Synthetic hydrogels 2. Polymerization induced phase separation in acrylamide systems

Acrylamide hydrogels were synthesized in the presence of various non-solvents for linear polyacrylamide to examine phase separation during polymerization. The process was found to be dependent upon the segmental volume, the chemical structure, and the concentration of the non-solvent. The concept of conversion-phase diagram for linear polymer is introduced and used qualitatively to understand polymerization induced phase separation (PIPS), and to predict the onset of PIPS during hydrogel synthesis.     

Estimation of phase diagrams for copolymer‐diluent systems in thermally induced phase separation

The binary interaction model was introduced to estimate phase diagrams of copolymer‐diluent systems in thermally induced phase separation. The crystallization curves and cloud points of poly(ethylene‐co‐vinyl alcohol) (EVOH) with 1,4‐butanediol, EVOH/1,3‐propanediol, and EVOH/glycerol were calculated and compared with experimental value or literature data. Fair agreement was obtained. To confirm the importance of incorporating intramolecular interactions, calculations with and without the consideration of intramolecular interactions were performed and compared. It was found that better results can be obtained if intramolecular interaction was introduced. The reason for the small differences between the calculated value and the experimental data of the liquid–liquid phase separation is discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Polymerization induced phase separation in poly(ether imide)-modified epoxy resin cured with imidazole

This paper studies the phase separation in poly(ether imide) (PEI) modified epoxy resin using imidazole (C₁₁Z-CNS) as epoxy hardener to control its morphology. The sponge-like phase structures were founded at higher PEI concentration (10-25 phr), while homogeneous structures are formed at low PEI concentration (5 phr). The effects of PEI concentration on curing kinetics and phase structures were studied by differential scanning calorimeters (DSC) and scanning electron microscopy (SEM). It is shown that although the addition of PEI does not change the curing mechanism, the separated morphology becomes finer at high PEI concentration. The curing rate and conversion decrease with the increase of the content of PEI. The chain growth polymerization of these systems caused an early gelation (conversion <10%) and early freezing of morphologies. The evolution of phase separation in the early stage was monitored by synchrotron radiation small angle X-ray scattering (SR-SAXS) and transmission electronic microscopy (TEM). It is suggested that the formation of sponge-like phase structure could be attributed to the strong viscoelastic effects in the early stage of phase separation.     

A systems approach to assessing new petrochemical technology

Using a systems model of the petrochemical industry. it is shown that new petrochemical processes are more likely candidates for success if their introduction would result in better resource use by the industry as a whole. This principle is then used to estimate the relative probability of success for four recently developed processes. Such studies may be useful in modeling the long-range development of the industry and may assist the industry in setting long-range research and development goals.     

Thermally induced phase separation in poly(lactic acid)/dialkyl phthalate systems

Thermally induced phase separation in poly(lactic acid)/dialkyl phthalate systems was investigated. Poly(DL ‐lactic acid) (PDLLA) and poly(L ‐lactic acid) (PLLA) with different molecular weights were used. A series of dialkyl phthalates, with different numbers of carbon atoms in the alkyl chain, were employed as solvents to control the interaction between polymer and solvent. The liquid–liquid phase‐separation temperature of the poly(lactic acid) solutions decreased systematically with a shorter alkyl chain in the phthalate. Based on the interaction between polymer and solvent and the molecular weight of polymer influencing liquid–liquid phase‐separation temperature significantly but crystallization temperature only slightly, proper thermal conditions were employed to investigate competitive phase separation and crystallization in PLLA solutions. Factors that can influence the final morphology of PLLA solutions were examined. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2224–2232, 2003     

Formation of microporous polymeric membranes via thermally induced phase separation: A review

A review of recent research related to microporous polymeric membranes formed via thermally induced phase separation (TIPS) and the morphologies of these membranes is presented. A summary of polymers and suitable diluents that can be used to prepare these microporous membranes via TIPS are summarized. The effects of different kinds of polymer materials, diluent types, cooling conditions, extractants and additive agents on the morphology and performance of TIPS membranes are also discussed. Finally new developments in TIPS technology are summarized.

