Dieter Jehnichen

Structural characteristics and flammability of fire retarding EPDM/layered double hydroxide (LDH) nanocomposites

A high performance elastomeric flame retardant nanocomposite was prepared which was based on maleic anhydride grafted ethylene-propylene-diene terpolymer (mEPDM), a one-step synthesised organo-layered double hydroxide (LDH), and an intumescent flame retardant (FR) comprised of pentaerythritol (PER), ammonium polyphosphate (APP) and methyl cyanoacetate (MCA). The morphology, fire behavior and mechanical properties of the flame-retarded mEPDM/LDH nanocomposite have been studied in detail. Wide angle X-ray scattering (WAXS), small angle X-ray scattering (SAXS) and TEM observation confirmed an exfoliated structure of LDH in a particular composite containing 2 phr (parts per hundred) LDH and 38 phr FR. As an effective flame retardant synergistic agent, MgAl–LDH shows a significant decrease in the heat release rate (HRR), low mass loss (ML) and low fire growth rate (FIGRA) of the nanocomposite. The flame retardant mechanism has been proposed, which is mainly due to the condensed phase flame retardant mechanism to form reinforced char layers during combustion, leading to the low volatiles produced. Moreover, as far as the mechanical properties of the vulcanizates are concerned, in all cases of flame retardant mEPDM and flame retarded mEPDM/LDH nanocomposites, they exhibit superior values compared to the gum compound.

Comparisons Among Electrical and Rheological Properties of Melt-Mixed Composites Containing Various Carbon Nanostructures

The present investigation compares different carbon-based nanoscaled materials with regard to their effectiveness in producing thermoplastic polymers with antistatic and electrically conductive behavior. The dispersed phases are carbon black (CB) as spherical particles, multiwalled carbon nanotubes (MWNT) as fiber-like filler, and expanded graphite (EG) as platelet-like filler. Each was incorporated into polycarbonate by small-scale melt mixing. The electrical percolation concentrations were found to be 2 wt% for MWNT, 4 wt% for EG, and 8.75 wt% for CB which parallels the aspect ratios of the fillers. For EG a strong dependence of morphology and electrical resistivity on mixing time was observed, indicating a structural change/destruction during intensive shear mixing. Rheological percolation thresholds were found to be lower than electrical percolation threshold for the MWNT and CB, but similar in the case of EG. The general impact on complex melt viscosity decreases in the order MWNT, CB, EG. For EG, at higher loadings (above 4wt%) the viscosity increase with filler content is delayed as is the decrease in resistivity.

An in‐situ ATR‐FTIR study on polyelectrolyte multilayer assemblies on solid surfaces and their susceptibility to fouling

In-situ attenuated total reflection (ATR)-FTIR spectroscopy was used to monitor the consecutively alternating adsorption of polyethylenimine (PEI) and poly(acrylic acid) (PAC) onto both Si crystals (SiO) and CO2 plasma-treated polypropylene (PP) films. The vibration band vas(COO−) and v(CO) of PAC are diagnostic for the polyelectrolyte layer build-up and sensitive to protonation changes. Human serum albumine (HSA) adsorption experiments revealed a strong decrease of fouling for the PP films, which were modified with polyelectrolyte multilayers, in comparison to the unmodified ones.

Controlled growth of Ag nanoparticles decorated onto the surface of SiO2 spheres: a nanohybrid system with combined SERS and catalytic properties

A versatile water-based method for depositing silver nanoparticles (Ag NPs) with controllable and uniform metal size onto the surface of silica (SiO2) spheres is reported. The hybrid particles exhibited a raspberry-like morphology, and their potential for SERS and catalytic applications has been demonstrated. SiO2 spheres (∼120 nm) were synthesized first and modified with polyethyleneimine (PEI) to introduce amine surface functionalities. The amine groups were coordinated with silver ions (Ag+) and reduced to Ag seeds (∼4 nm), uniformly distributed onto the SiO2 surface (SiO2@Ag-seed). In order to improve the optical responses and catalytic activity of SiO2@Ag-seed system, two subsequent silver growth steps were performed. The diameter of Ag seeds was increased to 12 and 19 nm, respectively, hereafter denoted as SiO2@Ag-1 and SiO2@Ag-2. The immobilization and controlled growth of Ag NPs was confirmed by UV-vis spectroscopy, and scanning and transmission electron microscopy (SEM and TEM, respectively). All specimens displayed satisfactory SERS activity increasing with the Ag NP size, showing clear Raman peaks of Rhodamine 6G (R6G) at very low concentration. The SiO2@Ag particles were also tested and compared for their catalytic efficiency towards the reduction of 4-nitrophenol (4-Nip) by NaBH4. The principal advantages of this study lie in the ability to tune the Ag NP size, the long-term colloidal stability of all fabricated SiO2@Ag systems in aqueous media, and the limited use of hazardous chemicals and pollutant organic solvents during the synthetic process.

