Biofuels production and utilisation can reduce the emission of greenhouse gases, dependence on fossil fuels and also improve energy security. Ethanol is the most important biofuel in the transportation sector; however, its production from lignocelluloses faces some challenges. Conventionally, lignocellulosic hydrolysis and fermentation has mostly been performed by separate hydrolysis and fermentation (SHF) or simultaneous saccharification and fermentation (SSF). SHF results in product inhibition during enzymatic hydrolysis and increased contamination risk. During SSF, suboptimal conditions are used and the fermenting organism cannot be reused. Bacterial contamination is another major concern in ethanol production, which usually results in low ethanol yield. In these studies, the above-mentioned challenges have been addressed. A novel method for lignocellulosic ethanol production ‘Simultaneous saccharification filtration and fermentation (SSFF)’ was developed. It circumvents the disadvantages of SSF and SHF; specifically, it uses a membrane for filtration and allows both the hydrolysis and fermentation to be carried out at different optimum conditions. SSFF also offers the possibility of cell reuse for several cultivations. The method was initially applied to pretreated spruce, with a flocculating strain of yeast Saccharomyces cerevisiae. SSFF was further developed and applied to pretreated wheat straw, a xylose rich lignocellulosic material, using encapsulated xylose fermenting strain of S. cerevisiae. High solids loading of 12% suspended solids (SS) was used to combat bacterial contamination and improve ethanol yield. Oil palm empty fruit bunch (OPEFB) was pretreated with fungal and phosphoric acid in order to improve its ethanol yield. An evaluation of biofuel production in Nigeria was also carried out. SSFF resulted in ethanol yield of 85% of the theoretical yield from pretreated spruce with the flocculating strain. Combination of SSFF with encapsulated xylose fermenting strain facilitated simultaneous glucose and xylose utilisation when applied to pretreated wheat straw; this resulted in complete glucose consumption and 80% xylose utilisation and consequently, 90% ethanol yield of the theoretical level. High solids loading of 12% SS of pretreated birch resulted in 47.2 g/L ethanol concentration and kept bacterial infection under control; only 2.9 g/L of lactic acid was produced at the end of fermentation, which lasted for 160 h while high lactic acid concentrations of 42.6 g/L and 35.5 g/L were produced from 10% SS and 8% SS, respectively. Phosphoric acid pretreatment as well as combination of fungal and phosphoric pretreatment improved the ethanol yield of raw OPEFB from 15% to 89% and 63% of the theoretical value, respectively. In conclusion, these studies show that SSFF can potentially replace the conventional methods of lignocellulosic ethanol production and that high solids loading can be used to suppress bacterial infections during ethanol productions, as well as that phosphoric acid pretreatment can improve ethanol yield from lignocellulosic biomass. / <p>Thesis for the degree of Doctor of Philosophy at the University of Borås to be publicly defended on 31 October 2014, 10.00 a. m. in room E310, University of Borås, Allégatan 1, Borås.</p>

Many aspects associated with conversion of lignocellulose to biofuels and other valuable products have been investigated to develop the most effective processes for biorefineries. The goal of this research was to improve the efficiency and effectiveness of the lignocellulose conversion process by achieving a more basic understanding of pretreatment and enzymatic hydrolysis at high solids, including kinetic modeling and separation and recovery of glucose. Effects of NaOH pretreatment conditions on saccharide yields from enzymatic hydrolysis were characterized in low- and high-solids systems. Factors associated with pretreatment and hydrolysis were investigated, including duration of pretreatment at different temperatures and NaOH loadings, as well as different solids and enzyme loadings. Under relatively mild pretreatment conditions, corn stover composition was essentially equivalent for all time and temperature combinations; however, components were likely affected by pretreatment, as differences in subsequent cellulose conversions were observed. Flushing the hydrolyzate and reusing the substrate was also studied as a method for inhibitor mitigation while increasing overall glucose yields. Flushing the PCS throughout the hydrolysis reaction eliminated the need to wash the pretreated biomass prior to enzymatic hydrolysis when supplementing with low doses of enzyme, thus reducing the amount of process water required. The robustness of an established kinetic model was examined for heterogeneous hydrolysis reactions in high-solids systems. Michaelis-Menten kinetics is the traditional approach to modeling enzymatic hydrolysis; however, high-solids reactions violate the main underlying assumption of the equation: that the reaction is homogeneous in nature. The ability to accurately predict product yields from enzymatic hydrolysis in high-solids systems will aid in optimizing the conversion process. Molecularly-imprinted materials were studied for use in both bulk adsorption and in column chromatography separations. Glucose-imprinted materials selectively adsorbed glucose compared xylose by nearly 4:1. Non-imprinted materials were neither selective in the type of sugar adsorbed, nor were they capable of adsorbing sugar at as high a capacity as the glucose-imprinted materials. Liquid chromatography with imprinted materials was not a suitable means for separating glucose from solution under the conditions investigated; however, many factors impact the effectiveness of such a separation process and warrant further investigation.