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A new approach to fluid separation modelling in the columns equipped with structured packings

An analogy between the flow patterns in real separation columns equipped with structured packing and film flow is used to develop a new modelling approach. The packing is represented as a bundle of channels with identical triangular cross section. The dimensions of the channels as well as their number are derived from the packing geometry. The channel inner surface is wetted by a liquid flowing downwards, whereas the rest of the volume is occupied by a countercurrent vapour flow. Both phases are assumed to be totally mixed at regular intervals, determined by the corrugation geometry of the packing. The mathematical model is based on a set of partial differential equations describing hydrodynamics and mass and heat transport phenomena. These equations are complemented by the conjugate boundary conditions at the phase interface. A numerical solution of the model yields velocity profiles as well as concentration and temperature fields throughout the column. The model is verified using experimental data for a binary distillation in a column equipped with Montz-Pak A3-500.     

Thermally induced phase separation and electrospinning methods for emerging membrane applications: A review

In this review, thermally induced phase separation (TIPS) and electrospinning methods for preparation of fluoropolymer membranes are assessed, particularly for the polyvinylidene fluoride (PVDF) and polyethylene chlorotrifluoroethylene membranes. This review focuses on controlling the membrane morphology from the thermodynamic and kinetic perspectives to understand the relationship between the membrane morphology and fabrication parameters. In addition, the current status of the nonsolvent induced phase separation (NIPS) method and the combined NIPS‐TIPS (N‐TIPS) method, which is a new emerging fabrication method, are discussed. The past literature data are compiled and an upperbound curve (permeability vs. tensile strength) is proposed for the TIPS‐prepared PVDF membranes. Furthermore, the key parameters that control and determine the membrane morphology when using the electrospinning method are reviewed. Exploiting the unique advantages of the electrospinning method, our current understanding in controlling and fine‐tuning the PVDF crystal polymorphism (i.e., β‐phase) is critically assessed. © 2015 American Institute of Chemical Engineers AIChE J, 62: 461–490, 2016     

A new approach to quantifying vehicle induced turbulence for complex traffic scenarios

Traffic-related pollutants adversely affect air quality, especially in regions near major roadways. The vehicleinduced turbulence (VIT) is a significant factor that controls the initial dilution, dispersion, and ultimately the chemical and physical fate of pollutants by altering the conditions in the microenvironment. This study used a computational fluid dynamics (CFD) software FLUENT to model the vehicle-induced turbulence (VIT) generated on roadways, with a focus on impact of vehicle-vehicle interactions, traffic density and vehicle composition on turbulent kinetic energy (TKE). We show, for the first time, that the overall TKE from multiple vehicles traveling in series can be estimated by superimposing the TKE of each vehicle, without considering the distance between themwhile the distance is greater than one vehicle length. This finding is particularly significant since it enables a new approach to VIT simulations where the overall TKE is calculated as a function of number of vehicles. We found that the interactions between vehicles traveling next to each other in adjacent lanes are insignificant, regardless the directions of the traffic flow. Consequently, simulations of different traffic scenarios can be substantially simplified by treating two-way traffic as one-way traffic, with less than 5% difference in the overall volume-averaged TKE. We also developed equations that allow the estimation of the overall volume-averaged TKE as a function of the number and the type of vehicles.     

