共查询到20条相似文献,搜索用时 13 毫秒
1.
Carboxylated styrene-butadiene rubber (XSBR) latexes were prepared by emulsifier-free batch emulsion copolymerization of styrene and butadiene with different types of carboxylic acid monomers (AA, MAA, IA). It was found that the particle growth is dependent on the hydrophilic nature of carboxylic acid monomers. SEM studies showed that Np is almost constant in the particle growth stage (conversion above 10%). Through some calculations by data obtained from DLS technique, average diameter of monomer swollen polymer particles of all the XSBR latexes at the same conversion of 0.4 was obtained to be 368.91, 174.17 and 437.15 nm for AA, MAA and IA, respectively. Several kinetic parameters related to the particle growth stage such as the average number of growing chain per particle were calculated to be 0.474, 0.370 and 1.685 for AA, MAA and IA, respectively. It was observed that these kinetic parameters increase with increasing average diameter of monomer swollen polymer particles, which is consistent with the emulsion polymerization kinetics. Moreover, results indicated that the polymerization rate per particle or equivalently the average number of the growing chain per particle (particle growth stage) decreases by replacing a part of styrene with butadiene in the emulsion copolymerization recipe of styrene-carboxylic acid monomer. 相似文献
2.
Carboxylated styrene–butadiene rubber latexes were prepared through the emulsifier‐free emulsion copolymerization of styrene and butadiene with various carboxylic acid monomers. The effects of various carboxylic acid monomers on the particle formation process were investigated. The type of carboxylic acid monomer strongly affected the particle nucleation. The number of particles and thus the polymerization rate increased with the increasing hydrophobicity of the carboxylic acid monomers. There was a significant difference in the polymerization rate per particle. The results showed that particle nucleation and growth were dependent on the hydrophilic nature of the carboxylic acid monomers. The average particle diameter of the carboxylated styrene–butadiene rubber latexes in the dry state was obtained through some calculations using direct measurements of the average particle diameter in the monomer‐swollen state by a dynamic light scattering technique. Several parameters, such as the polymerization rate, number of latex particles per unit of volume of the aqueous phase, and polymerization rate per particle, were calculated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 相似文献
3.
The free radical transfer between aqueous phase and latex particles was investigated in the seeded emulsion polymerization using potassium persulfate (KPS) as an initiator. The effects of seed particle size, initiator concentration and polymerization temperature on the radical entry into and/or exit from the particles were emphatically examined. The results suggest that the aqueous-phase radical entry into the particles should be a competitive process, i.e. the competition between radical diffusion from the bulk aqueous phase to the interface of particles and its reactions in the aqueous phase determines whether it may be adsorbed into the particles or not. This implies that the reactions and properties of radicals in the aqueous phase play an essential role in particle nucleation in the emulsion polymerization. 相似文献
4.
The particle nucleation mechanism in emulsion polymerization of styrene with a novel polyester emulsifier, 5‐sulfoisophthalic acid dimethyl ester sodium salt‐modified tetracarboxylic acid‐terminated polyester (SMTAPE), was investigated. The consumption of SMTAPE micelles was monitored by the measurement of surface tension during the emulsion polymerization. Kinetic studies and emulsifier consumption clearly showed that a continuous nucleation mechanism without Smith–Ewart interval II was characteristic of this system. It was attributed to the high concentration of SMTAPE emulsifier in the polymerization, which led to a large surface area and a vast number of micelles around 10 nm in size that served as the major locus of particle nucleation. A broad particle size distribution was observed throughout the reaction, and the nucleation period lasted well into the reaction until the disappearance of the micelles or the disappearance of monomer droplets. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1061–1070, 2001 相似文献
5.
《Polymer》2003,44(19):5541-5546
An unconventional amphiphile (1-[ω-(4′-methoxy-4-biphenylyloxy)octyl]pyridinium bromide, PC8) was used as surfactant in the emulsion polymerization of styrene. At low surfactant concentration (6, 12 or 36 mmol l−1), curves of polymerization rate versus conversion obeyed the typical behavior characterized by intervals I, II and III. However, at high concentration (48 or 72 mmol l−1) the interval II was not observed. The particle size distribution curves showed two families of polymer particles, indicating the participation of at least two mechanisms of particle formation, one being the simple micellar nucleation and the other probably the coagulative nucleation of precursor particles. The latter was considered to occur during the nucleation interval. 相似文献
6.