Lignocellulosic biomass pretreatment is a fundamental step in the production of renewable fuels and chemicals. It is responsible for the disruption and removal of lignin and hemicellulose from the lignocellulosic matrix, improving the enzymatic hydrolysis of cellulose. Alkaline pretreatment has been shown to be successful on agricultural residues and dedicated energy crops. The objective of this study was to evaluate the pretreatment of switchgrass, wheat straw, corn stover, and miscanthus using calcium hydroxide, potassium hydroxide, and sodium hydroxide at the same hydroxyl concentration, 60% moisture content, and two temperatures for seven days. Enzymatic hydrolysis was also performed and the glucose produced measured. The composition of cellulose, hemicellulose, and lignin before and after pretreatment were quantified according to the standard procedures developed by the NREL for biomass. The hydrolysis was performed at 50°C and 150 rpm. The enzyme loading was 60 FPU/g cellulose. Overall, calcium hydroxide pretreatment resulted in the lowest delignification and structural carbohydrates after pretreatment, as well as lowest glucose yield; In addition to having a higher cost and carbon dioxide emission then sodium and potassium hydroxides. Sodium hydroxide and potassium hydroxide had similar performance in terms of composition changes due to pretreatment and glucose yield after enzymatic hydrolysis.

Additive manufacturing (AM) is a form of production that directly processes raw materials into their final form by building the product in a layer-by-layer fashion. Numerous types of AM exist, including selective laser sintering (SLS) of polymeric powders, vat polymerization (VP) of low viscosity photocurable resins, and material extrusion (MatEx) of thermoplastic or high viscosity composite materials. Because of its ability to reduce material waste while printing complex geometries, AM has the potential to revolutionize the manufacturing industry for a diverse set of materials and products. MatEx of thermoplastic feedstocks is most commonly performed using fused filament fabrication (FFF) – a form of melt extrusion. A solid filament is fed directly into a heated nozzle, where it melts onto a build bed before resolidifying in a matter of seconds. While this is the most common form of AM, especially among hobbyists, the material catalog is limited to thermoplastic polymers, and difficulties arise when fillers are introduced (e.g. reactions at elevated temperatures, clogging, disruption of polymer chain diffusion, and large increases in viscoelastic properties). To combat these challenges, direct ink write (DIW) AM extrudes highly viscous composites by applying pneumatic backpressure to a syringe, such that the material can be extruded in ambient conditions. This method enables processing of unreacted, thermosetting resins which have been filled with a large proportion of solid particulate fillers, called "highly filled" inks. The interparticle network formed from particle-particle interactions in the form of weak surface forces (e.g. Van der Waals forces) provides structural stability of the printed lines, such that they can sustain the weight of subsequent layers. In the realm of DIW 3D printing material discovery and processing, there are currently three major challenges. First, the high shear region of the nozzle frequently disrupts the interparticle network through a de-agglomeration process, such that there is a finite timescale for the interparticle network to reestablish itself. During this timeframe, the deformation/reformation process causes printed lines to sag, which negatively impacts both print quality and mechanical properties. Second, printed parts require a post-processing step to develop adequate mechanical properties suitable for the final product. The kinetics of this cure process are extremely slow, often taking multiple days or weeks to reach completion. Third, high shear rheological characterization of highly filled inks is challenging because of the numerous artifacts of error associated with high shear testing environments (e.g. sample loss/edge fracture, slip, and large sample size requirements). A literature review in Chapter 2 outlines the most recent advances in highly filled polyurethane processing for DIW, with a particular focus on how interparticle network recovery – in the form of thixotropy – can be tailored using a variety of reactive inks. The subsequent chapters of this dissertation address these challenges by systematically downselecting reactive inks appropriate for highly filled DIW extrusion while introducing numerous process relevant rheological protocols. An initial discussion in Chapter 3 covers the potential drawbacks of thermoplastic polyurethane (TPU) processing as it relates to industrial scale melt extrusion. Specifically, multiple side reactions and degradation processes are identified for a variety of TPU manufacturers. Such reactions elicit undesirable solid-like particulate buildup within the extrusion line, and the impacts/causes of these reactions are quantified using rheological criteria. These protocols offer evidence that differences in processability can arise not just between manufacturers, but also between lots of TPU from the same manufacturer. To address these concerns, Chapter 4 offers an alternative form of polyurethane processing in the form of a thermosetting reaction between hydroxyl-terminated