Fraunhofer Institute for Chemical Technology

Germany

Fraunhofer Institute for Chemical Technology

Germany
SEARCH FILTERS
Time filter
Source Type

Wurster S.,Fraunhofer Institute for Chemical Technology
Propellants, Explosives, Pyrotechnics | Year: 2017

The gap test has been used for several decades as a measure for the shock sensitivity of high explosives. Normally the axial pressure in the gap is used as the necessary initiation pressure of a high explosive for a shock to detonation transition. But it has been shown in the past that the pressure in the gap is not a suitable measure for shock sensitivity and other criteria like the James criterion in terms of critical energy fluence and critical specific kinetic energy should be used. To evaluate the James criterion in the 21mm and 50mm polymethylmethacrylate (PMMA) gap test numerical simulations are conducted. To validate the simulations a 21mm water gap test is simulated and compared to experimental results, where the axial pressure calibration can be reproduced with high accuracy. With the results from the simulation of the 21mm and 50mm gap test it is shown that at the same maximum axial pressure the energy fluence is higher in the 50mm gap test. This explains to some extent the higher initiation pressures observed in smaller gap tests. The James criterion is derived and it is shown that the two gap tests probe very different regions in the energy fluence vs. specific kinetic energy plane. The results can be used as a calibration for the gap tests and are intended to improve the comparability of gap test results among each other and with different initiation experiments like flyer or heavy fragment impact testing. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.


Wurster S.,Fraunhofer Institute for Chemical Technology
Propellants, Explosives, Pyrotechnics | Year: 2017

A model to simulate propellant combustion in a closed bomb and a method for burn rate measurement are presented. The model incorporates the 2D ICT-Cellular-Combustion-Algorithm which numerically simulates the 2D form function of an arbitrary shaped propellant cross section. With the help of preprocessing algorithms to calculate initial surface and volume and a lumped parameter model, which also takes into account pressure dependent thermochemistry, pressure vs. time curves and the dynamic vivacity can be simulated. The model is then coupled with different optimization algorithms to minimize an objective function for burn rate measurement with either pressure or vivacity data. Four different optimization algorithms are compared in detail using synthetic pressure-time and dynamic vivacity data of a 7 perforated propellant with and without white noise. The testing shows that the so called Nelder-Mead-Downhill-Simplex algorithm with a vivacity based objective function allows the most precise, robust and computationally cost effective burn rate measurement. Experimental results for 7 perforated JA2 propellant from a 306 cm3 closed bomb are used to determine Vieille's parameters α and β. The determined values of α=0,9520±0,006319 and β=0,1522±0,007592mm/s are in good agreement with previously reported values of α=0.9517 and β=0.1467mm/s. With the presented model and burn rate measurement method it is possible to determine the burning rates of solid propellants with a high degree of accuracy. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.


Geinitz S.,Fraunhofer Institute for Chemical Technology
ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials | Year: 2016

During carbon fibre production as well as fabrication of follow up products such as preforms various defects affecting quality and performance of the finished product may occur. While numerous defects such as fuzz balls, roving twists or undulations are easy to identify, filament fractures or inhomogeneous binder distributions are challenging to detect and monitor. Typical carbon fibre filament diameters lie within the order of 5-7 μm in contrast to a production line width of 2-3 m as commonly observed in mass production, make the detection of fibre fractures difficult. Similarly, the online observation of binder distribution along a production process is a challenging issue. Thus high image resolution, a large scan width as well as a high image acquisition rate in accordance with the production speed are inevitably required for proper monitoring purposes. Based on the above, the current study focuses on a system developed to increase scan width at very high resolution. The limiting factor for image acquisition remains the data transfer rate. In this study, the scan width is maximized through the the use of a line scan camera and a specialized optic. This optical system allows the continuous capture and the increase of the monitored area with a magnitude of three compared to current optics, with no loss in acquisition rate. The software processes the acquired camera information for image segmentation. The algorithms then scan various sets of lines in the image and highlight specific Regions Of Interest (ROI). With a resolution in the order of a few microns, defects from filament fractures and small foreign particles up to fuzz balls can be clearly marked. © 2016, European Conference on Composite Materials, ECCM. All rights reserved.


Treuel L.,Karlsruhe Institute of Technology | Treuel L.,University of Duisburg - Essen | Treuel L.,Fraunhofer Institute for Chemical Technology | Brandholt S.,Karlsruhe Institute of Technology | And 5 more authors.
ACS Nano | Year: 2014

