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Abstract  

The cyclic and Controlled Rate Thermal Analysis method (CRTA) has been used. The two rates automatically selected in the cyclic curve are small enough to allow the two states of the sample to be compared have nearly the same reacted fraction. Thus, the activation energy can be calculated without previous knowledge of the actual reaction mechanism. Provided that the activation energy,E, is known, a procedure has been developed for determining the kinetic law obeyed by the reaction by means of master curves that represent the values of the reacted fraction, α, as a function of−E/R(1/T-1/T 0.5),T 0.5 being the temperature at which α=0.5. This procedure has been tested by studying the thermal decomposition reaction of BaCO3.

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Abstract  

A study of an epoxy-cycloaliphatic amine system has been realized using a thermogravimetric technique (TG). Isothermal and non-isothermal (dynamic) methods were employed to determine the kinetic data of this system. Five methods were used for determining the activation energies of this system in the dynamic heating experiments. In two of them (Flynn-Wall-Ozawa, and Kissinger) it is not necessary to have a prior knowledge of the reaction mechanism of the degradation behaviour for this system. In the other ones (Coats and Redfern, Horowitz and Metzger, and Van Krevelen et al.) it is necessary to know this reaction mechanism, besides Criado et al. method was used for determining it. The results have shown that good agreement between the activation energies obtained from all methods can be achieved if it is assumed that the degradation behaviour of this system is of sigmoidal-rate type.

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Abstract  

The compatibility of some technically important polymer blends, namely BR/NR, NR/NBR and CR/NBR, has been investigated using the DSC method. In addition, dynamic mechanical measurements have been carried out for the NR/NBR blends over the frequency range of 10−4 Hz –200 Hz and temperatures ranging from −70 to +70°C. The results obtained show that the three rubber blends are not compatible over the entire composition range as proven by the DSC and mechanical measurements. By analyzing the heat capacity increases at the glass transitions of the separate phases in the NR/BR blend, it was possible to suggest the presence of a limited compatibility at the boundaries of the two phases. By comparing this work with prior measurements, it was possible to conclude that the calorimetric method is a more efficient tool for the study of compatibility of polymer blends when compared to ultrasonic and viscosity methods. Furthermore, it was found that polymers that show compatibility when measured with an ultrasonic method could behave compatible, semicompatible or incompatible when analyzed by DSC. On the other hand, blends that show incompatibility by the ultrasonic method are always incompatible by the DSC method.

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master curve The T g data in Fig. 1 are plotted on a semi-logarithmic scale in Fig. 2 . Every T g ( t ) seems to follow a similar trend along the logarithmic scale time axis, except for the step transition region. Figure 3 shows the T g

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Abstract  

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.

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Abstract  

Many of the isomers of polybutadiene and polyisoprene elastomers can be characterized by thermal analysis.T g is sensitive to side chain units (1,2 or 3,4 structure) for both polymers. Crystallinity measurements can characterizecis andtrans isomers. DMA and DEA master curves provide an idea of the heterogeneity of the chain units from the width of the loss factor curves in theT g region. Thermal and thermooxidative degradation, as followed by DSC and DTG, can differentiate specific natural and synthetic isomers of polyisoprenes in raw and vulcanized states.

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Abstract  

The crystallization kinetics of a melt spun Fe-Ni based alloy has been investigated, with both isothermal and continuous heating experiments, by means of differential scanning calorimetry. The alloy presents two separated crystallization processes. In order to perform the kinetic analysis of a melt spun metallic glass and to decide which kinetic model agrees better with the experimental crystallization data as the crystallized fraction x. We compare the experimental dependence of ln(k0f(x)) vs. (1-x) and that predicted, assuming different model equations for f(x). Both crystallization processes follow the JMAE equation and the master curve is the same for isothermal and non-isothermal data.

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Thermal and dynamic mechanical properties of carbon dioxide and propylene oxide alternative copolymer, poly(propylene carbonate) (PPC), and the end-capped PPC with maleic anhydride were investigated by means of TG and DMA. A master curve of the storage modulus vs. frequency can be deduced from the isochronal curves. Physical parameters of both plain and MA end-capped PPC were discussed. The results showed that for maleic anhydride (MA) end-capping PPC, an improvement of its thermal stability and mechanical properties accompanied with some modifications of the viscoelastic behavior were obtained.

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Abstract  

The properties of hydraulic mortars were studied by means of simultaneous thermal analysis (STA), according to a procedure proposed in the literature. Hydraulic limes, cement and/or slaked lime were mixed using different proportions of both inert and reactive aggregates, in order to test the effectiveness of such procedure in distinguishing the different degree of hydraulicity of such samples. The use of the normalized coordinates suggested in the literature results in overlapping of the clusters of different kinds of mortars. Modified coordinates are proposed, which give promising results in view of outlining a ‘master curve’ of hydraulicity.

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Abstract  

In polymer degradation and durability studies, as well as predicting shelf-life for medical devices, one is confronted with the need for accurate prediction and difficulties of long term real-time evaluation. Various ways to accelerate the degradation process have met with mixed success. However, recently, in our own studies, a ‘master curve’ like behavior was found to be valid for polypropylene samples studied. Evidently, for samples obeying the master curve, very few data points at high temperatures can be scaled to obtain reasonably accurate estimates on long term durability. Nevertheless, in a reference medium density polyethylene (MDPE) film material, the high temperature oxidative induction time data appear to diverge when run under air atmosphere compared with oxygen environments. In this article, we will present data on many of the polymer systems studied with an emphasis on extrapolation schemes for high temperature accelerated data to lower temperature very long-term durability. In this context, polymer and antioxidant reactivity toward oxygen, morphology, and mechanical property dependence on extent of degradation all need to be considered. And the potential and limitations of this approach will be discussed.

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