Emulsion Polymerization Of Vinyl Chloride Research Articles

Binary mixtures of anionic double-chain sulfonate emulsifiers in VCM emulsion polymerization with high solid content: effect of emulsifier’s combination ratio and concentration

Binary mixtures of anionic double-chain sulfonate emulsifiers, sodium di-isodecyl sulfosuccinate and sodium pentadecan-sulfonate (SPS) were employed in batch reactor at different combination ratios and concentration for vinyl chloride emulsion polymerization. Reaction performances were evaluated by monitoring conversion rate and molecular weight by K-value parameter. Particle size and its distribution were investigated as a criterion for particle nucleation and the growing process by calculating the number of latex particles and the average number of growing chains per particle, respectively. The final latexes were evaluated by means of the coarse matter content as a qualitative character of the latex. The results showed that the overall reaction rate increases by high amount of SPS. Also, by increasing SPS content in binary mixture, coarse particle formation decreased and latex stability and particle size distribution increased. Furthermore, it has been found that the particle size was nonlinearly dependent on the combined ratio and amount of emulsifier and has shown a minimum within the scope of the study.

A combinatorial approach to evaluation of monomer conversion and particle size distribution in vinyl chloride emulsion polymerization

This work is targeted to study emulsion polymerization of vinyl chloride monomer (VCM) using experimental and mathematical methods. To fulfill this goal, a computer code was developed on the basis of zero–one population balance by which the effects of initiator and emulsifier concentration on the evolution of VCM conversion were investigated in the course of polymerization. The model was also trained to capture the coagulation of the particles. This enabled to adopt a reliable way of evaluating the particle size distribution (PSD). In particular, the rates of homogeneous and micellar nucleation mechanisms were simulated and reasonably predicted alterations in the PSD and the number of polymer particles under the influence of aforementioned parameters. The results from modeling were satisfactorily consistent with the experimental outputs and obviously visualized the impact of initiator and surfactant concentration on the PSD of the prepared PVC latexes.

Particle Formation in Vinyl Chloride Emulsion Polymerization: Reaction Modeling

A mathematical model is developed to help quantify and improve our understanding of the formation of particles and the evolution of the particle size distribution (PSD) in the emulsion polymerization of vinyl chloride monomer (VCM). A special feature of the model is the computation of the coupled radical number and particle size distributions by means of the zero−one−two population balance equations. This approach is shown to be necessary when modeling processes that involve particle nucleation. Preliminary results are presented to illustrate the ability of the model in interpreting experimental data.

Application of Taguchi method to investigate the effects of process factors on the performance of batch emulsion polymerization of vinyl chloride

AbstractIn this article, the influences of five operating variables on the molecular weight (or K‐value), polydispersity index (PDI), as well as polymerization yield of emulsion poly (vinyl chloride) in batch reactor were investigated simultaneously using Taguchi experimental design approach. The variables were temperature (T), water to monomer weight ratio (r), concentrations of initiator ([I]) and emulsifier ([E]), and agitation speed (S). Statistical analysis of results revealed the significance order of factors affecting the product qualities and quantity. It was found that the reaction temperature is the principal operating factor to control the molecular weight, and this is attributed to promotion of chain transfer reactions to monomer in this system. The effect of this factor on PDI is also comprehensively discussed. The significance sequences of important factors on yield are: S > [E] > r. The polymerization yield increases with S and [E] but decreases as r is increased. The relative optimum condition for a typical paste application was also determined using overall evaluation criteria. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Particle Formation in Vinyl Chloride Emulsion Polymerization. Experimental Study

Particle formation in vinyl chloride emulsion polymerization has been investigated by means of ab initio and seeded experiments. A series of ab initio polymerizations was run in order to obtain reliable data regarding the dependence of the particle number on the emulsifier (SDS and SDBS) concentration, as well as to analyze the effect of the initiator concentration, stirring rate, and monomer-to-water ratio upon the particle number and the polymerization kinetics. Seeded polymerizations carried out at different concentrations of seed latex and surfactant made it possible to quantitatively evaluate the influence of these factors on the onset and extent of secondary particle formation.