Synthesis and properties of polyamidines

Polymers with amidine groups NHCRN in the main chain were prepared by acid catalysed melt polycondensation of 4,4′-diaminodiphenyl methane (DAPM) with various orthoesters. The resulting polyamidines were characterized by 1H-, 13C- and 15N-NMR spectroscopy, differential scanning calorimetry (DSC), thermogravimetry (TGA) and wide angle x-ray scattering (WAXS) measurements. The properties of the polyamidines are strongly determined by the substituent R on the amidine group. Some peculiarities of the polyformamidine (RH) could be attributed to the conformation of the amidine group. Glass transition temperatures varied from 106 to 161°C depending on the substituent R. All polyamidines possessed good thermal stability up to 370°C and, with exception of the polyformamidine, good solubility in common solvents.

A study on reaction-induced miscibility of poly(trimethylene terephthalate)/polycarbonate blends.

The effect of annealing on the miscibility and phase behavior of Sorona {poly(trimethylene terephthalate), PTT} and bisphenol A polycarbonate (PC) blends was examined. These blends exhibited heterogeneous phase-separated morphology and two well-spaced glass transition temperatures (Tgs) indicating immiscibility. The Sorona/PC blends were thermally annealed at 260 degrees C for different times to induce various extents of transreactions between the two polymers. After annealing at high temperature the original two Tgs of blends were found to merge into one single Tg, exhibiting a homogeneous morphology. It is interesting to note that upon extended annealing the original semicrystalline morphology transformed into an amorphous nature. This is attributed to chemical transreactions between the PTT and PC chain segments as evidenced with FTIR, DSC, DMA, 1H NMR, and WAXS measurements. A new characteristic aryl C-O-C vibration band present at 1070 cm(-1) in the FTIR spectra of the annealed blends indicated the formation of an aromatic polyester structure due to the transreactions between PTT and PC. The sequence structures of the produced copolyesters were determined by a NMR triad analysis, which showed that the randomness increased with time of heating. WAXS analysis confirmed that the PTT/PC blends completely lost their crystallinity when annealed at 260 degrees C for a period of 120 min or longer, indicating the formation of fully random copolyesters. A random copolymer formed as a result of the transreactions between PTT and PC serves as a compatibilizer at the beginning, and upon extended annealing this became the main species of the system which is finally transformed to a homogeneous and amorphous phase.

Surface structure of fluorinated polymers and block copolymers

SummariesThe self-organisation of semifluorinated segments was used to create polymers and block copolymers with ultra-low surface free energy. The aromatic polyester poly(p-phenylene oxydecyl-perfluorodecyl-isophthalate) showed an extremely low value ofγsv of 9mN/m. It was proven that this low value was caused by an ordered surface structure. Introduction of these semifluorinated polyester segments into block copolymers with a basic structure (A–B)n resulted in a combination of good film-forming properties of polysulfone with the low surface free energy of the semifluorinated polyester. Thus, materials were obtained having both good mechanical performance as well as anti-adhesion properties. The block copolymers can be used to prepare blends with the respective homopolymers with different degrees of phase separation.The polymers and block copolymers can form a self-cleaning surface when coated on roughened aluminium substrates. It was shown that the adsorption of proteins, such as human serum albumin and fibrinogen from buffer solutions, significantly decreased on such polymer surfaces.RésuméL’autoorganisation des segments semi-fluorés a été utilisée pour créer des polymères et des bloc copolymères avec une énergie surfacique libre ultrabasse. Le polyester poly(p-phenylène oxydécylperfluorodécyl-isophthalate) aromatique a montré une très basse valeur deγsv de 9mN/m. Il a été prouvé que cette basse valeur était causée par une structure surfacique ordonnée. L’introduction de ces segments de polyester semi-fluorés dans des bloc copolymères ayant une structure fondamentale (A–B)n a ajouté les bonnes qualités du polysulphone vis à vis de la formation du feuil à la basse énergie surfacique libre du polyester semi-fluoré. Donc on a obtenu des matériaux qui démontraient une bonne performance mécanique aussi bien que des propriétés d’anti-adhésion. Les bloc polymères peuvent être utilisés avec les homopolymères respectifs pour préparer des mélanges ayant de différents degrés de séparation de phase.Les polymères et les bloc polymères peuvent former une surface autonettoyante quand ils revêtissent un substrat d’aluminium rendu rugeux. On a montré que l’adsorption des protéines telles que le sérum humain, albumine et le fibrinogène des solutions tampon diminue sur de telles surfaces polymériques.ZusammenfassungDie Selbstausrichtung von semifluorinierten Segmenten wurde verwendet, um Polymere und Block-Copolymere mit extrem niedriger freier Oberflächenenergie herzustellen. Das aromatische Polyester Poly(p-phenylen oxydecyl-perfluorodecyl-isophthalat) zeigte einen extrem niedrigen gsv-Wert von 9mN/m. Es wurde gezeigt, daß dieser niedrige Wert auf eine gut geordnete Oberflächenstruktur zurückgeführt werden konnte.Die Hinzufügung von semifluorinierten Polyestersegmenten zu Block-Copolymeren mit einer Struktur von (A–B)n ergab eine Kombination von den guten filmbildenden Eigenschaften von Polysulfon mit der niedrigen freien Oberflächenenergie von semifluoriniertem Polyester — in anderen Worten, ein Material das gute mechanische Eigenschaften mit einer niederen Adhäsionskraft vereinbarte. Durch die Verwendung von Block-Copolymeren lassen sich Mischungen mit den respektiven Homopolymeren mit verschiedenen Graded der Phasentrennung herstellen.Die Polymere und Block-Copolymere können auf aufgerauhte Aluminiumoberflächen aufgetragen werden, wo sie eine selbstreinigende Oberfläche bilden. Es wurde ausserdem gezeigt, daß die Adsorption von Proteinen wie Serum Albumin oder Fibrinogen von Pufferlösungen auf so beschichteten Oberflächen deutlich zurückging.

