جستجوی مقالات مرتبط با کلیدواژه « emulsion polymerization » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

One of the challenges in emulsion polymerization over the past two decades has been how to increase the solid content of polymer latex. Compared to conventional latex, high solid content latex (HSC) has a large volume fraction of the monomer dispersed phase, even more than 70% by weight. Increasing the concentration of polymer in latex, has important advantages such as increasing the space-time efficiency of the reactor, reducing the film formation and drying time, as well as reducing its storage and transportation costs. Conventional emulsion polymerization, mini-emulsion polymerization, self-emulsification polymerization, and concentrated emulsion polymerization have all been used to prepare HSC latexes, and good results have been reported in recent years. Production of HSC latexes in a reproducible manner requires precise control of the particle size distribution. To obtain a solid content above 60% or 70% by weight, the particle size distribution must be quite broad or multimodal. In addition, viscosity of HSC latex is highly sensitive to particle size distribution. In this study, the advances of the last few years, which are mainly in the preparation processes of such latexes and their applications are briefly reviewed.

From the past to the present day, various methods of printing have been used in terms of application, among which the most widely used method of them is electrophotography. The increasing demand for this technique increases the importance of obtaining high-resolution images in electrophotography. Therefore, the processes and the materials that are used are continuously improving and progressing. In this paper, at the first the toner and its components are introduced, then the properties of toner that effect on its quality is expressed. Followed by, different methods of toner production, especially the in situ emulsion polymerization method are described. The emulsion polymerization can be of great interest in toner production because of its ability to form composite particles with encapsulated structure and spherical shape as well as high reaction conversion. In this regard, different effective parameters and components of this method to produce of toner are introduced. Finally, the benefits of this method are expressed in comparison to other production methods of toner.

Acrylic-styrene latexes are being used in various industries such as textiles, rubber,plastics, adhesives and coatings due to unique properties such as good durability,compatibility with other materials, adhesion and ability to form continuous film, highresistance to ultra violet, oxygen, water and solvents. In this paper, the most effectivefactors on optimization of acrylic-styrene latexes' synthesis are studied namely: the typeand concentration of monomer, initiator and emulsifier, and temperature of polymerizationreaction. Optimized stable latex with the desirable performance may be achieved throughthe following conditions: using butyl acrylate monomer as an optimum acrylate monomerin combination with styrene hard monomer in the weight ratio 1-1.35, respectively; addingfunctional monomers like α-methacrylic and acrylic acid of about 2 wt% relative to thetotal weight of monomers, improving the film forming process via imparting cross-linkingcites into the acrylic chains; utilizing anionic emulsifier alone (like DSB and SDS) or incombination with nonionic ones (like OP-10 and TX100) of about 0.5 wt% to 3 wt% ofthe monomers; and using radical initiators like persulfates of potassium and ammoniumof about 0.25-0.5 wt% relative to the total monomers' weights. The reaction optimumtemperature range is determined to be approximately 75-80 °C. Adding fillers such asrosin and silica nanoparticles into the acrylic-styrene matrix as much as 4 and 5 wt%,respectively, results in improved water resistance of their films.

Effect of colloidal nanosilica (SiO2) on the mechanical, thermal and rheological properties of poly(vinyl acetate) synthesized by in situ emulsion polymerization method was investigated. For this purpose, a poly(vinyl acetate) latex containing 1.5 wt% colloidal silica nanoparticles was produced and the results were compared with of a blank sample. The effect of nanoparticles on the shear strength of a blank and modified poly(vinyl acetate) was characterized by tensile test. The effect of nanoparticles on glass transition temperature (Tg), thermal stability and char yield of pristine poly(vinyl acetate) and its nanocomposite was evaluated by differential scanning calorimetric (DSC) and thermogravimetric analysis (TGA), respectively. The rheological behavior of the products was studied by rheometric mechanical spectrometry (RMS). Eventually, field emission scanning electron microscopy (FE-SEM) coupled with elemental mapping of X-ray spectroscopy (EDX) was used to study the morphology and elemental analysis of the nanocomposite. The results showed that the shear strength was improved by 11% with increasing 1.5 wt% colloidal silica nanoparticles into poly(vinyl acetate). Besides, with the addition of silica nanoparticles, Tg increased approximately 1°C due to creating more free volume between the polymer chains. The TGA results showed that the nanocomposite char yield increased by 3.8% at 800°C in comparison with the blank polymer char yield, suggesting a thermal stability improvement in the presence of colloidal silica nanoparticles as a result of molecular interactions. The results of RMS revealed the shear thinning behavior of the latexes. The FE-SEM-EDX results showed a uniform dispersion of nanoparticles throughout the poly(vinyl acetate) matrix.

