Filtern
Erscheinungsjahr
Dokumenttyp
- Zeitschriftenartikel (55) (entfernen)
Schlagworte
- DSC (8)
- Elastomer (7)
- Compression set (5)
- DMA (5)
- Glass transition (5)
- Crosslinking (4)
- Dynamic mechanical analysis (4)
- Low temperature behaviour (4)
- Prepreg (4)
- Sealing material (4)
- Ultrasound (4)
- Vulcanisation (4)
- Cross-linking (3)
- Cure process (3)
- Curemeter (3)
- Dielectric parameters (3)
- EVA (3)
- Microwave methods (3)
- Prozesskontrolle (3)
- Thermoset (3)
- Ultraschall (3)
- Vitrification (3)
- Aushärtegrad (2)
- Aushärtung (2)
- Biodiesel (2)
- Carbon fibre (2)
- DMTA (2)
- Druckverformungsrest (2)
- Dynamic-mechanical analysis (2)
- Elastomere (2)
- Elastomers (2)
- Epoxy (2)
- Fuel sorption (2)
- Gelation (2)
- Impact strength (2)
- Kochversuch (2)
- Monitoring (2)
- Moulding compound (2)
- PE-HD (2)
- Phenolharz (2)
- Sensoren (2)
- Thermosets (2)
- Vulcanization (2)
- Vulkanisation (2)
- Acoustic propagation (1)
- Adhesion (1)
- Aminoharz (1)
- Atomic force microscope (1)
- Aushärtungsverlauf (1)
- Autoclave (1)
- Bakelit (1)
- Bauteilversuche (1)
- CFC (1)
- CRP (1)
- Cellular polypropylene (1)
- Charpy impact test (1)
- Component test (1)
- Composite material (1)
- Composites (1)
- Cross linked polyethylene insulation (1)
- Crystal melting (1)
- Cure (1)
- Curing (1)
- Degree of cure (1)
- Degree of curing (1)
- Desorption (1)
- Devitrification (1)
- Dichtung (1)
- Dichtungen (1)
- Dielektrik (1)
- Differential scanning calorimetry (1)
- Elastic-plastic properties (1)
- Elektroinstallationsteile (1)
- Epoxidharz (1)
- Epoxy system (1)
- Ethylene vinyl acetate (1)
- Ferroelectret (1)
- Fertigungskontrolle (1)
- Filled rubber compounds (1)
- Force-distance curves (1)
- Glass transition temperature (1)
- Glasübergang (1)
- Gütesicherung (1)
- Harnstoffformasse (1)
- Harnstoffharz (1)
- Harnstoffharze (1)
- Indentation (1)
- Injection moulding (1)
- Interdiffusion (1)
- Interphase/interface (1)
- Keramische Grünfolien (1)
- Klebfolie (1)
- Kunstharze (1)
- Low temperature (1)
- Materialparameter (1)
- Materialprüfungsamt (1)
- Mechanical variables measurement (1)
- Mechanische Prüfung (1)
- Melamine (1)
- Mould (1)
- Mould wall coupling (1)
- Nasschemische Analyse (1)
- Natural rubber (1)
- O-Ring (1)
- O-Ringe (1)
- O-ring (1)
- On-line monitoring (1)
- Online control (1)
- Ozonbeständigkeit (1)
- Ozonkonzentrationsbestimmung (1)
- Phenol (1)
- Phenolharze (1)
- Phenolic resin (1)
- Photovoltaik (1)
- Polymer (1)
- Post-curing (1)
- Process controlling (1)
- Qualitätssicherung (1)
- Relaxation (1)
- Resins (1)
- Rheology (1)
- Rtm (1)
- Schallgeschwindgkeit (1)
- Schallgeschwindigkeit (1)
- Schrumpf (1)
- Schubmodul (1)
- Seal (1)
- Sensors (1)
- Silicone rubber (1)
- Sound velocity (1)
- Spectroscopy (1)
- Spritzgießen (1)
- TMDSC (1)
- Technische Vereinigung (1)
- Temerature (1)
- Thermal analysis (1)
- Thermal properties (1)
- Thermische Analyse (1)
- Thermoset manufacturing (1)
- Tiefe Temperatur (1)
- Time-temperature superposition principle (1)
- UV-Spektroskopie (1)
- Ultrasonic (1)
- Ultrasonic monitoring (1)
- Ultrasound sensors (1)
- Verlustmodul (1)
- Vernetzung (1)
- Vernetzungsreaktion (1)
- Verzug (1)
- Viscoelastic (1)
A new method for the evaluation of the low temperature properties of rubber materials is presented. The method emulates the standardized compression set measurement, which is frequently used for sealing materials, but can be performed within a considerably shorter time. The results are compared with the standard test and found to be qualitatively the same. Slight differences are discussed on the basis of the differences in the measurement procedures. Further data evaluation is done by fitting functions to describe the material behaviour.
