Size reduction and polymer encapsulation of carbon black in gas-expanded solvents

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, February 2010.Cataloged from PDF version of thesis.Includes bibliographical references.Ink jet printing is a demanding application that requires carefully formulated inks in order to quickly and reliably produce high-quality printed images. Although ink jet inks are currently produced via an aqueous process, supercritical fluids (SCF) and gas-expanded liquids (GXL) present alternative processing media for particle coating operations that may offer significant benefits with respect to the production of polymer-encapsulated pigment particles for these inks. The main thesis objective is the demonstration and analysis of a particle size reduction and encapsulation process which takes place in CO₂-expanded acetone and produces colloidal carbon black particles. These particles should be uniformly coated with functionalized hydrophobic resins such that they are easily redispersed in water or solvent to form stable nanoparticle dispersions suitable for use in ink jet inks. A prototype size reduction and encapsulation system has been constructed based on a high-pressure stirred reaction vessel designed to operate at pressures up to 200 bar (3000 psi). The prototype vessel has a fluid volume of 1 liter with a multidisc agitator capable of rotating at more than 3400 RPM. Pigment particles are initially milled in a solution of non-aqueous solvent and dissolved dispersing resin. Size reduction is achieved within the apparatus via the grinding action of 1.2 mm spherical ceramic media contacting the micron-size pigment particles. As milling progresses, high-pressure CO₂ is slowly introduced to the vessel; the CO₂ acts as an anti-solvent, lowering polymer solubility and driving adsorption of the dispersing resin onto the pigment particles as new surface area is exposed.(cont.) After encapsulation is complete, the system is flushed with CO₂ and the product particles are retained as a dry powder in a high-pressure filter. The solvent-free particles are then recovered by venting the system to atmospheric pressure, and subsequently re-dispersed in water for analysis in inks. The apparatus under investigation provides a new process approach to particle size reduction and coating that affords greater freedom in ink formulation, while offering a path to improved ink quality and possible cost savings in a highly competitive market. Specifically, the use of CO₂-expanded liquids enables the deposition of hydrophobic polymers on the surface of particles for use in aqueous inks, thus significantly increasing the variety of polymers that are available for use in these systems. A representative model system of carbon black pigment and benzyl methacrylate/methacrylic acid (BzMA/MAA) copolymer dispersing resins of varying monomer compositions (BzMA/MAA mass ratio = 85/15, 80/20, and 75/25) has been studied in order to assess the feasibility of the high-pressure milling and encapsulation process for ink jet applications. These components have been successfully employed in high-pressure coating operations to produce encapsulated carbon black particles which were recovered as a dry, flowable powder. Dry product particles were redispersed in water to obtain stable aqueous dispersions with a number average particle size of 135-190 nm.(cont.) In order to guide the selection of appropriate process conditions for the encapsulation system, the high-pressure solid-liquid-vapor phase equilibrium of ternary CO₂-solvent-polymer systems has been probed experimentally and modeled with the PC-SAFT equation of state. Precipitation of BzMA/MAA copolymers generally required a larger overall CO 2 mole fraction - and thus a higher system pressure - for more dilute polymer solutions; however, a minimum in the precipitation pressure was observed for all polymer compositions and temperatures near a CO₂-free polymer mass fraction of 0.03. The ternary systems were characterized by a rapid reduction in polymer solubility over a relatively narrow range of pressure (between 200 psig and 400 psig, depending on the polymer and system temperature); the precipitation pressure increased with increasing temperature and BzMA mass fraction (per polymer mass unit). The PC-SAFT EOS was successfully employed to correlate the phase behavior data by adjusting only two binary interaction parameters; the average relative error associated with the predictions of precipitation pressure for each polymer was 3.7%. Characterization of the encapsulation process also requires knowledge of the thermodynamics and kinetics of polymer adsorption onto particle surfaces from CO₂- expanded solvents. To this end, interactions with the particle surface have been investigated through the collection and correlation of experimental adsorption isotherm data.(cont.) Adsorption of 85/15 and 75/25 BzMA/MAA polymers onto carbon black from CO₂-expanded acetone was measured at 35°C and pressures between 0 psig and 300 psig over a range of mixture compositions relevant to particle coating operations. Pressurization with CO₂ to pressures up to 200 psig caused a decrease in the amount of polymer adsorbed on particle surfaces, but further increases in pressure resulted in higher polymer loadings. In the case of 75/25 BzMA/MAA polymer, the polymer loading increased significantly between 200 psig and 300 psig as the solubility limit was approached or exceeded. Our results are valuable not only in providing quantitative data to facilitate process optimization, but also in offering a more fundamental understanding of interactions among the pigment particles, the dispersant resin, and the gas-expanded liquid media. Such information is important to both process and product design.by Scott M. Paap.Ph.D

