German Institute for Polymers DKI

Darmstadt, Germany

German Institute for Polymers DKI

Darmstadt, Germany
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Dong X.,Fudan University | Wu P.,Fudan University | Hellmann G.P.,German Institute for Polymers DKI | Wang C.,Fudan University | And 2 more authors.
Langmuir | Year: 2017

We present a general, convenient, and efficient synthetic concept for the coating of colloidal particles with a silica (SiO2) shell of well-defined and precisely controlled morphology and porosity. Monodisperse submicroscopic polystyrene (PS) particles were synthesized via two-stage emulsifier-free emulsion polymerization and subsequent swelling polymerization, enabling selective particle surface modification by the incorporation of ionic (methacrylic acid, MAA) or nonionic (hydroxyethyl methacrylate, HEMA or methacrylamide, MAAm) comonomers, which could be proven by zeta potential measurements as well as by determining the three-phase contact angle of the colloidal particles adsorbed at the air-water and n-decane-water interface. The functionalized particles could be directly coated with silica shells of variable thickness, porosity, and controlled surface roughness in a seeded sol-gel process from tetraethoxysilane (TEOS), leading to hybrid PS@silica particles with morphologies ranging from core-shell (CS) to raspberry-type architectures. The experimental results demonstrated that the silica coating could be precisely tailored by the type of surface functionalization, which strongly influences the surface properties of the colloidal particles and thus the morphology of the final silica shell. Furthermore, the PS cores could be easily removed by thermal treatment, yielding extremely uniform hollow silica particles, while maintaining their initial shell architecture. These particles are highly stable against irreversible aggregation and could be readily dried, purified, and redispersed in various solvents. Herein we show a first example of coating semiconducting CdSe/ZnS nanocrystals with smooth and spherical silica shells by applying the presented method that are expected to be suitable systems for applications as markers in biology and life science by using fluorescence microscopy methods, which are also briefly discussed. © 2017 American Chemical Society.

Maria R.,German Institute for Polymers DKI | Rode K.,German Institute for Polymers DKI | Brull R.,German Institute for Polymers DKI | Dorbath F.,Suddeutsches Kunststoff Zentrum SKZ | And 3 more authors.
Polymer Degradation and Stability | Year: 2011

Plastic pipes are often exposed to a range of environmental conditions which may lead to their degradation. The most important influence factors are UV radiation, humidity and temperature. These can cause leaching of long-term and light stabilisers and finally oxidation of the polymer. In this study we demonstrate how the elemental steps of the photooxidative degradation of polyethylene pipes can be monitored by IR-microscopy. In detail the influence of UV radiation leads to a depletion of the phenolic long-term stabiliser, Irganox 1010. Calibration of the spectroscopic data enables IR-microscopy to be carried out in a quantitative manner and the rate constants for the stabiliser loss to be calculated for the first time. The results obtained from IR-microscopy are well in agreement with those obtained by mechanical sample preparation and measurement of the oxidative induction time (OIT) as well as extraction coupled with chromatographic analysis (HPLC). A mechanism based on Norrish type cleavage is proposed. Also the formation of trans-vinylidene groups as unsaturated degradation products of the PE can be observed. In summary it can be shown that IR-microscopy is highly superior to the conventional approach of mechanical sample preparation with regard to spatial resolution and offers the advantage of being less labour intensive. © 2011 Elsevier Ltd. All rights reserved.

Dolle V.,LyondellBasell | Albrecht A.,German Institute for Polymers DKI | Brull R.,German Institute for Polymers DKI | MacKo T.,German Institute for Polymers DKI
Macromolecular Chemistry and Physics | Year: 2011

It is demonstrated that copolymers of ethylene with higher 1-olefins can be separated using bare silica gel as the stationary phase and a gradient of ethylene glycol monobutyl ether and 1,2,4-trichlorobenzene as the mobile phase at 160°C. The separation of ethylene 1-hexene copolymers according to their composition is confirmed by linking the chromatographic separation to infrared spectroscopy. Using well-characterised model fractions from temperature rising elution fractionation or solvent/non-solvent fractionation ("Holtrup") , it can be shown that both the content and type of the comonomer mainly govern the elution in two peaks which differ in their comonomer content. The molar mass only plays a subordinate rule. Interactive chromatography using a selective solvent allows the separation of linear low-density polyethylenes with respect to their chemical composition. The entire separation scheme is complex and influenced by the chemical composition, the molar mass and the microstructure of the sample. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Kolupaev V.A.,German Institute for Polymers DKI | Yu M.-H.,Xi'an Jiaotong University | Altenbach H.,Otto Von Guericke University of Magdeburg
Acta Mechanica | Year: 2013

