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  • Author or Editor: A. Méndez x
  • Chemistry and Chemical Engineering x
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Abstract  

Bisphenol-A polycarbonate (BAPC) was crystallised by exposure to acetone vapours for a period of 9 h; it developed a 20% crystallinity according to WAXS measurements. The samples of semi-crystalline BAPC were then submitted to a series of thermal treatments including annealing, self-nucleation and subsequent isothermal crystallizations. The results showed that the polymer possesses a remarkable crystalline memory and a much faster recrystallization and reorganization capacity (lamellar thickening) than its very low thermal crystallization rate. This peculiar crystallization behaviour probably stems from its rigid backbone molecular structure.

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Abstract

The main objective of the present study is to study the behaviour of sewage sludge and biochar from sewage sludge pyrolysis after addition to soil in a context of a temperate agricultural soil. For this, an incubation experiment was designed during 200 days. Carbon mineralization of soil amended with sewage sludge and biochar at two different rates (4 and 8 wt%) was evaluated. Differential thermal analysis, thermogravimetry and the first derivate of the TG were performed in oxidizing conditions on soil samples before and after incubation. Biochar obtained from sewage sludge pyrolysis at 500 °C was more stable in soil than original sewage sludge. After incubation experiment, the reduction of soil organic matter content was significantly lower in soil amended with biochar than in soil amended with sewage sludge. The thermostability index WL3/WL2 decreases after incubation in soil amended with biochar, however it increases in case of soil treated with sewage sludge.

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Abstract

This study deals with thermal analysis of growing media obtained from mixtures of paper will waste materials (one de-inking paper sludge, HP, and one reject from paper mill producing paper from virgin wood, RT) with sewage sludge. For the growing media formulation, one sewage sludge (L) was mixed with both paper mill waste materials at 10, 20, and 30% in volume. An incubation experiment was designed in order to study their carbon mineralization. Addition of sewage sludge significantly increases the carbon mineralization of growing media based on RT. In case of HP, carbon mineralization increases after addition of sewage sludge in 30% (HP + 30L treatment). Thermogravimetric analysis (TG and DTG) of growing media was performed before and after incubation experiment in order to study the organic matter transformation. The higher the carbon mineralization, the greater the difference between TG curves of samples before and after the incubation. The WL3/WL2 ratio increases after incubation of samples as a result of organic matter stabilisation. For HP growing media, the highest value corresponds to HP + 30L whereas HP + 20L, and HP + 10L show similar values. In case of RT, the WL3/WL2 index shows a progressive increase with sewage sludge content.

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Abstract  

Dielectric experiments are often performed in non-isothermal conditions. Thus, there is a difference between the temperature of the sample and the sensor temperature. In this work we propose and compare three temperature calibration methods based on the detection of transitions or relaxations: i) the melting of high-purity metallic standards (indium and tin), ii) the 2nd order phase transition of a ferroelectric crystal (TGS); iii) the -relaxation of an amorphous polymer (poly(carbonate)). The results obtained from the three different methods were used to construct a calibration curve for a given heating rate.

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Journal of Thermal Analysis and Calorimetry
Authors: F. Fraga, V. Soto, J. Blanco-Méndez, A. Luzardo-Alvarez, E. Rodríguez-Núñez, J. Martínez-Ageitos and M. Pérez

Abstract  

Knowledge of the the kinetic study of chitosan/genipin allow to know the different effects that time and temperature have on the cure reaction of the material. The total enthalpy of reaction, the glass transition temperature and the partial enthalpies have been determined using DSC in dynamic mode. Two models, one based on chemical kinetics and the other accounting for diffusion were used. The incorporation of the diffusion factor in the second model allowed for the cure kinetics to be predicted the whole range of conversion.

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Summary

A stability-indicating liquid chromatographic (LC) method with UV detection was developed for the determination of doripenem in the marketed formulation (Doribax® 500 mg, powder for injection). A forced degradation study was conducted according to available guidelines and main references. Thermal, oxidizing, acidic and basic stress conditions were assayed to show the stability-indicating power of the method. Chromatographic separation was achieved using an isocratic elution method in a reversed-phase system using a mobile phase prepared from phosphate buffer and acetonitrile. Extensive degradation was observed under thermal, oxidative and basic treatment, and the products formed were detected without interference in the analysis of doripenem. To verify the efficiency of chromatographic run, the system suitability was studied. The theoretical plates (N = 5498.3) and tailing factor (tf = 0.951) were constant during repeated injections. The retention time of doripenem was 7.35 min and the method was validated within the concentration range 5–50 μg mL−1 (r = 0.999). Adequate results were obtained that indicate repeatability (RSD % = 1.03–1.37), inter-day precision (RSD % = 0.51) and accuracy. In comparison to spectrophotometric and microbiological methods, statistical analysis showed no significant difference between the obtained results. The proposed method was successfully applied to doripenem quantification, showing it is applicable to determine the antibiotic in the presence of degradation products and also that is a reliable method for routine analysis.

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