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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.

Scaffolds are of great importance for tissue engineering because they enable the production of functional living implants out of cells obtained from cell culture. These scaffolds require individual external shape and well defined internal structure with interconnected porosity. The problem of the fabrication of prototypes from computer assisted design (CAD) data is well known in automotive industry. Rapid prototyping (RP) techniques are able to produce such parts. Some RP techniques exist for hard tissue implants. Soft tissue scaffolds need a hydrogel material. No biofunctional and cell compatible processing for hydrogels exists in the area of RP. Therefore, a new rapid prototyping (RP) technology was developed at the Freiburg Materials Research Center to meet the demands for desktop fabrication of hydrogels. A key feature of this RP technology is the three-dimensional dispensing of liquids and pastes in liquid media. The porosity of the scaffold is calculated and an example of the data conversion from a volume model to the plotting path control is demonstrated. The versatile applications of the new hydrogel scaffolds are discussed, including especially its potential for tissue engineering. [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]

A metallocene-based isotactic polypropylene (m-iPP) was blended with various types of ethene-co-butene rubbers (EBR). Blend miscibility was examined by means of dynamic mechanical analysis (DMTA). In addition, morphology was studied on cyclohexane etched cryofractured samples. Stiffness and toughness properties were assessed and interpreted in function of the blend miscibility. Izod tests served for the dynamic fracture toughness characterization. The essential work of fracture (EWF) approach was used for the characterization of the static fracture toughness. It was found that the 1-butene content of the EBR strongly affects the blend miscibility. A disperse structure was found as prerequisite for outstanding overall toughness. When distiguishing between resistance to crack initiation and propagation, it was found that they are changing adversely to one another. [ABSTRACT FROM AUTHOR]

Thermal and mechanical properties of poly(methylmethacrylate-co-dodecylmethacrylate) nanocomposites based upon exfoliated organophilic layered silicates, were investigated as a function of the silicate and comonomer content. Layered silicates such as sodium bentonite were rendered organophilic by means of ion-exchanging sodium cations for N,N,N,N-dioctadecyl-dimethyl-ammonium cations. Silicate exfoliation was enhanced by means of 5 and 10 wt.-% dodecyl-methacrylate (LMA) addition to afford translucent reinforced acrylic nanocomposites. In contrast to conventional filled acrylic polymers, only 10 wt.-% organophilic silicate was sufficient to increase Young's modulus from 2200 to 4030 MPa, glass temperature from 72 to 80 °C and degradation temperature from 220 to 256 °C with respect to the neat MMA/LMA (90 wt.-%/10 wt.-%) copolymer. Flammability studies, performed on a cone calorimeter, revealed that the maximum heat release rate of MMA/LMA copolymer nanocomposite decreased from 837 kW/m2 to 566 kW/m2. The nanocomposite morphology was examined by means of transmission electron microscopy (TEM). [ABSTRACT FROM AUTHOR]

The synthesis of 4-alkyl-semicarbazones derived from reducing sugars and semicarbazides is presented as a convenient route for the preparation of amphiphilic saccharides. This semicarbazone route allows to employ a large variety of reducing sugars as hydrophilic building block for saccharide tensides. The preparation of two series of amphiphiles based on D-maltose with non-methylated and mono-N-methylated semicarbazone units is described. The n-alkyl chains were varied from n-octyl to n-hexadecyl. Various maltotriose derivatives have also been prepared. Critical micelle concentration (CMC) as well as critical gel concentration of the derivatives were studied in dependence of the n-alkyl chain length. Both values decreased with increasing length of the n-alkyl chain. Self-organization of the gels was studied by transmission electron microscopy of freeze-fractured samples. Due to the supramolecular organization of the amphiphiles, the gels consisted of twisted rope-like molecular assemblies with the same helical twist sense. The helical pitch depended on the hydrophilic/lipophilic balance. In contrast to gels on n-alkylgluconamides, the gels were formed in dilute aqueous solution and exhibited striking longevity without additional stabilization by surfactants. In the solid, the amphiphiles exhibited thermotropic transitions to partially disordered mesophases. [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]

