Search

Abstract: Sodium hydrosulfite is used to reduce graphite oxide in current study. The preparation of poly (vinyl alcohol) (PVA)/graphene nanocomposites is realized using two simple steps: the synthesis of PVA/graphite oxide (GO) nanocomposites film and immersion of such a film in the reducing agent aqueous solution. This method prohibits the agglomeration of GO during direct reduction in PVA/GO aqueous solution, and opens a new way to scale up the production of graphene nanocomposites using a simple reducing agent. A 40% increase in tensile strength and 70% improvement in elongation at break have been obtained with only the addition of 0.7wt.% of reduced graphite oxide. Furthermore, a good level of conductivity and a variation in the surface property of the prepared films have been observed for the composites containing graphene. [Copyright &y& Elsevier]

Abstract: Large amount of work has been reported on the annealing of polypropylene (PP) and the related changes in mechanical properties. However, the structure–property correlations and the physical origin of annealing induced microstructural evolution are still not very clear. In this work, taking β-form PP (β-PP) as example, the microstructural changes induced by annealing were investigated from macromolecular to crystalline lamellae level with Fourier transform infrared (FTIR) spectroscopy, conventional differential scanning calorimetry (DSC), temperature-modulated DSC (TMDSC), wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS) and dynamic mechanical analysis (DMA). Besides mobile amorphous fraction (MAF), the role of rigid amorphous fraction (RAF) in toughening PP is particularly taken into consideration. It is shown that annealing increases the chain mobility in MAF and decreases it in RAF. Such an effect is believed to be mainly associated with the formation of looser MAF and more RAF by the microstructural re-arrangement involving conformational ordering of partial amorphous chain segments and a significant interlamellae thickening. A thorough analysis of structure–property relationship through observing plastic deformation behaviors by scanning electron microscope (SEM) and estimating stress transmission between crystalline and amorphous phases, suggests that both MAF and RAF play important role on toughening β-PP. They can promote the initiation of microvoids effectively upon deformation by reducing the stress transmission. As a result, large-scale plastic deformation is triggered. This work is important and provides a new insight into the mechanisms of microstructural evolution and subsequent improvement in impact toughness during annealing. [Copyright &y& Elsevier]

In order to suppress the crack formation, water or air cooling after solution treatment is employed to introduce γ phase in a Fe 43.61 Mn 34.74 Al 13.38 Ni 8.27 alloy. In addition to the γ phase, nano-sized B2 and β -Mn phases with an average diameter of 7.8 nm are precipitated in α phase for water cooled samples, while nano-sized β -Mn phase of 11.5 nm is mainly found in the α phase for air cooled samples. This nano-sized coherent B2 phase is beneficial to improving the martensitic reversibility, while the nano-sized incoherent β -Mn phase has no positive effect on achieving the good martensitic reversibility. Furthermore, the nano-sized coherent B2 phase is more effective to avoid the formation of hairpin-shaped dislocations at γ′/α interface than the nano-sized incoherent β -Mn phase. The above two reasons are the main causes of that the reversibility of stress-induced γ′ martensite in the water cooled samples is better than that in the air cooled samples. As a result, the water cooled samples exhibit strong shape memory effect while the air cooled samples have weak one. For the purpose of obtaining the good shape memory effect in FeMnAlNi alloys, the nano-sized coherent B2 phase is expected to be precipitated. [ABSTRACT FROM AUTHOR]