Examinando por Autor "Maffi, Juan M."
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Artículo de Publicación Periódica Experimental and theoretical study of the use of multifunctional initiators in the high impact polystyrene bulk process(2018-02) Berkenwald, Emilio; Laganá, María Laura; Maffi, Juan M.; Acuña, Pablo; Morales Balado, Graciela Elizabeth; Estenoz, Diana"The performance of three multifunctional peroxide initiators in a bulk high impact polystyrene (HIPS) process was experimentally and theoretically investigated. For the experimental work, a series of batch reactions was carried out, comprising the main stages of an industrial HIPS bulk process using multifunctional initiators with varying functionality and structure: DEKTP (cyclic trifunctional), PDP (cyclic bifunctional) and L331 (linear bifunctional). The theoretical work consisted of the development of a comprehensive, generic yet detailed mathematical model for bulk HIPS polymerization using multifunctional initiators. The model predicts the evolution of the main polymerization variables (including conversion, molecular weights, grafting efficiency) as well as the detailed molecular structure of the polymeric species (free polystyrene, residual polybutadiene and graft copolymer), and the melt flow index of the obtained HIPS. The model was adjusted and validated using experimental results, obtaining a good agreement between measured and predicted values. The model was used to theoretically evaluate the effect of the operating conditions on the molecular and physical characteristics of the obtained polymer. It was found that the use of multifunctional initiators leads to high polymerization rates and high molecular weights simultaneously, while promoting the grafting of styrene onto butadiene, generating a microstructure with salami-type morphologies."Póster Fluid dynamics of the phase inversion process in the bulk polymerization of high impact polystyrene(2021) Maffi, Juan M.; Estenoz, Diana"In the synthesis of HIPS, phase inversion (PI) is the critical point at which a dispersed PS-rich phase becomes a continuous matrix, leaving behind a PB-rich phase as dispersed particles that may contain occluded PS-rich droplets inside (occlusions). The size and shape of these particles essentially determine the mechanical properties of the material, which makes PI a critical point during the reaction. In this work, the most popular mechanism for PI – an imbalance between coalescence and break-up of dispersed particles – is assessed through a population balance model, coupled with a heterogeneous polymerization model. Results are adjusted and discussed with experimental evidence gathered from TEM images."Artículo de Publicación Periódica Mechanisms and conditions that affect phase inversion processes. A review.(2020-07) Maffi, Juan M.; Meira, Gregorio R.; Estenoz, Diana"The phenomenon of phase inversion occurs in liquid-liquid dispersions found in a variety of chemical engineering fields. From simple oil-water mixtures to complex polymeric systems, the operating variables that affect this physical phenomenon are discussed in this work. The contribution on this matter by a large number of researchers is critically assessed, outlining both coherent and conflicting results. A detailed review of the mechanisms by which phase inversion takes place is also provided. While this subject has been studied for the past fifty years, this multivariate nonlinear process is not yet comprehensively understood, and this review article aims to describe the conclusions so far reached to provide insight for future research."Artículo de Publicación Periódica Mechanisms and conditions that affect phase inversion processes. The case of high-impact polystyrene(2019) Maffi, Juan M.; Casis, Natalia; Acuña, Pablo; Morales Balado, Graciela Elizabeth; Estenoz, Diana"The phase inversion during the bulk polymerization of the styrene-polybutadiene system (HIPS manufacturing process) is empirically and theoretically studied in this article. In the experimental work, a series of reactions were performed with benzoyl peroxide as initiator and at temperatures considered of industrial interest (80ºC and 90ºC), varying also the reactor stirring level. Phase inversion was determined by offline viscosity measurements and verified by scanning electron micrography in transmission mode (STEM). The rheological behavior of each reacting system was analyzed and an empirical correlation to predict its apparent viscosity from fundamental reaction parameters was derived. This was achieved successfully for bothbefore and after the phase inversion point."Artículo de Publicación Periódica On the evolution of particle size distributions during the bulk synthesis of high-impact polystyrene using PBM: Towards morphology and phase inversion prediction(2022-01-16) Maffi, Juan M.; Estenoz, Diana"The mechanism of the phase inversion (PI) process that occurs during the bulk polymerization of High Impact Polystyrene (HIPS) is studied in this article. Transmission electron micrographs (TEM) were obtained for different operating conditions, varying initiator concentration, temperature, and stirring speed from a previous work. Particle size distributions were retrieved from such micrographs, and were compared to theoretical predictions. To this end, a population balance model, coupled with a heterogeneous polymerization module, was developed. The evolution of particle growth, break-up and coalescence is discussed to assess the breakage/coalescence imbalance that is thought to occur at the inversion point. Results indicate that a different criterion for PI seems to be needed in this system."Artículo de Publicación Periódica On the use of espina corona gum as a polymeric additive in water-based drilling fluid(2022-10) Villada, Yurany; Taverna, María Eugenia; Maffi, Juan M.; Giletta, Sebastián; Casis, Natalia; Estenoz, Diana"The aim of this work is to evaluate the espina corona gum (ECG) as a sustainable viscosifier or filtration reducer additive in water-based drilling fluids (WBMs) as a potential replacement of guar gum (GG). ECG is a galactomannan isolated from leguminous seeds of Gleditsia amorphoides, trees that grow in South America with viscosifier properties and applications in the food area. ECG was characterized by FTIR, Z potential, intrinsic viscometry, TGA, and steady and oscillatory shear rheological analysis. Moreover, its effect on the main functional properties of WBMs was studied. Fluids containing bentonite (BT), polyanionic cellulose (PAC), GG or ECG were prepared, and rheological, filtration, thermal and structural properties were determined. In order to study the theoretical rheological behavior, several models such as power law, Sisko and Herschel-Bulkley were evaluated. The