UNIfipp application center

Electrochromic multilayer systems (electrochromic devices ECD) are capable of changing their optical properties due to an applied electrical voltage. As a result of the complex production and the limited substrate materials for ECDs, they are currently only used in isolated cases.

In this project, an electrochromic multilayer system based on the deposition of conductive polymers by electrochemical polymerization on transparent plastic electrodes is to be developed and integrated into a demonstrator by means of plastic processing.

For this purpose, a process for insitu polymerization of the electrochromic material onto a plastic substrate is to be developed at the Institute of Applied Polymer Research. One of the advantages over conventional processes is the precise adjustment of the layer thickness, which should result in a more homogeneous appearance.

At the Institute of Materials Engineering, the ECDs are to be integrated into two-dimensional, three-dimensional components in plastics processing. Various challenges arise here due to the temperature sensitivity as well as the mechanical stress on the functional layers of the ECDs, which are to be investigated in this research project and solved by various adaptations (variation of the thickness of the carrier material, etc.). In this context, injection-compression molding as a plastic processing technique is expected to contribute to the solution of the various challenges.

The research work includes the characterization of the different individual layers, the procurement of a tool for injection-compression molding of ECDs with an active area of 16 cm², the production of the ECDs and the upscaling of the geometry. In addition, a simulation will be used to gain knowledge about the temperature input and the mechanical stress in the various individual layers.

In this research project, the aging behavior of plastic-based chromogenic systems will be investigated. Chromogenic systems (CS) are materials or multilayer structures that change their color and/or transparency due to external stimuli (light, electrical voltage, temperature and pressure). A special group of CS are electrochromic devices (ECD), which change their optical properties due to an applied voltage. Their potential field of application is wherever glazing or displays are to be actively switched. A few systems are currently in use. All systems currently known from practice or literature show weaknesses with regard to aging behavior.

In this project, therefore, the aging of a special type of ECD suitable for plastics technology is to be investigated. In this project, material aging is understood to mean - in distinction to system fatigue as a result of a large number of switching operations - the change in the ECD as a result of the effects of humidity, temperature and UV radiation and their effect on the function of the system. The research work includes extensive experimental work, which is to be evaluated and made tangible by means of a model-based description.

An important aspect for the use of electrically conductive modified plastics is their contacting. In addition to processes that produce a contact subsequently, there are also numerous process-integrated methods. Injection molding should be emphasized here, but integration via other common primary molding, forming and joining processes is also conceivable. These contacting options lead to a specific state of the interface transition between metal and plastic and of the plastic boundary layers.

The aim of the project is to develop a model for describing the electrical contact resistance at the interface between electrically conductive modified plastics and metallic contacts, as a function of the parameters of the interface transition and the plastic boundary layers, to quantify this model and to validate it in the context of realistic manufacturing processes.

In cooperation with:

Institute of Propulsion Technology - Vehicle Systems and Fundamentals of Electrical Engineering, Prof. Dr. rer. nat. Ludwig Brabetz, University of Kassel.

The individual project is publicly funded by the German Research Foundation and will be carried out over a period of 36 months.

The aim of the project is to analyze the emission behavior of test specimens made of natural fiber-reinforced bio-polyamide and to correlate the emissions with the odor as a result of the process conditions during processing on screw machines.

In order to be able to analyze and evaluate both the chemical composition of the emissions and their olfactory effects, a number of human-sensory methods for olfactory evaluation of the materials or the emitting substances from the test specimens will be used in addition to chemical analysis by means of coupled gas chromatography and mass spectrometry (GC/MS).

A detailed gain of knowledge on relevant odor-causing compounds, their formation in the process control and potential (odor-) emission-causing interactions between the matrix material and the natural fiber can therefore be expected within the scope of the project. In particular, work on the coupling of overall odor, emissions and process conditions is not yet known in the literature.

This comprehensive, multidisciplinary collaborative project aims to develop and demonstrate "smart" and efficient building-integrated photovoltaics based on Luminescent Solar Concentrator (LSC) technology. The windows, as building-integrated elements, capture and convert incident direct and diffuse sunlight, transporting it to the end faces of the window, where highly efficient solar cells are located. This results in additional surfaces that can be used for electricity generation and were previously inaccessible. In addition to coupling and integration, the goal of this project is to extend the current state of research of LSC technology, particularly to increase its efficiency and bring both system size, performance, and fabrication closer to a practical scale.

The content and objectives are to view individual components down to the molecular level, nano- and microstructures, resulting macroscopic material properties and production processes, the application of materials as well as recycling as an inseparable unit in materials engineering. Materials science and materials engineering are at the center and are to be seen as a link for a distinct interdisciplinary collaboration (e.g. CINSaT). Proof of concepts are of central importance for the field of plastics technology and UNIfipp, with which the linking of nano- and microstructural functional elements with plastics and manufacturing technology is to be carried out.

Link

The Leistritz twin screw extruder is used for compounding and extrusion of plastics. Plastic pellets are fed into the extruder via gravimetric metering systems. There, different heating zones can be controlled individually. Thus, the different elements can be heated and maintained at different temperatures. The twin screw transports the granules through the various elements of the extruder. In the process, the granules are melted by shear and temperature increase.

The ZSE 27 iMAXX has the option of increased throughput. Upscaling trials are thus a possible application. Furthermore, large process windows can be processed by a high possible torque with a high material volume. The DSE offers the possibility to produce new material formulations for the adaptation of the plastics and to adapt them to the respective application. Via the two side feeders it is possible, for example, to add fibers, granulates, powders or liquids to the plastic. Due to the modular screw configuration, different setups can be realized. Materials (fibers, etc.) can thus be processed gently.

