% filler content. Our current contribution focused on modification of sPP with nano-sized calcium carbonate and with halloysite. In our pre- vious study (Pietrzak et al., 2016) the effect of calcium carbo- nate was enhanced in injection molded bars, therefore injection molding was selected as a sample preparation method. We de- monstrate that the toughening of sPP can be achieved at low content of nano-calcium carbonate, 7.5 vol.%. On the contrary, filling with halloysite worsened the impact strength, even at the same volume content, 17 vol.%, as the calcium carbonate con- tent in the previous report (Pietrzak et al., 2016). Besides the mechanical properties, the rheological and thermal properties of the materials were analyzed. 2 Experimental The study utilized sPP provided by Sigma Aldrich (St. Louis, MO, USA) having molar mass M w of 174 kg mol –1 ,M w M n –1 of 2.3, syndiotacticity of 93 %, and melt flow index of 2.2 g/ 10 min (230 8C, 2.16 kg). Precipitated calcium carbonate (cal- cite) Socal U 1 S 2 modified with 3 wt.% of stearic acid, provided 314 Ó Carl Hanser Verlag, Munich Intern. Polymer Processing XXXIII (2018) 3 * Mail address: Ewa Piorkowska, Centre of Molecular and Macro- molecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90 363 Lodz, Poland E-mail: epiorkow@cbmm.lodz.pl IPP 2018.33:314-321. by McMaster University on November 28, 2018. For personal use only.