The theory of plasticity operates with different yield criteria of incompressible behavior for isotropic materials. Mostly known are the criteria of Tresca, Schmidt-Ishlinsky and von Mises. The first two criteria have a hexagonal symmetry, and the criterion of von Mises has a rotational symmetry in the π-plane. All these criteria do not distinguish between tension and compression (no strength differential effect), but numerous problems are treated in the engineering practice using these criteria. Within this paper, the yield criteria with hexagonal symmetry for isotropic incompressible materials are compared. For this purpose, their geometries in the π-plane will be presented in polar coordinates. The radii at the angles of 15â - b and 30â - b will be related to the radius at 0 â - b. Based on these two relations, well-known criteria will be shown in one diagram. The extreme shapes of the yield surfaces are restricted by two criteria: the unified yield criterion (UYC) and the multiplicative ansatz criterion (MAC). The examinations of the UYC and MAC depict a linear combination of these extreme yield surfaces. The resulting criterion with two parameters describes all possible convex forms of hexagonal symmetry. On the other hand, this criterion has one disadvantage: It is not possible to solve explicitly the equation for the equivalent stress. Other known criteria (Sokolovsky, Ishlinsky-Ivlev, Dodd-Naruse, Drucker) are depicted in the proposed diagram and compared with the above mentioned criteria. Further criteria are derived from the consideration of solids with orthogonal symmetry planes in the shear stress space. New criteria are introduced for practical applications. The constraints of convexity are established for them. The proposed consideration of the yield criteria simplifies the selection of a proper criterion. The extreme solutions for the analysis of construction parts can be found using these criteria. © 2013 Springer-Verlag Wien.

Kolupaev V.A.,German Institute for Polymers DKI | Yu M.-H.,Xi'an Jiaotong University | Altenbach H.,Otto Von Guericke University of Magdeburg
Archive of Applied Mechanics | Year: 2013

The Unified Strength Theory (UST) provides the fundamentals for the systematic study of various strength hypotheses and yields criteria for isotropic materials. It shows relationship between known models (Mohr-Coulomb, Pisarenko-Lebedev, Twin-Shear Theory of Yu), and apart from these known models, this model contains also classical models like the normal stress hypothesis, von Mises, Tresca and Schmidt-Ishlinsky. The UST can be adapted for different types of materials. Thus, it is a suitable tool for the analysis of experimental data. For the UST, the inelastic Poisson's ratio and the maximum hydrostatic tension stress will be computed as a function of model parameters which simplifies the comparison with another model. The correlations between uniaxial, biaxial and hydrostatic stress will be illustrated and compared with classical models. For all classical models and for the UST, the uniaxial and biaxial tension failure stress and also the uniaxial and biaxial compression failure stress are equal. In this sense, the UST can be classified as a classical model. The failure behavior of new materials like some polymers and alloys differs from the classical one. The UST can be extended to such failure behavior. For this purpose, the Unified Yield Criterion (UYC) as part of the UST will be modified so that all known criteria of incompressible material behavior can be approximated. With the help of a simple substitution, the UYC can be further developed for compressible material behavior. Different convex lines can be adjust for the form of the meridian. With this substitution, the hydrostatic tension stress will be restricted with one of the parameters. Furthermore, the model can be applied for the description of failure behavior of ceramics, hard foams and sintered materials. For this application, both the hydrostatic tension and compression stress will be restricted too. Some reference values for hydrostatic loading are established. For the visual comparison of different parameter setting of the models, graphical methods can be used. The UST will be represented in the principal stress space. Further considerations will be carried out in the Burzyński-plane and in the π-plane. For engineering applications, the Burzyński-plane is preferred to the meridional cut. For better analysis and a direct comparison of fitted models to the experimental values, the line of the plane stress state will be shown in the Burzyński-plane and in the π-plane. © 2013 Springer-Verlag Berlin Heidelberg.

