For the successful implementation of electromobility, not only the vehicles but also the associated charging infrastructure play a decisive role. Various technologies are currently used to charge electric vehicles.

For the electronics of charging stations, Wevo offers temperature-stable adhesives and potting compounds based on silicone, epoxy resin and PU.

16:9

Silikone

Kunststoff Werkstoffe

Kfz-Elektronik

Elektronik

Harze, Epoxid

Duroplaste

Polyurethan

Klebstoffe

Verbindungstechnik Verfahren

Chemisches Fügeverfahren

Protection of Sensitive Charging Electronics

The traditional markets for glass fiber-reinforced thermoplastics remain stable. Thermoplastic composites are gaining fast with 3D-printing and hybrid processing techniques. The fiber composite industry is tackling the recycling issue with pragmatic ideas.

The Oechsler Drivematic drive actuator can be integrated into the 3D-printed CFRP monocoque frame of an Arevo „e-bike“

The Manifold New Collection of Reactive Systems and Thermoplastic Composites

Glasfasern / -matten

Verstärkungsstoffe

Reaktionsharze

Kohlenstofffasern / -matten

Sekundärfasern

Kunststoff-Rezyklat

Fasern

Halbzeuge und Zwischenprodukte

Kunststoff-Halbzeuge

Verbundwerkstoffe / Werkstoffverbunde

Aramidfasern

Harzsysteme für Composite-Herstellung

Phenolharze

Harzwerkstoffe

Andere Werkstoffe

Werkstoffe für additive Verfahren

Duroplastische Werkstoffe

Faserverbundwerkstoffe

Hochleistungskunststoffe

Thermoplaste

Fiber-Reinforced Plastics

Currently, small wind turbines can hardly be operated profitably in landlocked regions. This drawback has now been overcome by the partners EAB Gebäudetechnik Luckau GmbH and the Chair of Polymer-based Lightweight Design at the BTU Cottbus-Senftenberg: passive smartblades made from 3D-printed molds adapt independently to wind conditions. This is achieved by an intelligent layer structure and its bending-torsion-coupling.

This newly developed rotor blade is especially suited for weak-wind regions and adapts independently to the wind load

Additive Manufacture of FRP Injection Molds for FRP Components of Small Wind Turbines

Faserverarbeitung

Kunststoffverarbeitung: Maschinen und Komponenten

Simulation Produkt- / Formteildesign

Software

Simulation

Finite Methoden

Ingenieurwissenschaften

Technische Mechanik

Windkraft

Energieerzeugung

Erneuerbare Energie

Analysetools, FEM

Additive Fertigung

Highly Efficient Adaptive  Fiber-Composite Rotor Blades

This thesis deals with the development of novel materials with increased thermal conductivity and flame retardancy and their processing conditions for PCB substrate applications.

Flammschutzmittel

Additive

Elektrisch leitende Füllstoffe (Metalllegierungen, Ruß, Graphit)

Füllstoffe für Kunststoffe

Novel Thermally Conductive and Flame-Retardant Substrates for Printed Circuit Boards – Structure-Property Relationships

The new mobile communications standard 5G is advancing steadily. This development is also increasing the demand for materials that facilitate and ensure the high transmission rates for 5G signals. Plastics manufacturer Covestro has presented a corresponding thermoplastic polyurethane (TPU).

Covers for cell phones must not only protect the devices from shocks, but also allow mobile signals to pass through without interference

Kunststoff

Bauwesen

Baustoffe

Cell Phone Covers Made from TPU

The process chain of the direct coating process has now been optimized. Self-healing, fast-curing PU casting coatings and polycarbonate compounds are now available for this manufacturing process.

The DC process makes it easier and faster to produce sophisticated-looking components with integrated sensors and light elements

Direct Coating with Polyurethane Coatings Creates Opportunities in Design and Functionality

Automotive

Oberflächentechnik

Polycarbonat

Short Cycle Times and High Productivity for Smart Components

Lanxess put a new production line for the manufacture of water-based compounds into operation in Nantong, China.

