Thermally stimulated recovery, TSR, like as thermally stimulated depolarisation currents, is a suitable technique that allows
for the study of conformational mobility in polymeric systems. Due to its relatively low equivalent frequency and transient
nature, the viscoelastic data obtained from this technique are complementary to conventional dynamic mechanical analysis (DMA).
In this work TSR-like experiments, including TSR, thermally stimulated creep and thermal sampling (TS) experiments were carried
out in the same commercial DMA equipment, allowing for the direct comparison of the data. Some advises for running TSR experiments
are presented, such as the need of performing blank experiments and temperature calibrations. The analysis of the data to
obtain the thermokinetic parameters of TS experiments is revised. In particular, from the direct fitting of the data, it is
reported a tendency for a linear relationship between the pairs of values of (Ea, log τ0) that best adjust any TS single experiment. It is concluded that the usual equation for describing TS experiments possesses
an intrinsic compensation between these two thermokinetic parameters.
Authors:L. Barral, J. Cano, A. López, P. Nogueira, and C. Ramírez
Using dynamic mechanical analysis (DMA) we have studied the variation with the frequency of the dynamic mechanical properties
(storages modulus,E'; loss modulus,E'' and loss tangent or tan σ) for a system containg a diglycidyl ether of bisphenol A (DGEBA) and 1,3-bisaminomethylcyclohexane
(1,3-BAC). These properties were measured both in the glass transition and β transition regions. An increase in frequency
caused a shift of tan σ peak positions in both regions toward higher temperature. Finally, we report the activation energies
of a DGEBA/1,3-BAC expoxy system for α and β transitions.
Authors:B. Nandan, K. Pandey, G. Pandey, A. Singh, L. Kandpal, and G. Mathur
Binary blends of poly (ether sulphone) (PES) and Nylon-6 were prepared in a whole range of composition by melt extrusion.
Miscibility behaviour of the blends were studied using thermal analytical techniques like differential scanning calorimetry
(DSC) and dynamic mechanical analysis (DMA). Due to the rapid crystallization of Nylon-6 as it is cooled from the melt state,
its glass transition behaviour could not be detected even in the quenched samples by DSC. Furthermore, the crystallization
and melting behaviour of the blends have been studied by DSC. DMA results show that the dynamic storage modulus of the blends
were in-between those of the constituent polymers. Also the glass transition of Nylon-6 phase as determined by the peak in
loss tangent remains constant which shows that the two polymers are immiscible. Thermal expansion coefficient of the blends
as determined by TMA is greater than that of Nylon-6 signifying the increased dimensional stability of the blends at higher
temperatures. Morphological studies done by scanning electron microscopy (SEM) show the biphasic nature of the blends, with
clear cut boundaries between the phases because of poor interfacial adhesion. Dispersed particle size is small when Nylon-6
is the dispersed phase because of its lower melt viscosity as compared to PES. Thermal stability of the blends was measured
using thermogravimetric analysis (TG). Two-step decomposition behaviour was observed because of macro-phase separated morphology.
Authors:J. Van Elteren, H. Das, C. De Ligny, J. Agterdenbos, and D. Bax
Differentiation between As(III) and As(V) is accomplished using earlier developed selective preconcentration methods (carbamate and molybdate mediated (co)precipitation of As(III) and As(V) respectively) follewed by AAS detection of the (co)precipitates. Apart from this, separation of methylated arsenic species is performed by an automatable system comprising a continuous flow hydride generation unit in which monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA) are converted into their corresponding volatile methylarsines, monomethylarsine (MMA) and dimethylarsine (DMA) respectively. These species are cryogenically trapped in a Teflon-line stainless stell U-tube packed with a gas chromatographic solid-phase and subsequently separated by selective volatilization. A novel gas drying technique by means of a Perma Pure dryer was applied successfully prior to trapping. Detection is by atomic absorption spectrometry (AAS). MMAA and DMAA are determined with absolute limits of detection of 0.2 and 0.5 ng, respectively. Investigation of the behaviour of the methylarsines in the system was conducted with synthesized73As labeled methylated arsenic species. It was found that MMA is taken through the system quantitatively whereas DMA is recovered for about 85%. The opumized system combined with selective As(III)/As(V) preconcentration has been tested out for arsenic speciation of sediment interstitial water from the Chemiehaven at Rotterdam. The obtained concentrations are 28.5, 26.8 and 0.60 ng·ml–1 for As(III), As(V) and MMAA, respectively, whereas the DMAA concentration was below 0.16 ng·ml–1.