MacKo T.,German Institute for Polymers DKI | Cutillo F.,University of Naples Federico II | Busico V.,University of Naples Federico II | Brull R.,German Institute for Polymers DKI
Macromolecular Symposia | Year: 2010

Samples of polypropylene having different stereoregularities, i.e., differing in the isotactic or syndiotactic stereosequence distribution, were separated by means of high-temperature gradient adsorption liquid chromatography. The porous graphite was used as stationary phase in the column packing (Hypercarb®). Predominantly isotactic samples eluted in 1-decanol, while predominantly syndiotactic samples eluted in a binary gradient composed of 1-decanol and 1,2,4-trichlorobenzene. Their elution volumes increased with the average content of the syndiotactic units (racemo dyads mole fraction as determined with the NMR spectroscopy) in the samples. Thus these chromatographic separations represent a new method for the analysis and characterization of stereoregular polyolefins. It requires substantially less time and solvents than the commonly used methods. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Brull R.,German Institute for Polymers DKI | Maria R.,German Institute for Polymers DKI | Rode K.,German Institute for Polymers DKI
Macromolecular Chemistry and Physics | Year: 2010

The quantity of absorbance of linear polarized light depends for a given wavelength on the angle between an absorbing transition moment vector and the electric vector of the polarized light. Fraser used this relationship to interpret the infrared dichroism in axially oriented polymers. This model can be extended to calculate the orientation in three dimensions by transforming the Fraser's equation into a P2-Legendre polynomial. As a result the orientation in three directions-fx, fy, and fz-can be calculated directly from the individual absorbances measured with an electric vector along the axes of interest, the structural absorbance A0 of the sample, and the angle of the transition moment vector in reference to the chain axis. Applying the f values into 'Hermans' Orientation function', it becomes possible to calculate the average angle of the chain axis with reference to the axes of interest. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Kolupaev V.A.,German Institute for Polymers DKI | Bolchoun A.,German Institute for Polymers DKI | Altenbach H.,Martin Luther University of Halle Wittenberg
Applied Mechanics and Materials | Year: 2011

The analysis of well-known strength hypotheses leads to the derivation of a generalized model, which contains a number of known hypotheses as special cases and could be used for the description of the 3D-failure of hard foams. This model in the case of the strength hypothesis for hard foams is characterized by a closed surface in the principal stress space. In order to fit the model to the experimental data certain objective functions are formulated. The optimization results are shown in the PARETO-diagram (optimal solutions for several targets). The results of the fitting are plotted in the BURZYŃSKI-plane. It can be seen that reliable modeling requires the knowledge of the material behavior under hydrostatic tension and compression. © (2011) Trans Tech Publications, Switzerland.

Rajan V.V.,German Institute for Polymers DKI | Rajan V.V.,Dutch Polymer Institute | Waber R.,German Institute for Polymers DKI | Wieser J.,German Institute for Polymers DKI
Journal of Applied Polymer Science | Year: 2012

The polycarbonate/poly(acrylonitrile butadiene styrene) blends, (PC/ABS), are mainly degraded by sunlight known as photodegradation when exposed to outdoor conditions. It is the ultraviolet (UV) radiation that is responsible for the degradation of the blend. To stabilize against the harmful UV radiation and to scavenge the radical species which arise from UV or thermally induced degradation of the PC or the ABS, UV absorbers, and UV stabilizers are used. In this article three different UV absorbers namely, Tinuvin 1577-hydroxyphenyl triazine type, Cyasorb 5411-benzotriazole type, Uvinul 3030-cyanoacrylate type, and two different UV stabilizers, Tinuvin 765-monomeric hindered amine type, Tinuvin 622-oligomeric hindered amine were compounded in different combinations with PC/ABS blend at 240°C using a twin screw extruder. Accelerated aging of the compounded sample was done by Atlas Suntest apparatus. The photodegradation studies were done using UV-vis, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and Yellowing index measurement. The molecular weight of the compounded sample before aging was determined by gel permeation chromatography (GPC). It was found that samples protected with hydroxyphenyl triazine type UV absorber and oligomeric hindered amine show the best result for decreasing the degradation products, oxidation rate, and yellowing of the PC/ABS blend. © 2011 Wiley Periodicals, Inc.

MacKo T.,German Institute for Polymers DKI | Ginzburg A.,German Institute for Polymers DKI | Remerie K.,SABIC | Bruell R.,German Institute for Polymers DKI
Macromolecular Chemistry and Physics | Year: 2012

Fractionation techniques such as temperature rising elution fractionation or crystallization analysis fractionation fail to fractionate the ethylene-propylene (EP) copolymers, which are a component of high-impact polypropylene (hiPP), according to their chemical composition. High-temperature high-performance liquid chromatography separates blends of EP-copolymers and polypropylene. The elution volume of the EP-copolymers depends linearly on the average content of ethylene. The separation according to the chemical composition was hyphenated with size exclusion chromatography. In this way, the relationship between the distribution with regard to chemical composition and molar mass, that is, the full chemical heterogeneity of hiPP, was revealed for the first time. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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