Recent studies have firmly established that cellular uptake of nanoparticles is strongly affected by the presence and the physicochemical properties of a protein adsorption layer around these nanoparticles. Here, we have modified human serum albumin (HSA), a serum protein often used in model studies of protein adsorption onto nanoparticles, to alter its surface charge distribution and investigated the consequences for protein corona formation around small (radius ∼5 nm), dihydrolipoic acid-coated quantum dots (DHLA-QDs) by using fluorescence correlation spectroscopy. HSA modified by succinic anhydride (HSAsuc) to generate additional carboxyl groups on the protein surface showed a 3-fold decreased binding affinity toward the nanoparticles. A 1000-fold enhanced affinity was observed for HSA modified by ethylenediamine (HSAam) to increase the number of amino functions on the protein surface. Remarkably, HSAsuc formed a much thicker protein adsorption layer (8.1 nm) than native HSA (3.3 nm), indicating that it binds in a distinctly different orientation on the nanoparticle, whereas the HSAam corona (4.6 nm) is only slightly thicker. Notably, protein binding to DHLA-QDs was found to be entirely reversible, independent of the modification. We have also measured the extent and kinetics of internalization of these nanoparticles without and with adsorbed native and modified HSA by HeLa cells. Pronounced variations were observed, indicating that even small physicochemical changes of the protein corona may affect biological responses. © 2013 American Chemical Society.


News Article | December 1, 2016
Site: phys.org

The PCM cube maintains a temperature of 21 degrees Celsius until it is completley melted. Credit: Fraunhofer ICT When the summer sun burns in the sky, phase change materials (PCM) integrated in building envelopes absorb the heat – it remains cool inside. When it is getting colder outside, the materials give off heat. Several grams of these storage media can protect against overheating and undercooling for a long time. For the first time, researchers have combined insulating characteristics of foams with PCM thermal masses via established procedures of shaping processes. Due to this combination of materials the heat transfer through walls is reduced for hours. In the evening, it is nice and warm in the living room. However, when you enter the room in the morning it is chilly. It takes time until the heating gets started and the air in the room warms up again. Phase change materials – media made up of salts or organic compounds that store heat – can compensate for such temperature differences. Temperature peaks on hot summer days in indoor areas can also be mitigated. Researchers of the Fraunhofer Institute for Chemical Technology ICT in Pfinztal near Karlsruhe/Germany have combined the traditional advantages of a foamed insulation with the thermic regulating and storing characteristics of PCM within a single component. "The material is able to restore and give off huge amounts of heat within a short time intervall where it changes its temparature while tranforming to another aggregate condition. Via established procedures of shaping processes the PCM were integrated in foamed sheets for the first time. The next step will be to test the long-term resistance of these components," explains Sandra Pappert, a scientist at the ICT. Storage media are already available as microcapsules; they can be stirred into wall paint or plaster. What is special about the new technology: "Instead of a few micrograms, several grams of the phase change materials have been integrated. Therefore the thickness of the wall is not changing by increasing the thermal mass," says Pappert. The physical principle is known from lakes, which are covered by an ice layer on bitter cold days. Although the air is much colder, the water has a constant temperature of four degrees Celsius for the entire time until the last drop of water in the lake has frozen to ice. The freezing temperatures that the lake absorbs from the air do not cool the water down any further. Rather, they convert the water into ice. Phase change materials (technical term PCM) are able to absorb, restore and release huge amounts of heat in a small time intervall while changing their aggregate condition depending on their surrounding temperature. This works by storage media, such as salts or organic compounds, changing their aggregate states as soon as heat is added. If, for example, they change from the liquid to the solid state or vice versa, they absorb or release heat. Explore further: New study sheds light on cooling capacity of phase change materials


Nebhani L.,Karlsruhe Institute of Technology | Schmiedl D.,Fraunhofer Institute for Chemical Technology | Barner L.,Fraunhofer Institute for Chemical Technology | Barner-Kowollik C.,Karlsruhe Institute of Technology
Advanced Functional Materials | Year: 2010

The surface modification of divinylbenzene (DVB)-based microspheres is performed via a combination of reversible addition fragmentation chain transfer (RAFT) polymerization and rapid hetero-Diels-Alder (HDA) chemistry with the aim of quantifying the grafting densities achieved using this "graftingto" method. Two variants of the RAFT-HDA concept are employed to achieve the functionalization of the microspheres. In the first approach, the microspheres are functionalized with a highly reactive diene, i.e., cyclopentadiene, and are subsequently reacted with polystyrene chains (number-averaged molecular weight, Mn = 4200g mol-1; polydispersity index, PDI = 1.12.) that carry a thiocarbonyl moiety functioning as a dienophile. The functionalization of the microspheres is achieved rapidly under ambient conditions, without the aid of an external catalyst. The surface grafting densities obtained are close to 1.2 × 1020 chains per gram of microspheres. In the second approach, the functionalization proceeds via the double bonds inherently available on the microspheres, which are reacted with poly(isobornyl acrylate) chains carrying a highly dienophilic thiocarbonyl functionality; two molecular weights (Mn = 6000 g mol-1, PDI = 1.25; Mn = 26 000 g mol-1, PDI = 1.26) are used. Due to the less reactive nature of the dienes in the second approach, functionalization is carried out at elevated temperatures (T= 60°C) yet in the absence of a catalyst In this case the surface grafting density is close to 7 chains nm-2 for Mn = 6000 g mol-1 and 4 chains nm-2 for M n = 26000 g mol-1, or 2.82 × 1019 and 1.38 × 1019chains g-1, respectively. The characterization of the microspheres at various functionalization stages is performed via elemental analysis for the quantification of the grafting densities and attenuated total reflectance (ATR) IR spectroscopy as well as confocal microscopy for the analysis of the surface chemistry. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Musyanovych A.,Fraunhofer Institute for Chemical Technology | Musyanovych A.,Max Planck Institute for Polymer Research | Landfester K.,Max Planck Institute for Polymer Research
Macromolecular Bioscience | Year: 2014

