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In this article, we describe the fabrication by melt mixing of graphene‐polypropylene nanocomposites and present the effect of graphene addition on some selected properties of polypropylene (PP). The graphene nanosheets (GNs) used as nano‐reinforcing agents were obtained through chemical reduction of graphene oxide by hydrazine hydrate. GNs were characterized and successfully dispersed into PP matrix to produce PP/GNs nanocomposites. The effects of GNs content on thermal, mechanical, and rheological properties were reported, and the obtained results were discussed in terms of morphology and state of dispersion and distribution of the GNs within the polymer matrix. Characterization by scanning electron microscopy and X‐ray diffraction of the nanocomposites has shown a relatively good dispersion of GNs in the polymer matrix, with the presence of only few aggregates. Increasing GNs content resulted in a significant increase in both mechanical and thermal properties with only few percent of GNs loading. Rheological behavior of the PP/GNs nanocomposites showed a Maxwellian‐like behavior for low GNs concentrations and a viscoelastic solid‐like behavior for GNs content exceeding the concentration of the percolation threshold. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Many processing parameters can be adjusted to optimize the fused filament fabrication (FFF) process, a popular and widely used additive manufacturing techniques for plastic materials. Among those easily adjusted parameters are the nozzle temperature, printing speed, raster orientation, and layer thicknesses. Using poly(ether ether ketone) (PEEK) as the base material, a design of experiments analysis was performed on the main FFF parameters. A response surface methodology was applied to analyze the results and to maximize the output responses. Results have shown that the nozzle temperature is the most influential parameter on tensile properties and the crystallinity degree of printed PEEK by FFF process. Parts produced with optimized FFF parameters were then subjected to an annealing treatment to induce a relaxation of residual stress and to enhance crystallinity. The best properties for 3D printed PEEK parts were achieved with annealed parts prepared at 400°C with a printing speed of 30 mm/s, 0.15 mm layer thickness and raster orientation of [0°/15°/−15°]. The resulting parts have mechanical properties comparable to those of injected PEEK.

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Many parameters of fused deposition modeling (FDM) influence the resulting mechanical properties. This can become a key factor if those parts are intended for commercial applications. This study focuses on the influence of nozzle temperature and infill line orientations for parts made with short carbon fiber (CF)-reinforced polylactic acid (PLA). Tests bars made of PLA and PLA-CF composite were produced under carefully selected conditions. As expected, PLA-CF yields higher tensile properties compared to PLA, owing to the strengthening effect of high modulus CFs. Maximum tensile properties are attained for a nozzle temperature of 230°C, for both PLA and PLA-CF. This temperature was thus selected for probing the effects of infill orientations in test bars. Among the multiple orientations tested, the combination [0°, 15°, −15°] relative to the long axis of the test bar yields the highest levels of tensile properties for both PLA and PLA-CF over the “all-purpose” [45°, 135°] orientation. Annealing can also affect crystallinity and mechanical properties of manufactured parts. Through differential scanning calorimetric analyses, the degree of crystallinity was assessed for samples annealed under various conditions. Results show that annealing increases crystallinity in PLA and PLA-CF samples, with a lower cooling rate yielding higher values. The Young’s modulus exhibits the same behavior for annealed and as printed parts, with a lower cooling rate yielding higher modulus values. This is attributed to a relaxation of the material structure as well as to the orientation of polymer chains toward the CFs.

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Among energy storage technologies available or currently being developed, one of the most promising and attractive electrochemical system is the vanadium redox flow battery (VRFB). One of the key components in VRFB is the membrane required to separate the positive and negative half-cells. The role of this membrane is to prevent cross-mixing of vanadium ions while allowing the transport of certain ions to maintain the electrolytes’ electro-neutrality. Such a membrane represents a sizeable fraction of the system’s total cost while significantly affecting performance. Current research mostly consists of developing high-performance membranes offering high ionic conductivity, low permeability to vanadium ions, and good chemical and mechanical stability. A lower membrane cost is also desirable in order to reduce the overall system costs. This paper provides a comprehensive review of VRFB membranes and recent developments to allow for a better understanding of VRFB membranes’ characterization techniques and their different manufacturing methods, while exploring materials suitable as VRFB membrane. Modeling of ion transport mechanisms through the separator and development prospects for a high-performance VRFB membrane are also discussed. The characteristics of the newly developed membranes are summarized to serve as a reference guide for researchers.