53 research outputs found

    Influence of temperature on high molecular weight poly(lactic acid) stereocomplex formation

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    The influence of temperature on the formation of high molecular weight poly(lactic acid) (PLA) stereocomplex was studied by evaluation of the precipitates from dioxane solutions of PLA enantiomers (PLLA and PDLA). The racemic mixtures were characterized by Gel Permeation Chromatography, Infrared Spectroscopy, Differential Scanning Calorimetry, Scanning Electronic Microscopy, Wide-Angle X-ray Scattering and Vicat Softening Temperature. Precipitation was carried out under different solution temperatures, keeping constant the mixing ratio (XD), the molecular weight, the optical purity of both PLA enantiomers and the stirring rate. It was found that the precipitates contained only pure stereocomplex crystallites (racemic crystallites), without observing crystal phase separation between both homocrystals. The kinetics of the insoluble phase formation could be adjusted with the Avrami model, classically used for polymer crystallization in molten state. It was observed that the maximum PLA stereocomplex production rate was at about 40¬įC. However, more thermally stable racemic crystallites were formed at high solution temperatures. It was found that all the precipitates were sphere-like at 10 g¬∑dl‚Äď1 at the solution temperature of 25, 40, 60 and 80¬įCPeer ReviewedPostprint (author's final draft

    Síntesis y caracterización de poliamidas derivadas del ácido tartárico

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    Con la finalidad de obtener nuevos materiales de altas prestaciones a partir de recursos naturales, la memoria de la tesis "S√≠ntesis y caracterizaci√≥n de poliamidas derivadas del √°cido tart√°rico", presentada por Jordi Bou Serra, describe nuevos pol√≠meros preparados a partir de derivados de carbohidratos. Se presentan cinco nuevas clases de poliamidas preparadas con √°cido tart√°rico, un compuesto natural y biodegradable que se obtiene f√°cilmente tomando algunas frutas y vegetales como materia prima. Los comon√≥meros son diversos compuestos hidrocarbonatos (diaminas y di√°cidos) La tesis presenta la s√≠ntesis org√°nica de todos estos materiales, as√≠ como su caracterizaci√≥n qu√≠mica (an√°lisis elemental, espectro IR, espectro RMN de H y de 13C, rotaci√≥n √≥ptica espec√≠fica, dicro√≠smo circular, puntos de fusi√≥n y tama√Īo molecular. Se han evaluado algunas propiedades de inter√©s tecnol√≥gico, como su higroscopicidad, propiedades t√©rmicas, capacidad de cristalizar y formaci√≥n de piezas como fibras o pel√≠culas. Cabe remarcar tambi√©n que de algunas poliamidas (PxDMLT) se han determinado sus propiedades mec√°nicas y el√©ctricas, con resultados prometedores.Se detallan los resultados de todas estas t√©cnicas de caracterizaci√≥n y propiedades, as√≠ como los procedimientos seguidos.Tambi√©n es interesante resaltar la poliamida PELYTA, que se ha preparado a partir del √°cido tart√°rico y el amino√°cido lisina, sustancias ambas de origen natural.De la tesis se han publicado cinco trabajos en publicaciones cient√≠ficas de alto nivel y varias comunicaciones a congresos nacionales e internacionales. El director de la tesis ha sido el Dr Sebasti√°n Mu√Īoz Guerra.With the purpose of obtaining new materials of high performances from natural resources, the memory of the thesis "Synthesis and characterization of polyamides derived from the tartaric acid", presented by Jordi Bou Serra, describes new polymers prepared from carbohydrate derivatives. There appear five new classes of polyamides prepared with tartaric acid, a natural and biodegradable compound that is obtained easily taking some fruits and vegetables as a raw material. The comonomers are diverse hydrocarbon compounds (diamines and diacids)The thesis presents the organic synthesis of all these materials, as well as their chemical characterization (elementary analysis, IR spectra, H and 13C NMR spectra, optical specific rotation, circular dicroism, melting points and molecular size). There have been evaluated some properties of technological interest, like their hygroscopicity, thermal properties, capacity to crystallize and formation of pieces like fibers or films. It is important to note that of someone polyamides (PxDMLT) have determined their mechanical and electrical properties, with promising results.Details of the results of all these techniques of characterization and properties are presented, as well as the followed procedures.Also it is interesting to highlight the polyamide PELYTA, which has been prepared from tartaric acid and lysine (an amino acid) substances both of natural origin.Of the dissertation five works have been published in scientific publications of high level and several communications to national and international congresses. The director of the thesis has been Dr Sebasti√°n Mu√Īoz Guerra