Charles David ImmanuelFrancis Joseph Doyle III 《Chemical engineering science》2002,57(20):4415-4427
The open-loop generation of an optimal feed profile to attain a target particle size distribution (PSD) in the semi-batch emulsion co-polymerization of vinyl acetate and butyl acrylate is described. A nominal model of the process based on population balancing is utilized for this purpose. A Genetic Algorithm is employed as the optimization strategy. The optimal recipes generated in these studies are implemented on an experimental emulsion polymerization reactor. The end-point PSD obtained in these experiments closely matches the target in spite of the model uncertainties and process disturbances. Examination of the evolution of the PSD up to the end point provides useful information for feedback control strategies. 相似文献
7.
8.
The particle size distribution of polymer always develops in emulsion polymerization systems, and certain key phenomena/mechanisms as well as properties of the final product are significantly affected by this distribution. This review mainly focuses on the measurement methods of particle size distribution rather than average particle size during the emulsion polymerization process, including the existing off-line, on-line, and in-line measurement methods. Moreover, the principle, resolution, performance, advantages, and drawbacks of various methods for evaluating particle size distribution are contrasted and illustrated. Besides, several possible development directions or solutions of the in-line measurement technology are explored 相似文献
9.
Charles David Immanuel 《Chemical engineering science》2003,58(16):3681-3698
A computationally efficient solution technique is presented for population balance models accounting for nucleation, growth and coagulation (aggregation) (with extensions for breakage). In contrast to earlier techniques, this technique is not based on approximating the population balance equation, but is based on employing individual rates of nucleation, growth and coagulation to update the PSD in a hierarchical framework. The method is comprised of two steps. The first step is the calculation of the rates of nucleation, growth and coagulation by solving an appropriate system of equations. This information is then used in the second step to update the PSD. The method effectively decomposes the fast and the slow kinetics, thereby eliminating the stiffness in the solution. In solving the coagulation kernel, a semi-analytical solution strategy is adapted, which substantially reduces the computational requirement, but also ensures the consistency of properties such as the number and mass of particles. 相似文献
10.
Bassam Alhamad 《Chemical engineering science》2005,60(23):6596-6606
A multi-variable model predictive control (MPC) was formulated to solve control problems associated with a combination of regulation and targeting desired set-points. We investigated the simultaneous control of key polymer properties: the particle size (PSD) and molecular weight distribution (MWD) by manipulating the flow rates of the monomers (styrene, MMA), surfactant, initiator and the temperature of the reactor. A multi-input-multi-output (MIMO) formulation was constructed for the constrained optimal control problem to maximize the width of the PSD (with Mn at a constant set-point), and to maximize the average molar mass. The strategy developed within a gPROMS-API-DCS environment allowed real-time implementation of model-based control of the process. The optimal control problem was implemented via an interface to a dynamic optimization code. Major improvements in process operation and polymer property control resulted on the implementation of our multi-variable MPC algorithm. The manipulation of the four flow rates and the temperature increased the degree of freedom in the system and achieved tighter PSD and MWD control. The on-line performance of MPC for MWD and PSD control was found to be satisfactory. 相似文献
11.
In a further effort to understand the role of water‐soluble oligomers formed during the emulsion terpolymerization of styrene/butadiene/acrylic acid (St/Bu/AA), the reaction temperature, initiator concentration, and ionic strength were varied and the kinetics and resulting oligomers were characterized as a function of reaction time. The rate of polymerization (Rp) was observed to increase with increasing temperature and initiator concentration; the reasons for this vary. The increase in Rp with increasing initiator concentration is mainly attributed to the increase in the number of oligomeric radicals formed and, subsequently, the resulting number of particles (Np). Increasing the temperature increases the water solubility of both monomers and polymers, which results in changes in the composition and molecular weight of the oligomeric radicals being formed. The primary reaction locus in the St/Bu/AA system was noted to shift to the aqueous phase after most of the styrene and butadiene had reacted, based on the unreacted AA profile. The role of water‐soluble oligomers (both oligomeric radicals and dead oligomers) during the emulsion polymerization of St/Bu with acrylic acid can be described by three periods: (1) particle generation and (2) before and (3) after the critical surface saturation concentration (CSSC) is reached during the particle growth period. The incorporation of AA monomer into the oligomer chains after the CSSC may cause destabilization of the latexes through a bridging flocculation mechanism. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1988–1999, 2003 相似文献
12.