Partial discharges may cause damage to electrical insulation of high voltage equipment. They initiate elastic waves in the insulating material, e.g. in the stress cone of an outdoor termination. Localisation of the origin of such elastic waves can help to predict serious damaging processes in the electrical insulation. In order to measure and evaluate the wave propagation effects in typical multilayered elastomeric structures, knowledge of the material properties is required. The propagating velocity and the attenuation of longitudinal waves are important parameters. Values for these quantities found in the literature were not appropriate. Therefore, for cross-linked polyethylene (XLPE) and cured liquid silicone rubber (LSR), the longitudinal wave velocity and the attenuation were evaluated in the temperature interval from -20°C to 50°C and in the frequency range from 200 kHz to 600 kHz using a two-sample ultrasound technique. The loss factor was determined from these measured quantities. Additionally, low frequency Dynamic Mechanical Thermal Analysis (DMTA) was applied to investigate LSR and XLPE in a temperature interval between -100 and 50°C and to check qualitatively the ultrasound data.
Adhesion of amorphous polymers as a function of temperature probed with AFM force-distance curves
(2005)
Forcedisplacement curves have been obtained with a commercial atomic force microscope at different temperatures and probe rates on a thick film of poly(n-butyl methacrylate) and on two films of polystyrene with different molecular weight. In a previous publication [B. Cappella, S.K. Kaliappan, H. Sturm, Macromolecules 38 (2005)1874] the analysis of forcedisplacement curves has been focused on the stiffness and on the Young's modulus of the samples. In the present publication we consider the temperature dependence of the work of adhesion. We have obtained master curves of the work of adhesion at fixed maximum loads and, by comparing the results of the two analysis, we show that the work of adhesion follows the WilliamsLandelFerry equation with the same coefficients previously found for the Young's modulus. Furthermore, we show that the temperature dependence of the work of adhesion of the polymers is a consequence of the temperature dependence of the tipsample contact area and in the end of the temperature dependence of the stiffness and of the elasticplastic properties of the samples.
Carbon fibre prepregs have found widespread application in lightweight constructions. They are based on a carbon-fibre fabric impregnated with reactive epoxy resin. DMA measurements under temperature conditions similar to an autoclave programme were carried out using commercially available prepreg material with a high glass transition temperature. The characteristic of the temperature programme was a dynamic heating segment at 1.5 K/min followed by a longer isothermal segment at 180 °C. The courses of the storage modulus E', loss modulus E'' and tanδ were recorded. The measuring frequency was varied between 1 Hz and 33.3 Hz. Gelation and vitrification are assigned. The influence of the measuring frequency on the time to vitrification and the correlation with DSC are discussed. The reaction does not end even after 10 h curing at 180 °C, which is interpreted as the slow cessation of the reaction caused by vitrification.
The method for the determination of compression set values with a Dynamic Mechanical Analysis (DMA) setup at low temperatures, which was presented previously, allows a much faster and readily automated procedure than the standardized compression set test according to ISO 815-2. This method is applied to a series of different elastomeric materials that are commonly used for sealing applications. The results of the compression set test are compared with results from thermal analysis to allow an in depth comparison of the material behaviour at low temperatures.
Furthermore, a comparison between two EPDM materials is presented. These materials show very similar properties determined by thermo analytical methods such as Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) but differ clearly in their compression set behaviour. This comparison shows the importance and value of information of the compression set test in addition to thermal analysis to judge the behaviour of sealing materials and confirms the relevance of the new compression set test method for the investigation of low temperature properties of elastomers.
The curing conditions play an important role in the quality assurance of composite products.
