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The aminolysis of bio-based glycidylethers and limonene dioxide with aqueous ammonia represents a versatile one-step synthesis of multifunctional bio-based amine curing agents and does not require either organic solvents besides bioethanol or tedious purification. Moreover, the identical bio-based glycidylether serves as the raw material for both the amine curing agent and the polyfunctional cyclic carbonate, both of which are key intermediates in non-isocyanate polyhydroxyurethane (NIPU) production. This study elucidates the influences of molecular architecture and amine content of multifunctional β-amino alcohol (AA) curing agents, as determined by means of 13C-NMR spectroscopy, and the type of polyfunctional cyclic carbonates on the thermal and mechanical NIPU properties, NIPU degradation and NIPU solvent swelling. Preferably, owing to their rather high viscosities, polyfunctional AAs are blended together with hexamethylene diamine (HMDA) to enable facile NIPU cure at ambient temperatures. As compared to HMDA, the addition of the less reactive polyfunctional AAs increases gel time, as measured by oscillatory rheological experiments, and simultaneously improves NIPU stiffness, as determined by Young's modulus (+200%). [ABSTRACT FROM AUTHOR]

Most of the numerous emerging synthetic routes toward functionalized few- and multilayer graphene employ fossil resources such as graphite together with polar solvents. Herein we report on the solvent-free preparation of nitrogenated graphene and green carbon nanomaterials exploiting furfuryl alcohol (FA) and urea as renewable feedstocks. Typically, polyfurfuryl alcohol (PFA) reactor blends, prepared by cationic polymerization of furfuryl alcohol in the presence of urea or dicyandiamide (DICY), respectively, are carbonized by thermolysis. In sharp contrast to conventional PFA thermolysis, as verified by a microscopy (SEM, TEM, AFM) and WAXS, only PFA thermolysis in the presence of urea and DICY affords nitrogenated functionalized multilayer graphene. This is attributed to the in situ formation of carbon nitride nanosheets as thermally degradable template. Variations of process parameters such as the temperature ramp and the FA/urea and FA/DICY molar ratios enable control of graphene morphology development and properties. Thus, our green carbon approach toward functionalized multilayer graphene holds promise for fabricating renewable carbon nanosheet materials, meeting the demands of manifold applications. [ABSTRACT FROM AUTHOR]

Polymer nanocomposites are defined as polymers in which small amounts of nanometer size fillers are homogeneously dispersed by only several weight percent- ages. Addition of just a few weight percent of the nanofillers has profound impact on the physical, chemical, mechanical and electrical properties of polymers. Such change is often favorable for engineering purpose. This nanocomposite technology has emerged from the field of engineering plastics, and potentially expanded its application to structural materials, coatings, and packaging to medical/biomedical products, and electronic and photonic devices. Recently these `hi-tech' materials with excellent properties have begun to attract research people in the field of dielectrics and electrical insulation. Since new properties are brought about from the interactions of nanofillers with polymer matrices, mesoscopic properties are expected to come out, which would be interesting to both scientists and engineers. Improved characteristics are expected as dielectrics and electrical insulation. Several interesting results to indicate foreseeable future have been revealed, some of which are described on materials and processing in the paper together with basic concepts and future direction. [ABSTRACT FROM AUTHOR]

The microstructure and morphology of stereoblock polypropylenes containing sequences of isotactic (i) and syndiotactic (s) polypropylene (PP) were studied by 13C NMR spectroscopy, wide angle x-ray scattering (WAXS), size exclusion chromatography (SEC) combined with FT-IR analysis of the fractions, and atomic force microscopy. The 13C NMR spectra show the presence of long stereoregular sequences in the respective stereoblock polypropylene which are able to form the crystal modification known from the respective stereoregular homopolymers as revealed by WAXS measurements. A bimodal molar-mass distribution is detected by SEC. All SEC fractions contain i-PP and s-PP sequences, proven by FT-IR spectroscopy. It is shown by atomic-force microscopy that the stereoblock polypropylene, synthesized by homopolymerization of propylene using iso- and syndiotactic catalysts, form a microphase-separated morphology. The microphase separation is preserved also after treatment with hot toluene. A parallel investigation was conducted on a blend of i-PP and s-PP; it exhibits macrophase separation. Treatment of the blend with hot toluene results in the dissolution of the s-PP phase. [ABSTRACT FROM AUTHOR]