rheological studies revealed that WBMs containing ECG exhibit higher viscosities in comparison with those with GG. Herschel-Bulkley parameters indicated that the WBMs with high ECG concentration showed higher yield stress. In addition, the presence of ECG improves the thermal stability and filtration properties. The results indicate that ECG can be considered as an innovative, renewable and non-toxic alternative to partially or totally replace GG in WBMs."Póster Phase inversion prediction during the bulk synthesis of high-impact polystyrene: a fluid-dynamic approach(2021-11) Maffi, Juan M.; Estenoz, Diana"High-Impact Polystyrene (HIPS) is a heterogeneous material constituted by a rubber (PB) particles dispersed in a vitreous polystyrene (PS) matrix. Two typical morphologies are usually identified: ‘salami’ (larger rubber particle with several PS occlusions) or ‘core-shell’ (smaller particle with one large occlusion). The industrial continuous bulk HIPS process involves four main stages: dissolution, pre-polymerization, finishing and evolatilization. During the pre-polymerization, the mixture consists of a continuous PB-rich phase where PS-rich droplets grow as the reaction proceeds. At a critical point, the dispersed vitreous phase reaches a volume such that it becomes the continuous phase, through a co-continuous transition. This is the phase inversion (PI) point, and the material morphology is essentially defined at this stage, characterized by a sudden drop in the mixture’s apparent viscosity."Artículo de Publicación Periódica Predicting phase inversion in agitated dispersions with machine learning algorithms(2020-09) Maffi, Juan M.; Estenoz, Diana"In agitated systems, the phase inversion (PI) phenomenon – the mechanism by which a dispersed phase becomes the continuous one – has been studied extensively in an empirical manner and few models have been put forward through the years. The underlying physics are still to be fully understood. In this work, the experimental evidence published in literature is used to train machine learning models that may infer the inherent rules that lead to a given dispersion type (O/W or W/O), as well as predict the value of the dispersed phase volume fraction at the edge of the inversion point. Decision trees, bagged decision trees, support-vector machines and multiple perceptrons are implemented and compared. Results show that it is possible to infer an ensemble of physical rules that explain why a given dispersion is O/W or W/O, where a strong “turbulence constraint” is identified. The intuitive rule that PI occurs at 50% dispersed phase almost never holds. Moreover, neural networks have shown a better performance at predicting the PI point than the other algorithms tested. Finally, a theoretical study is performed in an effort to produce a phase inversion map with the relevant operating variables. This study showed a strong non-linear effect of the impeller-to-vessel size ratio, and an asymmetrical behavior of the interfacial tension on the phase inversion points."Artículo de Publicación Periódica Preparation and characterization of nanoencapsulated synthetic soybean oil derivative-an abundant and environmentally friendly phase change material-heat transfer analysis and applications(2020-10) Bergamo, Jorge; Rossi, Ezequiel; Maffi, Juan M.; De Angelis, Laura; Errea, María Inés"The thermal properties of a phase change material (PCM), together with its environmental health risks and natural abundance are important aspects to consider when choosing one for a domestic application. In this work, a soybean oil derivative, which comes from one of the most abundant crops on Earth, is proposed as PCM. A heat transfer model was developed to compare the performance of the proposed PCM, under the same boundary and initial conditions, with other materials reported in literature that have well-known disadvantages in terms of flammability, renewability, abundance and environmental care. Results showed that its performance was as good as theirs. Nanocapsules of the PCM coated with TiO2 were prepared and characterized physical, thermal and morphologically. Thermal studies were carried out in a device designed and constructed simulating a water heater, and a reduction of about 70% of the PCM phase thermal resistance due to the TiO2 shell was observed. Furthermore, the calculated thermal energy stored in the device filled with nanoencapsulated PCM was 10.6% higher with respect to the blank, and the total cooling time of the water was increased by over 18% thanks to the PCM."Artículo de Publicación Periódica The organic chemistry behind the recycling of poly(bisphenol-A carbonate) for the preparation of chemical precursors: A review(2022-07) Gilbert, E.; Polo, Mara Lis; Maffi, Juan M.; Guastavino, Javier Fernando; Vaillard, Santiago Eduardo; Estenoz, Diana"Production and consumption of poly(bisphenol-A carbonate) resins are seeing a worldwide increase. However, their usage lifetimes are short and their final disposition as landfills pose environmental and health risks, due to the release of toxic bisphenol-A (BPA). The development of alternative recycling routes is thus becoming subject of increasing interest. In this review, the main recycling processes of poly(bisphenol-A carbonate) are described and critically compared, with special focus on the chemical mechanisms. While mechanical recycling is possible, the end products are restricted only to polymer blends, whose main mechanical properties decrease with each compounding cycle. In turn, chemical recycling can produce BPA monomer and a variety of byproducts that can be used in different industries, including the polymeric field, as synthesis reagents and precursors. The operation conditions of each method are reviewed, as well as the different results obtained in terms of product yield, composition, selectivity and reaction times. Reaction mechanisms are described in detail and a view on the usability of each end product is offered."Tesis de doctorado Theoretical and experimental study on the phase inversion process during the bulk synthesis of high impact polystyrene(2021-03-26) Maffi, Juan M.; Estenoz, Diana; Berkenwald, Emilio"In this thesis, the phenomenon of phase inversion is studied from a qualitative, theoretical and experimental point of view. The general objective is to contribute to the understanding of this fuid- and thermodynamic phenomenon in its particular application in the case of HIPS. The aim is to develop a physical-mathematical model capable of predicting the point of phase inversion during the reaction from the reactor conditions. Among the different alternatives, approaches based on the rheological evolution of the reaction mixture and others based on the fuid dynamics of the dispersed system are explored."