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Abstract  

Isothermal annealing at temperatures between 90 and 250°C and radiation annealing at 40, –76 and –196°C were studied in sodium periodate crystals doped by rapid crystallization and by spray techniques. The results showed the occurrence of transfer annealing because the dopant was converted to the oxidized forms of iodate and periodate depending on the treatment conditions. Similarities with the annealing behaviour of recoil species in neutron irradiated periodate systems are established and the Bellido and Wiles stepwise oxidation model is used to explain the mechanism of the processes.

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Journal of Thermal Analysis and Calorimetry
Authors:
Juliana Cordeiro Cardoso
,
Ricardo Luiz C. Albuquerque Jr.
,
Francine Ferreira Padilha
,
Felipe Oliveira Bittencourt
,
Osvaldo de Freitas
,
Paula Santos Nunes
,
Newton L. Pereira
,
Maria José Vieira Fonseca
, and
Adriano Antunes S. Araújo

Abstract

The use of biodegradable natural polymers has increased due to the over-solid packaging waste. In this study, a chemical modification of the casein molecule was performed by Maillard reaction, and the modified polymer was evaluated by polyacrylamide gel electrophoresis (PAGE), thermogravimetry/derivative thermogravimetry (TG/DTG), FT-IR, and 1H-NMR spectroscopy. Subsequently, films based on the modified casein were obtained and characterized by mechanical analysis, water vapor transmission, and erosion behavior. The PAGE results suggested an increase of molecular mass of the modified polymer, and FT-IR spectroscopy data indicated inclusion of C–OH groups into this molecule. The TG/DTG curves of modified casein presented a different thermal decomposition profile compared to the individual compounds. Mechanical tests showed that the chemical modification of the casein molecules provided higher elongation rates (45.5%) to the films, suggesting higher plasticity, than the original molecules (13.4%). The modified casein films presented higher permeability (0.505 ± 0.006 μg/h mm3) than the original polymer (0.387 ± 0.006 μg/h mm3) films at 90% relative humidity (RH). In pH 1.2, modified casein films presented higher erosion rates (32.690 ± 0.692%) than casein films (19.910 ± 2.083%) after 8 h, suggesting an increased sensibility for erosion of the modified casein films in acid environment. In water (pH 7.0), the films erosion profiles were similar. Those findings indicate that the modification of molecule by Maillard reaction provided films more plastic, hydrophilic, and sensitive to erosion in acid environment, suggesting that a new polymer with changed properties was founded.

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