The two-stage mechanochemical amination of graphite by dry ball milling of graphite in a planetary ball mill under Ar followed by NH3 yields aminated multilayer graphene (AMFG) as intermediates for carbon/polymer hybrids and nanocomposites. Opposite to efficient edge-selective graphene functionalization under Ar, CO2 and N2 pressure, the onestage ball milling under NH3 pressure affords rather low N content (<0.5 wt%) and fails to reduce the graphite platelet size. According to DFT (Density Functional Theory) calculations NH3 exhibits low mobility between graphene layers and forms weak bonds to carbon which impair breakage of carbon bonds. In the two-stage ball-milling of graphite under Ar affords reactive carbon nanoparticles which react with NH3 in the second stage. With increasing milling duration of the second stage the nitrogen content increases to 3.2 wt%. As verified by XPS (X-ray photoelectron spectroscopy) measurements primary amine groups are formed which couple with various dicarboxylic anhydride groups including maleated PP to produce imidefunctionalized graphene. This is of interest to produce compatibilizers and dispersing agents for carbon/PP nanocomposites exhibiting improved mechanical properties. Two-stage mechanochemistry holds promise for carbon nanoparticle functionalization well beyond amination. [ABSTRACT FROM AUTHOR]

Herein we report on the characterizationof rheological, morphological,and electrical properties of graphene/polystyrene nanocomposites asa function of graphene functionalization. Hydrophobic modified graphiteoxide was grafted with polystyrene chains (PS-g-FG),thus enabling a high degree of compatibility with the polystyrenematrix. While nongrafted and noncompatibilized graphene showed a particlenetwork in accordance with the time–temperature superpositionprinciple, the grafted PS-g-FG revealed a structuraldevelopment with time, which is the consequence of superior but unstabledispersion of the latter. This results in an increasing elasticityof the graphene network as well as in an enhanced electrical conductivityof the composite material. Kinetic investigations showed a multistepprocess being the basis of this structural evolution. While extensiveshear (large amplitude oscillatory shear, LAOS) led to a destructionof the network, small shear impact (small amplitude oscillatory shear;SAOS) in combination with elevated temperature was crucial for aneffective buildup of the graphene particle network. In addition, therheological and electrical percolation threshold was determined simultaneouslyby a combined rheodielectric setup. The structure development wassuccessfully monitored by electron microscopy, showing an increasein number and size of interconnected graphene domains, accompaniedby an exfoliation of aggregated graphene stacks. Thus, the presentinvestigation is a rare example of comparing compatibilization ofgraphene with detailed characterization of melt rheology, electricalproperties, and computer-aided morphological analysis. [ABSTRACT FROM AUTHOR]

A facile one-step mechanochemicalprocess converts graphite intohighly active graphene-supported iron catalysts for ethylene polymerizationand the in situ formation of graphene/polyethylene nanocomposites.Key feature is the dry grinding of graphite in a steel ball mill undercarbon dioxide pressure, affording high surface area edge-carboxylatedgraphene accompanied by simultaneous immobilization of Fe2+, formed by iron abrasion and electron transfer reaction. In contrast,as evidenced by Mössbauer spectroscopy, grinding graphite inthe absence of carbon dioxide under nitrogen or argon pressure producespredominantly Fe0together with Fe3+supportedon nitrogen-functionalized graphene or micronized graphite, respectively.On addition of bisiminopyridine (BIP) and activation with methylaluminoxane(MAO), only the Fe2+catalyst supported on edge-functionalizedgraphene (Fe@MG-CO2) polymerizes ethylene in high yields,producing polyethylene with a molar mass of 180 kg/mol and a polydispersityof 6.1. According to the transmission electron microscopic analysisof polyethylene morphology, functionalized graphene with low aspectratio is uniformly dispersed in the polyethylene matrix. Hence, thismechanochemical catalyst preparation enables the fabrication of graphene/polyolefinnanocomposites with high carbon content by polymerization fillingusing cost-effective graphite as raw material without requiring tediousand expensive graphite functionalization in separate steps. [ABSTRACT FROM AUTHOR]