polybutadiene (HTPB) and isophorone diisocyanate (IPDI). When uncatalyzed at room temperature, full conversion takes place over the course of multiple weeks which necessitates an accelerated kinetic analysis. Hence, a combination of chemorheological and spectroscopic methods are used to rapidly probe for changes in isocyanate reactivity using limited sample quantities, which substantiate the advantages and disadvantages of chemorheology and spectroscopy in the context of curing studies. While this synthetic pathway provides mechanical properties appropriate for the final printed product, a major concern is retention of green body strength post deposition. In order to maintain the shape of printed beads, ultraviolet (UV) light can be shined in-situ onto the nozzle of a DIW printhead, which actively cures the urethane acrylate ink through free radical polymerization. This technique, termed UV-assisted direct ink write (UV-DIW), assists recovery of the interparticle network. A novel rheological method proposed in Chapter 5, termed the "UV-assisted three interval thixotropy test" (UV-3ITT), quantifies the contribution of UV light towards structural stability and printability. This is accomplished by applying stepwise changes in strain on a torsional photorheometer, optionally applying UV light in the third interval, and then quantifying the contribution of UV light towards process-relevant recovery parameters. Resultingly, the threshold of solid particulate fillers required for UV light to improve print fidelity is determined. While most discussions revolve around torsional rheology, this method has one major drawback: it cannot probe the high shear properties of high solids content materials due to sample loss/edge fracture during steady shear measurement. Capillary rheometers are able to probe the viscosity profiles of highly filled materials in high shear environments, but the cost of the device and the sample requirements are burdensome. To resolve this challenge, the "microcapillary rheometer" is developed in Chapter 6 using common laboratory equipment at a fraction of the cost of a full-scale capillary rheometer, which enables rapid characterization of high solids content materials at extrusion-relevant conditions while exploiting small sample quantities. This study illustrates the accuracy and precision of the microcapillary rheometer when comparing the high shear properties of several highly filled systems to the full-scale capillary rheometer. Results highlight that application of the Bagley and Weissenberg-Rabinowitsch corrections is possible using this novel device, which facilitates calculation of true shear viscosity of high solids content systems. The limited sample requirement facilitates characterization of novel or potentially hazardous materials in a much safer, efficient manner, which accelerates material discovery while improving safety standards. / Doctor of Philosophy / Subtractive manufacturing technologies, which reduce raw materials down from their bulk state into a final product, make up a significant portion of the manufacturing sector today due to the convenience and ease of material processing. Some of the most common forms of subtractive manufacturing include lathing, milling, cutting, drilling, and grinding; these methods are applicable for a diverse set of materials ranging from metals to plastics. By the nature of this process, subtractive manufacturing yields substantial material waste, while limiting the complexity of a final product's design. To combat these unintended consequences, a novel form of production termed additive manufacturing (AM) has grown dramatically in the past several decades. AM directly processes raw materials into their final form which reduces material waste while enabling complex geometries to be "printed." Although there are numerous types of additive manufacturing, the most common forms utilize material extrusion, whereby the raw material is deposited through a nozzle and stacked in a layer-by-layer fashion onto a build bed, thus constructing a final product. For materials that melt and flow at elevated temperatures (i.e. thermoplastic materials), fused filament fabrication (FFF) is ideal since a solid filament can be fed into a heated nozzle, melted onto a build bed, and then quickly re-solidified. However, many polymers do not melt at elevated temperatures, and instead degrade; these materials are termed "thermosetting." To print these materials, unreacted thermosetting precursors, which are filled with a large proportion of solid fillers ("highly filled inks"), can be extruded by applying pneumatic back pressure to a syringe at ambient conditions. The process of extruding these materials layer-by-layer describes the direct ink write (DIW) technique. The solid particulate fillers form structural "networks" due to weak electrostatic forces on the surface of the fillers. These forces provide structural stability and enable the printed lines to hold the weight of subsequent layers. Unfortunately, the high-pressure region of the nozzle disrupts this network, causing the printed lines to sag over time. This effect can be reduced by actively applying ultraviolet (UV) light onto the nozzle during extrusion, which helps to hold the particles in place by curing the resin, thus increasing the capacity for a line to sustain the weight of subsequent layers. This form of material extrusion is termed UV-assisted