    Effect of the annealing procedure and the molecular weight on the crystalline phase morphology and thermal properties of polylactide

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    "This is the peer reviewed version of the following article: Hort√≥s, M. , Anakabe, J. , Arrillaga, A. , Espino, S. and Bou, J. J. (2019), Effect of the annealing procedure and the molecular weight on the crystalline phase morphology and thermal properties of polylactide. Polym. Int., 68: 1767-1775, which has been published in final form at https://doi.org/10.1002/pi.5887. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions."The thermomechanical properties of poly(lactide) (PLA) are strongly related to its semicrystalline microstructure and morphology. Thermal annealing is a strategy to improve the crystallinity of PLA. However, the different techniques and specimen types needed for each kind of characterization could lead to misleading conclusions. In this work, annealed samples of three PLA grades with different molecular weights were studied by DSC, wide angle X-ray scattering and polarized optical microscopy (POM) and the results are related to their thermomechanical and impact properties. Special focus is put on the POM results obtained by different approaches and the suitability of each of them to be related to the thermomechanical properties. By annealing medium molecular weight PLA specimens at 140 ¬įC an important increase of the heat distortion temperature was obtained, which was not related to the spherulite size but to the combination of high crystallinity degree together with high a/a' crystal type ratio. However, the impact properties of annealed PLA decreased with increase in the annealing temperature according to an increment in crystallinity and in the a/a' crystal ratio.Peer ReviewedPostprint (author's final draft

    In vitro validation of biomedical polyester-based scaffolds: Poly(lactide-co-glycolide) as model-case

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    Monitoring and understanding the in vitro behaviour of polyester based scaffolds both comprising the study of the hydrolytic degradation and the cell seeding viability is essential to ensure the desired functionality, according to a given biomedical purpose. As a model case to compare the performance of techniques to monitor the in vitro behaviour, poly(lactide-co-glycolide) (PLGA) scaffolds were chosen. The in vitro hydrolytic degradation of PLGA scaffolds was carried out in water and phosphate buffered saline (PBS). The evolution of the mass loss, the molar mass, the thermal properties and the surface morphology were monitored. The hydrolytic degradation media was correspondingly evaluated by means of the study of the pH, the amount of acid released and the conductivity. In addition, the in vitro biocompatibility regarding the cell culture viability was studied under physiological conditions. The cellular adhesion, cellular ability to proliferate on the scaffold, the scaffold inflammatory profile and the effect of the scaffold degradation compounds on the cells were assessed. A comparative analysis of the exploited techniques in terms of promptness of identification, depth of knowledge, simplicity of obtaining results and cost of the technique was implemented. The results showed that, depending on the balance between the interest in ascertaining the trigger of degradation or deep into the knowledge of the causes and effects of cell culture viability, an appropriate plan of analysis of the validation of polyester-based scaffolds could be designed.Peer ReviewedPostprint (author's final draft

    Modificación de los parámetros del polímero en el termofijado del poliéster a diferentes temperaturas