Abstract: In this study fibre reinforced laminates with a graphene oxide modified epoxy matrix were manufactured using a filament winding technology for prepreg production. Dispersion of the nano-particles was achieved with a three roll mill. Cross-ply laminates with carbon and glass fibres and different nano-particle loadings were produced. Impact damage was introduced with an instrumented drop weight tower. Prior to mechanical testing damage size was determined using ultrasonic c-scans and pulse phase thermography. The defect size was reduced significantly with increasing graphene oxide loading in the matrix. Residual compressive properties of the laminates improved significantly for the modified specimen, with the glass fibre laminates showing the highest improvement of 55% when compared to unmodified specimens. In addition to the improved mechanical properties the matrix modification also improved the phase contrast of the thermography data thus enabling better detection of defects and improved detection limits. [Copyright &y& Elsevier]

Abstract: This study is focused on the investigation of thermo-mechanical properties of an epoxy resin filled with thermally reduced graphene oxide (TRGO) and multi-wall carbon nanotubes (MWCNT) after exposure of samples to hot distilled water. Addition of low contents of TRGO and MWCNTs greatly reduces the water sorption capacity of the epoxy polymer and improves its resistance to hydrothermal ageing. The glassy and rubbery moduli of the neat epoxy decreased for about 20% and 80%, respectively, while TRGO-based epoxy filled with 0.3 wt.% of TRGO showed only 6% reduction of both moduli. Hydrothermal ageing resulted in an enormous drop in the glass transition temperature (T g ) of the neat epoxy, by about 90 °C, while the shift in T g of the nanocomposites did not exceed 8 °C. After re-drying of samples, the position and shape of the peak was completely recovered for the nanocomposites. Irreversibility of water influence on the neat polymer appeared in the broadened and shifted glass transition region. The improvement of the thermo-mechanical properties of the neat epoxy from the addition of TRGO is higher than that achieved by incorporating MWCNTs. This trend is valid in both unexposed state and after hydrothermal ageing of the nanocomposites. [Copyright &y& Elsevier]

A vinylester–urethane hybrid resin (VEUH) was toughened by adding various vinyl-functionalized branched polyethers in 10 and 20 wt%. Two sets of hyperbranched polymers (HBPs) with different branching density were compared with a set of six-arm star polymers. Besides the architecture, the polymers also varied in their characteristics (molecular mass and mass distribution, vinyl/hydroxy ratio). The morphology of the modified VEUH was studied by dynamic-mechanical thermal analysis (DMTA), transmission (TEM) and scanning electron microscopy (SEM). The toughness was characterized by the fracture energy (Gc) determined on compact tension specimens at room temperature. It was established that the architecture and vinyl/hydroxy ratio of the HBPs are those parameters which control the morphology and thus the related linear elastic fracture mechanical response. Less compact star-like polymers with long, flexible arms and with high vinyl functionality produced the largest toughness improvement in VEUH. [Copyright &y& Elsevier]

Organophilic layered silicates (OLS), modified by means of cation exchange, were added in amounts of 5–15 wt.% to vinylester (VE)/epoxy (EP) hybrid resins which can form interpenetrating networks (IPN) after curing at T=150 °C. The resulting phase structure was studied by atomic force microscopy (AFM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was established that the OLS were intercalated by the hybrid resin. On the microscale silicate particles surrounded by a broad EP interphase were formed. This “encapsulation” was considered as the major cause for the reduction in both stiffness and glass transition temperature (Tg) of the resins. Irrespective to the coarse dispersion of the OLS, the fracture energy of the resins was doubled by adding 5 wt.% OLS. The fracture energy decreased, however, with increasing OLS content. This was explained by changes in the failure mode concluded from fractographic studies. The type of the organic cation modification of the OLS had no effect on either morphology or toughness. This was attributed to the coarse dispersion of the OLS and its encapsulation by the EP phase in the VE/EP hybrid resins. [Copyright &y& Elsevier]