In this work, to achieve good dispersion state of graphite in the nonpolar intractable polymer, polypropylene (PP), two specific compounding/molding techniques, rotating solid-state mixing (RSSM), and dynamic packing injection molding (DPIM), were used during the preparation of PP/graphite nanocomposite. The enhanced dispersion/exfoliation of graphite substance in PP matrix induced by RSSM and/or DPIM treatment was well identified by a combination of polarized optical microscopy, wide-angle X-ray diffraction, and scanning electronic microscopy. A comparative analysis indicated that RSSM mainly pulverizes graphite pristine-particles into tactoids with significantly decreased diameter-size, while DPIM offers strong melt shear force for exfoliating graphite tactoids into nanosheets whose thicknesses are about tens nanometers and length of 1 micron. Uniform dispersion of graphite nanosheets leaded to substantial increase in heterogeneous crystallization rate and mechanical properties. Our present study proposes a facile effective approach for large-scale preparation of polymer/graphite nanocomposite with high-performances. POLYM. COMPOS., 35:1943–1951, 2014. © 2014 Society of Plastics Engineers

Bioresource natural sisal fiber (SF) was used to prepare single fiber-reinforced isotactic polypropylene (iPP) composites. Three kinds of interfacial crystalline morphologies, spherulites, medium nuclei density transcrystallinity (MD-TC) and high nuclei density transcrystallinity (HD-TC), were obtained in the single fiber-reinforced composites by implementing quiescent or dynamic shear-enhanced crystallization and by modulating the compatibility interaction between SF and iPP. The development of interfacial shear strength (IFSS) during the interfacial crystallization process was demonstrated for the first time using a combination of single-fiber fragmentation testing and optical microscope observation. A close correlation between IFSS and morphological characteristics of interfacial crystallization was well elucidated. The increases in IFSS were very different for spherulitic, MD-TC and HD-TC morphologies. The highest IFSS obtained was 28 MPa, after the formation of HD-TC, which was about 62% of the tensile strength of neat iPP (45 MPa). These results offer powerful and direct evidence that interfacial crystallization could play an important role in the enhancement of interfacial adhesion of real SF/iPP composites. © 2013 Society of Chemical Industry

The phase morphology and toughening behavior of impact polypropylene copolymer (IPC) with and without nucleating agent (NA), prepared at different processing melt temperatures (T_p), were investigated. Interestingly, three different structures can be formed in the IPC samples by adding NA or tuning T_p. A well-defined core–shell structure is obtained in samples with α-NA or without NA prepared at all T_p. A developing multilayered structure is mainly formed at high T_p with added β-NA, while an incomplete phase separation structure with interpenetrating chains is the dominant structure for IPC samples prepared at low T_p with added β-NA. In this case, because of the synergistic effect between phase morphology and relatively high β-form crystal content, the chain interaction among the components and chain mobility of the amorphous portion of IPC are distinctly improved, resulting in a largely improved toughness under 0 °C. This improvement in toughness is very important for applications. © 2012 Society of Chemical Industry

