Polypropylene (PP)/clay nanocomposites prepared by melt blending using different clays and coupling agents based on maleic anhydridegrafted PP (MA-PP) were studied. Clay dispersion using field emission gun scanning electron microscope (FEG-SEM) and transmission electron microscopy (TEM), and PP matrix morphology were characterized. Clay dispersion was improved in the presence of MA-PP, as shown by the higher particles surface density (number of particles/mm 2) at all micro-, sub-micro-and nano-levels. The PP spherulite diameter was affected by both the presence of MA-PP and clay dispersion. Clay intercalation, characterized by both complementary X-ray diffraction (XRD) and TEM, was greatly influenced by the characteristics of MA-PP. The use of low molecular weight (M w) MA-PP led to a good and uniform intercalation but with no further possibility to exfoliation. The use of higher M w MA-PP led to a heterogeneous intercalation with signs of exfoliation. The crystallization behavior of nanocomposites was studied by differential scanning calorimetry (DSC). When fine clay dispersion was achieved with MA-PP, clay-nucleating effect was limited and lower crystallization temperature and rates were observed. It was also shown by wide angle X-ray diffraction (WAXD) that clay induced some orientation of a-phase PP crystallites.

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The effect of different concentrations of single‐walled carbon nanotubes (SWNTs) on the nonisothermal crystallization kinetics, morphology, and mechanical properties of polypropylene (PP) matrix composites obtained by melt compounding was investigated by means of X‐ray diffraction, differential scanning calorimetry, optical and scanning electron microscopy, and dynamic mechanical thermal analysis. Microscopy showed well‐dispersed nanotube ropes together with small and large aggregates. The modulus was found to increase by about 75% at a level of 0.5 wt % nanotubes. The SWNTs displayed a clear nucleating effect on the PP crystallization, favoring the α crystalline form rather than the β form. The crystallization kinetics analysis showed a significant increase in activation energy on incorporating nanotubes. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2445–2453, 2005

The mechanical behavior of compression‐molded polyamide‐6 (PA6) reinforced with 2 wt% of organo‐nanoclay (montmorillonite intercalated with ω‐amino dodecanoic acid) has been studied and compared to that of PA6. The tensile strength and the Young's modulus of the PA6/clay were 15% higher than those of PA6. Differential scanning calorimetry, Fourier transform infrared spectroscopy, and X‐ray diffraction showed that the crystalline structures of PA6 and PA6/clay differed considerably. A crystallinity of 25% with a dual structure composed of the γ and α forms was obtained in PA6/clay, while a crystallinity of 31% with the α form as the dominant crystalline structure was obtained in PA6. To understand the role of the crystalline structure of PA6, the molding process was modified to obtain PA6 specimens with different levels of crystallinity and different crystalline forms. Quenching molten PA6 at a cooling rate sufficiently high to prevent crystallization gave a material that was predominantly amorphous (crystallinity of 7%) with traces of the mesomorphic β or γ* form. Annealing this material at 80°C considerably increased crystallinity to 21%, which was also of the mesomorphic β or γ* form. PA6 with a predominant crystalline γ form could not be generated. Comparisons with PA6/clay in terms of crystallinity and mechanical behavior lead to the conclusion that the improvements in rigidity and strength observed when montmorillonite is added to PA6 are related to the reinforcing filler and not to a modification of the crystalline structure.

The preparation of nanoclay‐reinforced polypropylene nanocom posites by means of melt processing was investigated. In order to optimize the dispersion of the nanoclay and the nanoclay‐matrix interface, experiments were performed with three different nanoclays, two different maleic‐anhydride–grafted PP coupling agents, and two different mixing procedures. The physicochemical and mechanical properties of the prepared samples were characterized by means of various techniques. The coupling agents increase the degree of clay intercalation and exfoliation, the latter resulting in part from a “peeling off” mechanism. Significant improvements in tensile and flexural strength and modulus are obtained with Cloisite® 15A nanoclay and a coupling agent characterized by high molecular weight and low grafting content, and these improvements are also accompanied by an increase in Izod impact strength. Little difference was observed between the two mixing procedures used. The improvements were not as pronounced when the coupling agent was characterized by low molecular weight and high grafting content, or when Cloisite® 30B nanoclay was used. In the latter case, there was evidence of greater thermal instability than for Cloisite® 15A. Polym. Eng. Sci. 44:1212–1219, 2004. © 2004 Society of Plastics Engineers.