Authors:G. Mosselmans, Monique Biesemans, R. Willem, J. Wastiels, M. Leermakers, H. Rahier, S. Brughmans, and B. Van Mele
The reaction of phosphoric acid with wollastonite has been studied for reaction mixtures with a molar ratio r=P/Ca from 0.39 up to 2.9. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) reveal the formation
of the crystalline products brushite (when r is smaller than 1.4) and monetite and calcium dihydrogenphosphate monohydrate (when r is above 1). Magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) and FTIR show that amorphous silica is
also formed which contains some residual calcium and hydroxyl groups. The proposed reactions are confirmed by the evolution
of the reaction enthalpy measured with differential scanning calorimetry (DSC). The reaction was monitored with temperature
modulated DSC (TMDSC) and dynamic mechanical analysis (DMA). The sharp increase of the elasticity modulus coincides with the
onset of decrease in heat capacity. The setting of the reaction mixture does not slow down the reaction rate.
Authors:Yang-Xin Yu, Tie-Zhu Bao, Guang-Hua Gao, and Yi-Gui Li
In order to obtain the exact information of atomic number density in the ternary system of HNO3−UO2(NO3)2−H2O, the densities were measured with an Anton-Paar DMA60/602 digital density meter thermostated at 298.15±0.01 K. The apparent
molal volumes for the systems were calculated from the experimental data. The present measured apparent molar volumes have
been fitted to the Pitzer ion-interaction model, which provides an adequate representation of the experimental data for mixed
aqueous electrolyte solutions up to 6.2 mol/kg ionic strength. This fit yields θV, and ψV, which are the first derivatives with respect to pressure of the mixing interaction parameters for the excess free energy.
With the mixing parameters θV, and ψV, the densities and apparent molar volumes of the ternary system studied in this work can be calculated with good accuracy,
as shown by the standard deviations.
Authors:N. Havard, E. Dargent, P. Lebaudy, L. Lecamp, and J. Grenet
Photo-initiated polymerisation of dimethacrylate oligomers provide an easy method for producing highly crosslinked polymer
networks. The physical properties of the material are dependent on the polymerisation conversion value. The determination
of this conversion value is quite difficult on the final product. The first step is to measure a characteristic temperature
of the glass transition. The weakness of the DSC glass transition signal makes this measure unrealisable while the DMA tan
peak is broad and weak. At the difference of these two thermal analysis techniques, TSDC gives an observable signal and a
Tα temperature close to the glass transition temperature region. The bad sample preparation reproducibility observed was attributed
to the high conversion rate.
Authors:L. Barral, J. Cano, J. López, I. López-Bueno, P. Nogueira, C. Ramírez, A. Torres, and M. Abad
The effect of thermal degradation on the mechanical behaviour of a system containing both tetraglycidyl-4-4′-diaminodiphenylmethane
(TGDDM) and a multifunctional novolac glycidyl ether (EPN) resins, cured with 4,4′-diaminodiphenylsulphone (DDS) has been
studied using dynamic mechanical analysis (DMA) and tensile tests. Different curing paths using the isothermal time-temperature-transformation
(TTT) diagram for this system were designed, obtaining thermosetting materials with different conversions. The influences
of the degree of cure and of the aging temperature were also studied. The results showed different trends in the dynamic mechanical
properties and an increase in the stiffness of the material with increasing aging time. Changes were faster and more intense
with the higher temperature.
Authors:M. Keating, K. Gardner, H. Ng, D. Marks, W. Yung, P. Avakian, and H. Starkweather
Our X-ray work of Dytek-A, 2-methyl-pentamethylenediamine, containing polyamides shows polymorphism, whereas the polyamides
with linear diamines do not. The polyamide of Dytek-A and dodecanedioic acid, MPMD-12, is singled out for discussion and
compared with the unbranched analogs of polyamides 6,12 and 5,12. Due to the presence of the -CH3 side group in the 2-position of the diamine, the polyamide MPMD-12 exhibits two stable crystal conformations. The new δ polymorph
is not seen in linear polyamides 6,12 and 5,12.
Studies by DSC polyamide MPMD-12 clearly illustrates at least two crystal forms, γ and δ, coexisting over a wide temperature
range, and the isolation of each phase is possible by controlling temperature and time. The DMA modulus in the temperature
region between the glass transition (or alpha relaxation) and melting transition shows strong dependence on the thermal history
as demonstrated in a study of crystallization kinetics.
Authors:K. Pandey, K. Debnath, P. Rajagopalan, D. Setua, and G. Mathur
Studies have been made on differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and dynamic mechanical
analysis (DMA) of binary blends of isobutylene-isoprene (IIR) copolymer and polychloroprene (CR) elastomers. Blends of IIR
and CR are incompatible and showed separateTg peaks in DSC curves similar to Tanδ peaks. However, addition of chlorinated polyethylene (CM) elastomer, as compatibilizer,
imparts miscibility between IIR and CR which could be judged both through DSC as well as by dynamic loss measurements (Loss
modulusE″ and Tanδ). The storage modulus (E′) showed variation of stiffness due to structural changes associated with the addition of compatibilizer. TG plots for these
blends showed improvement of thermal stability both by addition of a suitable compatibilizer as well as due to formation of
crosslinked structures associated with the vulcanization of the blends by standard curative package.