DBFact: A better approach to calculate the minimum variance control law for nonminimum phase MIMO systems

This paper presents the diagonal with Blaschke products factorization (DBFact) approach to factor out multivariable time delay and nonminimum phase zeros from multi-input multi-output (MIMO) systems. Based on that, a new output-order independent minimum variance (MV) control law for MIMO systems is proposed. The DBFact method is a two-step factorization procedure, relying on the diagonal and Blaschke factorization methods. This method has the advantage of being a direct and non-iterative procedure. This new factorization approach allows the calculation of an MV control law considering the multivariable time delay as a limiting-performance factor and the nonminimum phase zeros and their corresponding directions. Based on the proposed MV control law, a performance benchmark is introduced, which can be calculated by the DBFact filters and routine operating data. The DBFact methodology was applied to two control structures of the linear plant model of Linde's heat integrated air separation, in which the MV control law output-order dependency property and the suitability of the performance benchmark were evaluated. Some results were compared with those obtained by admitting the generalized interactor matrix instead of the DBFact filters. The results show the capability of the DBFact methodology to factor the nonminimum phase terms to provide a reliable MIMO controller performance benchmark and illustrate the importance of considering the nonminimum phase zeros and their actual directionality in the MV control law.     

Polymerization of methyl methacrylate in micellar phase: A kinetic study

Polymerization of methyl methacrylate (MMA) using Ce(IV) as initiator in aqueous nitric acid solution in the presence of sodium lauryl sulphate (NaLS) has been studied kinetically at a temperature range of 25–35°C. The rate of polymerization (R_p) increases with increasing concentration of NaLS, and it was also proportional to [MMA]²; but, in the presence of NaLS, the change of R_p with respect to [Ce(IV)] and [H⁺] were not linear and similarly the rate of Ce(IV) disappearance was not proportional to its original concentration. The overall activation energy of the polymerization process in presence of 0.01M NaLS was found to decrease by ～ 7.0 kcal mol^?1. The monomer–micelle association constant has been calculated to be 5.135 × 10⁴ mol^?1 L. The polymer obtained in surfactant medium is sparingly soluble in benzene and DMSO. From infrared spectra clear evidence of vinyl polymerization was obtained.     

Liquid-liquid phase separation in multicomponenent polymer systems: XV thermodynamic aspects of polymer compatibility

Cloud-point curves in mixtures of short-chain polymers often have irregular shapes, showing shoulders or two maxima. Limits of the thermodynamic stability as measured by Pulse Induced Critical Scattering also appear to be bimodal in such cases. A possible explanation of this phenomenon might be that the constituent molecules influence each other's chain flexibility, the more flexible chains becoming less flexible upon addition of stiffer ones, and vice versa. Such a feature is incorporated i.a. in Huggins' new theory in which orientational entropy correction terms relate the average randomness of orientation of a segment with respect to the preceding one in the chain to the surroundings of the segment.     

A combined relaxation-newton method as a new global approach to the computation of thermal separation processes

Two basically different methods, formerly used sequentially to solve multicomponent thermal separation problems, are now allowed to function simultaneously within a single algorithm to ensure a rapid yet stable convergence to the solution. By combining the stability of the Rose-Sweeney-Ball method with the rapidity of the Newton-Raphson method, the solution is easily reached without encountering the difficulties of employing these methods separately.     

A new approach in modeling of mechanical properties of binary phase polymeric blends

Modeling of polymeric blends has attracted considerable attention due to simplification of blending processes, rapidity in usage and its inexpensive cost. So far, a great deal of effort has been made to seek new models with embodied correct assumptions and application of mathematical calculation process. In this work, direct and independent approximation model (DIA) including a consistency parameter, F(D), is proposed to predict the modulus of polymeric blends. Using F(D), two entirely different models are unified; one implies droplet-matrix structure and the other characterizes the modulus of co-continuous structure. Furthermore, a fraction of interconnected dispersed droplets (co-continuous sector) after percolation threshold is introduced by parameter R(D), which is also based on percolation theory. However, both introduced parameters are mathematically evaluated, and unlike the other proposed models they can simplify the calculation procedure significantly by preventing complicated geometrical shapes and parameters. Furthermore, as another advantage, any model which expresses the mechanical properties of co-continuous and/or droplet-matrix structure could be used as basis of DIA model. Considering pre-indicated volume fractions, a blend of polyamide and polyolefin elastomer was designed to compare the experimental data with DIA model predictions. Also, some other experimental data from other related research findings were used. The coincidence of the experimental data with the corresponding predictions of DIA model shows its high accuracy and validity.     