direct ink write (UV-DIW). Because UV light only partially cures the material during prints, a separate, slower thermosetting reaction can occur as the material rests in an oven or in ambient conditions, which completely cures the printed part and provides sufficient mechanical properties. The combination of UV-curable resins, thermosetting resins, and sufficiently large amounts of solid particulate fillers for material extrusion describes the dual-cure nature of this highly filled UV-DIW process. To understand the curing patterns, flow behavior, and the amount of structural deformation that occurs within the nozzle, rheology becomes a powerful characterization tool. This branch of physics deals with the deformation and flow of matter ranging from simple fluids to complex polymer melts. As such, it is possible to probe reaction progress (chemorheology), structural deformation/reformation (thixotropy), and high-shear regimes representative of the DIW process. The research contained within this dissertation provides a holistic understanding of the overlap between rheology and DIW material extrusion for dual-reactive materials. This process begins by evaluating challenges during melt extrusion of thermoplastic polyurethane while quantifying the rate of degradation side reactions. An alternative form of polyurethane synthesis in the form of a thermosetting reaction is then introduced, whereby the reaction progress is evaluated using both rheological and spectroscopic techniques. Next, a novel rheological protocol is introduced which can predict the structural deformation/reformation of an ink during UV-DIW. This research concludes by proposing a downscaled version of the high-shear capillary rheometer which requires only several grams of material in contrast to the dozens of grams required for full-scale capillary rheometry. In essence, the work presented here rapidly evaluates the complex flow behavior and cure progression of various materials relevant for extrusion processes by utilizing limited sample quantities, thus preserving valuable resources while improving the economics of material discovery.

Submitted by Neusa Fagundes (neusa.fagundes@unioeste.br) on 2018-09-10T17:43:56Z No. of bitstreams: 2 Santiago_Pereira Neto2018.pdf: 1174069 bytes, checksum: 82494df7c5196d52518cc45a8c47da33 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2018-09-10T17:43:56Z (GMT). No. of bitstreams: 2 Santiago_Pereira Neto2018.pdf: 1174069 bytes, checksum: 82494df7c5196d52518cc45a8c47da33 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2018-02-16 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this study, the influence of the load progression was evaluated, using poultry litter in reactors that had already been operating with swine waste, in relation to physical-chemical and operational parameters. In order to evaluate the solids content of the chicken litter, CSTR reactors were used with a useful volume of 12 L, the control reactor (R1) with only swine manure and the reactor for co-digestion swine and poultry litter (R2). It was possible to notice that the increase in methane productivity was up to 56% in the VOCs of 2.1 and 3.0 kgSV.m-3.d-1 based on the volatile solids (SV) of the chicken bed added. Average methane yield at R2 reached 0.54 LN CH4. Loor-1. d-1 for VOCs of 3.0 and 4.5 kgSV.m-3d-1. The values of AI/P and short-chain organic acids changed from 3.6-3 and 4.5 kgSV.m-3.d-1 (values close to 0.1 to 0.4), but the pH of the system remained stable due to the alkalinity of the swine manure. The total solids content (ST) at which the reactor was operated was 11.7% (m.v-1), during which time a large quantity of foam was formed in the system, which led to operational problems due to the reactor’s overload. In view of the limitation of many reactors operating with higher solids contents, CSTR is an important option for anaerobic co-digestion of a poultry litter and swine manure, two residues of relevant agroindustrial chains in Brazil and in the world. / Nesse estudo foi avaliada a influência da progressão de carga, utilizando cama de frango em reatores que já operam com dejeto suíno, em relação a parâmetros físico-químicos e operacionais. Tendo em vista o teor de sólidos da cama de frango, utilizaram-se reatores do modelo CSTR com volume útil de 12 L, o reator controle (R1) somente com dejeto suíno e o reator para codigestão dejeto suíno e cama de frango (R2). Foi possível notar que o incremento na produtividade de metano foi de até 56% nas COVs de 2,1 e 3,0 kgSV.m-3.d-1 com base nos sólidos voláteis (SV) da cama de frango adicionados. A produtividade média de metano em R2 alcançou 0,54 LN CH4.Lreator-1. d-1 para as COVs de 3,0 e 4,5 kgSV.m-3.d-1. Os valores de AI/P e ácidos orgânicos de cadeia curta sofreram alterações a partir da carga 3,6 3,0 e 4,5 kgSV.m-3.d-1 (de valores próximo a 0,1 para 0,4), mas o pH do sistema se manteve estável devido à alcalinidade do dejeto de suíno. O teor de sólidos totais (ST) limite em que o reator foi operado foi de 11,7% (m.v-1). Nesse período houve formação de grande quantidade de escuma no sistema, o que levou a problemas operacionais devido à sobrecarga do reator. Tendo em vista a limitação de muitos reatores em operar com teores de sólidos maiores, o CSTR é uma opção importante para a codigestão anaeróbia da cama de frango e dejeto de suíno, dois resíduos de cadeias agroindustriais relevantes no Brasil e no mundo.

