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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]

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]

Reconstruction of bone defects in the field of craniomaxillofacial surgery is a relevant problem. In regenerative medicine, autologous bone is not available sufficiently. The full replacement of autologous bone grafts is required. A promising research field is the bone engineering. Especially the application of rapid prototyping (RP) enables new perspectives concerning the scaffold design. The aim of the study was to compare scaffolds produced by RP‐technology (native and plasma‐coated PLGA‐scaffolds) with conventionally produced scaffolds (agar plates with hydroxyapatite and hyaluronic acid coated agar plates with hydroxyapatite) relating to proliferation, adhesion, and morphology of osteoblasts to get knowledge about the application potential of such 3D‐manufactured matrices for bone engineering. TissueFoil E served as reference. To compare the scaffolds, 12 ovine and 12 human osteoblast‐like cell cultures of the skull were used. Results were obtained by EZ4U, scanning electron microscopy, and light microscopy. The highest cell proliferation rate of human osteoblast‐like cells was measured on TissueFoil E followed by plasma‐coated PLGA‐scaffolds and uncoated PLGA‐scaffolds, whereas of ovine osteoblast‐like cells on plasma‐coated PLGA‐scaffolds followed by TissueFoil E and uncoated PLGA‐scaffolds. Human and ovine osteoblast‐like cells on coated and uncoated agar plates had significant lower proliferation rates compared with TissueFoil E and PLGA‐scaffolds. These results showed the potential of RP in the field of bone engineering. Mechanical properties of such scaffolds and in vivo studies should be investigated to examine if the scaffolds hold up the pressure it will undergo long enough to allow regrowth of bone and to examine the revascularization. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res 2007 [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]

Focuses on the synthesis of silicate nanocomposites based on high-performance epoxy resin using fluorohectorite. Modification of fluorohectorite by interlayer cation exchange; Influence of surface modifiers on curing reactions and glass transition temperature of epoxy matrix; Tensile and fracture tests.

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]

Two families of polyaramides containing well defined oligo(tetrafluoroethene) segments were prepared from novel N,N'-bis(m-and p-aminophenyl)-perfluoroalkane-cwdicarboxamides in a solution polycondensation processes. The influence of the fluorine content, the substitution pattern of the aromatic rings and the oligo(tetrafluoroethene) segment lengths on solubilities, thermal degradation and phase transition temperatures was investigated. [ABSTRACT FROM PUBLISHER]