The design and development of multifunctional polymer capsules with controlled chemical composition and physical properties has been the focus of academic and industrial research in recent years. Especially in the biomedical field, the formulation of novel polymer-based encapsulation systems for the early-stage disease diagnostic and effective delivery of bioactive agents represent one of the most rapidly advancing areas of science. The stimuli-responsive release of cargo molecules from the carrier gains remarkable attention for in vitro and in vivo delivery of contrast agents, genes, and pharmaceutics. In this Review, the current status and the challenges of different polymer-based micro- and nanocapsule formulations are considered, emphasizing on their potential biological application as carriers for specific drug targeting and controlled release upon applying of external stimulus. A considerable research has been conducted in recent years on development of multifunctional polymer capsules with controlled chemical composition and physical properties. This Review discusses different types of bio-oriented polymer-based colloidal systems, emphasizing on formulation aspects, site-specific drug targeting, and controlled release of a "payload" upon applying of external stimulus. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Koch E.-C.,Information and Analysis Center | Weiser V.,Fraunhofer Institute for Chemical Technology | Roth E.,Fraunhofer Institute for Chemical Technology
Angewandte Chemie - International Edition | Year: 2012

Deceiving with TNT: Melt-cast pyrotechnic mixtures based on 2,4,6-trinitrotoluene (TNT)/KClO 4 (see picture for flame) spectrally matched infrared decoy flares and show superior performance and greatly reduced sensitivity in comparison to common pyrotechnic or double-base material currently in use for IR countermeasure flares. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Konig A.,Fraunhofer Institute for Chemical Technology | Kroke E.,TU Bergakademie Freiberg
Polymers for Advanced Technologies | Year: 2011

Flexible polyurethane foams are widely used in many industrial applications, such as upholstered furniture and mattresses, automotive applications, etc. The chemical nature of the polyurethane, the low density, the high air permeability, and the open cell structure cause this material to be highly flammable. In this study, the influencing variables on the burning behavior of flexible polyurethane foams are investigated. Additionally the synthesis, formulation, characterization, and testing of a new phosphorus flame retardant (FR) methyl-DOPO 9,10-dihydro-9-oxa-methylphosphaphenthrene-10-oxide in flexible polyurethane foam with low density is performed. The new FR shows an excellent flame retarding behavior by acting mainly in the gas phase. Here the vaporization of methyl-DOPO occurs in the same temperature region as the depolymerization of the urethane and the bisubstituted urea groups during pyrolysis of the foam. Furthermore TG-MS measurements revealed the release of high concentrations of low molecular weight species like HPO, CH3PO, or PO2 in the mentioned temperature region. These species are able to scavenge the H- and OH-radicals in the radical chain reactions of the flame leading to a significant increase of the CO/CO2 ratio during cone calorimeter experiments. © 2010 John Wiley & Sons, Ltd.


Konig A.,Fraunhofer Institute for Chemical Technology | Kroke E.,TU Bergakademie Freiberg
Fire and Materials | Year: 2012

The chemical nature of flexible polyurethane (flex PU) foams, the low density, the high air permeability and the open cell structure cause this material to be highly flammable. The new phosphorus flame-retardant (FR) methyl-DOPO (9, 10-dihydro-9-oxa-methylphosphaphenanthrene-10-oxide) is known to show an excellent flame retarding behavior in flex PU foam by acting mainly in the gas phase. In this study, the FR working mechanism of methyl-DOPO and its ring-opened analogue MPPP (methylphenoxyphenyl-phosphinate) is investigated by TGA, TG-MS, FMVSS 302 and Cone Calorimeter measurements. Under TG-MS conditions comparable concentrations of low molecular weight species such as HPO, mathrmCH 3PO or PO 2 are released. These species are able to scavenge the H- and OH-radicals in the radical chain reactions of the flame leading to a significant increase in the CO/CO 2 ratio and the smoke density during cone calorimeter experiments. Finally, the flame retardancy of MPPP is determined to be less efficient in flex PU foam because of the higher vapor pressure compared with methyl-DOPO. Here, the vaporization of methyl-DOPO occurs in the same temperature region as the depolymerization of the urethane and the bisubstituted urea groups during pyrolysis of the foam leading to an optimal interaction. Copyright © 2010 John Wiley & Sons, Ltd.

Loading Fraunhofer Institute for Chemical Technology collaborators
Loading Fraunhofer Institute for Chemical Technology collaborators