Navegando por Palavras-chave "degradation"

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    Kinetic studies on clavulanic acid degradation
    (Elsevier B.V., 2005-03-01) Bersanetti, Patricia Alessandra [UNIFESP]; Almeida, Renata M R G; Barboza, Marlei; Araujo, Maria Lucia G; Hokka, Carlos Osamu; Univ Estadual Paulista; Universidade Federal de São Carlos (UFSCar); Univ Ribeirao Preto; Universidade Federal de São Paulo (UNIFESP)
    Clavulanic acid (CA), a potent beta-lactamase inhibitor, is very sensitive to pH and temperature. It is produced by Streptomyces clavuligerus and to optimize both the fermentation step and the downstream process, the expression of the hydrolysis kinetics has to be determined. in the present work the CA degradation rate from various sources was investigated at temperatures of 10, 20, 25, 30 and 40degreesC and PH values of 6.2 and 7.0. the results showed that first-order kinetics explained very well the hydrolysis kinetics and the Arrhenius equation could be applied to establish a relationship between the degradation rate constant and temperature, at both pHs. It has been observed that CA from fermentation medium was much more unstable than that from standard solution and from a commercially available medicine. Also, it was observed that CA was more stable at PH 6.2 than at pH 7.0, irrespective of the CA source. (C) 2004 Elsevier B.V. All rights reserved.
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    Reprocessability of PHB in extrusion: ATR-FTIR, tensile tests and thermal studies
    (Assoc Brasil Polimeros, 2017) Rivas, Leonardo Fabio; Casarin, Suzan Aline; Nepomuceno, Neymara Cavalcante; Alencar, Marie Isabele; Marcondes Agnelli, Jose Augusto; de Medeiros, Eliton Souto; Wanderley Neto, Alcides de Oliveira; de Oliveira, Mauricio Pinheiro [UNIFESP]; de Medeiros, Antonio Marcos; Ferreira e Santos, Amelia Severino
    Mechanical recycling of biodegradable plastics has to be encouraged, since the consumption of energy and raw materials can be reduced towards a sustainable development in plastics materials. In this study, the evolution of thermal and mechanical properties, as well as structural changes of poly(hydroxybutyrate) (PHB) up to three extrusion cycles were investigated. Results indicated a significant reduction in mechanical properties already at the second extrusion cycle, with a reduction above 50% in the third cycle. An increase in the crystallinity index was observed due to chemicrystallization process during degradation by chain scission. On the other hand, significant changes in the chemical structure or in thermal stability of PHB cannot be detected by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analyses (TGA), respectively.