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Meng X.,China University of Petroleum - Beijing | Meng X.,Beijing Key Laboratory of Failure | Liu X.,China University of Petroleum - Beijing | Liu X.,Beijing Key Laboratory of Failure | And 3 more authors.
Polymer Engineering and Science | Year: 2014

The free volume parameters of styrene-butadiene-styrene copolymer/polystyrene (SBS/PS) blends were investigated with positron annihilation lifetime spectroscopy (PALS) in this study. The behaviors of free volume distribution, average free volume, and relative fractional free volume revealed the difference of interfacial miscibility. Based on different models, inter-chain interaction parameter β, geometric factor γ, and hydrodynamic interaction parameter α obtained from free volume data were employed to further determine the effect of molecular architecture and styrene content on the miscibility. The results suggest the better miscibility in star-shaped SBS/PS blends than that of corresponding linear SBS/PS systems, even than that of systems containing more styrene unit. In addition, differential scanning calorimetry, dynamic mechanical analysis, and scanning electron microscopy, which are sensitive to heterogeneities in larger domain size, give different results of miscibility from free volume data. It should be attributed the difference of characterization scale. The mechanical property corroborates the results of miscibility. © 2013 Society of Plastics Engineers. Source


Meng X.,China University of Petroleum - Beijing | Meng X.,Beijing Key Laboratory of Failure | Liu X.,China University of Petroleum - Beijing | Cong C.,China University of Petroleum - Beijing | And 3 more authors.
Polymer Composites | Year: 2015

To fabricate multiwalled carbon nanotubes (MWCNTs)/tetrafluoroethylene-propylene elastomer (TFEP) nano-composite, the surface architecture of MWCNTs was tailored based on TFEP molecular structure. Silane coupling agent (SC) and fluorocarbon surfactant (FC) were separately used to improve the interaction and compatibility between MWCNTs and polymer matrix. The C=C group of SC can participate in the crosslinking reaction of TFEP, which results in the formation of covalent connection between MWCNTs and matrix. The fluorine atom in FC has better compatibility with tetrafluoroethylene segment of TFEP, which effectively promotes the compatibility between MWCNTs and matrix. The organic modifiers were successfully attached to the surface of MWCNTs, as verified by the results of infrared spectroscopy, thermogravimetric analyses, field emission scanning electron microscopy, and energy dispersive spectrum. Owing to functionalization of surface, the dispersions of MWCNTs were obviously improved. A comprehensive upgrade of mechanical property was achieved, and the elasticity of fluoroelastomer was not deteriorated. Meanwhile, the resistance to medium ageing performance property presented a significant advantage. The effect of interface tailoring was verified by the superiority of morphology and properties. © 2014 Society of Plastics Engineers. Source


Cai Z.,China University of Petroleum - Beijing | Cai Z.,Beijing Key Laboratory of Failure | Meng X.,China University of Petroleum - Beijing | Meng X.,Beijing Key Laboratory of Failure | And 10 more authors.
Materials and Design | Year: 2014

In this study, the mechanical properties and structure orientation of pure polyamide 1212 (PA1212) were compared with those of PA1212-carbon nanofibers (CNFs) nanocomposites. The tensile strength of the composite containing 0.3. wt.% modified CNFs was improved from 328. MPa (pure PA1212) to 373. MPa after drawing. The reinforcing effect was investigated in terms of crystallization behavior, crystal morphology, alignment of CNFs, and crystal orientation degree. Spherulites developed into oriented crystals after drawing, and the CNFs aligned along the drawing direction. The heterogeneous nucleation effect of the aligned CNFs improved the crystal orientation degree, which produced the reinforcing effect. The oriented fibril structures with rigid nanofibers acting as nuclei reinforced the entire oriented crystals in the composites. © 2014 Elsevier Ltd. Source

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