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Organisationseinheit der BAM
Durch das Füllen von Polymeren mit Nanopartikeln oder Nanoröhren werden verbesserte Materialeigenschaften z.B. bezüglich mechanischer Stabilität, Witterungsbeständigkeit, elektrischer Leitfähigkeit und Flammschutz angestrebt. Mit dem vermehrten Einsatz derartiger Nanokomposite gewinnen aber auch Fragen des Umwelt- und Gesundheitsschutzes an Bedeutung. Es gilt zu klären, ob durch Herstellung, Benutzung und Witterungsbeanspruchung möglichweise nanoskalige Partikel freigesetzt werden können. Zu diesem Zweck wurden mit Kohlenstoffnanoröhren, Carbon Nanotubes (CNT), gefüllte Polymerkomposite spektral breitbandig wie auch quasimonochromatisch unter variierter klimatischer Beanspruchung bestrahlt. Die sich vor allem an der Oberfläche mit der Alterung abzeichnenden Veränderungen wurden mikroskopisch und spektroskopisch charakterisiert.
It has been shown that selected types of substituents are able to vary the oxidative behavior of multi-walled carbon nanotubes. Such substituents investigated were sterically hindered secondary amino groups bonded in grafted piperidine units and covalently bonded bromine groups. Their interference and activity was preliminary determined in the model cumene and then in oil diesel fraction and low density polyethylene oxidation reactions. Results obtained indicate that chemical linking of amine moieties containing –NH groups directly to the carbon nanotubes core significantly increases their intrinsic anti-oxidative capacity while the grafting of Br-groups provokes the opposite functioning of the pristine samples. This inference was proved by thermogravimetric and differential thermal analysis of the polyethylene composites and experiments on profound aerobic oxidation of petroleum naphthenic fraction derived from the commercial Baku oils blend diesel cut.
Waste disposal of carbon nanotube (CNT) containing products is expected to be the most important pathway for release of CNTs into the environment. In the present work, the use of radiolabelled CNTs (14C-CNT) for polycarbonate polymer nanocomposites with 1 wt% 14C-CNT content allowed for the first time to quantify and differentiate the CNT release according to the type of impact along the materials' ageing history. After an initial exposure of the nanocomposite by solar-like irradiation, further environmental impacts were applied to composite material. They aimed at mimicking disposal site conditions that may induce further ageing effects and CNT release. This study included shaking in water, rapid temperature changes, soaking in humic acid solution as well as waste water effluent, and, finally, gentle mechanical abrasion. All ageing impacts were applied sequentially, both on pristine (control) and on solar-irradiated nanocomposites. All experiments were accompanied by absolute quantification of radioactive release as well as chemical and morphological analyses of the nanocomposite surfaces using infra-red (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The morphological analysis showed that spectral irradiation can uncover CNT networks on the outer nanocomposite surface layers by polymer degradation. After having subjected the solar-irradiated nanocomposite to all studied disposal site effect, the total radioactive release was quantified to amount to 64 mg CNT/m2, whereas only 0.8 mg CNT/m2 were found for the un-irradiated control sample. Solar degradation of polymers was thus found to significantly increase the propensity of the studied polymer nanocomposites to release CNTs during ageing effects at the product's end-of-life typical for disposal sites.
Pulsed and cw microwave plasma excitation for surface functionalization in nitrogen-containing gases
(2003)
Results are presented of polymer surface functionalization processes in pulsed and continuous wave (cw) microwave-excited plasmas in nitrogen-containing gases under admixture of hydrogen. A maximum selectivity of 100% for amino groups with respect to all nitrogen functional groups (NH2/N) was obtained in cw microwave (MW) plasmas either for very short treatment durations below 100 µs in pure NH3, or within approximately 10 s in hydrogen-rich nitrogen-containing plasmas. The amino and overall nitrogen surface densities, NH2/C and N/C, reach up to 3.5% and 35%, respectively. Post plasma processes of functionalized polymers are discussed in the light of monofunctionalization. Down to pulse duration of 1 ms, plasma decomposition rates of NH3, determined by infrared absorption spectroscopy, are found to scale linearly with the duty cycle. In this regime, the main effect of a duty cycle variation in pulsed NH3 plasmas on surface functionalization can be interpreted to result from changes in the concentration of the dominant stable species in the gas phase, NH3, N2 and H2, which are activated by subsequent plasma pulses. With increasing duty cycle, NH3 decomposition to N2 and 3H2 more and more dominates over the supply of fresh NH3. The nitrogen-removing role of hydrogen in the plasma is discussed in detail, whereas the role of the numerous transient nitrogen-containing species remains to be studied in the future.