Batch emulsion polymerization of vinyl chloride: Application of experimental design to investigate the effects of operating variables on particle size and particle size distribution

AbstractIn this article, the influences of operating variables on the particle size (PS) and particle size distribution (PSD) of emulsion poly(vinyl chloride) in batch reactor were investigated using Taguchi experimental design approach. The variables were temperature (T), water to monomer weight ratio (R), concentrations of initiator ([I]) and emulsifier ([E]), and agitation speed (S). Scanning electron microscope was used together with image analysis software to determine the PS and PSD. Statistical analysis of results revealed that the PS of emulsion poly(vinyl chloride) strongly depends on emulsifier and initiator concentrations, respectively, whereas the other factors have no significant effects in the range of levels investigated in this study. Except initiator concentration, all factors have important influence on the PSD (significance sequence: S > R > T > [E]). It is implied from the greater influence of agitation speed relative to temperature on PSD that the shear coagulation predominates the Brownian coagulation in this system. The relative optimum condition for a typical paste application was also determined using overall evaluation criteria. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Synthesis of Bimodal PVC Latexes by Emulsion Polymerization: An Experimental and Modeling Study

AbstractThe onset and extent of secondary particle formation in the seeded emulsion polymerization of vinyl chloride were investigated by performing a series of seeded polymerizations at different concentrations of seed latex and surfactant. It was found that, in general, both the onset and the extent of secondary particle formation are determined not only by the rate of homogeneous nucleation, but also by the rates of particle coagulation. A comparison of methods to compute the evolution of the particle size distribution in vinyl chloride emulsion polymerization was also carried out. For growth processes, the widely‐used pseudo‐bulk model gives correct answers. For processes involving particle formation, on the other hand, this model cannot be used because it neglects, among others, the effects of nucleation and coagulation on the radical number distribution. To surmount this problem, we propose to use the zero‐one‐two model, for which the full population balance equations are given here.

Poly(vinyl chloride) on the way from the 19th century to the 21st century

AbstractDespite all the technical and economic problems and the public discussions on the environmental dangers and hazards of chlorine chemistry, poly(vinyl chloride) (PVC) is the second most produced plastic (with a worldwide capacity of about 31 million tons), placing after polyolefins and before styrene polymers. Presently, PVC production worldwide is growing at a rate of more than 4% per year. The application of PVC was first described in a patent in 1913, but only after 1930 did a sustained interest in PVC arise in several industrial laboratories. The most remarkable milestones in PVC history and their importance to the development of macromolecular chemistry are briefly described, and some present PVC research and industrial applications, with respect to polymerization, stabilization, bulk property modification, and chemical and material recycling of PVC waste, are discussed. Some actual selected topics include the emulsion polymerization of vinyl chloride with polymeric surfactants and controlled free‐radical polymerization with nitroxyls, whereas ionic and metal organic initiators have not found any technical applications. Chemical reactions offer many possibilities for the modification of PVC, but they have been not used on a technical scale yet. Much work has been done on stabilization with nontoxic or metal‐free systems. The bulk properties of PVC can be influenced by impact modification through the addition of graft copolymers or by blending with other polymers. Also presented are some problems and recent developments in PVC recycling. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 578–586, 2004

The Effect of Oxygen on the Kinetics and Particle Size Distribution in Vinyl Chloride Emulsion Polymerization

A comprehensive mathematical model is developed to quantify the effect of the oxygen concentration on the polymerization rate and particle size distribution in an unseeded vinyl chloride batch emulsion polymerization reactor. Particle formation is assumed to proceed by both the homogeneous and micellar nucleation mechanisms. Dynamic species mass balances are derived to follow the evolution of the polymerization rate and particle size distribution (PSD) in the batch reactor. It is shown that, at low initial oxygen concentrations, the polymerization rate increases with the oxygen concentration. On the other hand, the average latex particle size exhibits a U-shaped behavior with respect to the initial oxygen concentration. The experimental observations on the polymerization rate and the average particle size are explained by the combined role of oxygen as an inhibitor and a radical generator through the formation and subsequent decomposition of vinyl polyperoxides. The predictive capabilities of the present model are demonstrated through the successful simulation of experimental data on monomer conversion and PSD obtained from an industrial pilot-plant batch PVC reactor operated with various initial oxygen and initiator concentrations.