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    Se ha termofijado un tejido de poli√©ster a temperaturas nominales entre 160 y 220¬ļC. De los sustratos correspondientes se han determinado la temperatura efectiva, la cristalinidad, el peso molecular medio y su distribuci√≥n, el contenido de grupos carbox√≠licos y de olig√≥meros superficiales, el grado de blanco y el √≠ndice de amarillo. De este modo se han podido evaluar los cambios de cristalinidad y la migraci√≥n de olig√≥meros a la periferia de la fibra, as√≠ como una posible redistribuci√≥n de pesos moleculares y un ataque qu√≠mico-t√©rmico en la operaci√≥n de termofijado.A polyester cloth was heatset at nominal temperatures between 160 and 220¬ļC. From the corresponding substrates the effective temperature, the cristallinity, the mean molecular weight and its distribution, the content of carboxylic groups and of superficial oligomers, the degree of whiteness and the yellow index were determined. In this way it was possible to evaluate the changes of cristallinity and the migration of oligomers to the periphery of the fibre, along with a possible redistribution of molecular weights and a chemico-thermal attack in the heat-fixing operation.Nous avons thermofix√© un tissu en polyester √† des temp√©ratures nominales allant de 160 √† 220 ¬ļC. A partir des substrats correspondants, nous avons d√©termin√© la temp√©rature effective, la cristallinit√©, le poids mol√©culaire moyen et sa distribution, le contenu de groupes carboxyliques et d‚Äôoligom√®res superficiels, le degr√© de blancheur et le pourcentage de jaune. Nous avons donc pu √©valuer les changements de cristallinit√© et la migration des oligom√®res √† la p√©riph√©rie de la fibre, ainsi que la redistribution √©ventuelle des poids mol√©culaires et l‚Äôattaque chimique et thermique pendant la thermofixation

    The debate between the students: element of learning knowledge and skills

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    The debate, between different participants, in that there are requested those who they compete for a working place that they defend an idea. There is valued his (her) capacity of persuasion, his (her) fluency of speech, his (her) degree of adequacy to the companions and other aspects. The debate has been prepared for a additive compounds, a subject from Food Technology. The students have defended the positions with valid arguments (the same ones that were in use previously in the exhibition on the part of the professorship on having given these topics). It is a good skill to face up to themes with contradictory scientific information.Peer Reviewe

    Isocyanate toughened pCBT: reactive blending and tensile properties

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    Electronic version of an article published as "Express polymer letters" vol. 7, n¬ļ. 2, February 2013, p. 172-185. Cyclic butylene terephthalate oligomers (CBT) were reacted in a ring-opening polymerization with three types of isocyanates: a bifunctional aromatic type, a bifunctional aliphatic type and a polymeric aromatic isocyanate. All reactions took place in a batch mixer. The use of 0.5 to 1 wt% isocyanate led to a dramatic increase in elongation at break of polymerized cyclic butylene terephthalate (pCBT), from 8 to above 100%. The stiffness and strength of the modified pCBT, however, were found to slightly decrease. Proton nuclear magnetic resonance (NMR) analysis shows that the formation of thermally stable amide groups is the dominant chain extension reaction mechanism. Gel content measurements suggest a linear structure for samples containing bifunctional isocyanates while pCBT modified with polyfunctional isocyanate exhibited some gel formation at higher isocyanate content. Melting and crystallization temperatures as well as degree of crystallinity were found to decrease with increasing isocyanate content. No phase separation was detected by scanning electron microscopy (SEM) analysis. Moreover, a high degree of polymerization is deduced due to the absence of CBT oligomer crystals.Peer ReviewedPostprint (published version

    In vitro validation of biomedical polyester-based scaffolds: Poly(lactide-co-glycolide) as model-case