At its Nantong site, China, which covers over 100,000 m2, Lanxess produces urethanes and lubricants

Specialty Chemicals Company Launches Production Line

In cooperation with partners in industry and academia, Bayer MaterialScience AG, Leverkusen, Germany, has developed an effective and cost-efficient seismic protection system for buildings. An extremely tear-resistant woven fabric is applied with a special adhesive directly to the wall, like wallpaper, forming a permanent bond. In the event of an earthquake, the “wallpaper” holds large areas of the masonry together and should keep it stable for some time. The objective is to delay or even prevent the collapse of the walls, giving the occupants time to flee the building to safety. The key component of the system is the adhesive formulated with Dispercoll U, a waterborne polyurethane dispersion from Bayer MaterialScience. Partners in the patent-pending development are the Karlsruhe Institute of Technology (KIT) and Kast, the manufacturer of the fabric, based in Sonthofen, Germany. 

The flexible and tear-resistant fabric is affixed to walls with a special adhesive much like wallpaper (photo: Bayer Material-Science) 

Efficient and Affordable Seismic Protection 

Environment-Friendly Adhesive 

In a sandwich construction alongside fixing the glass fiber mats the PU matrix also binds the paper honeycomb core to the surface skin. Application of the material is a highly significant factor in this context. For this process Hennecke GmbH, Sankt Augustin, Germany, has developed their PU-CSM technology which allows a uniform and reproducible distribution of the polyurethane and fibers. This is necessary in respect of warpage and low material usage. 

Trunk Load Floors – Minimizing Warpage 

PU-CSM 

Plastics can also remember things. This is made clear by a new thermoplastic polyurethane. The shape memory polymer can be temporarily fixed in a deformed state and then converted back almost entirely into its original shape. Potential applications exist in trademark protection and mechanical engineering as well as in the textile, sports, leisure and toy industries. 

Thermoplastic Polyurethane: Programmed to Have a Keen Memory 

Previously unknown possibilities in terms of quality, economy, ergonomy, and robust processes have been opened up by new approaches and solutions for the manufacture of fiber composite components on a series scale. Moreover, such components can also be designed with filigree or even bionic surface structures in future – also with in-mold painting. 

Fiber Composite Components: Start of a New Era 

In the last three years, global consumption of polyurethane has been growing by approx. 5 % per year. In 2012, it reached a volume of 15.3 million t. This encouraging growth trend can be expected to continue in both the middle and long term. The global factors strongly contributing to this include increasing urbanization and mobility, the economic growth driven by rising living standards, mainly in threshold countries, and last but not least, worldwide measures for saving energy. 

Stable Growth: Polyurethane (PU) 

An innovative process makes it possible for the first time to recover polyol from production scrap generated in standard flexible polyurethane foam block manufacture. Thanks to this process, the production scrap is suitable for recycling back into flexible foam manufacture, so bringing ecological and economic advantages. 

PU Recycling: Flexible Stays Flexible 

The rotor blades of wind power plants have to withstand enormous loads: Velocities of up to 300 km per hour are sometimes reached at the blade tips. And there is impact from rain, hail, snow, sand and UV radiation. Particular load acts upon the edges of the rotor blades. This is because rotor blades – which are mostly between 40 and 60, but sometimes even up to 90 meters long – consist of several components connected to each other. They are adhesion bonded, with the bond seam exactly at the blade edge. To protect the edge from erosion, sand and water, BASF SE, Ludwigshafen, developed the new Relest Wind LEP product. This new generation of polyurethane coating is due to protect the sensitive area of the rotor blade better than the known products. 

Shelter from the Wind and Storm 

Polyurethane Coating Relest Wind LEP 

Even though the solidification behavior of reactive polyurethane (PU) differs from that of thermoplastics, this material can be used for the projectile injection technique. The technology combines the excellent properties of PU with the economic benefits of injection molding and enables the production of complex elastomeric fluid-conducting hoses with adjustable flexibility and high impact strength. Additionally, the integration of a continuous fiber reinforcement leads to improved bursting strength in comparison to short fiber-reinforced thermoplastics. 

Fluid-Conducting Hoses with Complex Geometries Can Be Made of Reactive  Polyurethanes Now 

Spritzgießen

Fluidinjektionstechnik

Improved Properties with Reactive Polyurethanes 

Measuring Cell Enables Characterization of Fast-Reacting Polyurethanes and Epoxy Resins

The processing of highly reactive resin systems requires a detailed understanding of the material behavior during component manufacture. The characterization of systems using DSC to date has reached its limits, especially in the case of polyurethanes. A specially developed measuring cell, on the other hand, delivers better results.

Reactive resin systems such as polyurethanes (PU) or epoxides (EP) are used as matrix materials in fiber-reinforced composites (FRP) or processed into compact molded parts in the transportation and automotive industries, the construction sector, aerospace, medical technology, or in the field of regenerative energy production [1–3]. Industrial developments focus on highly reactive systems with reaction times of a few minutes or even seconds [4, 5]. Although these systems enable short cycle times, they pose a major challenge for robust process design.