Seeded emulsion polymerization of vinyl chloride. A new approach to mechanism and kinetics

Some peculiarities concerning the mechanism and the kinetic behaviour of the vinyl chloride emulsion polymerization are described. Seeded emulsion polymerizations in the presence of an adequate mixture of anionic and non-ionic surfactants were carried out in order to avoid the micellar initiation. New kinetic parameters were determined from the experimental data as follows: (i) MSA, the minimum surface area of polymer seed particles necessary to capture all ion-oligoradicals generated in aqueous phase at a given initiator concentration; (ii) MCCI, the maximum critical concentration of initiator per unit surface of polymer particle under which the formation of new polymer particles is avoided; (iii) PVR1, the polymer volume per active growing radical, necessary to be within the particle for 1 s. It was found that the average number of propagating radicals per particle, n, depends on the size of the polymer particle, as a resultant of entry and exit and then of the initiation and termination reactions. The practical consequences of the accurate control of the polymer particles growing during seeded emulsion polymerization of vinyl chloride were emphasized. Einige Eigenheiten bezuglich des Mechanismus und der Kinetik der Vinylchlorid-Emulsionspolymerisation werden beschrieben. Die Saat-Emulsionspolymerisation wurde in Gegenwart einer adaquaten Mischung aus anionischen und nichtionischen Tensiden ausgefuhrt, um die micellare Initiation zu vermeiden. Neue kinetische Parameter wurden aus den experimentellen Daten wie folgt bestimmt: (i) MSA, die minimale Oberflache der Polymer-Keimpartikel, die zum Einfangen aller in der wasrigen Phase bei einer bestimmten Initiatorkonzentration erzeugten Ionenoligoradikale notwendig ist; (ii) MCCI, die maximale kritische Konzentration an Initiator pro Oberflacheneinheit eines Polymerpartikels, unterhalb welcher die Bildung von neuen Polymerpartikeln unterbleibt; (ii) PVR1, das Polymervolumen pro aktiv wachsendem Radikal, das notwendig ist, um 1 s innerhalb des Partikels zu verbleiben. Es zeigte sich, das die mittlere Zahl wachsender Radikale (n) von der Grose des Polymerpartikels abhangt, als Resultat von Eintritt und Austritt und der Initiierungs- und Abbruch-Reaktionen. Auf die praktischen Konsequenzen der genauen Kontrolle des Wachstums der Polymerpartikel wahrend der Saat-Emulsionspolymerisation von Vinylchlorid wird hingewiesen.

Modeling sustained oscillations in continuous emulsion polymerization of vinyl chloride

AbstractA simple mathematical model for the continuous emulsion polymerization of vinyl chloride based on nonlinear ordinary differential equations for the variation of particle concentration, total particle volume, and water‐soluble oligomeric products was developed and used to investigate which reactions influence whether or not sustained oscillations of latex properties occur at high conversion steady state. Results of the calculations are in good qualitative agreement with experimental data. Specifically, numerical analysis showed that the occurrence of sustained oscillations depends on particle coalescence as well as on the conversion dependence of both particle volume growth rate and particle coalescence rate. The model makes it possible to calculate the dynamic behavior of continuous emulsion polymerization reactors with regard to latex properties such as particle concentration, mean particle size, latex surface tension, solid content, and degree of coverage of latex surface with emulsifier from the start‐up into a high conversion steady state.

Synthesis, characterization and application of surface active initiators

AbstractSurface active azo initiators have been synthesized starting from 2,2′‐azoisobutyronitrile (AIBN) and different a, o‐diols. Values of the production rate of free radicals from these initiators (2fkd) were obtained from ESR investigations of initiator solutions with a spin labelling technique as well as from solution polymerization of acrylonitrile and from emulsion polymerization of vinyl chloride under monomer starved conditions. The 2fkd values from the polymerization experiments were higher than those from the ESR investigations. Furthermore, the results show an influence on the kinetic constants and latex properties of the initiator structure. The emulsion polymerization of styrene was investigated at temperatures from ambient to 373 K with different initiator‐emulsifier systems (IES) including persulphate, AIBN and surface active initiators. From these data were obtained Arrhenius plots for the mean degree of polymerization (DP) and for the particle number (N ), and overall activation energies were estimated. These activation energies show a strong dependence on the IES employed.

Formation of latex particles during the continuous emulsion polymerization of vinyl chloride

AbstractThe dispersion degree of latex particles during the continuous emulsion polymerization of vinyl chloride depends on the emulsifier concentration in the system. The particle sizes of the latex vary around average values in connection with the surface area which can be covered with emulsifier in a state of maximum packing.