Brominated single-walled carbon nanotubes [(Br)n-SWCNT) produced by the plasma-chemical technique were involved in the liquid-phase process of hydrocarbons aerobic oxidation. The significant catalytic effect of the (Br)n-SWCNT was revealed at first by the cumene initiated model oxidation and then in experiments on profound aerobic oxidation of petroleum naphthenic fraction derived from the commercial Azerbaijan (Baku) oils blend diesel cut. The ability of (Br)n-SWCNT to accelerate the aerobic oxidation of the hydrocarbons was found out for the first time. Obviously this phenomenon originates from the peculiarities of electronic configuration of the (Br)n-CNT patterns. The plausible mechanism of (Br)n-SWCNT catalytic action is inclined to the formation of reactive oxygen species. The catalytic activity of (Br)n-SWCNT markedly exceeds the activity of the industrial catalysts, manganese salt of indigenous petroleum acids, used for the liquid phase petroleum hydrocarbons oxidation process.
On the Applicability of Plasma Assisted Chemical Micropatterning to Different Polymeric Biomaterials
(2002)
A plasma process sequence has been developed to prepare chemical micropatterns on polymeric biomaterial surfaces. These patterns induce a guided localized cell layover at microscopic dimension. Two subsequent plasma steps are applied. In the first functionalization step a microwave ammonia plasma introduces amino groups to obtain areas for very good cell adhesion; the second passivation step combines pattern generation and creation of cell repelling areas. This downstream microwave hydrogen plasma process removes functional groups and changes the linkages of polymer chains at the outermost surfaces. Similar results have been obtained on different polymers including polystyrene (PS), polyhydroxyethylmethacrylate (PHEMA), polyetheretherketone (PEEK), polyethyleneterephthalate (PET) and polyethylenenaphthalate (PEN). Such a rather universal chemical structuring process could widen the availability of biomaterials with specific surface preparations.
Mit einer langfristigen Forschungsstrategie begleiten die für die Sicherheit von Mensch und Umwelt zuständigen Bundesoberbehörden (Umweltbundesamt, Bundesinstitut für Risikobe-wertung, Bundesanstalt für Arbeitsschutz und Arbeitsmedizin, Bundesanstalt für Materialfor-schung und -prüfung und Physikalisch-Technische Bundesanstalt) die rasch voranschreiten-de Entwicklung neuer Materialien unter den Gesichtspunkten des Arbeits-, Verbraucher- und Umweltschutzes. Die Strategie steht daher in enger Verbindung zu den öffentlichen Förder-programmen für Nanomaterialien und andere innovative Werkstoffe, z. B. des BMBF („Vom Material zur Innovation“) und der EU („Horizon 2020“).
Die Forschungsstrategie baut auf den bisherigen Ergebnissen der 2008 begonnenen und 2013 erstmals bilanzierten gemeinsamen Forschungsstrategie der Bundesoberbehörden „Nanotechnologie - Gesundheits- und Umweltrisiken von Nanomaterialien"1 auf und erweitert den Blickwinkel auch auf andere Materialinnovationen, bei denen vergleichbare Risiken für Mensch und Umwelt bestehen oder abgeklärt werden müssen. Darüber hinaus greift sie die Idee „anwendungssichere chemische Produkte“2 aus der Initiative „Neue Qualität der Arbeit“ (INQA) des Bundesministeriums für Arbeit und Soziales (BMAS) und das Konzept der nach-haltigen Chemie3 auf, das vom Bundesministerium für Umwelt, Naturschutz, Bau und Reak-torsicherheit (BMUB) unterstützt wird. Durch eine anwendungssichere und umweltverträgli-che Gestaltung innovativer Materialien und ihrer Folgeprodukte sollen nicht akzeptable Risi-ken für Mensch und Umwelt von Anfang an weitgehend ausgeschlossen werden. Dies kann erreicht werden durch
1.
die Verwendung sicherer Materialien ohne Gefahreneigenschaften für Mensch und Umwelt (direkte Anwendungssicherheit) oder
2.
eine Produktgestaltung, die über den gesamten Lebenszyklus emissionsarm und umweltverträglich ist (integrierte Anwendungssicherheit) oder
3.
eine Unterstützung des Anwenders (product stewardship) durch den Hersteller bei technischen, organisatorischen und persönlichen Schutzmaßnahmen zur sicheren Verwendung und Entsorgung des Produktes (unterstützte Anwendungssicherheit).