Especially as composite materials are widely used in high tech areas so that they are required to fulfil high quality Standards. Some problems which occur during curing, for instance undercuring, can hardly be detected using Standard NDT investigations, mainly because they are manifested only at high temperatures, particularly close to glass-rubber-transition. On-line eure monitoring has the outstanding advantage that it can monitor the material parameters even at the highest temperatures possible.
In recent years eure monitoring with ultrasonic methods has become more populär. In comparison to dielectric methods mechanical parameters are measured directly. The quantities to be measured are the velocity and the attenuation of the sound wave. On this basis the storage and loss modulus can be calculated. Depending on the form of excitation with longitudinal or transversal waves these moduli are referred to as long wave or shear modulus.
Well developed Computer based technology and sensor materials are available in the non-destructive testing (NDT) market. The measuring equipment employed a commercial NDT System, which worked computer-aided. With a special Software the demands of automatic Operation under industrial conditions was accomplished. This measurement equipment was tested on composites. Its structure, performance and some practical results will be presented in the following paper.
Ultrasound on-line NDT methods have been demonstrated as a useful tool for monitoring the curing reaction of thermosets. In order to achieve this ultrasound sensors are incorporated into compression, injection and RTM (resin transfer) mould. For many commercial products imprints or any surface markings upon the moulded product are undesirable. Due to its physical properties ultrasound has a large advantage over other techniques for similar applications. The sound wave can pass through the wall of the mould and direct contact with the moulded part is not required. In this particular case one fundamental problem is a good coupling of the sensors to the mould wall. Several mediums came into question but because of the high technical (e. g. temperature and long time stability) and practical demands, it was decided that dry (non-fluid) coupling would be the most promising candidate. A handful of coupling foils suitable also at high temperatures and for long time application under industrial conditions were tested and are presented in this paper.
In processing fibre-reinforced composites, the curing reaction can be significantly retarded if the temperature and reaction time are not optimally set. In such situations, complete curing is sometimes impossible under practically relevant conditions. It is difficult for processors to recognize or detect incomplete curing. The equilibrium glass transition temperature plays an important role in complete curing in the production process.
Cure monitoring of epoxy films by heatable in situ FTIR analysis: Correlation to composite parts
(2014)
The curing mechanism of an epoxy film containing dicyandiamide (DICY) and an epoxy formulation based on diglycidyl ether of Bisphenol A (DGEBA) polymer was studied as a function of various temperature programs. The investigation was performed in situ, using a thin film of the epoxy mixture on a silicon wafer substrate in a heatable transmission tool of a FTIR spectrometer. Based on these model-curing experiments, a major curing mechanism was proposed, taking into account the appearance, the decrease, and the development of characteristic bands at various temperatures. The conclusions of the model curing were correlated to FTIR measurements on a real, 50-mm-thick glass fiber reinforced component composite part from a technical process. It could be shown that characteristic bands that develop at curing temperatures above 150°C appear especially in the center of the thick sample. From the chemical or molecular point of view, this demonstrates the established technician's understanding that temperature control inside a large-scale fiber composite of, for example, aircraft, wind-turbine, automotive applications component is of major importance.
Carbon-fibre prepregs have found widespread use in lightweight applications. They are based on a carbon-fibre fabric impregnated with reactive epoxy resin. Prepreg materials are generally pre-cured so that they have a higher molecular weight than typical resins in order to reduce resin flow, which facilitates storage and later processing properties.
The measurements were carried out using commercially available materials and follow the published DMA investigations of the same material. TMDSC was used to find the correlation between curing conditions, the degree of cure and glass transition temperature. TMDSC has the advantage over standard DSC that it enables better determination of the glass transition temperature, which is often accompanied by an exothermic curing reaction, and thus overshadowed. The influence of the amplitude of temperature modulation was tested in preliminary experiments. For non-cured material a glass transition temperature of approximately 0 °C was determined; whereas for the totally cured material it was approximately 230 °C. The changes in degree of cure, temperature of actual glass transition and post-reaction are given as a function of curing time at 180 °C. The correlation between actual glass transition temperature and degree of cure is derived.
