Authors:L. Barral, J. Cano, A. J. López, J. López, P. Nogueira, and C. Ramírez
The diffusive and dynamic mechanical behavior of the DGEBA/1,3-BAC epoxy resin system was studied during water absorption. The diffusion of water was investigated at 100% relative humidity, by immersion of specimens in water at 60, 80 and 100°C. In all absorption experiments, water diffusion followed Fick's law. Diffusion coefficients and saturated water concentrations are given for these temperatures. The activation energy for diffusion was determined from the relationship between the diffusion coefficient and the reciprocal of the absolute temperature. The value obtained was 31.2 kJ mol−1. Dynamic mechanical analysis of samples immersed in 100°C water and with various water contents showed both a shift of Tg, defined by thetanδ peak, to lower temperatures and a slight decrease in the dynamic modulus in the presence of water. These effects are probably a result of plasticization.
Within industrial thermal analysis applications there is an increasing requirement for more rigorous standardisation to ensure
that the data obtained can be reproduced within any other laboratory, using the same procedures. Fundamental to all Quality
Accreditation programmes is the need to generate ‘equivalent data’. The paper highlights TA applications where this is not
achieved despite the use of standard calibration procedures, where true calibration is difficult to establish due to hardware/software
design limitations or the absence of proven and traceable reference materials. Lack of standardisation can have important
commercial or legal consequences for both instrument manufacturer and end-user.
Authors:Lisardo Núñez-Regueira, M. Villanueva, and I. Fraga-Rivas
Differential scanning calorimetry was used to study the influence of
an epoxy reactive diluent, vinylcyclohexane dioxide, on the curing reaction
of a polymeric system composed of diglycidyl ether of bisphenol A (n=0) and 1,2-diaminecyclohexane (DCH). Heat evolution
and glass transition temperature, were measured in terms of the added diluent
percentage. Experimental results show that both the curing degree and the
glass transition temperature of the polymeric system decrease with an increase
in the diluent percentage.
Dynamic mechanical analysis of several
samples also showed that Tg
decreases with the increase of diluent percentage, thus corroborating DSC
The thermal behavior of perfluorosulfonated membranes of three equivalent mass (EW=910, 1000 and 1100 g eq−1) has been studied for membranes in acid form and in the alkali metal countercations substituted samples. The water contents
of the membranes decrease progressively with increasing EW and the countercations charge density. The monovalent cations substitutions increase the membranes thermal stability. DSC
curves show a single endothermic peak around 120�C that give low peak temperature for low EW and high peak temperature for large cations size. The membrane mechanical properties changed for different EW and temperatures of membranes. Stress-strain analysis showed that K+ substituted membranes at both temperatures present a highest YM compared to the other alkali cation substitutions. The thermal
properties of perfluorosulfonated membranes depend on the water contents, cation size, temperature and also on EW value.
Authors:Lisardo Núñez-Regueira, M. Villanueva, I. Fraga, C. A. Gracia-Fernández, and S. Gómez-Barreiro
The thermal degradation
of an epoxy system consisting of a diglycidyl ether of bisphenol A (DGEBA, n=0) and m-xylylenediamine (m-XDA)
was studied by both thermogravimetric analysis (TG) and dielectric analysis
(DEA). It has been checked a deviation of the typical behaviour in the Arrhenius
plot expected for this kind of systems, owing to the thermal degradation.
Both, structural relaxation time and conductivity values, were represented
as a function of the mass loss, that allow a relationship to be obtained between
characteristic relaxation time and the degree of degradation at the beginning
of the degradation process.
A new chelating copolymer (HQDMA) has been synthesized through copolymerization of 8-hydroxyquinoline and dimethylolacetone
monomers in the presence of base as a catalyst. This newly developed copolymer ligand (H2L) has been used to prepare a series of five polymeric chelates (ML) by using Zn(II), Cu(II), Ni(II), Co(II) and Mn(II) metal
ions. Both the parent ligand and its metal chelates have been systemically investigated in detail to elucidate the chemical
structure and thermal behaviour by elemental analyses, spectral (IR and electronic) characterization, number-average molecular
determination and thermogravimetric analysis (TG). In addition to these, magnetic susceptibility measurements have also been
carried out for studying geometry and metal-ligand stoichiometry of polymeric chelates.
The chemical structure of polychelates on the basis of elemental and IR characterization suggests that the bidentate ligand
(H2L) coordinates to metal ions through oxygen atom of the phenolic hydroxyl group by replacing hydrogen atom and nitrogen of
the quinoline ring. The studies of magnetic moments and electronic spectra reveal that all polychelates with octahedral geometry
are paramagnetic in nature except that of Zn(II) chelate, which is diamagnetic. The thermogravimetric analysis of parent ligand
and its metal chelates have shown remarkable difference in mode of thermal decomposition and their thermal stabilities. The
kinetic parameter, energy of activation (Ea) of thermal decomposition has also been estimated by Broido method.
The reinforcement of nano-barium titanate in ferrite filled poly-ether-ether-ketone (PEEK) composites caused a shift in the
decomposition temperature, at which maximum mass loss occurred, to higher side and enhancement in char yield in thermogravimetric
analysis. Loss tangent and glass transition temperature of ferrite filled PEEK composites were also found to be increased
with the reinforcement of nano barium titanate. The effect of nano barium titanate on the melting behaviour of ferrite filled
PEEK composites was negligible.
Temperature modulated dynamic mechanical analysis (TMDMA) was performed in the same way as temperature modulated DSC (TMDSC)
measurements. As in TMDSC TMDMA allows the investigation of reversible and non-reversible phenomena during crystallisation
of polymers. The advantage of TMDMA compared to TMDSC is the high sensitivity for small and slow changes in crystallinity,
e.g. during re-crystallisation. The combination of TMDMA and TMDSC yields new information about local processes at the surface
of polymer crystallites. It is shown that during and after isothermal crystallisation the surface of the individual crystallites
is in equilibrium with the surrounding melt.
Authors:P. Budrugeac, Andrei Cucos, and Lucreţia Miu
), differential scanning calorimetry (DSC), Micro Hot Table (MHT), thermo-mechanical analysis (TMA), and dynamic mechanical analysis (DMA), are potentially useful to conservation scientist (see, for example [ 7 ]). In this article, the results reported in the