A quantitative treatment of particle size distributions in emulsion polymerization (original) (raw)
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Polymer, 1988
For emulsion polymerization of a 'zero-one' system, the method of moments is applied to the model proposed by Lichti et al. to describe the particle size distribution (PSD). Using the explicit expressions so obtained for the first four moments, the average number of free radicals par particle, ~, and kinetic parameters of the system involving the rate coefficients for adsorption and desorption of free radicals, p and k, and the propagation rate coefficient, kp, can be obtained easily by use of PSD data without involving a complicated curve fitting procedure as was required in their work. Detailed calculations on the styrene system data of Lichti et al. show that both p and k are proportional to particle surface area. The result for k is opposite to that proposed by those workers, in which k was considered to be inversely proportional to the particle surface area. After further manipulation and approximation of the expressions so obtained, explicit expressions for the number-average volume, 6n, the standard deviation, tr, and the skewness, u~, in terms of surfactant and initiator levels, temperature and reaction time are also obtained. The effects of the variations of these variables on the three characteristic parameters of the PSD can be determined.
Polymer-Plastics Technology and Engineering, 2005
The objective of the present paper is to demonstrate that the explicit radical-particle size distribution approach correctly predicts the effect of compartmentalization on the overall reaction rates and therefore chain length averages. Modeling results for the seeded emulsion polymerization of styrene were compared with experimental results. Several experiments were carried out with systematically varied compartmentalization of radicals by varying seed latex particle numbers and the amount of initiator. The overall polymerization rate was measured using reaction calorimetry and the final particle size distribution was measured using Transmission Electron Microscopy. The results demonstrated that the model is able to predict successfully the rate of polymerization and particle size distributions as a function of time for all recipes. This proves that the model deals correctly with the effect of compartmentalization on overall reaction rates and thus on chain length averages. The work described in this paper demonstrates that the explicit radical particle size distribution approach is a powerful method for predicting emulsion polymerization kinetics and product properties, such as particle size distributions and chain length distributions.
Scale-up of Emulsion Polymerization Process : impact of changing characteristic times
2016
A framework, consisting of a computational fluid dynamics (CFD) simulation model coupled to a population balance model (PBM) is developed to study the effect of various parameters on the performance of an emulsion polymerization process which leads to the production of a fine dispersion of polymer particles in a continuous aqueous medium.Like most polymer products, latexes are “products-by-process”, whose main properties are determined during polymerization. One of the main parameters influencing the final quality of the latexes is the particle size distribution (PSD). Modeling the evolution of PSD is usually accomplished through the addition of a set of PBEs to the kinetic model. PBE provides a means of considering the contribution of different phenomena in the PSD evolution, being nucleation, growth of polymer particles by polymerization, and coagulation of particles due to brownian or fluid motion (Perikinetic and Orthokinetic coagulation, respectively).To assess the impact of no...
Journal of Applied Polymer Science, 2006
It is understood that a major controlling factor in the development of latex particle morphology is the extent to which second stage oligomeric radicals can diffuse into the particles after entry from the aqueous phase. This leads to the expectation that any factor which decreases the diffusion rate of second stage radicals should decrease radical penetration, and thus favor the formation of core-shell type morphologies. The occurrence of crosslinking reactions during the second stage may be one such factor, since the branched and crosslinked chains diffuse much more slowly (if at all) than their linear counterparts. This paper addresses the effect of the addition of crosslinking agent (a divinyl monomer) during the second stage polymerization on par-ticle morphology. It is shown experimentally that, contrary to what one might expect, crosslinking during the second stage has very little, if any, effect on morphology. Modeling suggests that the reason is that the probability for radicals to develop a branch before penetrating a significant distance into the particles is very low (under conditions where full penetration is possible in the absence of crosslinking agent), especially for what is considered to be typical concentrations of crosslinking agent.
Advances in Emulsion Polymerization
2001
The development of waterborne coatings continues to be of primary interest to the coatings industry be cause of environmental concerns. Coatings with zero volatile organic compounds (VOC), external weather durability, good block resistance, fast curing at room temperature, good adhesion to a variety of substrates, and low water sensitivity, are just some of the required properties of such coatings. During the past 50 years, emulsion polymerization has proven to be a versatile process for the preparation of a wide variety of water-based coatings. Some of the advances in emulsion polymerization include the ability to design and control latex particle morphology, with the potential of achieving many of the above coatings properties. The use of latex blends, with predetermined particle size and surface properties, is a frequently utilized strategy with significant relevance to the coatings industry for enhancing the mechanical strength, durability, and gloss of a waterborne coating. Ano...
Styrene emulsion polymerization: Particle-size distributions
Journal of Polymer Science: Polymer Chemistry Edition, 1981
Data are presented on the time evolution of particle-size distributions (PSDs) in seeded and ab initio styrene emulsion polymerization systems. Initiation was by chemical reagent (potassium persulfate) or y-radiation. The unswollen PSDs at various times during interval I1 of the polymerization were obtained by direct measurement of calibrated electron micrographs. Experimental results were fitted with the equations that describe the time evolution of an initial PSD. Analytic solutions to these equations that allow for entry, exit, and propagation of free radicals were obtained. The values of the rate coefficients for these processes used to fit the experimental data were in excellent agreement with those obtained from dilatometric kinetics experiments.
Journal of Polymer Science Part A-polymer Chemistry, 1988
The kinetics of emulsion copolymerizing systems during intervals I1 and I11 (i.e., after completion of latex particle formation) has been studied through the pseudo-homopolymerization approach. The Smith-Ewart equations for copolymers are reduced to the corresponding equations for homopolymers by introducing suitable pseudo-homopolymerization parameters. Analogies and differences between our results and those of previously reported treatments are critically discussed. On the grounds of the probabilistic approach developed in Part I of this series, a detailed description of the copolymer chain structure is derived for systems containing no more than one growing radical per particle. In particular explicit algebraic relationships are reported for both the two-dimensional molecular weight distribution and the unidimensional marginal distribution functions of molecular weight and chemical composition. A complete description of the chain microstructure is also reported. Equations are derived specifying the time evolution of the monomer sequence distribution and polymer end groups.
Fundamentals of Emulsion Polymerization
Biomacromolecules
A comprehensive overview of the fundamentals of emulsion polymerization and related processes is presented with the object of providing theoretical and practical understanding to researchers considering use of these methods for synthesis of polymer colloids across a wide range of applications. Hence, the overview has been written for a general scientific audience with no prior knowledge assumed. Succinct introductions are given to key topics of background science to assist the reader. Importance is placed on ensuring mechanistic understanding of these complex polymerizations and how the processes can be used to create polymer colloids that have particles with well-defined properties and morphology. Mathematical equations and associated theory are given where they enhance understanding and learning and where they are particularly useful for practical application. Practical guidance also is given for new researchers so that they can begin using the various processes effectively and in ways that avoid common mistakes.