A cognitive approach to develop dynamic models: Application to polymerization systems

An alternative procedure based on cognitive approach is applied to develop dynamic models. The solution copolymerization of methyl methacrylate and vinyl acetate in a continuous stirred tank reactor is analyzed to illustrate the cognitive model development. Factorial planning was used to discriminate the process variables with higher impact on the process performance (effects) and they are used to built‐up a dynamic model based on the functional fuzzy relationship of Takagi–Sugeno type. Gaussian membership functions are considered for the cognitive sets and subtractive clustering method supplied the parameters of the premises of the model. Consequence functions are obtained through an optimization problem solved by a least square based algorithm. The kinetic parameters and reactor operating conditions are obtained from the literature and a mathematical model is considered as plant for identification data generation. Dynamic cognitive models showed satisfactory predictive capabilities and may be an interesting alternative to attack problems of modeling in chemical processes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

A new approach to coagulation phenomena in wet-spinning

A new physicochemical model was built to describe the phenomena occurring during wet-spinning of polyacrylonitrile, in order to relate the integral time of coagulation to the major variables of the spinning bath. According to this model, counterdiffusion of solvent and coagulant leads the system to overcome the thermodynamic equilibrium conditions, so that precipitation of polymer occurs, at a distance from the fiber axis variable with time. This causes a moving-interface dope-coagulated polymer to build up. The integral time required by this interface to reach the fiber axis, i.e., the coagulation time, is related, by simple equations to initial radius, to temperature via diffusional coefficients, to “bath hardness” (i.e., coagulant content), and to thermodynamic phase equilibrium conditions.     

A new approach to evaluate kinetic parameters and mass transfer coefficients in continuous stirred tank reactors. Application to antibiotic separation

A new method is proposed to evaluate kinetic parameters and mass transfer coefficients for adsorption processes carried out in continuous stirred tank reactors. This method, employing a biphasic model, does not linearize nonlinear solute concentration versus time data, nor does it assume the existence of equilibrium in a typical nonequilibrium situation as is currently done. For a nonlinear adsorption isotherm, the coupled differential equations need to be solved numerically, but using an elegant analytical solution it is possible to determine rate constants and mass transfer coefficients in the case of nonlinear kinetics with a linear adsorption isotherm. This solution (biphasic model, linear isotherm) is obtained and compared with solutions incorporating (i) a linear model (linear isotherm) and (ii) a numerical solution (nonlinear isotherm) for recovery of the antibiotic novobicoin in stirred tank reactors. For novobiocin adsorption versus time data, use of the biphasic model results in a lower mean percentage error than either the linear model or the numerical simulation; further, it provides a far superior fit of short-time adsorption behavior. Hence, we strongly advocate that the biphasic model be routinely employed along with linear models and numerical simulations of Langmuir/Freundlich isotherms for interpretation of adsorption data.     

Advanced chemically induced phase separation in thermosets: Polybenzoxazines toughened with multifunctional thermoplastic main-chain benzoxazine prepolymers

Multifunctional thermoplastic main-chain benzoxazine prepolymers were synthesized and systematically varied in their structure in order to function as high-performance toughener additives. Their unique chemical composition allows multiple covalent crosslinking with many thermoset network systems including benzoxazines and epoxides in conjunction with a defined chemical induced phase separation (CIPS) upon curing. This was successfully shown using a benzoxazine-based thermoset resin matrix as an example. The corresponding morphologies were addressable in a predictable manner and brought into context with the obtained macroscopic mechanical and thermal properties. In this relationship the CIPS process was classified and compared with the literature in more general means for advanced morphology control by differentiating between covalently attached and so-called gradient domain structures. The prepolymers were characterized by ¹H NMR, FT-IR, DSC and TGA. The thermoset morphologies were investigated by TEM and AFM. The fracture toughness (K_Ic) and the elastic modulus (E) were measured by fracture and three point bending experiments. Thermal properties of the resulting films have been tested by DMA.