Browsing by Author "Pospiech, Doris"
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- ItemDesign of Polymer-Embedded Heterogeneous Fenton Catalysts for the Conversion of Organic Trace Compounds(Basel : MDPI, 2021) Horn, Christoph; Ihmann, Stephanie; Müller, Felix; Pospiech, Doris; Borchert, Konstantin B. L.; Hommel, Rolf; Qin, Kaite; Licha, Kai; Allertz, Peter J.; Drache, MarcoAdvanced oxidation processes are the main way to remove persistent organic trace compounds from water. For these processes, heterogeneous Fenton catalysts with low iron leaching and high catalytic activity are required. Here, the preparation of such catalysts consisting of silica-supported iron oxide (Fe2O3/SiOx) embedded in thermoplastic polymers is presented. The iron oxide catalysts are prepared by a facile sol–gel procedure followed by thermal annealing (calcination). These materials are mixed in a melt compounding process with modified polypropylenes to stabilize the Fe2O3 catalytic centers and to further reduce the iron leaching. The catalytic activity of the composites is analyzed by means of the Reactive Black 5 (RB5) assay, as well as by the conversion of phenol which is used as an example of an organic trace compound. It is demonstrated that embedding of silica-supported iron oxide in modified polypropylene turns the reaction order from pseudo-first order (found for Fe2O3/SiOx catalysts), which represents a mainly homogeneous Fenton reaction, to pseudo-zeroth order in the polymer composites, indicating a mainly heterogeneous, surface-diffusion-controlled process.
- ItemEffective Halogen-Free Flame-Retardant Additives for Crosslinked Rigid Polyisocyanurate Foams: Comparison of Chemical Structures(Basel : MDPI, 2022) Lenz, Johannes U.; Pospiech, Doris; Komber, Hartmut; Korwitz, Andreas; Kobsch, Oliver; Paven, Maxime; Albach, Rolf W.; Günther, Martin; Schartel, BernhardThe impact of phosphorus-containing flame retardants (FR) on rigid polyisocyanurate (PIR) foams is studied by systematic variation of the chemical structure of the FR, including non-NCO-reactive and NCO-reactive dibenzo[d,f][1,3,2]dioxaphosphepine 6-oxide (BPPO)- and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-containing compounds, among them a number of compounds not reported so far. These PIR foams are compared with PIR foams without FR and with standard FRs with respect to foam properties, thermal decomposition, and fire behavior. Although BPPO and DOPO differ by just one oxygen atom, the impact on the FR properties is very significant: when the FR is a filler or a dangling (dead) end in the PIR polymer network, DOPO is more effective than BPPO. When the FR is a subunit of a diol and it is fully incorporated in the PIR network, BPPO delivers superior results.
- ItemEnzymatic Synthesis of Poly(alkylene succinate)s: Influence of Reaction Conditions(Basel : MDPI, 2021) Pospiech, Doris; Choińska, Renata; Flugrat, Daniel; Sahre, Karin; Jehnichen, Dieter; Korwitz, Andreas; Friedel, Peter; Werner, Anett; Voit, BrigitteApplication of lipases (preferentially Candida antarctica Lipase B, CALB) for melt polycondensation of aliphatic polyesters by transesterification of activated dicarboxylic acids with diols allows to displace toxic metal and metal oxide catalysts. Immobilization of the enzyme enhances the activity and the temperature range of use. The possibility to use enzyme-catalyzed polycondensation in melt is studied and compared to results of polycondensations in solution. The experiments show that CALB successfully catalyzes polycondensation of both, divinyladipate and dimethylsuccinate, respectively, with 1,4-butanediol. NMR spectroscopy, relative molar masses obtained by size exclusion chromatography, MALDI-TOF MS and wide-angle X-ray scattering are employed to compare the influence of synthesis conditions for poly(butylene adipate) (PBA) and poly(butylene succinate) (PBS). It is shown that the enzymatic activity of immobilized CALB deviates and influences the molar mass. CALB-catalyzed polycondensation of PBA in solution for 24 h at 70 °C achieves molar masses of up to Mw~60,000 g/mol, higher than reported previously and comparable to conventional PBA, while melt polycondensation resulted in a moderate decrease of molar mass to Mw~31,000. Enzymatically catalyzed melt polycondensation of PBS yields Mw~23,400 g/mol vs. Mw~40,000 g/mol with titanium(IV)n-butoxide. Melt polycondensation with enzyme catalysis allows to reduce the reaction time from days to 3–4 h.
