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Journal of Thermal Analysis and Calorimetry
Authors:
Marta Conceição
,
Manoel Dantas
,
Raul Rosenhaim
,
Valter Fernandes
,
Ieda Santos
, and
Antonio Souza

Abstract  

Oxidative stability is very important in the quality control of oils and biodiesel. Chemical characteristics, as acid, iodine and peroxide values, show the differences among samples and can be used by industries to evaluate the oxidation degree. In relation to advanced techniques, the use of PDSC to measure the oxidative induction time is very important. These measurements were used to evaluate the properties of castor oil after refining process and consequently the biodiesel characteristics. Oxidative induction time indicated that biodiesel samples were more stable than the refined oils. The biodiesel obtained from neutralized oil had a higher stability being probably related to the acid value.

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Abstract  

Results obtained from three round robin tests, performed in 1998, 2000 and 2004, are summarized and presented. Oxidation Induction Time (OITtime) and Oxidation Induction Temperature (OITtemp) on six different grades of polyethylene were measured by DSC. The measured data were collected by Empa and evaluated using a robust statistical method concerning repeatability and reproducibility standard deviation. The results of the tests indicate that the determination of OITtime is associated with a high degree of uncertainty, especially for low OITtime values. Thus, OITtemp measurements could be a valuable alternative for testing less stabilized or non-stabilized polyolefin in particular. However, OITtemp data reveal that the ability to distinguish between different polymer samples decreases drastically as OITtemp values increase.

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Abstract  

Oxidation induction times (OIT) and oxidation onset temperatures (OOT) of a low density polyethylene melt were evaluated in air using DSC. Good regression fits to OOT data were obtained using global values for the activation energy (E) that are specific for each antioxidant but assumed independent of concentration. Gimzewski’s postulate that OIT and OOT correspond to the same level of antioxidant depletion was tested by attempting to predict OIT values from OOT generated model parameters. The deviations between predicted and experimental OIT values were comparable in magnitude to the inherent scatter in the data. However, regression of the dynamic OOT data yielded statistically significant lower values for the activation energy than are obtained by direct regression of isothermal data.

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Journal of Thermal Analysis and Calorimetry
Authors:
Luzia Patricia Fernandes Carvalho Galvão
,
Anne Gabriella Dias Santos
,
Amanda Duarte Gondim
,
Marcela Nascimento Barbosa
,
Antonio Souza Araujo
,
Luiz Di Souza
, and
Valter José Fernandes Junior

154.2 517.9 Oxidative induction time (OIT) indicated that the as extracted oils have higher stability than the biodiesel comes from them ( Table 5 ). This occurs

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Evaluation of the residual stability of polyurethane automotive coatings by DSC

Equivalence of Xenotest and desert weathering tests and the synergism of stabilizers

Journal of Thermal Analysis and Calorimetry
Authors:
P. Šimon
,
Marta Fratričová
,
P. Schwarzer
, and
H.-W. Wilde

Abstract  

Degradation of poly(ester-urethanes), poly(ether-urethanes) and poly(acrylic-urethanes), as a base for automotive paintings in interior applications, has been studied by DSC. The samples were clearcoat and black-pigmented paints, unstabilized and stabilized with HALS Tinuvin 292, UV absorber Tinuvin 1130 and antioxidant Hostanox O3, exposed to weathering in Xenotest and in Arizona desert. From the dependences of oxidation onset temperature on the heating rate, the kinetic parameters enabling to calculate the oxidation induction time for a chosen temperature have been obtained. From the values of oxidation induction time, the protection factors of the additives and the residual stability of the polymer after an ageing stress has been evaluated. It has been shown that the equivalence between the two methods of weathering depends on the polymer composition. A new criterion for the evaluation of synergism/antagonism of additives in the stabilizing mixture has been proposed.