In this study, spherical-like polypyrrole nanoparticles with diameter smaller than 100 nm were synthesized via emulsion polymerization using FeCl3 as dopant and initiator simultaneously. Chemical structure of polypyrrole was confirmed with FTIR spectra. Furthermore, the morphology and the size of polypyrrole nanoparticles were investigated by SEM images. The structural order of samples was investigated using XRD analysis and the conductivity of samples was measured by four point probe method. In this work, effective factors on the conductivity of resulted polypyrrole including reaction temperature, initiator concentration and feeding strategy were investigated. In this study, without the use of complex equipment of synthesis or the use of different raw materials simply by optimizing the reaction conditions, a product with a conductivity of 8.5 S/cm was obtained. Moreover the aging effect on the conductivity of product was discussed.

The particle size distribution (PSD) is one of the most important parameters of emulsion polymerization latexes. This parameter affected the rheological and optical properties, adhesion, film formation and mechanical strength of latexes. Therefore, the modeling of PSD is of utmost importance in terms of application and mechanistic studies. Dynamic evolution of PSD is described by a set of population balance equations which involved various phenomena such as nucleation, growth, and coagulation. The extensive application and especially annually massive production of poly(butylacrylate) and polybutadiene produced by emulsion polymerization, highlights the significant of modeling these processes, which could resulted in better mechanistic knowledge and tailor-made polymer materials. In this paper, a mechanistic model based on population balance equations is developed for butyl acrylate and butadiene emulsion polymerization in a batch reactor. This model is used to predict the evolution of particle size distribution and the finite volume method as a precise technique is used for discritizing PBEs. The simulation results compared with the measured values during the evolution of conversion and average particle diameter for different initial surfactant concentrations.

Nitrile rubber/clay nanocomposites were prepared via in-situ emulsifier-free emulsion polymerization technique in the presence of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and pristine sodium montmorillonite (Na-MMT). The morphology of the nanocomposites was studied using X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM). The XRD results showed exfoliated morphology for the nanocomposites containing up to 3 wt% nanoclay and exfoliated-intercalated morphology for the nanocomposite containing 5 wt% nanoclay. The basal spacing of the nanocomposite، containing 5 wt% nanoclay، was increased to 1. 8 nm، which was 0. 61 nm wider than that obtained using pristine Na-MMT. Compared to neat rubber، the thermogravimetric analysis (TGA) revealed improvements in the thermal stability of all nanocomposite samples، in which the thermal degradation temperature was increased by increasing the clay content. The maximum increase in the thermal stability of the nanocomposites was obtained for the nanocomposite containing 5 wt% nanoclay with exfoliated-intercalated morphology. The tensile testing results showed remarkable improvements in the mechanical strength of the nanocomposites. In comparison with the neat nitrile rubber، the exfoliated nanocomposite، containing 3 wt% nanoclay، showed 302% and 219% increases in tensile modulus and tensile strength، respectively. The reason for improvementin mechanical properties of a nanocomposite، containing 3 wt% of nanoclay with respect to the nanocomposite containing 5 wt% of nanoclay، was related to the better dispersion of nanoclay platelets in the matrix and formation of exfoliated morphology. In addition، elongation-at-break and hardness were increased in the nanocomposites، when compared with the neat nitrile rubber.

