Acetone, one of the most important molecules in organic chemistry, also a precursor of prebiotic species, was found in the interstellar medium associated with star-forming environments. The mechanisms proposed to explain the gas phase abundance of interstellar acetone are based on grain mantle chemistry. High energy photons coming from the stellar radiation field of the nearby stars interact with the ice mantles on dust grains leading to photoionization, photodissociation, and photodesorption processes. In this work we investigate the photodesorption and the photostability of pure acetone ices due to soft X-ray impact. Absolute desorption yields per photon impact for the main positive ionic fragments were determined at the O 1s resonance energy (531.4 eV). The photostability of acetone ice was studied by exposure to different irradiation doses with a white beam of synchrotron radiation. The degradation of the ice was monitored by NEXAFS around the O 1s threshold. From this study we determine the photodissociation cross-section to be about 1.5 × 10 −17 cm 2 which allowed us to estimate the half-life for acetone ice in astrophysical environments where soft X-rays play an important role in chemical processes.
Whereas increasing plastic solid waste production constitutes one of the main challenges of modern society, mainly due to the lack of suitable recycling technologies, chemical recycling represents an attractive solution for the conversion of plastic solid waste into valuable chemical intermediates. Herein, a kinetic model for the pyrolysis of a dental industry waste, ethylene glycol dimethacrylate (EGDMA) crosslinked poly (methyl methacrylate) (PMMA), is presented for the first time. Kinetics parameters and their statistical significance have been estimated from eight non-isothermal thermogravimetric analysis (TGA) experiments with heating rates varying between 5 and 50 °C•min-1 by using nonlinear regression. Our analysis indicates that the mechanism of depolymerisation of EGDMA crosslinked PMMA is likely to involve a consecutive reaction pathway involving two steps. The developed kinetic modelcontaining five kinetic parameters only-was able to predict well all non-isothermal TGA runs, and was validated against isothermal TGA experiments at 400 °C.
Core–shell polymer supports with different morphological features and compositions are prepared through combined suspension and emulsion polymerizations. It is shown that proper manipulation of the divinylbenzene (DVB) feed content allows for maximization of specific areas, porosities, and mechanical resistances. Additionally, it is shown that feeding of previously prepared miniemulsions leads to core–shell particles with smaller specific areas, due to less efficient coating of the cores. Particularly, the combined manipulation of polymerization times and DVB feed compositions allows for production of particles with pronounced specific area (50 m2 g−1) and porosity (0.30 cm3 g−1). Produced core–shell polymer particles are employed as supports for the immobilization of lipase B from Candida antarctica, and the obtained enzymatic activities for both hydrolysis (A hyd) and esterification (A est) reactions are very high (A hyd = 34.7 ± 3.8 U/g; A est = 3564.6 ± 581 U/g), even when compared to activities obtained using the reference commercial biocatalyst Novozym 435 (A hyd = 7.6 ± 1.8 U/g, A est = 2384.7 ± 307.2 U/g). Finally, biocatalysts prepared with the core–shell supports present higher enzymatic activities than biocatalysts prepared with supports of higher specific area obtained through conventional emulsion polymerizations, indicating that the porous structure of the shell can be beneficial for the immobilization and activity of the enzymes.
The use of natural polymers has attracted much interest in many different areas, especially in fields where biodegradability and biocompatibility constitute major requirements, as in the pharmaceutical and biomedical areas. For this reason, the present work explores the production of crosslinked starch microparticles in vegetable oil through inverse suspension polymerizations under different experimental conditions, using glucose as a crosslinking agent and manipulating the agitation speed, reaction temperature, starch concentration in the suspended phase, surfactant concentration and crosslinking agent concentration in accordance with a statistical experimental design. Analyzed response variables include morphological aspects, particle size distribution, swelling ratio and solubility in aqueous medium. It is observed that glucose can promote significant modification of the material properties and lead to changes in its solubility in water. Besides, the operation variables exert significant effects on the morphological properties of the obtained powders. For this reason, empirical models are proposed to describe the solubility of the material in water and particle sizes as function of the preparation variables. The results indicate that glucose and starch content are the most influential variables on the solubility of the microparticles in water and that glucose, stirring rate and temperature play the most influential effects on the particle size distributions.
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