Peter Reichert

Thermal Behaviour of Poly(propylene) Layered Silicate Nanocomposites

The thermal degradation behaviour of nanocomposites based upon poly(propylene)/organoclay, modified with protonated octadecyl amine (C18) in comparison to that of non-exfoliated microcomposites based upon organoclay, modified with protonated butyl amine (C4), was studied by thermogravimetry. In the case of the nanocomposite, the temperature at which volatilisation occurs increases as compared of the microcomposite. Moreover, the thermal oxidation process of the polymer is strongly slowed down in the nanocomposite with high char yield both by a physical barrier effect, enhanced by ablative reassembling of the silicate, and by a chemical catalytic action due to the silicate and to the strongly acid sites created by thermal decomposition of the protonated amine silicate modifier.

Polyolefin nanocomposites formed by melt compounding and transition metal catalyzed ethene homo- and copolymerization in the presence of layered silicates

Nanocomposites of high density polyethylene (HDPE), linear low density polyethylene (LLDPE) and highly branched polyethylene rubbers were prepared both by means of melt compounding and ethene homo- and copolymerization in the presence of layered silicates which were rendered organophilic via ion exchange with various quaternary alkyl ammonium cations. In comparison to melt compounding, in-situ ethene homo- and copolymerization, catalyzed with MAO-activated zirconocene (MBI), nickel (DMN) and palladium (DMPN) catalysts, proved more effective in nanocomposite formation, as evidenced by larger interlayer spacings and formation of exfoliated anisotropic nanosilicates with high aspect ratio.

Rubber Nanocomposites: Morphology and Mechanical Properties of BR and SBR Vulcanizates Reinforced by Organophilic Layered Silicates

Abstract Rubber compounds based on butadiene rubber (BR) or styrene—butadiene rubber (SBR) containing organophilic layered silicates were prepared. Organophilic silicates were swollen in a rubber/toluene solution. Matrix—filler reactive bonding was performed by adding bis(triethoxysilylpropyl)-tetrasulfan (TESPT) during swelling. Excellent dispersion of organoclay nanofillers in rubber matrices was demonstrated by transmission electron microscopy (TEM) and atomic force microscopy (AFM) exhibiting intercalated and partially exfoliated silicate layers. Matrix—filler interfacial coupling by TESPT led to reduced strain at break and reduced hysteresis for both organoclay and silica-based vulcanizates as expected for successful matrix filler coupling. Organoclay vulcanizates exhibited enhanced hysteresis when compared to silica compounds. This is related to orientation and sliding of anisotropic silicate layers, as determined by online wide-angle X-ray scattering (WAXS) measurements during cyclic tensile testing.

Morphological Stability of Poly(propylene) Nanocomposites

Poly(propylene) compounds containing organophilic layered nanosilicates were prepared by means of melt extrusion at 210°C in order to investigate the influence of maleic anhydride-grafted poly(propylene) (PP-g-MA) as a compatibilizer on morphology development and rheological properties. It was found that the addition of PP-g-MA leads to the strong exfolliation of silicate layers within the matrix as investigated by WAXS. This process is associated with the build up of an unstable morphology as probed by dynamic rheology and with the violation of the time-temperature superposition principle. Annealing of the samples at extrusion temperature level leads to a coarsening of the silicate superstructure and further improvement of the exfoliation at the same time. This process results in a stable morphology with unique rheological properties indicating network-like superstructure of silicate layers.

Solid-liquid interfaces of ionic liquid solutions—Interfacial layering and bulk correlations

The influence of the polar, aprotic solvent propylene carbonate on the interfacial structure of the ionic liquid (IL) 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate on sapphire was investigated by high-energy x-ray reflectivity. Experiments at solvent concentrations between 17 mol. % and 83 mol. % bridge the gap between diluted electrolytes described by the classical Gouy-Chapman theory and pure ionic liquids. Analysis of our experimental data revealed interfacial profiles comprised of alternating anion and cation enriched regions decaying gradually into the bulk liquid. With increasing solvent concentration, we observed a decrease in correlation length of the interfacial layering structure. At high ion concentrations, solvent molecules were found to accumulate laterally within the layers. By separating like-charged ions, they reduce their Coulomb repulsion. The results are compared with the bulk structure of IL/solvent blends probed by x-ray scattering and predictions from fundamental fluid theory.