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Development and Validation of a Risk Score for Chronic Kidney Disease in HIV Infection Using Prospective Cohort Data from the D:A:D Study

Ristola M. on työryhmien DAD Study Grp ; Royal Free Hosp Clin Cohort ; INSIGHT Study Grp ; SMART Study Grp ; ESPRIT Study Grp jäsen.Background Chronic kidney disease (CKD) is a major health issue for HIV-positive individuals, associated with increased morbidity and mortality. Development and implementation of a risk score model for CKD would allow comparison of the risks and benefits of adding potentially nephrotoxic antiretrovirals to a treatment regimen and would identify those at greatest risk of CKD. The aims of this study were to develop a simple, externally validated, and widely applicable long-term risk score model for CKD in HIV-positive individuals that can guide decision making in clinical practice. Methods and Findings A total of 17,954 HIV-positive individuals from the Data Collection on Adverse Events of Anti-HIV Drugs (D:A:D) study with >= 3 estimated glomerular filtration rate (eGFR) values after 1 January 2004 were included. Baseline was defined as the first eGFR > 60 ml/min/1.73 m2 after 1 January 2004; individuals with exposure to tenofovir, atazanavir, atazanavir/ritonavir, lopinavir/ritonavir, other boosted protease inhibitors before baseline were excluded. CKD was defined as confirmed (>3 mo apart) eGFR In the D:A:D study, 641 individuals developed CKD during 103,185 person-years of follow-up (PYFU; incidence 6.2/1,000 PYFU, 95% CI 5.7-6.7; median follow-up 6.1 y, range 0.3-9.1 y). Older age, intravenous drug use, hepatitis C coinfection, lower baseline eGFR, female gender, lower CD4 count nadir, hypertension, diabetes, and cardiovascular disease (CVD) predicted CKD. The adjusted incidence rate ratios of these nine categorical variables were scaled and summed to create the risk score. The median risk score at baseline was -2 (interquartile range -4 to 2). There was a 1: 393 chance of developing CKD in the next 5 y in the low risk group (risk score = 5, 505 events), respectively. Number needed to harm (NNTH) at 5 y when starting unboosted atazanavir or lopinavir/ritonavir among those with a low risk score was 1,702 (95% CI 1,166-3,367); NNTH was 202 (95% CI 159-278) and 21 (95% CI 19-23), respectively, for those with a medium and high risk score. NNTH was 739 (95% CI 506-1462), 88 (95% CI 69-121), and 9 (95% CI 8-10) for those with a low, medium, and high risk score, respectively, starting tenofovir, atazanavir/ritonavir, or another boosted protease inhibitor. The Royal Free Hospital Clinic Cohort included 2,548 individuals, of whom 94 individuals developed CKD (3.7%) during 18,376 PYFU (median follow-up 7.4 y, range 0.3-12.7 y). Of 2,013 individuals included from the SMART/ESPRIT control arms, 32 individuals developed CKD (1.6%) during 8,452 PYFU (median follow-up 4.1 y, range 0.6-8.1 y). External validation showed that the risk score predicted well in these cohorts. Limitations of this study included limited data on race and no information on proteinuria. Conclusions Both traditional and HIV-related risk factors were predictive of CKD. These factors were used to develop a risk score for CKD in HIV infection, externally validated, that has direct clinical relevance for patients and clinicians to weigh the benefits of certain antiretrovirals against the risk of CKD and to identify those at greatest risk of CKD.Peer reviewe

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Guiding optimal biofuels : a comparative analysis of the biochemical production of ethanol and fatty acid ethyl esters from switchgrass.

