Crystallization kinetics of a commercial poly(lactic acid) based on characteristic crystallization time and optimal crystallization temperature

This version of the article has been accepted for publication, after peer review and is subject to Springer Nature’s AM terms of use, but is not the Version of Record and does not reflect post-acceptance improvements, or any corrections. The Version of Record is available online at: https://doi.org/10.1007/s10973-020-10081-7[Abstract]: A model is proposed to fit differential scanning calorimetry (DSC) isothermal crystallization curves obtained from the molten state at different temperatures. A commercial 3D printing polylactic acid (PLA) sample is used to test the method. All DSC curves are fitted by a mixture of two simultaneous functions, one of them being a time derivative generalized logistic accounting for the exothermic effect and the other, a generalized logistic, accounting for the baseline. There is a rate parameter, which is allowed to vary across different temperatures. The rate parameter values obtained at different temperatures were jointly explained as a result of three crystallization processes, each one defined by a characteristic crystallization time, a characteristic temperature, and a dispersion or width factor. Apart from the very good fittings obtained at all temperatures, the results agree with the existence of a few crystal forms of PLA, which were demonstrated by other authors. Thus, the main significance of this work consists in providing a new approach in order to mathematically describe the isothermal crystallization kinetics of a polymer from the melt. Such a kinetic description is needed in order to predict the extent of a crystallization process as a function of time at any isothermal temperature. The approach used here allows to understand the overall crystallization of the PLA used in this work as the sum of three crystallization processes, each of them corresponding to a different crystal form. Each experimental crystallization exotherm, which may include more than one crystal form, can be reproduced by a generalized logistic function. The overall rate factor at a given temperature is the weighted sum of the rate factors of the different crystal structures at that temperature. The rate factor of each of these three processes is described by a Gaussian function whose parameters are a crystallization time, a characteristic temperature and a temperature dispersion factor. Therefore, the crystallization rate for each crystal form can be interpreted as a relative likelihood to crystallize at a given temperature. On the other hand, the characteristic crystallization time parameter refers to the time needed for a given crystal structure to be formed at the temperature at which the relative likelihood to crystallize of that form is highestThis research has been supported by the Spanish Ministry of Science and Innovation, MINECO Grant MTM2017–82724-

Thermal behavior and antibacterial studies of a carbonate Mg–Al-based layered double hydroxide (LDH) for in vivo uses

The goal of this work is to study the thermal behavior and the antibacterial properties of a MgAl-CO3 layered double hydroxide (LDH), which demonstrated high efficiency in removing chromium (VI) from contaminated industrial wastewater. The compound has been synthesized via co-precipitation route (direct method) followed by hydrothermal treatment, obtaining nanoscopic crystallites with a partially disordered (turbostratic) structure. After its synthesis, the compound was characterized by means of X-ray powder diffraction, field emission scanning electron microscope, inductively coupled plasma atomic emission spectroscopy and analysis and Fourier transform infrared spectroscopy. On the other hand, with the view to check the drug delivery and surgical tools usage of MgAl-CO3, antibacterial tests, performed according to the Kirby–Bauer method, revealed the inability the growth of the pathogenic bacterial strains. Thermogravimetry and differential thermal analysis revealed that evolution of water from the material occurs in two stages upon heating and a noticeable interaction takes place between water (in the vapor phase) and MgAl-CO3. Kinetic analysis of both steps provides almost constant values of activation energy, with the following average values in the range 0.1 < a < 0.9: E1 = (66 ± 9) kJ mol‒1; E2 = (106 ± 7) kJ mol‒1. Finally, prediction of reasonable reaction times extrapolated at 25 and 37 °C has been made from kinetic parameters of the first step, while almost unrealistic reaction time values were determined using the same procedure with kinetic parameters related to the second step

Multi-technique characterization and thermal degradation study of epoxy modified resins designed for multifunctional applications

Tetraglycidyl methylene dianiline (TGMDA) was mixed with 1,4-Butanediol diglycidyl ether (BDE) (in a 4:1 mass ratio) and with a stoichiometric amount of the curing agent diaminodiphenyl sulfone which was solubilized at 120 °C for 20 min in the liquid mixture TGMDA + BDE. The so obtained unfilled epoxy resin matrix, denoted as ER, was blended with glycidyl polyhedral oligomeric silsesquioxane and carbon nanotubes in suitable proportions to obtain binary and ternary mixtures. Characterization of the formulated materials was performed using different experimental techniques, such as Dynamic mechanical analysis, Thermogravimetry (TG), Field emission scanning electron microscopy. Furthermore, the investigation of the flame behavior was carried out by the limiting oxygen index and mass loss calorimeter measurements. Direct current measurements and investigation by Tunneling atomic force microscopy of the conductive nanodomain map allowed the evaluation of the electrical properties of the developed nanofilled systems. The TG data related to thermal decomposition of ER and its binary and ternary mixtures were processed according to isoconversional kinetic analysis by assuming a non-Arrhenian behavior of the temperature function, and lifetime prediction was estimated at suitable relatively low temperatures and possible relation between the thermal stability and the presence of each component was discussed. This method of kinetic analysis paves the way for the possibility of evaluating in a more realistic way, on the basis of thermal stability, the potential application of structural resins with primary load functions in contact with hot areas of aeronautical aircraft engines