Continuous Emulsion Polymerization Research Articles

Identification of Vitronectin as a Major Plasma Protein Adsorbed on Polymer Surfaces of Different Copolymer Composition

The arrays of proteins adsorbed from plasma onto a series of polystyrene copolymeric latexes were analyzed by enzyme-linked immunosorbent assay (ELISA) of washed beads and immunoblotting of proteins desorbed from the beads and separated by polyacrylamide gel electrophoresis (PAGE). Beads were prepared by continuous emulsion polymerization in the absence of surfactant. Coomassie brilliant blue staining of gel electropherograms of desorbed proteins indicated that the presence of small amounts of comonomers (1 to 10 mole %) significantly influenced the composition of the adsorbed protein layer. Immunoblotting revealed that fibrinogen, fibronectin, and vitronectin were adsorbed by all surfaces investigated. C3 and Clq adsorption varied significantly with copolymer composition. The ELISAs revealed that although the concentrations of vitronectin and fibronectin in plasma are similar, the extent of vitronectin adsorption from 70% to 85% plasma was greater by two orders of magnitude than fibronectin adsorption. Vitronectin adsorbed on carboxylic acid-containing copolymers reacted more strongly with a conformationally sensitive antivitronectin monoclonal antibody (MoAb) than vitronectin adsorbed to polystyrene and was more susceptible to cleavage by plasma proteases(s). The results show that vitronectin is a major protein adsorbed from concentrated plasma and that small changes in the chemical composition of a copolymer profoundly affects the extent and nature of protein adsorption from complex mixtures such as plasma.

Identification of vitronectin as a major plasma protein adsorbed on polymer surfaces of different copolymer composition

The arrays of proteins adsorbed from plasma onto a series of polystyrene copolymeric latexes were analyzed by enzyme-linked immunosorbent assay (ELISA) of washed beads and immunoblotting of proteins desorbed from the beads and separated by polyacrylamide gel electrophoresis (PAGE). Beads were prepared by continuous emulsion polymerization in the absence of surfactant. Coomassie brilliant blue staining of gel electropherograms of desorbed proteins indicated that the presence of small amounts of comonomers (1 to 10 mole %) significantly influenced the composition of the adsorbed protein layer. Immunoblotting revealed that fibrinogen, fibronectin, and vitronectin were adsorbed by all surfaces investigated. C3 and Clq adsorption varied significantly with copolymer composition. The ELISAs revealed that although the concentrations of vitronectin and fibronectin in plasma are similar, the extent of vitronectin adsorption from 70% to 85% plasma was greater by two orders of magnitude than fibronectin adsorption. Vitronectin adsorbed on carboxylic acid-containing copolymers reacted more strongly with a conformationally sensitive antivitronectin monoclonal antibody (MoAb) than vitronectin adsorbed to polystyrene and was more susceptible to cleavage by plasma proteases(s). The results show that vitronectin is a major protein adsorbed from concentrated plasma and that small changes in the chemical composition of a copolymer profoundly affects the extent and nature of protein adsorption from complex mixtures such as plasma.

CLOSED-LOOP CONTROL OF A SEEDED CONTINUOUS EMULSION POLYMERIZATION REACTOR SYSTEM

A reactor configuration for continuous emulsion polymerization is proposed consisting of a plug flow reactor followed by a train of CSTR's. Monomer conversion is controlled by manipulating the quantity of water and monomer which are allowed to bypass the plug flow reactor and enter the first CSTR directly. A multivariate pole-placement adaptive controller is used to implement the controls. Simulation results indicate good control of both conversion and particle size. Open-loop experimental results indicate the effectiveness of the plug flow reactor for eliminating the oscillations sometimes found in CSTR emulsion polymerization.

CONTINUOUS MINIEMULSION POLYMERIZATION: KINETIC INVESTIGATIONS

Experimental data on the dynamic behavior of the miniemulsion polymerization of methyl methacrylate in a CSTR are presented. These data are contrasted with those for similar conventional emulsion polymerizations. The dominance of nucleation in monomer droplets in miniemulsion systems is shown to be responsible for the absence of the decaying oscillatory transients observed in continuous emulsion polymerization. Rates of polymerization for the miniemulsion system are reported to be twice those of the equivalent emulsion system. In addition, the polymer produced in this study is of high molecular weight, indicating a high degree of segregation within the polymer particles. These last two observations are attributed to the extremely small monomer droplets produced by the combination of the addition of a cosurfactant and the high shear to which the unpolymerized emulsion is subjected

Continuous emulsion polymerization: design and control of CSTR trains

During conventional continuous emulsion polymerization of many monomers, sustained oscillations (limit cycles) occur in all latex and polymer properties, creating severe problems commercially. A novel redesigned continuous reactor configuration is clearly shown to eliminate these undesirable oscillations and to offer greatly increase flexibility in controlling particle size and conversion. This control is accomplished by manipulating the initiator feedrate to the first (small) reactor, and the split of the monomer and water feedrates between the small and the first large reactor of the train.

