A description is given of modifications to a dynamic mechanical analyser (DMA) to allow controlled relative humidity (RH) experiments to be performed under isothermal or thermal scanning conditions. Free film samples of polyester melamine paints
(under-cured, normal-cured and over-cured) were supplied and the viscoelastic properties measured in the tensile mode of the
DMA. A reduction in the glass transition temperature (Tg) of up to 10C was found as the controlled RH was increased.
In order to be able to perform a complete characterisation
of nitrocellulose, as a subject of a surveillance program for the MoD, different
techniques (DSC, TMA, DMA) were compared, attempting to measure the different
thermal transitions in nitrocellulose gunpowder. The sample preparation in
this investigation is fully discussed. With DMA the shear mode was applied,
trying to indicate the phase transitions. A clear conclusion could be drawn
about the optimal technique to measure the relaxation behaviour. Also some
considerations are given about the possibility to use this characterisation
in a surveillance program.
Authors:G. Singh, I. Kapoor, J. Srivastava, and J. Kaur
Three dimethylanilinium sulfates (DMAS) have been prepared and characterised by elemental and spectral studies. Thermal decomposition of these salts has been studied by TG and simultaneous TG-DTG technique and kinetic parameters were evaluated from both dynamic and isothermal TG data using mechanism based kinetic equations. The thermal decomposition pathways have also been suggested and it has been found that DMAS salts give dimethyl aminobenzenesulfonic acids (DMABSA) via solid state reaction. The primary step in the thermal decomposition involves proton transfer followed by sulfonation.
Polyamide-6-block-polybutadiene copolymers have been prepared by the anionic polymerization of ɛ-caprolactam in presence of
α,ω-dihydroxy terminated polybutadiene. TG, Hi-Res™ TGA, DSC, TMDSC and DMA techniques have been applied. The suitability
of the methods used to determine the content, thermal stabilities and glass transition temperatures of the components constituting
the block copolymer is discussed.
Authors:P. V. Verdes, M. M. Mato, J. Salgado, J. L. Legido, and M. I. Paz Andrade
Summary Excess molar volumes of methyl tert-butyl ether (MTBE)+1-pentanol+octane and the binary mixtures MTBE+1-pentanol and 1-pentanol+octane, were measured at 298.15 K and atmospheric pressure, using a DMA 4500 Anton Paar densimeter. All the experimental values were compared with the results obtained by empirical expressions for estimating ternary properties from binary results.
DMA is a tool for studying linear viscoelastic behavior of polymers over ranges of temperature and frequency. Viscoelasticity has its origin in the complex molecular behavior of the polymer. A theoretical master curve has been constructed, based predominantly on thermodynamic theories of polymer molecular conformations, and their intermolecular cooperativity.
Authors:M. Ginic-Markovic, N. Choudhury, J. Matisons, and D. Williams
A two-pack polyurethane coating was analyzed using thermoanalytical techniques. The curing reaction, monitored using pressure differential calorimetry (PDSC), rheometry and dynamic mechanical analysis (DMA) shows the temperature dependency of activation energy and hence rate of curing. In-situ ATR-FTIR shows the formation of urethane linkage over time. The decomposition behavior carried out under non-isothermal mode using thermogravimetric analysis (TGA) shows bimodal behavior. The activation energies of the initial step (10% decomposition) from both iso and non-isothermal experiments are in very good agreement with each other. The use of dynamic mechanical analysis (DMA) shows the difference in glass transition behavior (Tg) and elastic modulus (E') due to the different state of cure. Also the coating exhibits a very broad loss modulus peak (E'') indicating higher energy dissipation with deformation.
Working groups of the German Society for Thermal Analysis (GEFTA) are active in the fields of calibration of dynamic calorimeters
(DSC), calibration of dilatometers, evaluation of DSC curves and standard samples for dynamic mechanical analysis (DMA). Two
papers on the temperature calibration of DSC instruments have been published, which recommend a calibration procedure and
calibration materials. Another recommendation on caloric calibration is in preparation. Certified calibration samples for
dilatometers are available for the temperature range −190° to 700°C.
Thermally Stimulated Current (TSC) technique is a relaxation technique, such as DMA, but works at very low equivalent frequency
(10−3–10−4Hz) and thus clearly resolves the peaks related to the molecular mobility. The effect of orientation on Polypropylene fibers,
the relaxation of internal stresses on Polycarbonate disks, and the effect of aging on acrylic airplane windows have been
investigated using the TSC method.