Modeling and simulation of the phase‐inversion process during membrane preparation

The objective of this work is to present a simple mathematical model to describe the main features of phase inversion by immersion precipitation. The model was developed for planar geometry and is used to simulate membrane synthesis. Two systems commonly used for membrane preparation were used for simulations: cellulose acetate/acetone/water and polyetherimide/N‐methylpyrrolidone/water. The influence of nonsolvent addition to initial polymer casting solutions, solvent addition to the coagulation bath, and geometric variables, such as polymer film thickness, on the final precipitation conditions were studied through simulation and compared to available experimental data. The results are in good agreement with published results. 1 - 3 It is shown that polymer film composition profiles at the moment of precipitation may give important information about the structure and substructure of formed membrane. It is also shown, for both polymeric systems investigated in this work, that the dynamics of the mass transfer process seems to be much more important than the influence of the concentration on the diffusion and thermodynamic partition coefficients, as fair agreement with available experimental data was obtained even when these coefficients were assumed to be constant. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3036–3051, 2001     

Fluidized‐bed reactor modeling for polyethylene production

Gas‐phase technology for polyethylene production has been widely used by industries around the world. A good model for the reactor fluid dynamics is essential to properly set the operating conditions of the fluidized‐bed reactor. The fluidized‐bed model developed in this work is based on a steady‐state model, incorporating interactions between separate bubble, emulsion gas phase, and emulsion solid polymer particles. The model is capable not only of computing temperature and concentration gradients for bubble and emulsion phases, calculating polymer particle mean diameter throughout the bed and polyethylene production rate, but also of pinpointing the appearance of hot spots and polymer meltdown. The model differs from conventional well‐mixed fluidized‐bed models by assuming that the particles segregate within the bed according to size and weight differences. The model was validated using literature and patent data, presenting good representation of the behavior of the fluidized‐bed reactor used in ethylene polymerization. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 321–332, 2001     

Synthesis of polar vinyl monomer–olefin copolymers by α‐diimine nickel catalyst

Vinyl acetate, methyl methacrylate, acrylonitrile and methyl vinyl ketone were investigated for co‐ and terpolymerization with ethylene and ethylene–propylene. Precursor [bis(N,N ′‐dimesitylimino)acenaphthene]dibromonickel, activated by methylaluminoxane was used as a catalyst system and trialkylaluminium was employed to block the polar groups for these polymerizations. Polymerization activities of the order of magnitude of 10⁶ in the case of vinyl acetate and methyl methacrylate, and 10⁵ in the case of acrylonitrile were achieved. Microanalysis and GPC of acrylonitrile copolymers found about 17 units of acrylonitrile per polymer chain. Copolymers with very different properties from the parent homopolymers were obtained in all cases except that of methyl vinyl ketone. © 2001 Society of Chemical Industry     

Electrospinning of gelatin fibers using solutions with low acetic acid concentration: Effect of solvent composition on both diameter of electrospun fibers and cytotoxicity

Gelatin fibers were prepared by electrospinning of gelatin/acetic acid/water ternary mixtures with the aim of studying the feasibility of fabricating gelatin nanofiber mats at room temperature using an alternative benign solvent by significantly reducing the acetic acid concentration. The results showed that gelatin nanofibers can be optimally electrospun with low acetic acid concentration (25%, v/v) combined with gelatin concentrations higher than 300 mg/mL. Both gelatin solutions and electrospun gelatin mats (prepared with different acetic acid aqueous solutions) were analyzed by Fourier transform infrared spectroscopy and differential scanning calorimetry techniques to determine the chemical and structural changes of the polymer. The electrospun gelatin mats fabricated from solutions with low acetic acid content showed some advantages as the maintenance of the decomposition temperature of the pure gelatin (～ 230°C) and the reduction of the acid content on electrospun mats, which allowed to reach a cell viability upper than 90% (analyzed by cell viability test using human dermal fibroblast and embryonic kidney cells). This study has also analyzed the influence of gelatin and acetic acid concentration both on the solution viscosity and the electrospun fiber diameter, obtaining a clear relationship between these parameters. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42115.     