The modeling of batch and continuous emulsion polymerization reactors. Part I: Model formulation and sensitivity to parameters

AbstractA detailed model for the prediction of the behavior of batch or continuous emulsion polymerization reactors has been formulated, and an efficient numerical scheme for simulation developed. The model makes use of population balance equations and detailed mechanisms for chemical and physical rate processes. The numerical procedure chosen for its solution is orthogonal collocation on finite elements. In this paper, a few comparisons with experimental data are presented to demonstrate the model validity. Finally, a parametric sensitivity study is carried out to identify the most important kinetic and physical parameters. In the sequel, a comprehensive comparison of model predictions with a wide variety of experimental data will be presented.

The modeling of batch and continuous emulsion polymerization reactors. Part II: Comparison with experimental data from continuous stirred tank reactors

AbstractA detailed model for emulsion polymerization is compared with extensive data from continuous stirred tank reactors. Model predictions are compared with both steady‐state and dynamic data, for polymerization of styrene, methyl methacrylate, and vinyl acetate. Good agreement between model and experiment is achieved with one set of parameters and without any data fitting. The results show that the model is capable of predicting all of the experimentally observed phenomena including steady‐state multiplicity, sustained oscillations, ignition and extinction dynamics, and overshoot during start‐up.

On-line Control Studies of Continuous Emulsion Polymerization Systems

A redesigned latex reactor train configuration for the continuous production of emulsion poly (vinyl acetate) is being employed in order to test and implement on-line computer control stategies. Multivariable computer control of the final latex polymer particle size and monomer conversion is achieved using several algorithms which manipulate the feedrate of initiator to the first reactor of the train, and the flow split of the monomer and water feedrates between the first two reactors. The control algorithms include simple single loop feedback, multivarable, and optimal controllers. Both set-point changes and disturbance rejection (mainly water soluble impurities or oxygen contamination) are being covered. Control is implemented using a VAX 11/750 with a PDP-11 front end system interfaced to our pilot plant stainless steel 1-gallon reactors.

The dynamics of the continuous emulsion polymerization of methylmethacrylate

AbstractExperimental data on the dynamics of the continuous emulsion polymerization of methylmethacrylate are presented. Techniques for on‐line reaction monitoring and digital data acquisition as reported previously are used to generate dynamic data on the monomer conversion and free emulsifier concentration. Data are reported confirming the existence of multiple steady states and limit cycles in the CSTR (continuous stirred tank reactor) emulsion polymerization of methylmethacrylate. Data are also reported suggesting the presence of steady states in the absence of micelles in the reactor. The possible causes of these phenomena, and the conditions under which they occur are discussed.

Stability of continuous emulsion polymerization reactors: A detailed model analysis

A detailed steady state and dynamic model for continuous emulsion polymerization reactors is analysed for bifurcation structure. Both the steady state multiplicity and dynamic stability structures are determined. The analysis is compared with experimental data for methylmethacrylate polymerization. Simple S-shaped multiplicity and Hopf bifurcation are the dominant features of the dynamic behavior. The reactor residence time and radical desorption rate are found to be key parameters governing reactor stability.

Control of particle size distribution in latices through periodic operation of continuous emulsion polymerization reactors

AbstractA method is proposed which allows to obtain latices with prespecified number particle size distributions (NPSD), with the only restriction that the said distributions must be monotonically descendent. To this effect, the forced periodic operation of the total feed flow into a continuous stirred‐tank reactor (CSTR) is considered. The method is limited to emulsion polymerizations occurring within intervals 1 and 2 of Harkins' mechanism (1), and verifying kinetics of case II (2,3,4). Furthermore, because the procedure has been developed through a steady state (SS) model, the method is strictly valid in the limit of very low frequencies of oscillation. The technique is illustrated by means of a numerical example.

The effect of radical desorption on the particle size distribution in vinyl acetate emulsion polymerization

AbstractThe effect of free radical desorption is studied by using a mathematical model of particle size distribution in continuous emulsion polymerization. By comparing the theoretical prediction with experimental data, the value of Do for the vinyl acetate (VAc) system is best chosen as 0.19 × 10−7 cm2/h. The effect of radical desorption as well as mean residence time on the absolute particle size distribution, total concentration of polymer particles, conversion, and average number of radicals per polymer particle are analyzed by the model proposed.

Kinetic model for continuous emulsion polymerization of vinyl chloride at subsaturation pressure

AbstractThe dependence of the polymerization rate on the concentrations of monomer, surfactant and initiator and on temperature in the semicontinuous emulsion polymerization of vinyl chloride at subsaturation pressure was determined experimentally. A kinetic model for the continuous emulsion polymerization of vinyl chloride at subsaturation pressure, based on the equation of total material balance of vinyl chloride and the experimentally determined kinetic equation of polymerization, is established.