Epoxy composites used for high-end structural applications are typically cured under the influence of temperature and pressure causing a number of complex chemical and physical transformations. On heating a mould, temperature gradients will occur through the component which will depend largely on the thermophysical properties of the specific composite. The crosslinking reaction is exothermic leading to additional heat release, thus complicating heat transportation models. If such effects are not accounted for, it can lead to variations in resin flow, poor fibre wetting causing voiding and inhomogeneous cure, leading to shrinkage and unfavourable variations in moulded part geometry. Limited information is available for thermal models used in the manufacture of reinforced thermosets. Autoclave [1, 2] and laser or infra-red curing processes [3, 4] typically use constant values determined on fully cured parts. In this work, the variation in thermal conductivity (K) (W/(m K)), thermal diffusivity (a) (m(2)/s) and specific heat capacity at constant pressure (c(p)) (J/(g K) is determined for a carbon fibre prepreg during cure. It is the intention to improve understanding of how these parameters are related to chemical or physical transformations occurring during cure, and where estimates or shortcuts may be used for heat transfer models
The technique normally used to measure Cp during isothermal cure is Temperature Modulated - Dynamic Scanning Calorimetry TM-DSC. It is however not standardised, experimentally complicated and quite time intensive. As will be shown, Cp may also be estimated during isothermal cure just from using dynamic heating experiments on a fully cured sample. Such values are often sufficient for isothermal heat transfer models that otherwise employ a constant Cp value obtained from the fully cured epoxy. Secondly, the results from dynamic heating experiments provide a quick means, in comparison to isothermal TMDSC measurements, of estimating Cp variation during cure as well as providing a good estimate value for Cp towards the end of isothermal cure. As will be shown, such values obtained from a standardised measurement procedure are very helpful in setting up TMDSC experiments that are more sensitive to experimental error influenced by factors such as sample weight and geometry.
The DSC results illustrate that the measured heat capacity Cp for a fully cured epoxy over a temperature range are very similar to values for samples partially cured at corresponding isothermal temperatures, under the prerequisite that vitrification takes place. In such cases the primary influence on Cp is specific measurement temperature and not degree of cure. For isothermal cure temperatures investigated between 150 and 200 °C, the total change of Cp during cure is nearly constant and correlates well with values published by authors on other epoxy based systems. Taking Cp variation as constant, it is possible from just dynamic heating experiments on the cured epoxy to estimate Cp for the uncured epoxy system at specific cure temperatures. The next step would be to estimate the full Cp profile during isothermal cure, however, in such cases, the time to vitrification would also be needed as additional information.
Dargestellt wird eine Gegenüberstellung der Ergebnisse von Messungen zur Ozonkonzentrationsbestimmung nach zwei Verfahren. International wird in der Kautschukindustrie ein UV-spektroskopisches Verfahren angewandt. Die deutsche Kautschukindustrie verwendet ein nasschemisches Verfahren. Die beiden Verfahren ergeben nicht die gleichen Ergebnisse. Daher wird der Unterschied genauer ermittelt.
Die Auswirkungen der unterschiedlichen Ozonkonzentrationsbestimmungen auf die Prüfung der Ozonbeständigkeit an Elastomeren werden gezeigt.
Der Druckverformungsrest (DVR) stellt insbesondere für Dichtungsanwendungen eine wichtige Kenngröße zur Beurteilung der Eignung eines Elastomers dar. Er ermöglicht die Einschätzung des zeitabhängigen Rückstellverhaltens eines Werkstoffs nach Deformation. Neben der Prüfung bei erhöhten Temperaturen, zur Beurteilung des Alterungsverhaltens, lässt sich bei der Durchführung bei tiefen Temperaturen die limitierende Einsatztemperatur bestimmen. Die Versuchsdurchführung unterscheidet sich je nach angewandter Norm und kann einen deutlichen Einfluss auf den DVR-Wert haben. Um bei tiefen Temperaturen eine schnelle Aussage zu gestatten, ist eine im Vergleich zu genormten Methoden deutlich schneller durchzuführende, automatisierte Methode entwickelt und mit Standardmethoden verglichen worden. Durch kontinuierliche Messung des Druckverformungsrests kann die Kinetik der Materialrückstellung betrachtet und dadurch ein effizienter Materialvergleich und eine effiziente Materialauswahl ermöglicht werden. Compression set (CS) is especially for sealing applications an important parameter for material selection. It allows an assessment of the time dependent recovery after deformation.