Detailed knowledge of the thermal and rheological material behavior in the mold is essential for determining stable process parameters. A large number of models for describing the reaction progress can be found in literature [6, 7]. The most common method for characterizing reactive materials and determining input data for numerical models is Differential Scanning Calorimetry (DSC) [6]. However, the behavior of highly reactive resin systems with reaction times of a few minutes can only be measured to a limited extent, since sample preparation can take more than two minutes and measurement speeds are limited. In addition, the influence of the process parameters can often not be taken into account with conventional analysis methods. As a result, there is a lack of fundamental data for model development of these materials, which can be used for process design and simulation.

At the Institute of Plastics Processing in Industry and Craft at RWTH Aachen University (IKV), Germany, possibilities for analyzing thermal reaction behavior were therefore investigated in a publicly funded research project, and a measuring cell was developed for characterizing highly reactive resin systems under process-related conditions. Based on the data obtained, models are then determined to describe the reaction process.

Characterization of Highly  Reactive Polymers

To analyze the influence of the reaction time on the characterization of the reaction behavior of PU and EP resins, taking into account the sample preparation, three materials of different reactivity were investigated in a DSC Q2000 of the manufacturer TA Instruments (Table 1).

 In addition to an EP, whose processing or gel time allows a complete characterization, two polyurethanes were also selected, whose curing reaction cannot be completely recorded by conventional DSC. The measurement data generated serves as reference values for the validation of the measuring cell developed at IKV.

For sample preparation, the starting components were weighed and mixed manually for at least 15 s. A drop (approx. 20 µl) of the material was then placed in an aluminum DSC crucible and positioned in the DSC. The preparation time was measured for each test and ranged from 120 to 130 s. The weight of the samples ranged from 20 to 23 mg.

Figure 1 shows the measured heat flux versus temperature in the thermogram of the non-isothermal DSC measurements of the three investigated material systems for an exemplary system-dependent heating rate in each case. The curves of the EP and the first PU show the typical exothermic peak, although this is only fully developed in the case of the EP and previously shows a steady-state region with constant heat flux. In the case of the EP, a complete characterization is thus obtained, which can be used to derive models for process design.

In the case of the first PU, the reaction starts even before a steady-state measuring region with constant heat flux is set. The resulting temperature distortion due to the rapid reaction of the PU system prevents the complete analysis of the sample. An extrapolation of the thermogram shows that the reaction already begins well below 20 °C. However, an exact starting temperature cannot be determined. Furthermore, a complete characterization of the reaction enthalpy is not possible, which is why material data cannot be determined. Finally, an even more reactive material was investigated with the second PU system. The course of the curve deviates considerably from the typical reaction course. Therefore, no statements can be derived for the reaction enthalpy and characteristic values, such as the reaction start temperature, since the setting of the steady-state measuring region is superimposed on the exothermic heat flux of the reaction.

The investigations show that a complete and reproducible characterization of the reaction behavior of crosslinking polymers by means of DSC becomes more difficult with increasing reaction rates due to the time-consuming experimental preparation of the samples and a limited measuring speed of the analytical method. Basically, two types of highly reactive systems can be distinguished. On the one hand, there are systems that cure at room temperature in less than 120 s and on the other hand, systems whose reaction starts well below room temperature.

Measuring Cell for the Analysis of Highly Reactive Resin Systems

In order to better understand the reaction behavior of highly reactive material systems, the influence of pressure, temperature and material conditioning on crosslinking are analyzed at IKV. These factors are the focus of the investigations, as experience has shown that they are of particular importance for the processing of the materials under investigation.

For this purpose, a novel, automatable measuring cell based on the principle of DSC (Fig. 2) was developed. The cell consists of an aluminum furnace in which a measurement chamber and a reference chamber are symmetrically arranged on a bridge. Therefore, heat fluxes from the furnace flow equally into both chambers. The setup allows quantitative measurement of exothermic effects in the sample for isothermal conditions as well as for heating rates between 2 and 50 K/min. The bridge consists of a nickel-copper alloy whose thermoelectric properties are constant in the temperature range considered. Thermocouples are positioned at the junctions between the bridge and the two cells to record the incoming and outgoing heat fluxes. The different behavior of the sample and the reference allows the thermal properties of the sample to be determined.