The sipomer Pam 100(sp100) monomer is introduced by Rodia company as adhesion promoter of lattices. In this research, an acrylic- styrene latex is synthesized. Sp100 was included in the range of 1-10% by the weight of the monomers. The other monomers were styrene methyl methacrylate (MMA), ethyl acrylate(EA) and acrylic acid(AA). Optimum contenet of sp100 was obtained at 10%. In the next step the effect of Tg on corrosion and adhesion in the absence of sp 100 was investigated using Fox equation. The best result of adhesion was obtained at Tg 30°C; and the least corrosion occurred at -10°C.In the third step of this research the synthesized lattices were neutralizeaed with different bases: NaOH, amonia and monoethanolamine then they compared with their acid form.The best adhesion and corrosion resistance was obtained by the sample which neutralized by NaoH and Ammonia respectively. Adhesion evaluated by cross cut test and corrosion was studied by salt spray under the standards ASTM D3359 and ASTM D714 respectively. J. Color Sci. Tech. 7(2013), 53-59© Institute for Color Science and Technology.

In this research, polymeric photonic crystals with fcc packing structure were prepared and studied. Firstly, monodispersed colloidal spheres with core-shell structure were synthesized; they consisted of a polystyrene (PS) core and a copolymer shell of butyl acrylate (BA) and methyl methacrylate (MMA). The sample with total solid content of 32% was obtained and total conversion of polymerization was about 98 %. Then, the latex was coagulated in methanol, filtered and dried. After complete drying, the samples were hot pressed to make thin films of one millimeter thickness. In this crystallization procedure, the soft shells of latex spheres permit melt-like flow and the cores were organized to fcc packing structure in the elastomeric matrix. Uv spectrometer measurement showed two different refracted picks before and after press proving ordered structure of particles after hot press molding of dried latex.

A mixture of sodium lauryl sulfate (SLS) as ionic emulsifier and stearyl alcohol as non-ionic emulsifier was employed in a vinyl chloride emulsion polymerization reaction to study the influence of various interactive parameters involved in the reaction system. It was found that the particle size was dependent on the amount and type of emulsifier. The average particle size of polyvinyl chloride was dropped by higher amount of emulsifying agents. At the gel point, more heat was generated by higher amount of vinyl chloride fed into the reaction system. The molecular weight of the polymer was decreased by increases in reaction temperature while, it increased by augmenting the amount of emulsifier. According to the 13C NMR and FTIR spectroscopic data no defect was detected in the chain structure of synthetic polyvinylchloride product. An optimization of polymerizationreaction condition was reached based on ultimate particle size desired for its favorabledistribution in plastisols.

Nowadays production of water- base resins by emulsion polymerization method is more interested because of the importance of environmental considerations. Reaction calorimetry is a powerful means for the monitoring, process control and research for thereactions kinetic. Calorimetry is able to estimate the heat of reaction and conversion using a few on-line information from the process (e.g. temperature data). Finding a useful mathematical model of process and accurate identification of its parameters isan important issue in this technique to achieve the accurate robust results. Since this models have various and complicated terms, it is important to specify the importance of each term in order to reach the simple model that had an acceptable performance. In this work, calorimetry and its applications are introduced at first, and then a reaction calorimetric model is produced for laboratory reactor of polymerization based on energy balance. Finally, this model is applied in production of poly butyl acrylate in an emulsion polymerization reactor and model accuracy is verified by the experimental data. J. Color Sci. Tech. 2(2009), 199-212.© Institute for Colorants, Paint and Coatings.

In this paper, the synthesis of methyl metacrylate-butylacrylate copolymer used in water-based paints by emulsion polymerization was investigated. The synthesize planning in the case of selection of the type and ratio of the monomers, was based on the chemical structure analysis of an imported industrial resin and using the other characterization of referred resin like as particle size distribution and glass transition temperature measurement. In the emulsion polymerization, to attain the desired final properties, the whole of system include the type and the quantity of the applied monomers and emulsifiers, reaction temperature follow with the molecular weight and Tg of produced polymer as well as the particle size distribution must be controlled. In this research, after different synthesize, the results of the different analysis methods proved the successfulness synthesize. J. Color Sci. Tech. 2(2008), 159-169.© Institute for Colorants, Paint and Coatings.