Chemical analytics
Chemical analytics
To carry out our research and development projects, the following analytical methods are available at the teaching and research area Structural Polymer Composites:
- Infrared spectroscopy
- Differential Scanning Calorimetry (DSC)
- Thermogravimetry with IR coupling (TGA-FTIR)
- Dynamic Vapour Sorption (DVS)
- Electrochemical processes (EIS, CV)
- Rheological investigations
- Light/polarisation/fluorescence microscopy
- Ion detection
As part of an internationally active research and testing institute in the field of materials in construction, we also offer these within the framework of standardised or individually developed innovative testing services for special problems. For more information and enquiries about measurements on behalf of or in cooperation with us, please contact us directly.
Infrared spectroscopy
For the identification of known and unknown individual substances as well as for the quantification of known substances in mixtures (Figure 1), infrared spectroscopy based on the principle of attenuated total reflection is available at ibac. This method is very well suited for conformity testing, material monitoring and quality control, for example according to DIN EN 1767 or DIN 51451.
In addition to the analysis of homogeneous liquids and solids, the method is particularly suitable for characterising the surfaces of opaque materials such as polymer films and paint layers, regardless of the underlying layers. By using special ATR crystals, even highly light-absorbing samples such as tyre rubber or bitumen sheets can be analysed in-house.
In addition, IR spectroscopy can be used to monitor various reactions live, e.g. the cross-linking of EP and UP resins (Fig. 2). The compact design also allows mobile use, e.g. on construction sites.
Picture 1. Examination of polyurethanes with correct mixing ratio (blue) and an excess of isocyanate (red). The excess is shown by the resonance of the isocyanate group at 2274 cm.−1.
Picture 2. Time tracking of the cross-linking reaction of an unsaturated polyester with styrene. The decrease of the sytrol concentration and the increase of the poly(styrene) concentration can be seen.
Contact person: Nils Münstermann
Differential Scanning Calorimetry (DSC)
With every change in a system (e.g. phase transformation, chemical reactions), heat is either absorbed or released. This can be quantitatively investigated using differential scanning calorimetry. At the ibac, cooling and heating processes from approx. -50 to 600 °C can be measured with a DSC 204 F1 Phoenix from Netzsch; the cooling and heating rates are adjustable from 0.1 to 100 K-min−1.−1 einstellbar.
Basically, phase transitions, specific heat capacities and decomposition points that are characteristic for the respective substance can be determined with this measurement technique. Furthermore, both exothermic and endothermic chemical reactions can be observed in a time-dependent manner. For polymer materials, the glass transition temperature and the degree of crystallisation are also determined if required. Only a small amount of sample material is required for the measurement (approx. 5 mg). The samples can be measured in air, nitrogen or pure oxygen atmosphere.
Picture 3. Determination of the glass transition temperature on an unsaturated polyester.
Using temperature-modulated DSC, it is possible to separate overlapping processes into reversible and non-reversible components. Glass transitions can therefore be very well separated from other effects, such as curing, decomposition, evaporation, relaxation or cold crystallisation.
The following parameters can be determined at the ibac:
- Melting and crystallisation temperatures and the associated thermodynamic parameters
- Degree of crystallinity of semi-crystalline substances
- Solid-solid transformations (e.g. polymorphism, glass transition temperature)
- Compatibility (e.g. compatibility in polymer blends)
- Cross-linking reactions, post-cross-linking of reactive resin systems
- Oxidation stability (OIT) and onset of decomposition
- Specific heat capacity
- Solid-liquid ratio
- Liquid crystal conversions
Contact person: Paul Marten
Thermogravimetry with IR coupling (TGA-FTIR)
In thermogravimetric analysis (TGA), the change in mass of a sample is determined as a function of temperature and time. This analysis method provides information about material properties such as temperature behaviour, decomposition temperatures, water content of inorganic as well as organic samples and in particular enables the creation of thermograms for the identification of polymer samples. For this purpose, the sample is placed in a temperature-stable, inert crucible made of platinum or aluminium oxide. The sample is heated up to 1000°C in this crucible. The sample holder is coupled to a microbalance. A thermocouple measures the temperature at the crucible. This combination enables the temperature-dependent measurement of the change in mass.
A change in mass can occur through chemical reactions, evaporation, decomposition or absorption of gases. For materials, the water content is often important and can be influenced by humidity. The measurement of this property is possible with the TGA by adjusting nitrogen and oxygen flows. It can also be used to characterise fillers in polymers such as soot particles or fibres.
Picture 4. TGA-FTIR investigation of an ethyl acetate-ethylene glycol sample in the temperature range of 30-900 °C at 10 K/min under inert gas. Plot of the mass loss (black) and the total intensity of IR spectra obtained (red) as a function of temperature. The IR spectra of the gases passed over the coupling were recorded every 15 s.
Picture 5. Individual IR spectra of the absorption maxima marked in Fig. 1 (green and blue). The two components ethyl acetate (green) and ethylene glycol (blue) can be identified. The proportions of the components in the sample can be determined via the total absorption and the mass loss of the respective areas.
