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Abstract  

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.

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Abstract  

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 (E a, 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.

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Abstract  

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.

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Abstract  

Cellulose acetate-based polycaprolactones (CAPCL's) were synthesized by the polymerization of -caprolactone which was initiated by non-substituted OH group in cellulose acetate. The CL/OH (mol mol–1) ratios of the CAPCL's were changed from 2 to 20. Thermal and viscoelastic properties of the CAPCL sheets were studied by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Glass transition, cold crystallization and melting were determined by DSC. Dynamic modules (E'), dynamic loss modules (E'') and tan were measured in a temperature range from –150 to 50°C by DMA. Apparent activation energy of a dispersion was calculated from the frequency dependency of E'' peak temperature. It was found that the main chain motion of both CA and PCL is observed in a CL/OH ratio from 0 to 10 mol mol–1. However, when CL/OH ratio exceeds 10 mol mol–1, the crystalline region which is rearranged by the PCL chain association is observed and only the main chain motion of PCL can be detected.

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Abstract  

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.

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Thermal analysis on influence of compatibilizing agents

Effect of vulcanization of incompatible elastomer blend

Journal of Thermal Analysis and Calorimetry
Authors: K. Pandey, K. Debnath, P. Rajagopalan, D. Setua, and G. Mathur

Abstract  

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 separateT g 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.

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Abstract  

Scintillation cocktail components were studied with regard to their impact on pulse decay discimination (PDD) and hence the separation of alpha from beta activity, using a Packard 2250 CA /. Di-isopropyl naphthalene (DIN) was found to be the most suitable solvent, both from safety considerations and also the fact that it acts in a very similar manner to naphthalene in stretching the pulses produced at the photomultiplier tube anode and hence enhancing the separation. Increasing the surfactant concentration and the use of dimethylanthracene (DMA) as secondary fluor degraded the cocktail's performance. PMT anode pulse shapes were found to be a useful indicator of PDD efficiency but could not give a quantitative guide.

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Determination of experimental excess molar properties for MTBE+1-propanol+octane

Analysis and comparison with different theoretical methods

Journal of Thermal Analysis and Calorimetry
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 x 1MTBE+x 21-propanol+(1-x 1-x 2)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.

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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 [1]. 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 [18], Jacob and Fitzner [19], Colinet [20], Knobeloch and Schwartz [21], Tsao and Smith [22], Toop [23], Scatchard et al. [24], Hillert [25], Mathieson and Thynne [26] were applied to estimate ternary properties from binary results.

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Experimental and predicted excess molar volumes of the ternary system.

Tert-butylmethylether+1-propanol+heptane at 298.15 K

Journal of Thermal Analysis and Calorimetry
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 x 1MTBE+x 21-propanol+(1-x 1-x 2) 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.

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