Effects of annealing temperature (Ta: 80-140°C) and time (ta: 3-30 h) on the crystalline phase transition in poly(lactic acid) (PLA) were studied by Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA). In the DSC curves, the sample annealed at Ta=80°C with time interval (ta: 10-30 h) demonstrates a peculiarly small exothermal peak (Texo) around 130°C, just prior to the melting point, corresponding to the disorder-to-order ('-to-) phase transition, while the sample annealed at temperature (Ta: 90-110°C) shows a double melting behavior considered as the '- phase transition. At Ta>110°C, the ′ -form of PLA was found to transform into the one during the annealing process. The '-phase transition around 100°C (Ta: 90-110°C), determined from the two melting peaks (Tm1 and Tm2) as function of Ta at different times ta, shows a good correlation with the substantial increase in the crystallinity rate (Xc) with a maximum of 32% at Ta=120°C. Towards low temperatures, the glass modulus Eg reported by DMA thermograms, shows an important increase (30 000 MPa) at Ta=80°C for ta=3 h, due to the nucleation density extremely high in low PLA materials crystallization. After a sharp drop to 3 600 MPa at Ta=110°C, a marked improvement of Eg (15 900 MPa) is observed around Ta=120°C for all samples, regardless of time ta, temperature region where PLA is usually molded in the industrial melt processing. This interesting effect (improvement of Eg in range Ta=100-120°C) can be correlated with the grow of crystallinity in the same domain of Ta, and the '- phase transition Ta (Ta: 90-110 °C) determinate by the double Tm melting DSC peak, which is confirmed by the increase of Tg for Ta=90-110°C.
La modélisation pluie-débit et les modèles hydrologiques sont devenus des outils indis - pensables permettant la prise de décision pour toutes les études et recherches dans le domaine de l’estimation et de la gestion des ressources en eau. L’approche envisagée dans ce contexte consiste à utiliser des modèles climatiques et hydrologiques basés sur une série de données hydropluviométriques, mesurées au niveau de la station de djebel Chouachi afin de simuler la réaction du bassin versant de l’oued Boukiou (Tafna, Algérie) aux sollicitations principalement pluviométriques. Pour ce faire, nous avons appliqué deux modèles hydrologiques, le GR (génie rural) et le Gardénia (modèle global à réservoirs pour la simulation de débits et de niveaux aquifères) au pas de temps journalier afin de tester leur réaction aux données du bassin et de comparer leur performance à simuler les phénomènes hydrologiques qui caractérisent le bassin de Boukiou. Les résultats obtenus indiquent que les deux modèles semblent bien adaptés aux données de l’oued Boukiou. Leur optimisation a été obtenue pour des valeurs élevées des critères de qualité (critère de Nash supérieur à 80 % et coefficient de corrélation de plus de 90 % pour les deux modèles). Toutefois, le modèle à réservoirs Gardénia paraît plus performant que celui du génie rural (GR) pour le bassin versant de l’oued Boukiou. Le modèle Gardénia utilise plus de paramètres hydrologiques et est plus facile à caler que le GR.
Effects of annealing temperature (Ta: 80-140°C) and time (ta: 3-30 h) on the crystalline phase transition in poly(lactic acid) (PLA) were studied by Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA). In the DSC curves, the sample annealed at Ta=80°C with time interval (ta: 10-30 h) demonstrates a peculiarly small exothermal peak (Texo) around 130°C, just prior to the melting point, corresponding to the disorder-to-order (a’-to- a) phase transition, while the sample annealed at temperature (Ta: 90-110°C) shows a double melting behavior considered as the a'- a phase transition. At Ta>110°C, the a′ -form of PLA was found to transform into the a one during the annealing process. The a’- a phase transition around 100°C (Ta: 90-110°C), determined from the two melting peaks (Tm1 and Tm2) as function of Ta at different times ta, shows a good correlation with the substantial increase in the crystallinity rate (Xc) with a maximum of 32% at Ta=120°C. Towards low temperatures, the glass modulus Eg reported by DMA thermograms, shows an important increase (~30 000 MPa) at Ta=80°C for ta=3 h, due to the nucleation density extremely high in low PLA materials crystallization. After a sharp drop to 3 600 MPa at Ta=110°C, a marked improvement of Eg (15 900 MPa) is observed around Ta=120°C for all samples, regardless of time ta, temperature region where PLA is usually molded in the industrial melt processing. This interesting effect (improvement of Eg in range Ta=100-120°C) can be correlated with the grow of crystallinity in the same domain of Ta, and the a’- a phase transition Ta (Ta: 90-110 °C) determinate by the double Tm melting DSC peak, which is confirmed by the increase of Tg for Ta=90-110°C.
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