The cooling process of isotactic polypropylene (iPP)/organoclay nanocomposites was followed by dynamic rheometry. Contrasting to typical linear increment of log G′ with decreasing temperature (log G′ ∝ 1/T) occurred on the melts for neat iPP and nanocomposites with small amounts of organoclay, an unusual rheological behavior was identified for composites with relative high organoclay content (≥5 wt %) as that: increasing of log G′ positively deviates to linear relation during cooling within certain high temperature region, thus yields an additional enhancement in viscoelastic properties. Furthermore, such unusual rheological phenomenon was found to be strongly impacted by initial dispersion level of organoclay, cooling rate, and construction of organoclay network. The origin of this unusual rheological phenomenon could be cautiously explained as due to the existence of unstable state of organoclay nanostructure, which could go further intercalation or exfoliation in some high temperature ranges. This might be a new rheological character and is meaningful for understanding the essentially structural behavior of polymer/layered clay nanocomposites, particularly containing mesoscopic clay network. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Graphene oxide (GO) is derived from oxidization of natural graphite and contains many active groups. These active groups make GO a potential compatibilizer for polymer blends or coupling agent for polymer composites. In this work, a novel core-shell structured hybrid submicroparticles of graphene oxide-encapsulated silica (GO-SiO₂) were fabricated using GO sheets via an electrostatic assembly between ultrathin negatively charged graphene oxide sheets and positively charged amino-modified silica. The possible application of this new hybrid filler was explored in preparation of maleated polypropylene (PP-g-MA)/GO-SiO₂ composites. The microstructure and interface enhancement of the prepared composites were analyzed by SEM, TEM, OM, TGA, FTIR, and DMA measurements. A uniform dispersion of GO-SiO₂ hybrids, enhanced interfacial adhesion and improved mechanical property were evidenced. The reason might be that graphene oxide can be covalently assembled onto the amino-modified silica surface, and simultaneously it provides strong interaction with the PP-g-MA due to similar polarity or possible hydrogen bonding. This work suggests a potential application of graphene oxide-encapsulated particle in preparation of high performance polymer composites. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The incorporation of carbon nanotubes (CNTs) is expected as an effective path for tailoring mechanical properties of polymer blends. In this study, acid-modified multiwalled CNTs (A-MWCNTs) were introduced into polystyrene/maleic anhydride-g-(styrene-ethylene-butadiene-styrene) (PS/SEBS-MA) blends. By altering the mass ratio of PS/SEBS-MA from 80/20 to 60/40, the biphase structure of blend was changed from sea-island-like type to quasi co-continuous structure, of different mechanical behaviors. In 80/20 mass ratio, the impact strength was improved while the tensile strength was unchanged with increasing A-MWCNTs content, whereas a simultaneously toughening and strengthening effect was achieved for the compound with 60/40 mass ratio. Scanning electron microscopy, polarized light microscopy, dynamic mechanical analysis, and rheological measurements were carried out to detect the distribution of A-MWCNTs in the blends. The results demonstrated as increasing the nanotube loading from 0 to 3 wt%, A-MWCNTs might gradually migrate into continuous PS phase in 80/20 mass ratio, due to the low content of SEBS-MA, while they were totally packed in SEBS-MA region within the entire loading range used in 60/40 mass ratio due to its high content of SEBS-MA. This study provides guidance on the design and preparation of high performance ternary polymer/elastomer/inorganic filler composites. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers

Special crystallization event of isotactic polypropylene (iPP) in a constrained environment, a layered clay network, was followed by in situ Fourier transform infrared (FTIR) spectroscopy during the cooling process. Before occurrence of nucleation/crystallization, a conformationally ordered phase, which consists of significant amounts of long 3₁ helices with 14 monomeric units, has been identified for the first time. More importantly, it was found that the long-ordering helices could play a more important role than short ones for the confined crystallization. It could be tentatively explained as due to the existence of constrained regions in the proximity of the nanoclay platelets or tactoids and the heterogeneous nucleation capability of the surface of nanoclay. Copyright © 2011 John Wiley & Sons, Ltd.

A crystallizable polymer, poly(ethylene oxide) (PEO), was used as new modifier to tailor the toughness of isotactic polypropylene (iPP). An optimum performance was achieved at a medium PEO content of 15 wt% where the toughness was enhanced by 300%, while the strength only decreased slightly. To elucidate the origin of toughening in the iPP/PEO blends, various crystallographic and morphological experiments including X-ray diffraction, electron microscopy and calorimetry were adopted to explore the dependences of polymorphic composition and crystallized morphology on PEO content. When the PEO content is less than 15 wt%, the dispersed PEO cannot crystallize, and these non-crystalline PEO microspheres are embedded in both α- and β-form iPP spherulites, which is mainly responsible for the toughening. In contrast, when the PEO content is higher than 15 wt%, the PEO phase becomes crystallizable, and significant phase segregation takes place, resulting in a marked deterioration in mechanical properties. Copyright © 2011 Society of Chemical Industry