In the current study, processes to produce either ethanol or a representative fatty acid ethyl ester (FAEE) via the fermentation of sugars liberated from lignocellulosic materials pretreated in acid or alkaline environments are analyzed in terms of economic and environmental metrics. Simplified process models are introduced and employed to estimate process performance, and Monte Carlo analyses were carried out to identify key sources of uncertainty and variability. We find that the near-term performance of processes to produce FAEE is significantly worse than that of ethanol production processes for all metrics considered, primarily due to poor fermentation yields and higher electricity demands for aerobic fermentation. In the longer term, the reduced cost and energy requirements of FAEE separation processes will be at least partially offset by inherent limitations in the relevant metabolic pathways that constrain the maximum yield potential of FAEE from biomass-derived sugars

Biochemical production of ethanol and fatty acid ethyl esters from switchgrass: a comparative analysis of environmental and economic performance

As advances in biotechnology have continued at a rapid pace, interest in the biochemical production of so-called " drop-in" fuels has increased as a way to avoid the well-known shortcomings of ethanol as a fuel molecule and to potentially exploit the processing advantages of a water-immiscible fuel to reduce product recovery costs and energy requirements. In the current study, processes to produce either ethanol or a representative fatty acid ethyl ester (FAEE) via the fermentation of sugars liberated from lignocellulosic materials pretreated in acid or alkaline environments are analyzed in terms of economic and environmental metrics. Simplified process models are introduced and employed to estimate fuel production, greenhouse gas emissions, net energy consumption, minimum fuel selling price, and water consumption for both processes. Monte Carlo analyses were carried out to identify key sources of uncertainty and variability, and an analysis of the impact of potential improvements to the FAEE process was performed. We find that the near-term performance of processes to produce FAEE is significantly worse than that of ethanol production processes for all metrics considered, primarily due to poor fermentation yields and higher electricity demands for aerobic fermentation. Even if these issues are addressed in the longer term, the reduced cost and energy requirements of FAEE separation processes will be at least partially offset by inherent limitations in the relevant metabolic pathways that constrain the maximum yield potential of FAEE from biomass-derived sugars

When the wait isn't so bad: The interacting effects of website delay, familiarity, and breadth

Although its popularity is widespread, the Web is well known for one particular drawback: its frequent delay when moving from one page to another. This experimental study examined whether delay and two other website design variables (site breadth and content familiarity) have interaction effects on user performance, attitudes, and behavioral intentions. The three experimental factors (delay, familiarity, and breadth) collectively impact the cognitive costs and penalties that users incur when making choices in their search for target information. An experiment was conducted with 160 undergraduate business majors in a completely counterbalanced, fully factorial design that exposed them to two websites and asked them to browse the sites for nine pieces of information. Results showed that all three factors have strong direct impacts on performance and user attitudes, in turn affecting behavioral intentions to return to the site, as might be expected. A significant three-way interaction was found between all three factors indicating that these factors not only individually impact a user's experiences with a website, but also act in combination to either increase or decrease the costs a user incurs. Two separate analyses support an assertion that attitudes mediate the relationship of the three factors on behavioral intentions. The implications of these results for both researchers and practitioners are discussed. Additional research is needed to discover other factors that mitigate or accentuate the effects of delay, other effects of delay, and under what amounts of delay these effects occur. © 2006 INFORMS