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.
The activation energy associated with the glass transition relaxation of an epoxy system has been determined by using the
three-point bending clamp provided in the recently introduced TA Instruments DMA 2980 dynamic mechanical analyzer. A mathematical
expression showing the dependency of modulus measurements on the sample properties and test conditions has also been derived.
The experimental results showed that the evaluation of activation energy is affected by the heating rate and test frequency,
as well as the criterion by which the glass transition temperature (Tg) is established. It has been found that the activation energy based on the loss tangent (tanδ) peak is more reliable than
on the loss modulus (E2) peak, as long as the dynamic test conditions do not cause excessive thermal lags.
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: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.
The dissolution enthalpies of glycine in aqueous solutions of acetamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylformamide,
N,N-diethylformamide and N,N-diethylacetamide were measured at 298.15 K. The enthalpic pair interaction coefficients of glycine
zwitterion-amide molecules were determined by using standard solution enthalpies of glycine in water and aqueous solutions
of amides. The additivity of groups concept of Savage and Wood was used to estimate the contribution of each of the functional
groups of the studied amides.
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:M. M. Mato, S. M. Cebreiro, P. V. Verdes, J. L. Legido, and M. I. Paz Andrade
Summary Experimental excess molar enthalpies and densities have been measured for the ternary mixture x1MTBE+x21-propanol+(1-x1-x2)octane and the involved binary mixtures at 298.15 K and atmospheric pressure. In addition, excess molar volumes were determined from the densities of the pure liquids and mixtures. A standard Calvet microcalorimeter was employed to determine the excess molar enthalpies. Densities were measured using a DMA 4500 Anton Paar densimeter. The UNIFAC group contribution model (in the versions of Larsen et al., and Gmehling et al.) has been used to estimate excess enthalpies values. Experimental data were also used to test several empirical expressions for estimating ternary properties from experimental binary results.
Authors:P. V. Verdes, M. M. Mato, J. Salgado, J. L. Legido, and M. I. Paz Andrade
Summary Densities at 298.15 K and atmospheric pressure have been measured, using a DMA 4500 Anton Paar densimeter, for the ternary mixture methyl tert-butyl ether (MTBE)+1-pentanol+decane and for the involved binary mixtures MTBE+1-pentanol and 1-pentanol+decane. The excess molar volumes for the binary mixture MTBE+decane was reported in an earlier work . In addition, excess molar volumes were determined from the densities of the pure liquids and mixtures. Suitable fitting equations have been used in order to correlate adequately the excess molar volumes. The empirical expressions of Kohler , Jacob and Fitzner , Colinet , Knobeloch and Schwartz , Tsao and Smith , Toop , Scatchard et al. , Hillert , Mathieson and Thynne  were applied to estimate ternary properties from binary results.
Authors:M. M. Mato, S. M. Cebreiro, P. V. Verdes, A. V. Pallas, J. L. Legido, and M. I. Paz Andrade
Summary Experimental excess molar volumes for the ternary system x1MTBE+x21-propanol+(1-x1-x2) heptane and the three involved binary mixtures have been determined at 298.15 K and atmospheric pressure. Excess molar volumes were determined from the densities of the pure liquids and mixtures, using a DMA 4500 Anton Paar densimeter. The ternary mixture shows maximum values around the binary mixture MTBE+heptane and minimum values for the mixture MTBE+propanol. The ternary contribution to the excess molar volume is negative, with the exception of a range located around the rich compositions of 1-propanol. Several empirical equations predicting ternary mixture properties from experimental binary mixtures have been applied.