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Kiliaris P.,National Technical University of Athens | Papaspyrides C.D.,National Technical University of Athens | Xalter R.,BASF | Pfaendner R.,Deutsches Kunststoff - Institute
Polymer Degradation and Stability | Year: 2012

In this study, the flame retardancy and physical properties of polyamide 6, melt processed in a twin-screw extruder with various amounts of melamine polyphosphate and layered silicates, were examined. Generally, there were indications that exfoliated nanocomposites were produced. During compounding, the presence of layered silicates was found to result in polymer degradation, which was further enhanced by the addition of the flame retardant. The additives were also shown to restrain the ability of polyamide 6 for crystallization. Tensile modulus and tensile strength were substantially improved, however polymer's ductility deteriorated. The incorporation of the additives exerted a positive effect also on the flame retardancy of polyamide 6, leading to materials of UL94 V-2 classification. © 2012 Elsevier Ltd. All rights reserved.


Ginzburg A.,Deutsches Kunststoff - Institute | MacKo T.,Deutsches Kunststoff - Institute | Dolle V.,LyondellBasell | Brull R.,Deutsches Kunststoff - Institute
European Polymer Journal | Year: 2011

Temperature rising elution fractionation hyphenated to size exclusion chromatography (TREF × SEC) is a routine technique to determine the chemical heterogeneity of semicrystalline olefin copolymers. A serious limitation is its applicability to non crystallizing samples. Comprehensive high temperature two-dimensional liquid chromatography (HT 2D-LC) gives an alternative to characterize the chemical heterogeneity of copolymers irrespective of their crystallizability. We have hyphenated interactive HPLC, which separates polyolefins according to their chemical composition, with high-temperature size exclusion chromatography (SEC), which distinguishes polyolefins with regard to their molar mass at 160 °C. The first separation step was based on a selective adsorption of macromolecules on a Hypercarb® column packed with porous graphite particles and subsequent desorption by a gradient 1-decanol → 1,2,4-trichlorobenzene at 160 °C. The SEC column was calibrated with polypropylene (PP) and polyethylene (PE) standards and it turned out that the injection solvent from the first dimension influenced the elution of PP in the SEC column, while the retention of PE was virtually constant. HT 2D-LC was then used to separate a broad variety of polyolefin blends containing PE, PP with different microstructure, ethylene-propylene (EP) and ethylene-propylene-diene (EP(D)M) rubber and ethylene/1-hexene copolymers. For the first time it has been shown that the elution of iPP in the gradient HPLC is molar mass dependent. The results from the HT 2D-LC separation were compared to those from TREF × SEC-experiments. The particular advantage of HT 2D-LC over TREF × SEC is the fact that HT 2D-LC is also applicable to non crystallizing polyolefin samples. The new technique therefore resolves the problem to analyze the chemical heterogeneity of non crystallizing olefin copolymers like EP and EP(D)M copolymers. © 2011 Elsevier Ltd. All rights reserved.


Schollenberger M.,Deutsches Kunststoff - Institute | Radke W.,Deutsches Kunststoff - Institute
Polymer | Year: 2011

A new approach to gradient chromatography of polymers is presented, in which the sample is introduced at the end of the gradient and elutes within the elution volume range typical for size exclusion chromatography (SEC). Due to the gradient the samples are retarded and elute nearly independent of molar mass at the adsorption threshold. The concept was proven for a series of narrowly distributed poly(methy methacrylate)s (PMMA) in a chloroform-tetrahydrofuran (THF) SEC-gradient. The application of the SEC-gradient to a blend of PMMA and polystyrene standards of similar molar masses, which could not be separated by SEC due to their similar hydrodynamic sizes, resulted in a clear separation according to chemical composition. Since SEC-gradients allow dissolving the sample in strong eluents, which might result in breakthrough peaks in conventional gradients, the new approach is a valuable alternative to conventional gradient chromatography. © 2011 Elsevier Ltd. All rights reserved.


Bashir M.A.,Deutsches Kunststoff - Institute | Radke W.,Deutsches Kunststoff - Institute
Journal of Chromatography A | Year: 2012

The retention behavior of a range of statistical poly(styrene/ethylacrylate) copolymers is investigated, in order to determine the possibility to predict retention volumes of these copolymers based on a suitable chromatographic retention model. It was found that the composition of elution in gradient chromatography of the copolymers is closely related to the eluent composition at which, in isocratic chromatography, the transition from elution in adsorption to exclusion mode occurs. For homopolymers this transition takes place at a critical eluent composition at which the molar mass dependence of elution volume vanishes. Thus, similar critical eluent compositions can be defined for statistical copolymers. The existence of a critical eluent composition is further supported by the narrower peak width, indicating that the broad molar mass distribution of the samples does not contribute to the retention volume. It is shown that the existing retention model for homopolymers allows for correct quantitative predictions of retention volumes based on only three appropriate initial experiments. The selection of these initial experiments involves a gradient run and two isocratic experiments, one at the composition of elution calculated from first gradient run and second at a slightly higher eluent strength. © 2011 Elsevier B.V..