Random copolymers of ethene with 1-octene were investigated by means of pressure-volume-temperature (PVT) measurements. Solubility parameters were calculated from the thermal expansion coefficients and isothermal compressibilities. While expansion coefficients are virtually independent of 1-octene content, compressibilities decrease with increasing 1-octene incorporation. The solubility parameters varied between 17.3 and 15.2 MPa1/2 when 1-octene incorporation was varied between 2 and 100 wt%. In the framework of the solubility parameter concept copolymers containing less than 95 wt% 1-octene were shown to be immiscible with isotactic poly(propene). [ABSTRACT FROM AUTHOR]

Homo- and copolymerizations of 1,5-hexadiene with ethene and styrene using halfsandwich metallocene catalyst Me2Si(Me4Cp)(N-tert-butyl)TiCl2 / MAO (Cp=cyclopentadienyl, Me=methyl, MAO=methylalumoxane) were investigated. According to 13C-NMR spectroscopic microstructure analysis, cyclopolymerization of 1,5-hexadiene afforded randomly distributed cis- and trans-cyclopentane rings in the homo- and copolymer backbone. 1,5-hexadiene incorporation reached 52 mol-%. The ratio of vinyl side chains to cyclopentane rings was controlled by 1,5-hexadiene concentration, where low 1,5-hexadiene concentration promoted cyclopolymerization. Copolymer glass transition temperatures increased with increasing content of cyclic units in the backbone. Styrene was used successfully as termonomer in ethene/1,5-hexadiene polymerization, resulting in a semicrystalline terpolymer with cyclic and styrenic units in the polymer backbone. [ABSTRACT FROM AUTHOR]

Upon heating above its melting temperature at 195°C, 2-(4-hydroxyphenyl)-1,3-oxazoline ( HPO) was polymerized thermally in melt phase within a few minutes to produce a polymer with etheramide and N-4-hydroxybenzoyl-ethyleneimine repeat units. Polymerization in solution afforded only oligomers with 93% etheramide structure after several hours. Reactive blending, combining 2-phenyl-1,3-oxazoline ( PO) grafting with in-situ HPO thermal polymerization in poly(ethene-co-methacrylic acid), was the key to novel self-reinforced multiphase ethene copolymer blends containing spherical dispersed poly( HPO) microphases. Poly( HPO) microstructures, blend morphologies, thermal and mechanical properties were investigated. [ABSTRACT FROM AUTHOR]

Different scanning force microscopy (SFM) modes were applied for the examination of drawn films of isotactic and syndiotactic polypropylene, iPP and sPP. Uniaxially stretched films with a draw ratio λ=6 were studied at ambient conditions, and under water. In iPP films striated patterns of 40-50 nm in width, which are oriented along the stretching direction, exhibit shish-kebab morphology. The dominating nanoscale features are nanofibrils of 10-15 nm in width, and lamellar platelets, which are 40-50 nm in width and 30-35 nm in length. In many places lamellar platelets are closely packed, and they form periodical sequences with a repeat distance of 30-35 nm, which is consistent with the long period. Similar and differing morphological features were found comparing the images of iPP and sPP films. Extended fibrillar patterns of sPP exhibit similar width in the 40-50 nm range, while the lamellar structure is more compact, and the platelets are less uniform in length than those in iPP. The length of lamellar platelets ranges from 30 to 60 nm, and they form local periodical patterns. [ABSTRACT FROM AUTHOR]

The insertion of oligo(tetraflouroethene) segments into the main chain of poly(aramide)s and poly(amide imimide)s is accompanied by a decrease of the glass temperature. The decrease is strictly related to the number of CF-units and is the same for both poly(aramide)s and poly(amide imide)s. The absolute glass temperature depends, however, on the initial structures of the monomeric units. As a consequence 'mastercurves' can be constructed by shifting the individual Tg vs. number of CF-units curves along the temperature axis. A detailed analysis of the data indicates that besides the Tg-mass/'flexible' bond of monomeric unit criterion additional volume and interaction dependant packing effects have to be considered for an accurate prediction of the glass temperatures of polymers. [ABSTRACT FROM AUTHOR]