In addition to testing at elevated temperatures which aims at the evaluation of the ageing behaviour, testing at low temperatures permits the determination of the low working temperature limit. The test procedure varies depending on the applied standard and can show a significant effect on the CS value. In order to allow a quick statement regarding low temperatures an automated procedure being significantly faster realisable in relation to the standardised methods has been developed and compared with standard procedures. Continuous measurement of the compression set allows evaluating the recovery kinetics and therefore an efficient comparison and selection of materials.
Epoxy carbon-fibre prepreg, Hexcel Type 6376 HTS, was investigated using Dynamic Mechanical Analysis (DMA). The DMA characteristic parameters are storage modulus E', loss modulus E' and loss factor tanδ. These parameters are ideally suited to observe the vitrification, referred to as glass transition, resulting from the cross-linking reaction. Detection of the cure state may also be achieved by determining the momentary glass transition temperature of partially cured samples. The consequent use of a multi-frequency measuring regime was used to derive the apparent activation energy for the glass transition process. Different temperature programs were also applied to monitor the curing process directly, as well as to investigate the different states of incomplete cure reached in preceding curing steps. The intention was to provide better understanding of the consequences of an interrupted autoclave curing process and to use DMA to detect the cure state achieved. With DMA, the continuation of an incomplete curing process also can be monitored. DMA measurements up to 300 °C showed, furthermore, that the final glass transition temperature was reduced by thermal degradation at high temperatures.
Über die in der Technik weit verbreitete typisierte Harnstoffformmasse UF 131.5, ein Aminoplast, wird berichtet, dass sie im Zuge der thermisch aktivierten Vernetzungsreaktion wegen "Überhärtung" mangelhafte Eigenschaften annimmt. Zur Verifizierung dieses Effektes werden mithilfe der Ultraschall-Prozesskontrolle gezielt Proben unterschiedlicher Aushärtegrade hergestellt. Sie werden mit verschiedenen Methoden, wie der "Kochprobe" und der Thermoanalyse, charakterisiert und auf ihre Materialeigenschaften untersucht. Dabei zeigt sich ein deutlicher Einfluss der Härtezeit auf die Glasübergangstemperatur der Formmasse. In den mechanischen Eigenschaften ist eine Veränderung allerdings nur in der Schlagzähigkeit festzustellen, die sich mit steigender Härtezeit sogar wesentlich verbessert.
The time-dependent sorption of biodiesel in a typical polyethylene for container applications is investigated in comparison to conventional diesel fuel at three different temperatures. In this context, the desorption behavior is also addressed. Subsequently, the effects of both penetrants on mechanical properties are characterized in terms of impact strength and dynamic-mechanical analysis. The discussion of property changes is firstly based on the sorption kinetics of biodiesel and diesel, which is determined by immersion experiments allowing for the calculation of respective diffusion coefficients. Changes in impact strength as determined by the Charpy method are further characterised in more detail by analyzing the fracture surfaces, and correlated with results of dynamic-mechanical analysis.
In a previous paper we investigated the influence of sorbed biodiesel or diesel on mechanical properties of a typical polyethylene grade for tank applications. Besides the basic sorption and desorption behavior of these two fuels, the study addressed the concentration-dependent mechanical properties as revealed by a non-instrumented Charpy impact test and dynamic mechanical analysis (DMA). In the present paper we extend this investigation focusing on the temperature-dependent impact fracture behavior. Therefore, an instrumented Charpy impact test was employed, allowing a more detailed analysis of the fracture behavior. Furthermore, from the load-time-diagrams obtained from the instrumented impact test, corresponding fracture times can be calculated, allowing a clear correlation of the fuel sorption induced changes in fracture toughness with the enhanced ß-relaxation observed by DMA. As in the previous study, the fracture surfaces of the impact tested specimens were analyzed in order to confirm the brittle or ductile character of the fracture indicated by impact strength and the corresponding load-deflection diagrams.