Finlayson C.E.,University of Cambridge | Spahn P.,Deutsches Kunststoff - Institute | Snoswell D.R.E.,University of Cambridge | Yates G.,University of Cambridge | And 4 more authors.
Advanced Materials | Year: 2011

Permanent ordering of sub-micrometer polymeric spheres by edge rotational shearing is reported. The resulting high-quality, bulk, 3D-ordered polymer opal thin-films exhibit strikingly intense, tuneable structural color, which is applicable for photonics, metamaterials, nanoassembly, and structural color applications Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Size-exclusion chromatography with light scattering detection experiments conducted on poly(acrylic acid) neutralized to different degrees or using hydroxides with different counterions suggest that the same counterion and degree of neutralization is observed at the detector, irrespective of salt concentration, degree of neutralization and counterion at the time of injection. This strongly supports that during the chromatographic experiment the counterions of the polyelectrolyte are exchanged with those of the eluent, resulting in an effective dialysis of the polyelectrolyte solution during the size-exclusion chromatography experiment. Consequently, the refractive index increment determined by a refractive index detector equals the refractive index increment obtained after excessive dialysis against the pure eluent. Therefore, the species detected and characterized by light scattering coupled to size-exclusion chromatography are not identical to the species injected into the chromatographic system. Despite this structural change during the chromatographic experiments, the correct molar mass for the injected species is obtained by size-exclusion chromatography with light scattering detection. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.


Schollenberger M.,Deutsches Kunststoff - Institute | Radke W.,Deutsches Kunststoff - Institute
Journal of Chromatography A | Year: 2011

A gradient ranging from methanol to tetrahydrofuran (THF) was applied to a series of poly(methyl methacrylate) (PMMA) standards, using the recently developed concept of SEC-gradients. Contrasting to conventional gradients the samples eluted before the solvent, i.e. within the elution range typical for separations by SEC, however, the high molar mass PMMAs were retarded as compared to experiments on the same column using pure THF as the eluent. The molar mass dependence on retention volume showed a complex behaviour with a nearly molar mass independent elution for high molar masses. This molar mass dependence was explained in terms of solubility and size exclusion effects. The solubility based SEC-gradient was proven to be useful to separate PMMA and poly(n-butyl crylate) (PnBuA) from a poly(t-butyl crylate) (PtBuA) sample. These samples could be separated neither by SEC in THF, due to their very similar hydrodynamic volumes, nor by an SEC-gradient at adsorbing conditions, due to a too low selectivity. The example shows that SEC-gradients can be applied not only in adsorption/desorption mode, but also in precipitation/dissolution mode without risking blocking capillaries or breakthrough peaks. Thus, the new approach is a valuable alternative to conventional gradient chromatography. © 2011 Elsevier B.V.


Kontogeorgos A.,University of Cambridge | Snoswell D.R.E.,University of Cambridge | Finlayson C.E.,University of Cambridge | Baumberg J.J.,University of Cambridge | And 2 more authors.
Physical Review Letters | Year: 2010

We use elastically induced phase transitions to break the structural symmetry of self-assembled nanostructures, producing significantly modified functional properties. Stretching ordered polymer opals in different directions transforms the fcc photonic crystal into correspondingly distorted monoclinic lattices. This breaks the conventional selection rules for scattering from the crystal planes, yielding extra multiply scattered colors when the phase-breaking stretch is in specific directions. Scattering is spectroscopically tracked in real time as the samples distort, revealing a new phase transition that appears for (121) -oriented deformations. © 2010 The American Physical Society.


Skipa T.,Deutsches Kunststoff - Institute | Lellinger D.,Deutsches Kunststoff - Institute | Bohm W.,Deutsches Kunststoff - Institute | Saphiannikova M.,Leibniz Institute of Polymer Research | Alig I.,Deutsches Kunststoff - Institute
Polymer | Year: 2010

Shear-induced destruction and formation of conductive and mechanical filler networks formed by multi-wall carbon nanotubes in polycarbonate melts were investigated by simultaneous time-resolved measurements of electrical conductivity and rheological properties under steady shear and in the quiescent melt. The steady shear experiments were performed at shear rates between 0.02 and 1 rad/s and for nanotube concentrations ranging from 0.5 to 1.5 wt%. The influence of thermo-mechanical history on the state of nanotube dispersion and agglomeration was studied in detail. For melts with well-dispersed nanotubes a shear-induced insulator-conductor transition was observed, which is explained by the agglomeration of nanotubes under steady shear and the formation of an electrical conductive network of interconnected agglomerates. Simultaneously, a drastic decrease of the shear modulus (G* = G′ + iG″) during steady shear was observed, which can be related to a reduction of mechanical reinforcement due to agglomeration of dispersed nanotubes. These findings indicate a substantial difference in the nature of "electrical" and "mechanical" network and contradict earlier assumptions that steady (or transient) shear is always destructive for the conductive filler network in highly viscous polymer composites. It was also shown that after a certain time of steady shear the filler network asymptotically reaches its steady state characterized by the constant electrical conductivity and shear modulus of the composite melt. Such asymptotic behaviour of composite properties was experimentally shown to be related to the interplay of the destructive and build-up effects of steady shear. For modelling of the electrical conductivity in presence of steady shear a kinetic equation was proposed for filler agglomeration with shear-dependent destruction and build-up terms. This equation was coupled to the generalized effective medium (GEM) approximation for insulator-conductor transition. © 2009 Elsevier Ltd. All rights reserved.


Haines A.I.,University of Cambridge | Finlayson C.E.,University of Cambridge | Snoswell D.R.E.,University of Cambridge | Spahn P.,Deutsches Kunststoff - Institute | And 2 more authors.
Advanced Materials | Year: 2012

Hyperspectral goniometry reveals anisotropic scattering which dominates the visual appearance of self-assembled polymer opals. The technique allows reconstruction of the reciprocal-space of nanostructures, and indicates that chain defects formed during shear-ordering are responsible for the anisotropy in these samples. Enhanced scattering with improving order is shown to arise from increased effective refractive index contrast, while broadband background scatter is suppressed by absorptive dopants. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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