Neste trabalho estudou-se a copolimerização em emulsão de estireno e acrilato de butila em processo semicontínuo onde o produto final é um látex com alto teor de sólidos. Foi dado enfoque à distribuição de tamanhos de partículas do látex e seus efeitos no produto. Foi realizada uma série de experimentos de copolimerização em emulsão em um reator de vidro, empregando receitas com teores de sólidos de até 64% em massa. Durante os experimentos, amostras eram retiradas periodicamente do reator visando analisar o teor de polímeros (conversão dos monômeros) por gravimetria, a concentração de monômero residual por cromatografia gasosa headspace, o diâmetro médio das partículas por espectroscopia de espalhamento dinâmico de luz e a distribuição de tamanhos de partículas por microscopia eletrônica de transmissão. A viscosidade do látex final era obtida em viscosímetro Brookfield. Aplicando estratégias para renucleação de novas partículas no decorrer do processo, foram obtidos látices com distribuição bimodal de tamanhos de partículas e com viscosidades reduzidas. Aplicou-se um modelo matemático para descrever o processo, incluindo a evolução no tempo da distribuição de tamanhos de partículas, calculada a partir de equações de balanço populacional para as partículas e para os radicais dentro das partículas. Para a solução das equações empregou-se discretização por método de classes e a técnica de pivô fixo. O modelo tem apenas dois parâmetros ajustáveis, referentes às eficiências de captura de radicais por micelas e por partículas. Estes parâmetros foram ajustados para os dados experimentais de um ensaio, e usados, sem reajuste, para outros ensaios em condições diferentes. Os resultados do modelo mostraram boa adequação aos resultados experimentais. / The aim of this work was the study of the high solid contents emulsion copolymerization of styrene and butyl acrylate in semi-batch process. In this context the particle size distribution and its effects on the product viscosity was studied. Copolymerization reactions were carried out in a glass reactor, and recipes with solid contents up to 64 wt.% were used. During each run, samples are periodically taken from the reactor, and analysis are performed to measure the polymer content (monomer conversion) by gravimetry, the concentrations of the residual monomers by head-space gas chromatography, the average particle size by dynamic light scattering, and the particle size distribution by transmission electronic microscopy. The viscosity of the final emulsion is also measured using a Brookfield viscosimeter. By applying operating strategies to nucleate new particles along the process, latexes with bimodal particle size distributions and low viscosities were obtained. A mathematical model was employed for simulating the polymerization process, including the evolution of the particle size distribution along the process, calculated from population balance equations for the particles and the radicals inside the particles. The numerical solution was obtained using the discretized population balance equations by the method of classes and the fixed pivot technique. The model has only two adjustable parameters, the efficiencies for radical capture by micelles and by particles. These two parameters were fitted to the experimental data of one run and used, without further readjustment, for other runs under different conditions. The model results presented satisfactory agreement with the experimental data.