Commercially available melamine/phenolic (MP) moulding compounds used for manufacturing electro installation parts were investigated by laboratory thermal analysis methods: Dynamic Mechanical Analysis (DMA), Differential Scanning Calorimetry (DSC) and Dielectric Analysis (DEA). The results were compared with on-line measurements in a compression mould using incorporated dielectric and ultrasound sensors. Softening and cross-linking behaviour were analyzed. For on-line process monitoring, only the ultrasound method worked well. The dielectric method was distorted by water formed as a by-product from the poly-condensation reaction.
Two types of commercially applied Ethylene/Vinyl Acetate Copolymers (EVA) for encapsulation of photovoltaic modules were investigated by the thermal analysis methods of Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) in the temperature range from -150 °C to 200 °C. Glass transition, crystal melting and cross-linking were analyzed. The aims of the investigations were to gain more information for incoming goods control and to get information about the whole temperature dependent material properties in the investigated temperature range, starting at very low temperatures up to the crosslinking temperature region.
EVA is a widely used material for the encapsulation of photovoltaic modules. It melts at elevated temperatures, and seals the module before it is crosslinked at temperatures above 130 °C by a peroxide-initiated crosslinking reaction. EVA has good optical properties necessary for application in solar modules. For process optimization and quality management, a method for the quick and reliable characterization of EVA crosslinking behaviour is of great value. Here, the practicability of ultrasound for online crosslinking monitoring is demonstrated. A sound velocity increase of about 8 m/s during the crosslinking reaction is found. The ultrasound results are compared with rheometer measurements performed with a curemeter typically used for the investigation of rubber crosslinking.
Carbon fibre prepregs have found widespread application in lightweight constructions. They are based on a carbon fibre fabric impregnated with reactive epoxy resin. Measurements were carried out using commercially available prepreg material. For Dynamic Mechanical Analysis (DMA), a single cantilever measuring device was applied. The DMA results were refined by additional DSC measurements. The measurements were carried out with dynamic heating in the temperature range -90 to 280 °C. The heating rates were 1 and 2 K/min, respectively. A glass transition of the uncured material (Tg0) near 1 °C, and crosslinking-induced vitrification and devitrification at the maximal glass transition temperature of the cured material (Tgmax) in the temperature range 220 to 230 °C were found. The activation energies for the glass transitions were determined using an Arrhenius plot. By detailed consideration of the influence of the frequency on the DMA data, indications for gelation were deduced.
Rubber is widely used as sealing material in various applications. In many fields the sealing function at low temperatures is necessary. Therefore the understanding of failure mechanisms is of high importance. Rubbers are normally used above their glass-rubber transition region but the minimum working temperature limit is not defined precisely. Therefore the lower operation temperature limit of rubber seals should be determined in dependence of the material properties. The results of Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) are combined with the results of the standardized compression set according to ISO 815 respectively a modified test using the DMA equipment.
Rubbers are widely used as sealing material in various applications. In many fieldsthefunction of seal materials at lowtemperatures is required. Therefore the understanding of faiiure mechanisms that lead to leakage at low temperatures is of high importance. Therefore the lower Operation temperature limit of rubber seals should be determined in dependence of the material properties.
The results of Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) are combined with results of standardized measurements as the compression set according to ISO 815. To reduce the test time of the Standard tests a faster and more efficient technique was developed and applied. In addition the breakdown temperature of the sealing function of O-ring seals at lowtemperatures is measured in a component test Setup in dependence of the material and the degree of compression.
A stoichiometric amineepoxy formulation was cured in the presence of a thermoplastic, namely poly(vinylpyrrolidone) (PVP). The epoxy system consisted of the resin diglycidyl ether of bisphenol A (DGEBA) and the aromatic curing agent 4,4'-diaminodiphenylsulfone (DDS). As shown for this system in a former study by Oyama et al. [Oyama HT, Lesko JJ, Wightman JP. J Polym Sci B 1997;35:33146. [36]], preferential absorption of amine molecules by PVP can occur. In the present study, the focus is on the variations of local elastic properties within the epoxy interphase adjacent to the PVP layer. The curing was performed close to the glass transition temperature, Tα, of the PVP film, namely at 170 °C. Variations of the local amine concentration were tracked using energy-dispersive analysis of X-rays (EDX), by taking benefit of the sulfur contained in DDS. Using temperature-dependent dynamic mechanical analysis (DMA), a series of epoxy reference samples of different amineepoxy concentration ratios, r, was investigated in order to work out the relationship between r and the epoxy storage modulus at room temperature. In the excess-epoxy regime, r<1, the modulus is observed to increase with departure from the stoichiometric ratio, r=1. Considering the respective suppression of the ß-transition, the observed characteristic can be explained by an antiplasticisation effect. Depth-sensing indentation (DSI) experiments across the epoxy/PVP interphase provided evidence for strong modulus variations. In consistency with the EDX and the DMA data, in the vicinity of the PVP layer the local epoxy modulus is increased. The total change of the epoxy Young's modulus is ~1.1 GPa. However, the total width of the modulus decay of ~175 µm is ~2.5 times larger than the one of the DDS concentration gradient. This finding is discussed in terms of additional spatial variations of the DGEBA concentration as well as long-range diffusion currents of DDS induced by the interdiffusion processes and their effect on the final network of crosslinks.