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    Monitoring and understanding the in vitro behaviour of polyester based scaffolds both comprising the study of the hydrolytic degradation and the cell seeding viability is essential to ensure the desired functionality, according to a given biomedical purpose. As a model case to compare the performance of techniques to monitor the in vitro behaviour, poly(lactide-co-glycolide) (PLGA) scaffolds were chosen. The in vitro hydrolytic degradation of PLGA scaffolds was carried out in water and phosphate buffered saline (PBS). The evolution of the mass loss, the molar mass, the thermal properties and the surface morphology were monitored. The hydrolytic degradation media was correspondingly evaluated by means of the study of the pH, the amount of acid released and the conductivity. In addition, the in vitro biocompatibility regarding the cell culture viability was studied under physiological conditions. The cellular adhesion, cellular ability to proliferate on the scaffold, the scaffold inflammatory profile and the effect of the scaffold degradation compounds on the cells were assessed. A comparative analysis of the exploited techniques in terms of promptness of identification, depth of knowledge, simplicity of obtaining results and cost of the technique was implemented. The results showed that, depending on the balance between the interest in ascertaining the trigger of degradation or deep into the knowledge of the causes and effects of cell culture viability, an appropriate plan of analysis of the validation of polyester-based scaffolds could be designed

    Essential work of fracture of poly(lactic acid) modified by reactive extrusion

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    En este trabajo se han evluado las variaciones en el comportamiento mecánico y a fractura de láminas de 1 mm de espesor de dos grados de P LA con contenidos diferentes de enantiómero D (2 y 4.5 % mol), procesadas mediante extrusión reactiva - caland rado (one - step REX - Calendering). Como agente reactivo se ha empleado un oligo - copolímero de estireno - glicidil - acrilato, el cual promueve durante el procesado reacciones de extensión y/o ramificación de cadenas.. De acuerdo con los parámetros mecánicos a tr acción evaluados, la modificación en la arquitectura molecular obtenida hace disminuir substancialmente la velocidad de envejecimiento físico, provocando los mayores cambios en el PLA con mayor contenido de enantiómero D. En cuanto al comportamiento a frac tura, el término esencial de trabajo específico de fractura (we) no presenta modificaciones sustanciales, pero sí el término no - esencial (bwp) relacionado con la resistencia a la propagación de grieta. En el caso del grado con menor contenido de enantiómer o se observó un aumento, mientras que en el de mayor contenido se observó una clara disminuciónPostprint (published version

    The evolution of the ventilatory ratio is a prognostic factor in mechanically ventilated COVID-19 ARDS patients

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    Background: Mortality due to COVID-19 is high, especially in patients requiring mechanical ventilation. The purpose of the study is to investigate associations between mortality and variables measured during the first three days of mechanical ventilation in patients with COVID-19 intubated at ICU admission. Methods: Multicenter, observational, cohort study includes consecutive patients with COVID-19 admitted to 44 Spanish ICUs between February 25 and July 31, 2020, who required intubation at ICU admission and mechanical ventilation for more than three days. We collected demographic and clinical data prior to admission; information about clinical evolution at days 1 and 3 of mechanical ventilation; and outcomes. Results: Of the 2,095 patients with COVID-19 admitted to the ICU, 1,118 (53.3%) were intubated at day 1 and remained under mechanical ventilation at day three. From days 1 to 3, PaO2/FiO2 increased from 115.6 [80.0-171.2] to 180.0 [135.4-227.9] mmHg and the ventilatory ratio from 1.73 [1.33-2.25] to 1.96 [1.61-2.40]. In-hospital mortality was 38.7%. A higher increase between ICU admission and day 3 in the ventilatory ratio (OR 1.04 [CI 1.01-1.07], p = 0.030) and creatinine levels (OR 1.05 [CI 1.01-1.09], p = 0.005) and a lower increase in platelet counts (OR 0.96 [CI 0.93-1.00], p = 0.037) were independently associated with a higher risk of death. No association between mortality and the PaO2/FiO2 variation was observed (OR 0.99 [CI 0.95 to 1.02], p = 0.47). Conclusions: Higher ventilatory ratio and its increase at day 3 is associated with mortality in patients with COVID-19 receiving mechanical ventilation at ICU admission. No association was found in the PaO2/FiO2 variation
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