- ItemGaseous- and Condensed-Phase Activities of Some Reactive P- and N-Containing Fire Retardants in Polystyrenes(Basel : MDPI, 2022) Tretsiakova-McNally, Svetlana; Baby, Aloshy; Joseph, Paul; Pospiech, Doris; Schierz, Eileen; Lederer, Albena; Arun, Malavika; Fontaine, GaëllePolystyrene (PS) was modified by covalently binding P-, P-N- and/or N- containing fire-retardant moieties through co- or ter-polymerization reactions of styrene with diethyl(acryloyloxymethyl)phosphonate (DEAMP), diethyl-p-vinylbenzyl phosphonate (DEpVBP), acrylic acid-2-[(diethoxyphosphoryl)methylamino]ethyl ester (ADEPMAE) and maleimide (MI). In the present study, the condensed-phase and the gaseous-phase activities of the abovementioned fire retardants within the prepared co- and ter-polymers were evaluated for the first time. Pyrolysis–Gas Chromatography/Mass Spectrometry was employed to identify the volatile products formed during the thermal decomposition of the modified polymers. Benzaldehyde, α-methylstyrene, acetophenone, triethyl phosphate and styrene (monomer, dimer and trimer) were detected in the gaseous phase following the thermal cracking of fire-retardant groups and through main chain scissions. In the case of PS modified with ADEPMAE, the evolution of pyrolysis gases was suppressed by possible inhibitory actions of triethyl phosphate in the gaseous phase. The reactive modification of PS by simultaneously incorporating P- (DEAMP or DEpVBP) and N- (MI) monomeric units, in the chains of ter-polymers, resulted in a predominantly condensed-phase mode of action owing to synergistic P and N interactions. The solid-state 31P NMR spectroscopy, Scanning Electron Microscopy/Energy Dispersive Spectroscopy, Inductively-Coupled Plasma/Optical Emission Spectroscopy and X-ray Photoelectron Spectroscopy of char residues, obtained from ter-polymers, confirmed the retention of the phosphorus species in their structures.
- ItemGrundlegende Untersuchungen zur Entwicklung von Hochtemperaturthermoplastblends mit verbesserter Phasenanbindung : Forschungsvorhaben auf dem Gebiet: "Exploratorische Materialforschung mit Nachwuchswissenschaftlerinnen und Nachwuchswissenschaftlern" ("Hot-Topics") ; Laufzeit: 04/2001 - 09/2002 ; Abschlußbericht(Dresden : Leibniz-Institut für Polymerforschung, 2003) Pospiech, Doris; Hoffmann, Thorsten; Altstädt, Volker[no abstract available]
- ItemImproving the flame retardance of polyisocyanurate foams by dibenzo[d,f][1,3,2]dioxaphosphepine 6-oxide-containing additives(Basel : MDPI, 2019) Lenz, Johannes; Pospiech, Doris; Paven, Maxime; Albach, Rolf W.; Günther, Martin; Schartel, Bernhard; Voit, BrigitteA series of new flame retardants (FR) based on dibenzo[d,f][1,3,2]dioxaphosphepine 6-oxide (BPPO) incorporating acrylates and benzoquinone were developed previously. In this study, we examine the fire behavior of the new flame retardants in polyisocyanurate (PIR) foams. The foam characteristics, thermal decomposition, and fire behavior are investigated. The fire properties of the foams containing BPPO-based derivatives were found to depend on the chemical structure of the substituents. We also compare our results to state-of-the-art non-halogenated FR such as triphenylphosphate and chemically similar phosphinate, i.e. 9,10-dihydro-9-oxa-10- phosphaphenanthrene-10-oxide (DOPO), based derivatives to discuss the role of the phosphorus oxidation state.