Direct Dosing of the Reactive Material into the Measuring Chamber

Unlike conventional DSC, the reactive material is dosed directly into the preheated measuring chamber (T = 10 – 200 °C). The enthalpy of reaction can therefore be measured as early as 10 s after mixing. The dosing is carried out by a piston dosing unit with static mixer developed at IKV, which allows the dosing of sample quantities below 1 g. To increase the mixing quality and reproducibility, a dosing adapter was also developed which reduces the material flow of an industrial high-pressure dosing unit to less than 1 g/s and can be connected directly to the measuring cell.

A cooling channel in the bottom of the measuring cell creates a constant heat sink, which is intended to minimize thermal fluctuations and increase measuring accuracy. In addition, defined cooling rates can be set in this way and measurement temperatures below 10 °C can be realized. A measuring pressure of ≤=100 bar can be applied via mechanical stamps in order to characterize the reaction behavior under process-related conditions. The heat fluxes flowing off via the stamps are quantified by additional thermocouples. Furthermore, a dielectric monotrode can be installed into the bottom of the measuring cell to determine the curing state of the reactive material by measuring the ion viscosity. This setup allows the simultaneous correlation of thermal and dielectric measured quantities to describe the reaction behavior of highly reactive plastics in real manufacturing processes.

In addition, the thermal characterization of foaming materials using DSC-based methods is to be investigated for the first time with the developed measuring cell. For this reason, both crucibles with a height of 5 mm and variants with a height of 10 mm can be used in the measuring cell. However, for the measurements it must be taken into account that there is an increase in the heat transfer area during foam expansion and consequently a falsification of the sensor signal. The consideration of this influence is part of future investigations.

Measurement Results Agree with Known Values

The commissioning of the measuring cell includes both a temperature calibration and a heat flux calibration. During temperature calibration, the temperature measured with the measuring cell is compared with a temperature of a chemical or physical transition known from the technical literature. Heat flux calibration determines a proportionality factor between the actual heat flux occurring and the voltage generated in the sensor. A large number of different reference materials with a defined phase transition described in literature are available. However, only materials that exhibit a melting process in the temperature range between 10 and 200 °C can be considered for the developed measuring cell. Under these boundary conditions, indium with a purity of 99.99 % from the company Strategic Elements was chosen for the investigations. The medium has a melting temperature of 156.6 °C and an enthalpy of fusion of 28.5 J/g [8].

Calibration was performed at four heating rates of 2, 5, 8 and 10 K/min. The sample mass was 300 mg for all measurements. It can be seen that with increasing heating rate, the minima of the curves decrease and shift to higher temperatures (Fig. 3).

 This dependence on the selected heating rate must be taken into account during temperature calibration. All measurements show good agreement with the melting temperature described in literature. Based on the determined areas under the measured curves, the calibration factor for calculating the heat flux is determined according to equation 1. The areas increase with the heating rate and must be normalized to the respective heating rate for calibration of the measuring cell.

This calibration results in the correction factors listed in Table 2 for the heating rates considered.

To validate the calibrated measuring cell, EP was measured as before in the DSC at a heating rate of 10 K/min. The test preparation was analogous to the measurement with the conventional DSC. The sample weight was 70 mg.

The thermogram determined with the measuring cell shows the typical exothermic reaction course of an EP resin and is comparable to the DSC measurement (Fig. 4). However, it is noticeable that the peak of the thermogram of the measuring cell is tilted to the left compared to the DSC measurement and shows a fundamental oscillation in the curve. The measuring cell measures a maximum heat flux of 2.92 W/g at 128.28 °C. From the peak area, the reaction enthalpy is 365.8 J/g. The relative deviation of the enthalpy from the DSC measurement is thus 4.5 % on average.

The choice of the baseline, the parameter-specific heat flux curve of a measurement without specimen (Fig. 4), still has a significant influence on the determined area at the current stage of development and is complicated by the fundamental oscillation. The fundamental oscillation is the result of an unstable furnace control system, which is to be completely avoided by optimized control parameters within the scope of current work. It is assumed that this fundamental oscillation in interaction with the increased sample mass is causal for the shifted peak area. Further measurements of the exothermy of the epoxy resin with optimized control parameters and at varying heating rates as well as sample masses will provide a better understanding of the observations.