The application of microwave measurements to the characterisation of rubber compounds vulcanisation is considered. The behaviour of mechanical and microwave (20 GHz) dielectric parameters during vulcanisation was investigated for rubber compounds with different concentrations of active and non-active carbon black. An increase of concentration or activity of carbon black results in the increase of both dielectric permittivity ε?(T) and loss ε?(T) and in the increase of torsion modulus as well. The start of the vulcanisation reaction is indicated by an increase of dielectric permittivity and torsion modulus in all investigated unvulcanised compounds with carbon black. While for compounds with non-active carbon black the vulcanisation can be better indicated by the ε?(T) anomaly, for compounds with active carbon black it is more clearly seen by the change of ε?(T) behaviour.
Today rubber is due to its unique property profile one of the most important materials for the production of bearings, dampers or also tires and tubes. In the production of rubber goods a chemical cross-linking reaction (vulcanisation) generates the final material properties. This process takes place during the shape giving of the rubber compound in the mould and can proceed for several minutes. The cross-linking process is influenced by the mixture of the basic polymer, the cross-linking agent, the influence of catalysts and inhibitors and especially the processing conditions. The quality of every ingredient, the reproducibility of the mixing ratio, the homogeneity of the mixture and the accurateness in temperature control can have a direct influence on the cross linking reaction. To control the quality of a rubber compound and verify the processing conditions in industry moving die rheometers, named curemeter, are involved in the production process. Starting from our experience in cure monitoring of thermosetting materials by measuring ultrasound velocity in the mould we extended the measuring principle to rubber vulcanisation monitoring. After first investigations using a compression mould we dealt here with on-line monitoring of vulcanisation in an injection moulding process which is one of the most used techniques in rubber industry.
Monitoring the vulcanization of elastomers: Comparison of curemeter and ultrasonic online control
(2009)
The vulcanization of elastomeric materials has a high impact on the properties of the final product. Therefore, it is important to monitor and control this crosslinking process. A common technique to attain the necessary curing time is the use of a curemeter in accordance with ISO 6502 in order to determine the time for full cure of a sample with a standardized geometry. Based on this result and a lot of practical experience, the required curing time for a given product geometry is estimated. Within the scope of this work, a new analysis technique will be compared with the standard procedure. The ultrasonic online control employs ultrasound waves to measure the changes in material properties caused by vulcanization. For this study, a natural rubber compound with a conventional curing system was investigated by both techniques. It was found that the results of the ultrasonic technique show good agreement with the results of the curemeter.
In consideration of the influence of the curing reaction on the material properties of elastomers, it is very important to control the vulcanization process properly.
As shown previously [1], the effects of the vulcanization reaction of an elastomer can be monitored by use of ultrasonic sound waves. This technique has to a certain degree a high similarity to the standard curemeter test according to ISO 6502 but can be applied also inside a production tool.
So far, the method was only applied to the vulcanization of one compound at a given temperature and sample thickness. This is now complemented with measurements on another compound system at different temperatures and sample thicknesses.
The expected effects of temperature and thickness on the curing behaviour were found by use of the ultrasound online control.
