All issues / Volume 8 (2014) / Issue 12 (December)
This is an editorial article. It has no abstract.
Various surfactants of different molecular weights, including alkylamine, poly(oxypropylene) diamine (POP), and maleic anhydride grafted polypropylene (PPgMA) oligomers, were used for simultaneous funtionalization and reduction of graphite oxide (fGO). In this study, the effect of molecular weight and compatibility of the surfactants on the morphology and properties of the nanocomposites are reported. Wide-angle X-ray diffraction (WAXD) exhibited a definite interlayer thickness for GOA (alkylamine intercalated GO), however, the diffraction peaks were nearly suppressed for fGOs combining ODA with either POP (GOAP) or PPgMA (GOAE). The uniform dispersion of the fGO flakes in the polypropylene matrix resulted in the significant increase in both the degradation temperature and the crystallization temperature. A single characteristic melting peak of monoclinic (α) crystalline phase was observed from DSC traces, which was consistent with WAXD results. Dynamic mechanical analysis clearly indicated increase in both the storage modulus and the glass transition temperature of the nanocomposites due to the enhanced affinity between fGO and the polypropylene matrix. However, GOAP composite showed lower E' and Tg than GOAE because POP is less compatible with the matrix than PPgMA oligomer. Dielectric analysis also showed significant increase in both dielectric permittivity and dielectric loss at low frequency regimes with GOAE showing maximum dielectric properties. The finely dispersed GOAE and its compatibility with polymer matrix manifested the interfacial polarization, which gave rise to much greater ε' and ε" than other nanocomposites.
Fiber-like polyaniline (PANI)/carbon nanohorn (CNH) composites (PACN composites) were prepared as electrode materials for supercapacitor by simple method that involves in-situ polymerization of aniline in the presence of CNH in acidic (HCl) medium with noteworthy electrochemical performances. Thus, the prepared PACN composites show high specific capacitance value of ≈ 834 F/g at 5 mV/s scan rate compared to ≈ 231 F/g for pure PANI and CNH (≈ 145 F/g) at same scan rate of 5 mV/s. CNHs are homogeneously dispersed throughout the matrix and coated successfully. Thus, it provides more active sites for nucleation and electron transfer path. In addition, the composites show high electrical conductivity in the order of ≈ 6.7•10–2 S•cm–1 which indicates the formation of continuous interconnected conducting network path in the PACN composites. Morphological study of the PACN composites was carried out by high resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM).
We present comparative studies on the effect of varying the carboxylic-group content of thermally reduced graphene oxides (TRGs) on the anticorrosive properties of as-prepared poly(methyl methacrylate) (PMMA)/TRG composite (PTC) coatings. TRGs were formed from graphene oxide (GO) by thermal exfoliation. The as-prepared TRGs were then characterized using Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Subsequently, the PTC materials were prepared via a UV-curing process and then characterized using FTIR spectroscopy and transmission electron microscopy (TEM). PTC coatings containing TRGs with a higher carboxylic-group content exhibited better corrosion protection of a cold-rolled steel electrode that those with a lower carboxylic-group content. This is because the well-dispersed TRG with a higher carboxylic-group content embedded in the PMMA matrix effectively enhances the oxygen barrier properties of the PTC. This conclusion was supported by gas permeability analysis.
Incorporation of fillers with high thermal conductivity to base materials has been recognized as an efficient way to increase the thermal conductivity of composite materials. In this study, the effects of the prismatic filler arrangement and cross-sectional shape on the thermal conductivity of the composites were investigated. This research addresses these problems by solving the heterogeneous two-dimensional heat conduction problem in the composite materials. A validated commercial software-FLUENT and finite volume method was used in the analysis. The close-packed, directional and random filler arrangements were considered. It was found that the prismatic filler arrangement and cross-sectional shape have great impacts on the thermal conductivity of the composite materials. Double Y shaped, I shaped, T shaped, elliptical, rhombic and rectangular cross-sectional fillers can greatly increase the thermal conductivity only in directional arrangement. The effects of circular, square, triangular and Y shaped cross-sectional are similar in directional and random arrangements. The close-packed arrangements for all cross-sectional shapes have small thermal conductivity. The double Y shaped, Y shaped and I shaped cross-sectional were found to be the best choice for composite materials regardless of the filler arrangements.
The aim of this work was to study the activity of several alkylpyrrolidinium, alkylpyridinium, alkylpiperidinium and benzylimidazolium ionic liquids (ILs) for the purpose of improving the dispersion degree of vulcanisation activator and filler nanoparticles in the acrylonitrile-butadiene elastomer (NBR). The effect of the ionic liquids on the vulcanisation kinetics of the rubber compounds, crosslink density and mechanical properties of the vulcanisates and their resistance to thermo-oxidative and UV ageing was studied. The use of ionic liquids allowed for a homogeneous dispersion of nanoparticles in the elastomer without detrimental effects on the vulcanisation process. The physical properties and the thermal stability of the obtained vulcanisates were significantly improved. Ionic liquids increased the crosslink density of the vulcanisates and their damping properties. Pirydinium and piperidinium hexafluorophosphates were most effective at increasing the crosslink density and improving the properties of NBR composites.
In this paper, we propose a green route to prepare insoluble poly(vinyl alcohol) (PVOH) cast films with potential application as antimicrobial packaging. First PVOH films were cast from different aqueous solutions and analyzed by Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) to determine their physical properties under two storage conditions. In order to obtain insoluble films, PVOH was then crosslinked by citric acid (CTR) as confirmed by Nuclear Magnetic Resonance (NMR) analyses. The crosslinking reaction parameters (curing time, crosslinker content) were studied by comparing the characteristics of PVOH/CTR films, such as free COOH content and glass transition temperature (Tg) value, as well as the impact of the crosslinking reaction on mechanical properties. It was found that for 40 and 10 wt% CTR contents, 120 and 40 min of crosslinking times were necessary to bind all CTR respectively. Brittle films were obtained for 40 wt% CTR whereas 10 wt% CTR content led to ductile films. Finally, films containing hydroxypropyl-β-cyclodextrin (HPβCD), chosen as a potential vector of antimicrobial agent, were prepared. The obtained results show that the incorporation of HPβCD in the PVOH matrix does not mainly influence the physical and mechanical properties of the films.
Cyclic butylene terephthalate (CBT®) is an interesting matrix material for the preparation of nanocomposites due to its very low, water-like melt viscosity which favours clay exfoliation. Nevertheless, polymerized CBT (pCBT) is inherently brittle. This paper reports the preparation of isocyanate-toughened nanocomposites made from CBT and organo-modified montmorillonite. The role of the organoclay as reinforcement and the polymeric isocyanate (PMDI) as toughening agent on the properties of pCBT was studied. The organoclay increased the stiffness and strength by up to 20% whereas the PMDI improved the deformation behaviour. However, the PMDI did not affect the degree of clay dispersion or exfoliation and flocculated-intercalated structures were observed. The compatibility between the pCBT matrix and clay was further increased by preparing PMDI-tethered intercalated organoclay. The modified organoclay then exfoliated during ring-opening polymerization and yielded true pCBT/clay nanocomposites. This work demonstrates that reactive chain extension of CBT with a polyfunctional isocyanate is an effective method to obtain toughened pCBT nanocomposites. Moreover, isocyanates can enhance the compatibility between pCBT and nanofiller as well as the degree of exfoliation.