Emulsion polymerization of vinyl chloride, 2 potassium persulfats decomposition in the presence of PVC latex

The decomposition rate of potassium persulfate (KPS) in aqueous solutions, in the presence of sodium dodecyl sulfate (SDS) and poly(vinyl chloride) latex (PVC) was studied. The dissolved SDS increases the decomposition rate constant (kd) while the SDS aggregation as micella and/or its adsorption on the polymer hydrophobic surface results in a decreasing kd. The emulsifier - free surface of the polymer particles increases the decomposition rate. A reaction mechanism based on emulsifier - emulsifier and emulsifier - polymer hydrophobic interactions is put forward.

Modeling of Emulsion Polymerization of Vinyl Chloride

Abstract A survey of the principles of emulsion polymerization modeling of vinyl chloride is presented. Experimental results and model equations for particle nucleation, particle coalescence, and particle growth are discussed. A mechanism for particle coalescence in the course of polymerization is proposed based on the assumption that radical desorption from a particle is the rate-determining step for coalescence. Equations for the coalescence rate and velocity constant are derived based on this assumption. The resulting population balance equations for describing the change of particle size distribution during emulsion polymerization of vinyl chloride can be applied to different polymerization procedures, e.g., discontinuous, continuous, and seeded polymerizations. Examples of model calculations are given for several polymerization procedures and compared with experimental data.

Suspension, bulk, and emulsion polymerization of vinyl chloride—mechanism, kinetics, and reactor modelling

AbstractA review of relevant microscopic processes, both chemical and physical, which occur during suspension, bulk and emulsion polymerization (both before and after pressure drop) is given. The state of the art of kinetic modelling of monomer consumption rate, reactor pressure, molecular weight and short and long chain branching development and polymer chain microstructure is illustrated. The effects of diffusion‐controlled termination and propagation reactions and the significant decrease in initiator efficiency and decomposition rate constant at high monomer conversions on the relative rates of various chemical reactions are discussed. The application of temperature programming and semibatch operation are emphasized. Finally, attempts to model polymer particle morphology are described.

The rate of batch emulsion polymerization of vinyl chloride

AbstractThe rate of batch emulsion polymerization of vinyl chloride is described by the equation where E is the overall activation energy. The reaction order with respect to the initiator, γ, depends on the type of the termination reaction; the reaction order with respect to the emulsifier, β, depends on the chemical nature of the emulsifier and on the amount of adsorbed emulsifier on the latex particles. The values of the coefficients and of the activation energy are determined for two initiation systems and two types of emulsifier.

Formation of latex particles during the batch emulsion polymerization of vinyl chloride

AbstractThe quantitative dependences between the emulsifier concentration in the emulsion water and the total surface area of the latex particles at the emulsion polymerization of vinyl chloride are investigated. From this it is possible to calculate the average volume/surface diameter. The exponent of emulsifier concentration in this relation reflects the variation of surface tension of the latex during the polymerization. This fact is due to the adsorption in time of the emulsifier on the surface of the latex particles.

Correlation between functional parameters of the reactor for continuous emulsion polymerization of vinyl chloride

AbstractThe determination of the polymerization rate, which is easily made in batch polymerization, may become difficult for continuous polymerization processes, because in the general equation Rp = –(1/V) dM/dt the parameter t reperesents the residence time tr and this depends not only on the feeding rates, but also on the composition of the reaction mixture, especially when polymerization occurs with a great volume contraction. In this study diagrams are presented which permit the rapid determination of Rp and tr for continuous emulsion polymerization of vinyl chloride from the functional parameters of the reactor.

The influence of the composition of the redox initiation system on the batch emulsion polymerization of vinyl of chloride

AbstractThe kinetics of the batch emulsion polymerization of vinyl chloride with redox initiation systems consisting of potassium persulphate, sodiumformaldehyde sulphoxylate and ferrous sulphate as a complex with Na2‐EDTA was studied. In these systems the main influence on the polymerization kinetics is provieded by the concentration of sodiumformaldehyde sulphoxylate and by the ration of the components. Potassium persulphate represents a kind of raw materials for generating the free radicals of initiation, but the amount of the radicals depends on the other components of the redox system.