For process monitoring and subsequent evaluation, the process data can be read out via the interface.

In addition, the possibility of microcellular foaming during extrusion is given via the Promix-NC350 module.

The Coatema coating system is used for discontinuous coating of flat samples (max. DIN A3 format / 297 x 420 mm) with subsequent drying of the coating.

The sample is fixed on a movable vacuum table with ground surface (planarity of 1 µm at 20 °C). Optionally, a manual clamping system is available for fixing open structures, such as textile material.

During coating, either the vacuum table or the coating beam is moved horizontally by motor via linear guides. The coating bar can be optionally equipped with the doctor blade or with the heatable wide slot nozzle.

The wide slot nozzle can be heated up to approx. 90 °C and is suitable for thin coats of water- or solvent-based liquids. Not for hot melts. The coating material is transported to the nozzle via a pump system. The accuracy of the slot die lips is +/- 4 µm.

For doctoring, the vertical gap setting of the coating bar to the vacuum table can be adjusted with a step size of 1 µm.

The total travel length of the table is approx. 950 mm, at the end of which the table can be moved exactly under the dryer unit. The dryer reaches a maximum temperature of 120 °C. The integrated exhaust fan with an exhaust air volume of 250^m3/h and the complete enclosure ensure sufficient removal of the solvents during the drying process. Flammable substances can also be coated.

The coating plant is used, among other things, for coating half cells for electrochromic applications. For example, thin polycarbonate films are coated with a few micrometers thick polymer-based electrochromic layer for the Epokis project.

The Freeformer from ARBURG enables additive manufacturing with thermoplastics based on standard pellets and thus offers a wide range of materials. In addition to standard types, filled materials up to a particle size of 10µm can also be processed.

The Freeformer's mode of operation is a combination of 3D printing (layer-by-layer build-up) and injection molding (plasticizing). The plasticizing unit includes a 12mm diameter screw and a non-return valve and can be heated up to 350°C. After melting, the thermoplastic material is fed into a discharge unit under pressure control and discharged in drop form via a piezo-controlled valve gate with a max. frequency of 300Hz. The layer-by-layer build-up of the 3D print is made possible by a component carrier table that can be moved in the X, Y and Z directions. As an open system, the Freeformer allows the user to adjust all process parameters and set the drop shape and deposition.

The Freeformer 300-3X has a total of three separate discharge units, each with integrated material drying. This makes it possible, for example, to produce multi-component functional components such as hard-soft joints with a support structure. The usable installation space is 234 x 134 x 230mm and can be heated up to temperatures of 120°.

The 3ntr A2v4 offers the possibility of additive manufacturing using the established FDM process. The large installation space of 611 mm x 360 mm x 500 mm, together with the high possible processing temperatures, an x/y resolution of 0.011 mm, as well as a layer resolution of 0.05 mm, enables the precise processing of both standard and technical plastic filaments. Thanks to the three nozzles, just as many components can be integrated into one component. Furthermore, flexible materials can also be used thanks to a special print head.

This in situ loading unit enables imaging, analytical examinations of mechanically loaded specimens in conjunction with the ZEISS Xradia 520 Versa X-ray microscope. For example, foam structures can be deformed, loaded fiber-reinforced materials can be viewed or possible flaws (e.g. cracks) within a specimen can be revealed under load. The resulting three-dimensional results can then be evaluated using pore analysis or fiber tracing, among other methods.

Features DEBEN CT5000RT:

• Mechanical loading during a µ-CT examination
• Tensile and compressive loads up to a maximum force of 5 kN
• Cyclic loads
• Continuous data recording

The thermogravimetric analyzer TGA Discovery 5500 from TA Instruments is suitable for determining the loss of mass as a function of temperature and time, and for detecting fillers and reinforcing materials. Furthermore, it is possible to determine the thermal stability, oxidation behavior and decomposition behavior of materials.

The integrated IR oven provides fast heating and cooling rates, measurements in a temperature range of up to 1200°C are possible. Furthermore, the connection of a mass spectrometer to the TGA is possible, allowing a determination of chemical substances from the mass loss.

TGA-MS is a coupling of the TA Instruments TGA Discovery 5500 thermogravimetric analysis module and the MKS Instruments CirrusTM 3 quadrupole mass spectrometer.

Thermogravimetric analysis (TGA) is a quantitative analytical method that measures the change in mass of a sample while it is heated, cooled, or maintained at a constant temperature in a controlled atmosphere. When coupled with an MS system, the resulting reaction and decomposition products can be further analyzed and qualified. This additional information makes, for example, the characterization and determination of an unknown sample much easier and more accurate.

In the system used at the Department of Plastics Technology, the sample is vaporized in the TGA and the sample gas is transferred to the inlet port of the mass spectrometer via a heated stainless steel capillary. In the quadrupole mass spectrometer, the sample gas is first ionized. The ions are then accelerated by an electric field and sorted in the alternating field of the mass filter according to the mass/charge ratio (m/z). The ions impinge on a detector with a measurement amplifier, which measures the ion current and is converted to count rates or partial pressure by the software of a connected computer. By measuring the mass numbers (m/z), conclusions can be drawn about the composition of the released gases. Individual substances are determined by comparing the ion diagrams obtained with corresponding patterns from databases.

The TGA-MS system is particularly suitable for the analysis of polymers, rubber and rubber compounds, microplastics and other polymer applications. In particular, the following questions can be answered:

• Thermal stability and decomposition of a material
• Identification and quantification of components, such as additives and fillers
• Moisture/solvent emissions and their composition