Synthesis and Phase Separation Behaviour of High Performance Multiblock Copolymers

The phase separation behaviour of block copolymers of the type (A–B) n (segmented block copolymers, multiblock copolymers) containing segments with different degrees of flexibility was investigated using a stepwise variation of the incorporated blocks A and B. Amorphous/rigid blocks (polysulfone segments) were systematically combined with amorphous/flexible blocks (poly(tetramethylene glycol), semiflexible/nematic blocks (different kinds of aromatic polyesters and poly(ester imides) as well as semicrystalline fluorinated polyester blocks). All multiblock copolymers were synthesized using a conventional transesterification polycondensation in the melt and the polycondensation results are discussed. The phase separation in the synthesized block copolymers was investigated both experimentally and theoretically. Flory–Huggins interaction parameters of the block copolymers were calculated and used together with mean field calculations in order to understand the phase separation behaviour of all block copolymers correlated to their chemical structure. On the other hand, the onset of phase separation in a series of block copolymers with a systematic variation of block molecular weights was examined experimentally, mainly by DSC and SAXS. Finally, the question is discussed whether or not the degree of phase separation in the investigated systems determines the properties of the polymers or not. This is for example outlined for the mechanical properties and, in particular, the surface properties of fluorinated block copolymers.

Template-Assisted Fabrication of Magnetically Responsive Hollow Titania Capsules

This study reports on the fabrication of magnetically responsive hollow titania capsules by confining the superparamagnetic Fe(3)O(4) nanoparticles within a hollow and porous titania (TiO(2)) shell. The employed protocol involves precipitation of titania shell on the magnetite (Fe(3)O(4)) encapsulated polystyrene beads followed by the calcination of resulting composite particles at elevated temperature. Scanning electron microscopy and transmission electron microscopy reveal the presence of a thick, complete but irregular titania shell on the magnetic polystyrene beads after the templating process. Electron energy loss mapping image analysis has been employed to investigate the spatial distribution of titania and magnetite phases of magnetic hollow titania capsules (MHTCs). Magnetic characterization indicates that both titania-coated magnetic polystyrene beads (TMPBs) and MHTCs are superparamagnetic in nature with the saturated magnetizations of 5.6 and 8.1 emu/g, respectively. X-ray diffraction (XRD) analysis reveals that titania shell of these capsules is composed of photoactive anatase phase. Nitrogen adsorption-desorption analysis has been employed to estimate the specific surface area and the average pore diameter of the fabricated hollow structures. Photocatalytic activity of the fabricated MHTCs for the photodegradation of rhodamine 6G dye has been demonstrated and compared with that of bulk titania nanoparticles.

The effect of specific nucleation on molecular and supermolecular orientation in isotactic polypropylene

The molecular and supermolecular orientation, morphology and structural changes observed during cold drawing of injection moulded isotactic polypropylene modified by specific a, and β nucleating agents were studied by polarised photoacoustic FTIR spectroscopy, wide-angle X-ray diffraction and differential scanning calorimetry. Significantly lower molecular orientation was found in the core of the β-nucleated injection moulded specimens as compared to unmodified and α-nucleated materials. This has been ascribed to the fast growth of the β-crystallites which inevitably dislocates the flow-induced orientation within the crystalline regions and in their vicinity. Moreover, it was found that the presence of the developed (3-crystallites distinctly diminishes the efficiency of the orientational solid-state drawing assessed on both levels of the hierarchical structure (molecular and crystalline). This structural observation is directly connected with macroscopic softening effect of the β-phase: lowering the yield stress and flattening the neck shoulder. Thus, the interrelation between the microstructural and macroscopic effects of the β-phase could be described as a feedback process.