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References 1 ASTM D3895-95, “ Oxidative Induction Time of Polyolefins by DSC ”, American Society for Testing and Materials . 2 ASTM E0487-79, “ Constant Temperature

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Journal of Thermal Analysis and Calorimetry
Authors:
A. Vasconcelos
,
M. Dantas
,
M. Filho
,
R. Rosenhaim
,
E. Cavalcanti
,
N. Antoniosi Filho
,
F. Sinfrônio
,
I. Santos
, and
A. Souza

Abstract  

The influence of drying processes in the biodiesel oxidation was investigated by means of the oxidative induction time obtained from differential scanning calorimetry data. For this purpose, corn biodiesel was dried by different methods including: chemical (anhydrous sodium sulfate) and thermal (induction heating, heating under vacuum and with microwave irradiation). The drying efficiency was evaluated by monitoring IR absorption in the 3,500–3,200 cm−1 range and by the AOCS Bc 2-49 method. In general, the oxidative induction times increased inversely to the heating degree, except that of microwave irradiation, which was selective to water evaporation and caused low impact over the unsaturation of biodiesel. The DSC technique was shown to be a powerful tool to evaluate with high level of differentiation the influence of the drying process on the oxidative stability of biodiesel.

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Abstract  

Degradation of polymeric materials used in nuclear power plants (NPP), especially polymeric cable insulation materials, in the course of their service can be monitored by measuring their properties by DSC, mainly oxidative induction time — OIT. The studied materials were in-laboratory aged by applying main stressors that act in NPP — ionising radiation and temperature. The dependence of OIT on radiation and thermal degradation of polymeric material was determined. The OIT values have been compared to elongation at break as a property that directly reflects the functionality of the studied material. The comparison of monitored OIT of real cable samples taken from NPP with dependencies on how the OIT values change with the elongation at break, makes possible to establish the extent of cable degradation. This method can be considered as a suitable and effective technique for lifetime assessment not only of cable insulations but also of many other plastics.

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Abstract  

Oxidation thermal parameters on samples of polypropylene (PP) stabilized with hydroxytyrosol were determined. For comparison purposes, α-tocopherol and a synthetic phenolic commercial antioxidant (Irganox 1076), were also analyzed. Oxidation induction time (OIt) and oxidation induction temperature (OIT) were determined by differential scanning calorimetry (DSC). The addition of hydroxytyrosol 0.1 mass% to PP was enough to obtain efficient stabilization during processing. Certain decrease in stabilizing properties of natural antioxidants was observed for compression moulded materials at high temperatures. However, these samples were still efficiently stabilized in comparison to the pure material. Hydroxytyrosol showed good performance as polypropylene antioxidant and it might be considered as promising alternative to the use of phenolic synthetic compounds.

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Sunflower biodiesel

Use of P-DSC in the evaluation of antioxidant efficiency

Journal of Thermal Analysis and Calorimetry
Authors:
M. L. A. Tavares
,
N. Queiroz
,
I. M. G. Santos
,
A. L. Souza
,
E. H. S. Cavalcanti
,
A. K. D. Barros
,
R. Rosenhaim
,
L. E. B. Soledade
, and
A. G. Souza

Abstract

The higher is the degree of unsaturation in ester chain of a biodiesel, the smaller is its oxidation stability. Sunflower biodiesel obtained by the ethyl route possesses a high amount of unsaturated fatty acids, mainly oleic acid (C18:1) and linoleic acid (C18:2), thus being more prone to the oxidation process. In Brazil, with the purpose of meeting the specifications of the Brazilian National Agency of Petroleum, Natural Gas and Biofuels (ANP), antioxidant additives, from synthetic and natural origins, have been added to the biofuel. Antioxidants are an alternative to prevent the oxidative deterioration of the fatty acid derivatives, as they are substances able to reduce the oxidation rate. In this study, the oxidative stability of sunflower biodiesel, obtained by the ethyl route and additivated with different concentrations of the antioxidants butylated hydroxytoluene (BHT) and t-butylhydroquinone (TBHQ), was evaluated by means of Pressure differential scanning calorimetry (P-DSC) and the Accelerated oxidative stability test (Rancimat, Method EN 14112). The results obtained by the two techniques showed the same oxidation tendency. Thus, P-DSC can be used as an alternative to determine the oxidative stability of biodiesel. The antioxidant TBHQ, added to biodiesel at the concentrations of 2000 and 2500 mg kg−1, raised the oxidation induction time to a value higher than 6 h, the limit established by the Resolution ANP number 7/2008, thus being the best alternative among the studied antioxidants.

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