The influence of 1-pentanol (C5OH) on the ST emulsion polymerization mechanisms and kinetics is investigated. The CMC of the ST emulsions first decreases rapidly and then levels off when the C5OH concentration ([C5OH]) increases from 0 to 72 mM. The effect of C5OH increases to a maximum and then decreases when the SDS concentration ([SDS]) increases from 2 to 18 mM. At [SDS]=2 mM, homogeneous nucleation controls the polymerization kinetics regardless of [C5OH]. At [SDS]=4 mM, the effect of [C5OH] appears due to the transition from homogeneous nucleation to a mixed mode of particle nucleation (homogeneous nucleation and micellar nucleation) occurs when [C5OH] increases from 0 to 72 mM. The effect of [C5OH] is the strongest at [SDS]=6 mM since the particle nucleation mechanisms span homogeneous nucleation (low [C5OH]), a mixed mode of particle nucleation (homogeneous nucleation and micellar nucleation) (medium [C5OH]) and micellar nucleation (high [C5OH]). At [SDS] >6 mM, in which micellar nucleation controls the polymerization kinetics, the effect of [C5OH] decreases rapidly with increasing [SDS]. 相似文献
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14.
Within-batch feedback control strategies are developed for the regulation of the particle size distribution (PSD) in a semibatch vinyl acetate (VAc)/butyl acrylate (BuA) emulsion copolymerization system. These strategies are also applicable for regulation of distributions in other particulate systems governed by population balances. In the first strategy, PID controllers are employed for regulating nucleation and growth events through tracking the nominal trajectories of total number of particles and the solids content by manipulating the feed-rates of the more reactive monomer, BuA, and the surfactant. The second control strategy is based on tracking nominal trajectories of the moments of the distribution with a quadratic dynamic matrix controller (QDMC). To determine the appropriate number of moments to describe the PSD during various stages of a nominal batch, a maximum-entropy approach is utilized. In the final and most complex approach, a nonlinear model predictive controller is designed utilizing the detailed population balance model of the system. The ill-conditioning resulting from the high-dimensionality of the resulting dynamical system is removed by principal component analysis (PCA)-based model order reduction and a multi-rate estimator is designed to compensate for the measurement delay associated with the PSD measurements. 相似文献
15.
Styrene miniemulsion polymerizations stabilized by sodium lauryl sulfate in combination with a reactive costabilizer, lauryl methacrylate (LMA) or stearyl methacrylate (SMA), were studied. A small amount of extremely hydrophobic dye was incorporated into monomer droplets (102 nm in diameter) to investigate particle nucleation and growth mechanisms. In addition to monomer droplet nucleation, particle nuclei generated in the aqueous phase (homogeneous nucleation) also play an important role in both LMA‐ and SMA‐containing polymerization systems. The way that these two nucleation mechanisms compete with each other is closely related to the water solubility of the costabilizer (LMA > SMA). The fraction of latex particles originating from homogeneous nucleation increases with decreasing hydrophobicity of the costabilizer. Zeta potential data of latex particles and the molecular weight and molecular weight distribution of emulsion polymers provide supporting evidence for the proposed competitive particle nucleation and growth mechanisms. © 2002 Society of Chemical Industry 相似文献
16.
Jana Machotova Stepan Podzimek Hedvika Zgoni Lubos Prokupek Roman Svoboda Adela Ruckerova 《Journal of Adhesion Science and Technology》2016,30(10):1095-1108
The effect of reducing the molar mass of the shell layer of core–shell latex particles on film-forming and final coating properties of self-crosslinking latexes was investigated. Latex particles were prepared by the semi-continuous non-seeded emulsion polymerization of methyl methacrylate, butyl acrylate and methacrylic acid as main monomers. The particle core was slightly cross-linked (using a constant amount of allyl methacrylate as a comonomer) to prevent the copolymers forming the core phase from migration into the shell phase. For interfacial cross-linking, diacetone acrylamide was copolymerized into the shell layer of latex particles to provide sites for subsequent reaction with adipic acid dihydrazide. The molar mass of copolymers forming the shell layer was systematically varied by isooctyl 3-mercaptopropionate chain transfer agent included in the synthesis of each of the shell layers and the molar mass distribution was determined using size exclusion chromatography coupled with a multi-angle light scattering detection. Fundamental properties of latexes and cast films were systematically compared. These properties included minimum film-forming temperature, pendulum hardness, adhesion, impact resistance, stress–strain properties as well as the characterization of water absorption. The results confirmed theoretical predictions and described empirically the effects of reducing the molar mass of the shell layer copolymer on final properties of coating films. 相似文献
17.