Die Fortschreibung der Forschungsstrategie soll als Bestandteil des Nanoaktionsplans 2020 der Bundesregierung Beiträge der Ressortforschung zu folgenden Schwerpunkten leisten:
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Charakterisierung und Bewertung der Risiken von Materialinnovationen
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Unterstützung von Forschungseinrichtungen und Unternehmen
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Fortschreiben von Rechtsvorschriften und Praxisempfehlungen
1
http://www.baua.de/nn_47716/de/Themen-von-A-Z/Gefahrstoffe/Nanotechnologie/pdf/Forschungsstrategie.pdf
2 http://www.baua.de/de/Themen-von-A-Z/Gefahrstoffe/Nachhaltige-Chemie/Nachhaltige-Chemie.html
3
http://www.umweltbundesamt.de/themen/chemikalien/chemikalien-management/nachhaltige-chemie
2
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Gesellschaftliche Akzeptanz
Die Forschungsstrategie soll mit Projekten und anderen forschungsnahen Aktivitäten umge-setzt werden. Dies umfasst die eigene Forschung der Häuser, die extramurale Ausschrei-bung und Vergabe von Forschungsdienstleistungen sowie die Beteiligung an vorwiegend öffentlich geförderten Drittmittelprojekten. Hinzu kommen Aktivitäten im Rahmen der Politik-beratung und der hoheitlichen Aufgaben. Mit inter- und transdisziplinären Ansätzen soll die Risiko- und Sicherheitsforschung enger mit der Innovationsforschung und Materialentwick-lung verknüpft werden. Die Forschungsstrategie ist aufgrund der raschen Entwicklungen auf diesem Gebiet für den Zeitraum bis 2020 angelegt. Die Forschungsziele adressieren die in diesem Zeitraum voraussichtlich umsetzbaren Forschungsansätze. Die Forschungsstrategie wird durch einen Arbeitskreis begleitet und spätestens mit Ablauf des Nanoaktionsplans 2020 evaluiert und angepasst.
In this work the flexural rigidity of individual large diameter multi-walled carbon nanotubes (MWCNTs) was investigated. The bending modulus were obtained by detecting the resonance frequencies of mechanically excited cantilevered carbon nanotubes using the so-called dynamic scanning electron microscopy technique, and applying the Euler–Bernoulli beam theory. For the nanotubes studied, we determined a modulus of up to 160 GPa. This agrees with values reported by other authors for MWCNTs produced by catalytic chemical vapor deposition, however, it is 6-8 times smaller than values reported for single and multi-walled carbon nanotubes produced by arc-discharge synthesis. Toxicological studies with carbon nanotubes have been showing that inhaled airborne nanofibers that reach the deep airways of the respiratory system may lead to serious, asbestos-like lung diseases. These studies suggested that their toxicity critically depends on the fiber flexural rigidity, with high rigidity causing cell lesions. To complement the correlation between observed toxicological effects and fiber rigidities, reliable and routinely applicable measurement techniques for the flexural rigidity of nanofibers are required.
Low-pressure gas-discharge plasmas are widely used for polymer surface functionalization on industrial scale. For biomaterial applications, the density and selectivity of the functionalization are of particular importance, because functional groups control the immobilization of biomolecules. Therefore, surface modification of biomaterials is a challenging task for low-pressure plasma technique. Plasma processes have been successfully applied to various polymer types in order to generate multifunctional surfaces. This paper discusses the present state and the prospects of non-coating plasma processes to generate mono functional surfaces of controlled amino group density. Such surfaces appear most desirable for many applications. The results of various microwave- and radio-frequency- excited plasma processes reported in the literature are reviewed and compared to a sequence of experiments that was conducted in a UHV reaction environment. Non-thermal plasmas are especially well suited for thermally damageable polymers. The effect of hydrogen admixture to discharges in nitrogen and ammonia is discussed in detail. The optimization of process parameters lead to highly selective amino functionalization of high density. The selectivity reached 100% -NH2/N at a surface density of amino groups of 3% -NH2/C.