Thermosetting moulding compounds are synthetic materials which can be easily formed in the molten state and achieve high temperature stability due to a cross-linking process which takes place during manufacture. To ensure thermal and mechanical properties, post-curing of moulded phenolic resin components is necessary for high quality applications. In the industrial practice, post-curing time-temperature-programs are heuristically acquired. In this paper, dynamical mechanical thermal analysis is employed to determine optimal post-curing conditions for injection moulded parts from phenolic resin.
Ultraschallwellen durchdringen Festkörper, ohne sie zu schädigen. Der Einsatzbereich von Ultraschall reicht von der Darstellung der inneren Organe in
der Medizin bis zur Prüfung des Inneren von Bauteilen im Maschinen- und
Anlagenbau. Ultraschall-Systeme können jedoch auch genutzt werden, um
sichtbar zu machen, wie sich mechanische Eigenschaften von Reaktionsharzen
während ihrer Verarbeitung im Werkzeug verändern.
Angesichts der spezifischen Bedeutung der Aushärtung von Phenolharzen für ihre Eigenschaften als Ingenieurwerkstoffe besteht großes Interesse an deren quantitativer Charakterisierung. Mittels DSC-Messungen unter hohem Druck (HP-DSC) kann die Vernetzungsreaktion der Phenolharzformmassen durch die Unterdrückung der Verdampfung niedermolekularer Substanzen ohne störende Überlagerungen verfolgt werden. Mittels verschiedener Vernetzungsgrade können die Einflussparameter der Aufheizrate und der Nachtemperung optimiert werden. Die Messergebnisse ermöglichen eine Modellierung der Reaktionskinetik mit dem Ziel einer verbesserten Prozessführung und Qualitätskontrolle in der industriellen Praxis.
Thermoanalytische Charakterisierung von Ethylen-Vinylacetat-Copolymer (EVA) für Photovoltaikmodule
(2011)
Das Ziel der Untersuchungen war mit Hilfe von DSC und DMA EVA-Folien im Anlieferungszustand hinsichtlich der Lage der Glasübergangstemperatur, des Schmelzverhaltens und der Temperaturabhängigkeit der Vernetzungsreaktion zu charakterisieren. Auf dieser Basis sollte die Lieferstabilität im Sinne einer Wareneingangskontrolle auf eine messtechnische Basis gestellt werden. In einem 2. Schritt sollte die vernetzte Folie dahingehend charakterisiert werden, ob infolge der Vernetzung eine Änderung der
Ultrasound waves penetrate solid objects without damaging them. Their fields of application range from the imaging of internal organs in medicine, to interior testing of mechanical and chemical engineering components. However, ultrasonic systems can also be used to visualise the way the mechanical properties of reactive resins change during processing in the mould.
In recent years eure monitoring with ultrasonic methods became more important. An on-line measurement System for industrial applications is presented in this paper. It operates in through-transmission and the measured parameters are the sound velocity and the attenuation of the sound wave. An objective of this paper is to establish the ränge of possible applications for an ultrasonic eure monitoring System.
Elastomers are widely used as the main sealing materials for containers for low and intermediate level radioactive waste and as an additional component to metal seals in spent fuel and high active waste containers. The safe encapsulation of the radioactive container inventory has to be guaranteed according to regulation and appropriate guidelines for long term storage periods as well as for temperatures as low as -40°C during transport. Therefore, the understanding of failure mechanisms that lead to leakage at low temperatures is of high importance. It is known that the material properties of elastomers are strongly temperature dependent. At low temperatures, this is caused by the rubber-glass transition (abbreviated: glass transition). During continuous cooling, the material changes from a rubber-like entropy elastic to a stiff energy elastic behaviour, which allows nearly no strain or retraction. Hence, rubbers are normally used above their glass transition, but the minimum working temperature limit is not defined precisely; this can cause problems during the above noted applications. Therefore, the lower operation temperature limit of elastomer seals must be determined in dependence of the material properties. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) are combined with standardised measurements to determine the compression set according to ISO 815. To reduce the test time of the standard tests, a faster technique than normally used was developed. Additionally, the breakdown temperature of the sealing function of complete O ring seals was measured in a component test set-up to compare it with the results of the other tests. The experimental set-up is capable of measuring the leakage rate at low temperatures by the pressure rise method. A fluorocarbon rubber (FKM) was selected for this investigation as it is often used for radioactive waste containers. The materials (seals and test sheets) were purchased from a commercial seal producer.