Using three representative reaction systems, it was shown to what extent the reaction rate is crucial for the complete characterization of the reaction course in DSC. Based on the difficulties identified, a measuring cell for the characterization of highly reactive non-foaming polymers was developed, which reduces the time delay between the start of the reaction and the start of the measurement by direct and automated dosing of the sample into the measuring chamber. Pressure stamps as well as a temperature control allow the setting of measurement conditions close to the production process (1 to 100 bar, 10 to 200 °C). The characterization of a slow-reacting epoxy resin demonstrates the suitability of the cell for quantified measurements of the reaction enthalpy. Based on this, further work will be carried out on fast-reacting polymer systems such as PU.

The measurement data obtained are then used to determine model parameters, and the reproducibility of the measurements and the quality of the parameters determined are evaluated by comparing the thermal reaction models with real components. For this purpose, components produced with an industrial dosing unit are demolded after defined curing times and the reaction conversion achieved is analyzed on the basis of the residual reaction enthalpy.

[1] Austin, A., Hicks, D. A.: A Review of the Global PU Industry 2016 and Outlook for 2017. PU Magazine International 14 (2017) 02, pp. 1–15

[2] Lövenich, C.; Aalbers, R.; Brassat, L.; Chrisochoou, A.; Ehbing, H.; Hättig, J.; Polyurethanes (PU). Kunststoffe international (2017) 10, pp. 46–51

[3] Austin, A.: Der europäische Weichschaummarkt 2018. PU Magazin 20 (2020) 01, pp. 28–32

[4] Boehm, M.: Reaction Kinetics and Cure Monitoring of Highly Reactive Epoxy Resins for Carbon Fiber Reinforced Plastics. Dissertation, Ludwig-Maximilians-Universität München, 2015

[5] Bernath, A.; Kärger, L.; Henning, F.: Accurate Cure Modeling for Isothermal Processing of Fast Curing Epoxy Resins. POLYMERS 8 (2016) 390, pp. 1–19

[6] Stanko, M.; Stommel, M.: Kinetic Prediction of Fast Curing Polyurethane Resins by Model-Free Isoconversional Methods. Polymers (2018) 10, S. 1–15

[7] Vyazovkin, S.: Isoconversional Kinetics of thermally Stimulated Processes. Springer, Cham, Schweiz, 2015.

[8] Schubnell, M: Temperature and Heat Flow Calibration of a DSC-Instrument in the Temperature Range Between –100 and 160°C. Journal of Thermal Analysis and Calorimetry (2000) 61, pp. 91–98

Institut für Kunststoffverarbeitung IKV in Industrie und Handwerk an der RWTH Aachen

https://www.ikv-aachen.de

Ausgabenartikel

Fig. 1. Thermograms of the reactions of an EP and two polyurethanes under non-isothermal conditions: the EP could be fully characterized. This is not the case for the PU.

Fig. 2. Measuring cell for thermal characterization of highly reactive resin systems: In contrast to DSC, the reactive material is dosed directly into the measuring chamber.

Fig. 3. Thermograms of the melting process of indium for four heating rates and a sample  mass of 300 mg: the measurements strongly correspond to the melting temperatures reported in literature.

Fig. 4. Comparison of the exothermic reaction of the epoxy resin Epicote 04976 in a DSC measurement and in the IKV measuring cell: the values strongly agree. The choice of the baseline has a great influence on the result of the measurement.

Table 1. Overview of EP and PU characterized by DSC

Table 2. Evaluation of the indium calibration of the developed measuringcell.

KUint4-22_IKV_Surray - Hauptartikel

Philipp Surray, M. Sc., is a research associate in the field of polyurethane technology and head of the work group for thermoset fiber reinforced plastics and polyurethanes at Institute of Plastics Processing (IKV) at RWTH Aachen University, Germany;

<a href="mailto:philipp.surray@ikv.rwth-aachen.de">philipp.surray@ikv.rwth-aachen.de</a>

Dr. Daniel Schneider is head of the department for Composites and Polyurethane Technology at IKV.

Dr. Kai Fischer is scientific director for Lightweight Design at IKV.

Prof. Christian Hopmann is head of IKV and holds the chair of plastics processing at the faculty of mechanical engineering at RWTH Aachen University.

The research project IGF 21030 N of Forschungsvereinigung Kunststoffverarbeitung was sponsored as part of “Industrielle Gemeinschaftsforschung (IGF)” by the German Federal Ministry for Economic Affairs and Climate Action (BMWK) due to an enactment of the German Bundestag through the AiF. We would like to extend our thanks to all organizations mentioned.