Dynamic modeling of emulsion polymerization reactors

AbstractThis paper is a survey of recent published works on the dynamic and steady state modeling of emulsion homo‐ and copolymerization in batch, semicontinuous, and continuous latex reactors. Contributions to our understanding of diffusion‐controlled termination and propagation reactions, molecular weight, long chain branching and crosslinking development, polymer particle nucleation, and of the dynamics of continuous emulsion polymerization are critically reviewed.

Simulation of particle size distribution in continuous emulsion polymerization styrene monomer

AbstractA detailed mathematical model for absolute particle‐size distribution in continuous emulsion polymerization of styrene monomer is proposed on the basis of the modified population‐balance theory. The computer simulation is then performed for styrene polymerization as an example of a nondesorption system. The effects of emulsifier and initiator concentrations as well as mean residence time on the absolute particle‐size‐distribution function, total concentration of polymer particles, conversion, average number and weight radii, average number of radicals per polymer particle, and polydispersity of radius are simulated by the model proposed.

Dynamic modelling of the continuous emulsion polymerization of vinyl chloride

AbstractA dynamic model for the continuous emulsion polymerization of vinyl chloride (VCM) in a train of stirred tank reactors has been developed. This model can predict monomer conversion, polymer particle size distribution (PSD), molecular weight distribution and long and short chain branching frequencies under non‐steady reactor operation during startup, reactor switching and during unstable operation when conversion and polymer and polymer particle properties oscillate with time. The model has been used to design a flexible reactor train configuration which operates in a stable mode and can produce latexes with a wide range of properties including a bimodal polymer particle size distribution.

PARTICLE SIZE DISTRIBUTION IN CONTINUOUS EMULSION POLYMERIZATION WITH FREE RADICAL DESORPTION

ABSTRACT A mathematical model of particle size distribution in continuous emulsion polymerization which accounts for the free radical desorption from polymer particles is presented. The desorption rate is based on the diffusion theories which suggest the rate coefficient should be inversely proportional to the surface area of the polymer particles. The number density and total particle number are estimated by our model. The average number of radicals per particle approaches Smith-Ewart case II In the range of large particle sizes. A means for predicting the nature of average desorption rate is proposed, and it seems to be influenced by concentrations of emulsifier and initiator, and residence times as well

Control of Emulsion Polymerization Reactors

An overview of some of the research projects on the modelling, optimization and control of emulsion polymerization reactors being carried out at the McMaster Institute for Polymer Production Technology will be presented. The objectives are to optimize production rates and to achieve control over 'product quality variables such as polymer particle size distribution, particle morphology, copolymer composition, sequence length, molecular weights, and long chain branching.The polymer systems under investigation include poly(vinyl acetate) and vinyl acetate copolymers (acrylic acid, butyl acrylate and 2-ethyl hexyl acrylate comonomers) and styrene copolymers (acrylonitrile and butadiene comonomers).One project in particular on the control of oscillations in conversion and latex properties in continuous emulsion polymerization in a CSTR train is discussed in more detail. It is shown that the oscillation phenomenon, which occurs in essentially all Case I emulsion polymerization systems (e.g. vinyl acetate and vinyl chloride emulsion polymerization), is conveniently eliminated with a specially designed reactor train. This design was found with the use of a dynamic model for a latex reactor.The design consists of a train of CSTR's in which the first reactor is a very small nucleating (seed) reactor and the feed streams are split between the first two reactors. The on-line control problem then reduces to the much simpler problem of controlling the "steady-state" generation of particles in the small seed reactor in order to achieve any desired final conversion and particle size. It is shown that this can easily be accomplished in this new reactor configuration by manipulating the split of monomer and water feed between the reactors, and the feedrate of initiator to the first reactor.

On‐line measurement of surface tension and density with applications to emulsion polymerization

AbstractThree process sensors are discussed, one for the determination of surface tension and two for the determination of liquid density. All three methods are on‐line, compatible with digital data acquisition systems, and capable of monitoring flowing process streams. The instruments are described and calibration data are given. Two mathematical models of the bubble tensiometer are developed. Data showing the application of these instruments to the monitoring of batch and continuous emulsion polymerization are given.

Emulsion polymerisation in continuous reactor systems

AbstractContinuous reactor systems find important applications in the production of sythetic polymer latexes and increased production rates are providing additional incentives for the development of new continuous systems. The fundamental factors that should be considered in the development of continuous processes are reviewed in this paper. Particular emphasis is placed on exploring the differences between batch and continuous reactors and why these difference can lead to different latex product, even if the same recipe is employed. These factors make the task of designing continuous reactor systems based on batch research and development very difficult and risky. Thus it is recommended that small‐scale continuous reactors be employed early in a product/process development effort if that effort is likely to lead to a continuous commercial process.The published literature on continuous emulsion polymerization reactors has been reasonably active in the past ten years. Our understanding of the chemistry and reactor modelling has been advanced but a number of areas for fruitful research remains. Some of these problems are reviewed and directions for new efforts are suggested.