New processes for the production of polymeric dispersions with high solids content and low viscosity were developed, investigated and characterized. The specifications required for the desired application of paper coating, which constitutes one of the major innovative aspects of this thesis, requires in average particle sizes smaller than 200 nm. This particle size is significantly smaller than obtained in previous work in this area. The main objective of this project was to increase the solids content of existing products from ~50 to ~60 wt% while keeping the viscosity at low levels (< 1200 mPa•s at 20 s-1). In order to produce high solids content latexes with low viscosity, bimodal particle size distributions were resorted to. To obtain highest packing fraction, the small particle size population should be about 7 times smaller than the large particles, bringing the size of the small particles to less than 30 nm. Modified (micro)emulsion processes were developed in order to produce small particle size latex with reduced surfactant concentration and increased solids content. The large particle population was developed using a semi-batch emulsion polymerization process, simulating a product that is commercially available (~52 wt% solids content and viscosity of ~500 mPa•s at 20 s-1). To increase the solids content of this product up to 60 wt%, a second population of small particles was created using two approaches. In the first approach, the small particles were generated in situ using the modified (micro)emulsion approaches developed previously. This process resulted in latexes of ~ 60% solids content and viscosities lower than 500 mPa•s at 20 s-1. In the second approach, the second population of particles was created by the addition of seeds by using small cross-linked particles as pseudo inert-fillers. This process resulted in products with ~58% solids and viscosities lower than 1400 mPa•s at 20 s-1. The slightly decreased solids content and increased viscosity relative to the previous approaches is due to the difficulty in producing cross-linked seeds with particle sizes smaller than 30 nm at an acceptable concentration, causing deviations from ideal conditions. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2011-05-03 13:58:44.22

No description available.

Neste trabalho estudou-se a copolimerização em emulsão de estireno e acrilato de butila em processo semicontínuo onde o produto final é um látex com alto teor de sólidos. Foi dado enfoque à distribuição de tamanhos de partículas do látex e seus efeitos no produto. Foi realizada uma série de experimentos de copolimerização em emulsão em um reator de vidro, empregando receitas com teores de sólidos de até 64% em massa. Durante os experimentos, amostras eram retiradas periodicamente do reator visando analisar o teor de polímeros (conversão dos monômeros) por gravimetria, a concentração de monômero residual por cromatografia gasosa headspace, o diâmetro médio das partículas por espectroscopia de espalhamento dinâmico de luz e a distribuição de tamanhos de partículas por microscopia eletrônica de transmissão. A viscosidade do látex final era obtida em viscosímetro Brookfield. Aplicando estratégias para renucleação de novas partículas no decorrer do processo, foram obtidos látices com distribuição bimodal de tamanhos de partículas e com viscosidades reduzidas. Aplicou-se um modelo matemático para descrever o processo, incluindo a evolução no tempo da distribuição de tamanhos de partículas, calculada a partir de equações de balanço populacional para as partículas e para os radicais dentro das partículas. Para a solução das equações empregou-se discretização por método de classes e a técnica de pivô fixo. O modelo tem apenas dois parâmetros ajustáveis, referentes às eficiências de captura de radicais por micelas e por partículas. Estes parâmetros foram ajustados para os dados experimentais de um ensaio, e usados, sem reajuste, para outros ensaios em condições diferentes. Os resultados do modelo mostraram boa adequação aos resultados experimentais. / The aim of this work was the study of the high solid contents emulsion copolymerization of styrene and butyl acrylate in semi-batch process. In this context the particle size distribution and its effects on the product viscosity was studied. Copolymerization reactions were carried out in a glass reactor, and recipes with solid contents up to 64 wt.% were used. During each run, samples are periodically taken from the reactor, and analysis are performed to measure the polymer content (monomer conversion) by gravimetry, the concentrations of the residual monomers by head-space gas chromatography, the average particle size by dynamic light scattering, and the particle size distribution by transmission electronic microscopy. The viscosity of the final emulsion is also measured using a Brookfield viscosimeter. By applying operating strategies to nucleate new particles along the process, latexes with bimodal particle size distributions and low viscosities were obtained. A mathematical model was employed for simulating the polymerization process, including the evolution of the particle size distribution along the process, calculated from population balance equations for the particles and the radicals inside the particles. The numerical solution was obtained using the discretized population balance equations by the method of classes and the fixed pivot technique. The model has only two adjustable parameters, the efficiencies for radical capture by micelles and by particles. These two parameters were fitted to the experimental data of one run and used, without further readjustment, for other runs under different conditions. The model results presented satisfactory agreement with the experimental data.