Numerical approach to describe continuous and intermittent drying including the tempering period: Kinetics and spatial distribution of moisture

Continuous and intermittent drying experiments were performed with whole bananas, using hot air at 70°C. The intermittent drying experiments were performed with intermittency ratio equal to 1/2 and tempering times of 0.5, 1.0, and 2.0?h. The conditions imposed to the experiments permitted to investigate the influence of these tempering times on the processes. A one-dimensional numerical solution of the diffusion equation coupled with an optimizer was used to determine the process parameters for four experiments. To describe the processes, a model was proposed. Model includes shrinkage, variable effective mass diffusivity, and two values for convective mass transfer coefficient (within and outside the dryer), enabling to consider moisture loss during the tempering period. For all experiments, the simulation of the drying kinetics has resulted in good statistical indicators. Proposed model also made it possible to predict moisture distributions during the entire processes, including the migration of moisture from the central part to the peripheral region of the cross section of the bananas, during the tempering period. The results indicated that, for the same effective operation time and intermittency ratio, increasing the tempering time implied moderate decrease in the final average moisture content.     

Comparative Fingerprint Changes of Toxic Volatiles in Low PUFA Vegetable Oils Under Deep-Frying

The volatile fraction of three vegetable oils recommended for deep‐frying due to their high MUFA:PUFA ratios, namely extra‐virgin olive oil, peanut oil and canola oil, was compared before and after frying potatoes, with a particular focus on toxic volatiles. For the purpose, a headspace solid‐phase‐micro extraction technique coupled with gas chromatography and mass spectrometry was optimized, with semi‐quantification achieved using two internal standards. Significant qualitative and quantitative differences were observed, both before and after frying. From a total of 51 compounds, aldehydes were the main group formed after deep‐frying, their nature and abundance being highly associated with the initial fatty acid composition, particularly linoleic acid (r² = ?0.999, p ≤ 0.001). Globally, extra‐virgin olive oil revealed fewer formations of unsaturated aldehydes, including toxic ones, and correlated with lower amounts of degradation indicators, as polar compounds (r² = 0.998, p ≤ 0.001) and p‐anisidine value (r² = 0.991, p ≤ 0.001). Despite the similarities in total unsaturation degree between canola and peanut oils, the former presented lower amount of volatiles, including E,E‐2,4‐decadienal and acrolein, the more toxic ones. These results highlight for the pertinence of volatile analyses to evaluate and compare oil degradation under thermal and oxidative stress, while complementing other degradation indicators. Additionally, the optimized methodology allows a direct comparison of different oil matrices, supporting further developments into more general methods for volatiles quantification, enabling more efficient comparison of results between research teams.     

Biopolymeric coatings for delivery of antibiotic and controlled degradation of bioresorbable Mg AZ31 alloys

Magnesium and magnesium alloys are attracting considerable interest as biodegradable materials with high potential for application as temporary implants. The high corrosion rate of Mg-based implants is considered a serious drawback, and it is crucial to design novel surface protection strategies that minimize the detrimental effects of corrosion, while contributing for introducing additional functionalities on the material surface. In this work, a layer-by-layer coating architecture composed of an inner poly(lactic-co-glycolic) acid layer, working as adhesion promoter, and additional polycaprolactone (PCL) layers working as reservoirs for antibiotic (levofloxacin) and for nanohydroxyapatite (nanoHA) particles was applied on the Mg alloy AZ31. The results demonstrate that the composition and number of PCL layers can tailor the biodegradation of the bare magnesium alloy, surface wettability, and the kinetics of release of antibiotic (levofloxacin). The distribution of nanoHA in the coating architecture plays a crucial role on tailoring the desired biocompatible functionalities and corrosion protection of the bare alloy.     

SUPERCRITICAL EXTRACTION OF LINSEED OIL: ECONOMICAL VIABILITY AND MODELING EXTRACTION CURVES

The aim of the present study was to use supercritical technology to recover linseed oil (Linum usitatissimum L.) using carbon dioxide (alone or modified with ethanol as solvent) to determine the influence of the technique on the chemical composition of the oil obtained, model the kinetic curves of extraction, and estimate the manufacturing cost of the process. The experiments were conducted at 323 K, pressure of 25 MPa, constant solvent flow of 1.7 × 10^?5 kg/s, and extraction time of 5 h. The highest yield was obtained with the addition of cosolvent (28.8%). The SFE process of linseed oil manufacture proved to be economically viable, resulting in a product with a specific cost of 13.21 US$/kg_oil. As to oil composition, the main fatty acids detected were linolenic and oleic acid.