An extended analysis of the thermal behaviour of sample is possible by means of coupled TGA/FTIR measurements. In addition to recording the pure mass loss, the gases produced can also be analysed using FTIR spectroscopy. For this purpose, the gases are transferred into a gas cell via a heated transfer line. It is thus possible to assign certain volatile components or decomposition products to the mass loss and to draw conclusions about the processes in the sample. For example, it can be investigated whether a mass loss is caused by escaping volatile components, by decomposition of the polymer or by decomposition of a filler. Coupled TGA/FTIR measurements are therefore often a useful analytical method for investigating the general thermal resistance of materials, for damage investigations on polymer materials, or for tracking reaction processes.
Picture 6. Thermogravimetric analysis of carbonated concrete: at 100 °C mainly water escapes, from approx. 600 °C calcium carbonate decomposes to calcium oxide and CO2.
Contact person: Fabian Weitenhagen
Dynamic Vapour Sorption (DVS)
Knowledge of the moisture management of materials is not only relevant for building materials. In addition to moisture transport, the absorption from and release to the ambient air plays an important role. By means of dynamic vapour sorption (DVS), the increase and decrease in the mass of a solid can be followed after a change in the ambient humidity and/or temperature.
At ibac, a DVS resolution from the company Surface Measurement System is available in the Polymer Materials working group, with which the sorption of organic solvents such as methanol, acetone, toluene or decane can be investigated in addition to water vapour.
Picture 7. Sorption isotherm of chitosan hydrochloride from 5 to 90 ± 0.1%-RH, expressed as relative weight gain (error±0.2%) at 25 ± 0.01 °C.
Picture 8. Isothermal absorption (a) and desorption (c) of chitosan acetate at 25 ± 0.01 °C, given as relative weight increase (error±0.2 %) from 5 to 90 ± 0.1 %-RH and zero weight determination at 0%-RH. Exemplary linearisation is shown as a simplified first order reaction approach of absorption (b) and desorption (d) processes.
Contact person: Tim Mrohs
Rheological investigations
The investigation of rheological properties is one of the most important methods for characterising liquid or viscoelastic substances. For this purpose, the Institute of Building Materials Research has an Anton Paar Modular Compact Rheometer MCR 102, which can be used to determine important quantities such as the viscosity and storage and loss modulus of a substance by shearing the sample between two geometric elements. It is also possible to determine the dynamic viscosity according to DIN EN ISO 3219.
The measuring method can be applied to low-viscosity liquids as well as to "viscous" oils, dispersions, solutions, gels and emulsions. Depending on the rheological properties of the sample, plate-plate, cone-plate or cylinder-top geometries are used (Fig. 9).
Picture 9. Cylinder-top geometry for low viscosity substances (a), as well as cone-plate geometry with a cone angle α =1° (b) and plate-plate geometry (c) both for higher viscosity systems.
Picture 10. Time tracking of the cross-linking reaction of one of the gel-forming monomers with the addition of different concentrations of reaction-accelerating hardener. The increasing storage moduli G' with increasing hardener content can be seen.
Furthermore, chemical reactions can be followed with the rheometer if the progress affects the flow properties of the sample. This is particularly the case with cross-linking reactions, e.g. with reaction resins or the formation of gels. Figure 10 shows the investigation of the cross-linking of gel-forming monomers with the addition of different concentrations of reaction-accelerating hardener.
Contact person: Tim Mrohs
Electrochemical processes (EIS, CV)
The investigation of electrochemical phenomena in concrete specimens as well as in ion-conductive polymers, polymer sensors, electrolyte solutions or other systems is a central aspect of research and materials testing at ibac. For this purpose, in the TaR Structural Polymer Composites three potentiostats "1010E" from Gamry Instrument and a further five potentiostats are available in the Steel and Corrosion working group. This enables various electrochemical measuring methods, such as recording electrochemical impedance spectra and cyclic voltammograms, as well as carrying out galvanostatic and potentiostatic experiments.
In electrochemical impedance spectroscopy, the AC resistance (impedance) of a given system is determined as a function of the frequency of an applied AC current. This allows statements to be made about the electrochemical processes taking place in a system. In addition, it is possible, for example, to determine the electrolyte resistance (Fig. 11).
Picture 11. Bode plot of an ionically conductive gel at different temperatures. The resistivity (filled symbols) and the phase angle (open symbols) are plotted against the frequency.
Picture 12. Cyclic voltammogram of ethylviologens in acetonitrile.
With the help of cyclic voltammetry, electrode processes of electrochemically active substances can be characterised. Two reversal potentials are selected between which the oxidation and reduction processes of the system take place. In this range, the applied potential is now varied cyclically with a defined voltage feed rate and the resulting current is measured. An example of the characterisation of ethyl viologen, an electrochemically active dye, is shown in Figure 12. The sequence of two reversible reduction and oxidation processes is striking here.
Contact person: Tim Mrohs
Ion detection
The main focus of the work is the quantitative potentiometric determination of the chloride content in building materials in accordance with DAfStb booklet 401 and, on request, in accordance with DIN EN 14629 and DIN EN 196-2.
In addition, the following verifications can be carried out qualitatively and quantitatively by wet chemical or photometric methods:
Contact person: Stephanie Sklenak