DSpace Repository :: Browsing by Author "Estenoz, Diana"

Browsing by Author "Estenoz, Diana"

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Bulk polymerization of styrene using multifunctional initiators in a batch reactor: A comprehensive mathematical model
(2016-02) Berkenwald, Emilio; Laganá, María Laura; Acuña, Pablo; Morales Balado, Graciela Elizabeth; Estenoz, Diana
"A detailed, comprehensive mathematical model for bulk polymerization of styrene using multifunctional initiators - both linear and cyclic - in a batch reactor was developed. The model is based on a kinetic mechanism that considers thermal initiation and chemical initiation by sequential decomposition of labile groups, propagation, transfer to monomer, termination by combination and re-initiation reactions due to undecomposed labile groups. The model predicts the evolution of global reaction variables (e.g, concentration of reagents, products, radical species and labile groups) as well as the evolution of the detailed complete polymer molecular weight distributions, with polymer species characterized by chain length and number of undecomposed labile groups. The mathematical model was adjusted and validated using experimental data for various peroxide-type multifunctional initiators: diethyl ketone triperoxide (DEKTP, cyclic trifunctional), pinacolone diperoxide (PDP, cyclic bifunctional) and 1,1-bis(tert-butylperoxy)cyclohexane (L331, linear bifunctional). The model very adequately predicts polymerization rates and complete molecular weight distributions. The model is used to theoretically evaluate the influence of initiator structure and functionality as well as reaction conditions."
Cellulose nanoﬁbrils as a replacement for xanthan gum (XGD) in water based muds (WBMs) to be used in shale formations
(2018-12) Villada, Yurany; Iglesias, María Celeste; Casis, Natalia; Erdmann, Eleonora; Peresin, María Soledad; Estenoz, Diana
"In this work, the potential replacement of xanthan gum (XGD) by cellulose nanofibrils in the composition of water based muds (WBMs) was studied. Bleached (B-CNF) and unbleached (L-CNF) cellulose nanofibrils, mainly differentiated by their lignin content, were tested and their performances were compared with that of XGD. The effects of cellulose nanofibrils on the rheological and filtration properties of WBMs were investigated. Rheometric analysis showed a shear-thinning behavior more noticeable for fluids containing B-CNF and XGD, while filtration properties were improved using L-CNF. The Sisko model was used to determine rheological parameters. Finally, it was found that by replacing XGD by double concentration of L-CNF in a WBM for Argentina shale, similar rheological properties were obtained. Structural changes were assessed by using Scanning Electron Microscopy (SEM). Particles agglomeration and good film formability were observed. Furthermore, WBMs with lignin-containing cellulose nanofibrils exhibited a better thermal stability after aging."
Curing process of benzoxazine systems. An experimental and theoretical study
(2019-09) Gilbert, E.; Forchetti, A.; Pesoa, Juan I.; Berkenwald, Emilio; Spontón, Marisa E.; Estenoz, Diana
"A mathematical model that simulates the curing process of benzoxazine (Bz) systems is presented. The model predicts the conversion, gel point and Tg along the curing process, and considers the diffusional limitations to mass transfer due to the increase in the system viscosity along the process. This model can be used to select an appropriate combination of time and temperature in order to obtain a material with pre-specified properties. The theoretical parameters were adjusted with experimental data: conversion, weight-average molecular weight, weight fraction of solubles and Tg. The Bz based on bisphenol A and aniline (BzBA) was used to adjust the model. The curing kinetic of this Bz was followed by FTIR, SEC and DSC, considering five different curing conditions. A very good agreement between experimental and simulated values was observed, even when curing is carried out under different temperatures profiles."
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."
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."
Functional characterization on colloidal suspensions containing xanthan gum (XGD) and polyanionic cellulose (PAC) used in drilling fluids for a shale formation
(2016) Villada, Yurany; Gallardo, Felipe Eusebio; Erdmann, Eleonora; Casis, Natalia; Olivares, Laura; Estenoz, Diana
"Drilling fluids are employed in the operation of hydrocarbon exploitation. Two kinds of drilling fluids are commonly used: water based muds and oil based muds. The oil based muds are characterized by their high performance in unconventional reservoirs due to the very low interaction with the reactive formation. Their environmental impact promotes the design of water based muds that present low toxicity. In this paper a water based mud for shale formation with similar rheological characteristics to the oil based mud used in the oil industry of Argentina was designed and the effect of xanthan gum and polyanionic cellulose on the main functional characteristics was studied. Rheometric analysis showed a shear-thinning behavior with notable effect on the concentration of polymers. After dynamic aging test, fluids with composition of PAC=8.00 g/L and XGD =3.00 g/L exhibited rheological properties very close to oil base mud. Structural changes were assessed from optical microscopy and scanning electron microscopy. Particles agglomeration due to the presence of polymers was observed. Furthermore, mud filtration essays allowed to evaluate the performance of PAC as control agent. The Carreau model and statistical analysis were used to determine rheological parameters."