Stable functional cationic latices were prepared by emulsifier‐free emulsion copolymerization of styrene (St) and butyl‐acrylate (BA) with 1‐butyl‐4‐vinylpyridinium bromide (qBVPBr) as functional comonomer and azobis(isobutyramidine hydrochloride) (AIBA) as initiator at (70 ± 1)°C. The influences of the reaction temperature, the initiator concentration, and comonomer concentration on the polymerization conversion (x %), polymerization rate (Rp) of poly(St/BA/qBVPBr) emulsions were investigated. The results indicated that x % and Rp increase with increasing qBVPBr or AIBA concentration and temperature, and Rp can be expressed as Rp = Kp[AIBA]0.73[qBVPBr]0.08 (rAIBA = 0.9968; rqBVPBr = 0.9946, both rAIBA and rqBVPBr are linear correlation coefficient) and the apparent activation energy (Ea) is 47.89 kJ mol?1. In the absence of emulsifier condition, curves of Rp versus reaction time obeyed the typical behavior characterized by Intervals I, II, and III as similar conventional emulsion polymerization. The formation and growth of poly(St/BA/qBVPBr) latex particles has been studied at different reaction times. The results indicate that Np decrease gradually with time at the early polymerization stages and then reach a constant value after about 20% conversion, but Dp by photon correlation spectroscopy grow continuously as all polymerization proceed. Both the particle size distribution and molecular weight distribution curves are of bimodal size distribution and indicate the participation of at least two mechanisms of particle formation, namely, homogeneous nucleation in the aqueous phase and micellar nucleation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 相似文献
18.
Emma M. Coen Robert G. Gilbert Bradley R. Morrison Hartmann Leube Sarah Peach 《Polymer》1998,39(26):7099-7112
An extensive model is given for the particle size distribution (PSD), particle number, particle size and amount of secondary nucleation in emulsion polymerisations. This incorporates what are thought to be all of the complex competing processes: aqueous phase kinetics for all radical species arising from both initiator and from exit (desorption), radical balance inside the particles, particle formation by both micellar and homogeneous nucleation mechanisms, and coagulation (the rate of which is obtained using the Healy–Hogg extension of DLVO theory). The predictions of the model are compared to extensive experimental results on rates, time evolution of the particle size distribution, and relative amounts of secondary nucleation, for styrene initiated by persulfate with sodium dodecyl sulfate and with sodium dihexyl sulfosuccinate as surfactants. For this system values of almost all of the many parameters needed for the model are available from independent measurements, and thus no significant parameter adjustment is plausible. Accord with experiment is imperfect but quite acceptable, supporting the validity of the various mechanisms in the model. Effects such as the experimental variation of particle number with ionic strength, as well as calculated coagulation rate coefficients as functions of particle size, suggest that coagulation of precursor (i.e., newly-formed) particles is a significant effect, even above the cmc. The modelling also suggests why secondary nucleation occurs readily in systems stabilised with polymeric surfactant. 相似文献
19.
This paper addresses the control of the full particle size distribution (PSD) in a semibatch emulsion copolymerization reactor.
The numerical approximation of a fundamental population balance model results in a high order system to accurately describe
the distribution of particle size; therefore, model order reduction is required. Pseudo random input signals are input to
the mechanistic model to generate a data set which covers the reachable region of the system, on the basis of which the transformation
matrices are calculated by principal component analysis (PCA). A linear time varying model with reduced order obtained from
the transformation matrices is augmented in the prediction equation of linear model predictive control. The performance of
the controller is evaluated to drive the particle size distribution at the final time of the batch to the desired distribution
in the presence of disturbances.
This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from the Seoul National University. 相似文献
20.
The role of methyl methacrylate on branching and gel formation in the emulsion copolymerization of BA/MMA 总被引:1,自引:0,他引:1
Iñigo González 《Polymer》2007,48(9):2542-2547
The effect of the monomer ratio on the microstructure of BA/MMA emulsion copolymers was investigated. Monomer ratios spanned from pure BA used for adhesives to 50/50 wt/wt BA/MMA copolymers used for coatings. The gel content varied from 55% for pure BA to nil for the 50/50 copolymer. The branching level was reduced from 2.6% for pure BA to 0.3% for a 75/25 BA/MMA copolymer. The mechanisms responsible for the reduction of gel content can be found in the lower reactivity of the MMA terminated chains for hydrogen abstraction, the absence of abstractable hydrogens in the MMA units and the fact that MMA radicals terminate predominantly by disproportionation. The reduction of the level of branches is mainly due to the lower reactivity of MMA for intramolecular transfer and the lower instantaneous conversions that favored propagation over backbiting. 相似文献