- ItemIn situ preparation of crosslinked polymer electrolytes for lithium ion batteries(Basel : MDPI, 2020) Röchow, Eike T.; Coeler, Matthias; Pospiech, Doris; Kobsch, Oliver; Mechtaeva, Elizaveta; Vogel, Roland; Voit, Brigitte; Nikolowski, Kristian; Wolter, MareikeSolid polymer electrolytes for bipolar lithium ion batteries requiring electrochemical stability of 4.5 V vs. Li/Li+ are presented. Thus, imidazolium-containing poly(ionic liquid) (PIL) networks were prepared by crosslinking UV-photopolymerization in an in situ approach (i.e., to allow preparation directly on the electrodes used). The crosslinks in the network improve the mechanical stability of the samples, as indicated by the free-standing nature of the materials and temperature-dependent rheology measurements. The averaged mesh size calculated from rheologoical measurements varied between 1.66 nm with 10 mol% crosslinker and 4.35 nm without crosslinker. The chemical structure of the ionic liquid (IL) monomers in the network was varied to achieve the highest possible ionic conductivity. The systematic variation in three series with a number of new IL monomers offers a direct comparison of samples obtained under comparable conditions. The ionic conductivity of generation II and III PIL networks was improved by three orders of magnitude, to the range of 7.1 × 10−6 S·cm−1 at 20 °C and 2.3 × 10−4 S·cm−1 at 80 °C, compared to known poly(vinylimidazolium·TFSI) materials (generation I). The transition from linear homopolymers to networks reduces the ionic conductivity by about one order of magnitude, but allows free-standing films instead of sticky materials. The PIL networks have a much higher voltage stability than PEO with the same amount and type of conducting salt, lithium bis(trifluoromethane sulfonyl)imide (LiTFSI). GII-PIL networks are electrochemically stable up to a potential of 4.7 V vs. Li/Li+, which is crucial for a potential application as a solid electrolyte. Cycling (cyclovoltammetry and lithium plating-stripping) experiments revealed that it is possible to conduct lithium ions through the GII-polymer networks at low currents. We concluded that the synthesized PIL networks represent suitable candidates for solid-state electrolytes in lithium ion batteries or solid-state batteries.
- ItemStructure and Bottom-up Formation Mechanism of Multisheet Silica-Based Nanoparticles Formed in an Epoxy Matrix through an In Situ Process(Washington, DC : ACS Publ., 2021) Branda, Francesco; Bifulco, Aurelio; Jehnichen, Dieter; Parida, Dambarudhar; Pauer, Robin; Passaro, Jessica; Gaan, Sabyasachi; Pospiech, Doris; Durante, MassimoOrganic/inorganic hybrid composite materials with the dispersed phases in sizes down to a few tens of nanometers raised very great interest. In this paper, it is shown that silica/epoxy nanocomposites with a silica content of 6 wt % may be obtained with an “in situ” sol–gel procedure starting from two precursors: tetraethyl orthosilicate (TEOS) and 3-aminopropyl-triethoxysilane (APTES). APTES also played the role of a coupling agent. The use of advanced techniques (bright-field high-resolution transmission electron microscopy, HRTEM, and combined small- and wide-angle X-ray scattering (SAXS/WAXS) performed by means of a multirange device Ganesha 300 XL+) allowed us to evidence a multisheet structure of the nanoparticles instead of the gel one typically obtained through a sol–gel route. A mechanism combining in a new manner well-assessed knowledge regarding sol–gel chemistry, emulsion formation, and Ostwald ripening allowed us to give an explanation for the formation of the observed lamellar nanoparticles.