Homogeneous hydrolytic degradation of poly(lactic-co-glycolic acid) microspheres: Mathematical modeling
(2015-12) Busatto, Carlos; Berkenwald, Emilio; Nicolás, Mariano; Casis, Natalia; Luna, Julio; Estenoz, Diana
"The homogeneous hydrolytic degradation of poly(lactic-co-glycolic acid) (PLGA) microspheres was investigated. A mathematical model was developed that estimates the evolutions of ester bonds concentrations and average molecular weights along the degradation process. The model is based on a detailed kinetic mechanism that includes the hydrolysis of the different types of ester bonds by random chain scission and considers the effect of polymer chemical composition and molecular structure. Novel and published experimental data were used to adjust and validate the model. The experimental work consisted of homogeneous hydrolytic degradation of PLGA microspheres. The predictions are in very good agreement with the experimental results."
Mathematical modeling of discontinuous bulk styrene polymerization processes using multifunctional initiators
(2016) Berkenwald, Emilio; Estenoz, Diana; Marqués, Dardo
"En esta tesis, se estudia el uso de iniciadores multifuncionales para la polimerización en masa de estireno. El objetivo general es desarrollar modelos matemáticos detallados, y a la vez genéricos, que permitan describir la compleja fisicoquímica de estos procesos y predecir las variables principales de polimerizacióon, la evolución de la estructura molecular y las caracteríticas físicas del producto obtenido. La labor teórica se complementa con trabajos experimentales que permiten ajustar y validar los modelos propuestos."
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."
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."
New advances in the mathematical modeling of the continuous bulk process for the production of high-impact polystyrene using multifunctional initiators
(2019-03) Laganá, María Laura; Berkenwald, Emilio; Acuña, Pablo; Enríquez Medrano, Javier; Morales Balado, Graciela Elizabeth; Estenoz, Diana
"New advances in the mathematical modeling of the bulk continuous high-impact polystyrene (HIPS) process are presented. The model consists of three modules that allow the simulation of: (1) a polymerization reactor train, (2) a devolatilization (DV) stage, and (3) structure–properties relationships. The model is based on a kinetic mechanism that includes thermal initiation, chemical initiation by sequential decomposition of a multifunctional initiator, propagation, transfer to monomer, transfer to rubber, termination by combination and re-initiation, as well as high temperature crosslinking and oligomer generation reactions. The present model is comprehensive from a kinetic perspective, since it can be used to simulate a HIPS process using initiators of any functionality and structure. The model is adjusted and validated using previously unpublished experimental data for bulk continuous HIPS polymerization in a pilot-scale plant. The experimental work includes a series of polymerizations using three different multifunctional initiators: (1) luperox-331 M80 (L331), (2) pinacolone diperoxide, and (3) diethyl ketone triperoxide. The pilot plant comprised the main stages of an industrial HIPS process: prepolymerization, finishing and DV. Theoretical results show a good agreement with the experimental measurements".
Nuevos desarrollos en el modelado matemático del proceso continuo para la producción en masa de polímeros de estireno en presencia de elastómeros =
(2022-07) Laganá, María Laura; Estenoz, Diana; Stripeikis, Jorge
"El objetivo general de esta tesis es investigar aspectos aún no dilucidados en el área de la ingeniería del proceso de polimerización en masa de estireno (St) en presencia de elastómeros para la producción de Poliestireno de alto impacto (HIPS). La investigación se enfoca en el entendimiento y modelado matemático de los fenómenos fisicoquímicos involucrados, en el estudio y empleo de nuevas técnicas de modelado para la simulación de sistemas complejos, y en la optimización de los procesos. Se pretende lograr desarrollos que contribuyan a diseñar y operar los procesos industriales continuos con alto grado de comprensión, y optimizados desde el punto de vista de la productividad y de la calidad del producto final."
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."
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."
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."
Polymeric Membranes from Colloidal Templates with Tunable Morphology
(2010-07) Casis, Natalia; Ravaine, Serge; Reculusa, Stéphane; Colvin, Vicki L.; Wiesner, Mark R.; Estenoz, Diana; Fidalgo de Cortalezzi, María Marta
"Polymeric porous membranes were fabricated from templates made from silica particles. The templates were obtained by self-assembly and by the Langmuir-Blodgett (L-B) technique. For the self-assembly technique, suspensions of silica particles in ethanol were used to create the deposits. L-B deposition was employed to produce templates of different particle sizes for the fabrication of asymmetric membranes. Two different polymers were tested to fabricate membranes: polystyrene (PS) and the diethyleneglycol dimethacrylate (DEGDMA)/urethane dimethacrylate (UDMA) copolymer. Templates and porous films were observed by SEM in order to analyze the pore morphology. Permeability of the poly(DEGDMA/UDMA) films was comparable to commercially available membranes. Proposed applications for these ordered porous structures include, sensors, filters, and catalytic materials."
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."
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."
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."

Browsing by Author "Estenoz, Diana"

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