Über die flockung von hochverdünnten monodispersen polystyrol-dispersionen mit polyvinylpyridiniumsalzen

Mechanically preemulsified monomer styrene in water, without the use of an emulsifier, gave under definite reaction conditions almost monodisperse polystyrene dispersions, as shown in the electronmicrographs. Some of these dispersions were used in a concentration of 50 ppm to test the flocculation activity of polyvinylpyridinium-salts (PVP-salts). These in turn were prepared by the solution polymerisation of vinylpyridine and a subsequent quaternisation of the polymer with alkyl halides. The molecular weight of the PVP-salts showed a marked influence, especially on very small particle size of the dispersions. Among the inorganic salts, a strong effect of the valency of the cation was noticeable. Cs⁺, Na⁺ and K⁺ have only a little influence, whereas La⁺⁺⁺ and Al⁺⁺⁺ increase the flocculation activity enormously.     

Hydroresin dispersions: tailoring morphology of latex particles and films

Hydroresin dispersions are a new class of emulsifier free polyacrylate secondary dispersions. They are prepared by the emulsification of self-emulsifying polymer blends in water. The blends typically consist of two polymers, one is a salt group containing copolymer, the other is a hydrophobic polymer without salt groups. The particle diameters can be controlled by the amount of salt group containing polymer and the concentration of salt groups in this polymer. One advantage over conventional secondary dispersions is the fact that they are not only water dilutable but free of organic solvents. Another advantage is the extremely low content of hydrophilic salt groups in the resulting polymer mixture, which leads to very hydrophobic films. The application properties of these aqueous systems are more similar to those of organic polymer solutions than to conventional emulsion polymers. Applications of these surfactant free binders are in areas such as solvent face road marking paints and corrosion protection coatings without active pigments. The technique for the preparation of hydroresin dispersions is also useful for the creation of latex particles with core-shell structures. Two examples are given, which differ in the glass transition temperature of both the cores and the shells. From these dispersions, films with defined morphology can be prepared. A blending of the polymers with hydrophobic low molecular weight compounds, before the emulsification step, is also possible. It can be used for the incorporation of additional functions into the latex particles. As an example, the loading of latexes with a hydrophobic fluorescent dye is given.     

Preparation and properties of polymer lattices polymerised without surfactants

Series of polystyrene and polymethyl methacrylate latex dispersions have been prepared in the absence of any surfactant using potassium persulphate as an initiator. The latex particles are stabilised by the electrical repulsion generated by the sulphate groups which are covalently linked to the polymer molecules and are not removed by dialysis. The effects of polymerisation temperature, monomer concentration and initiator concentration on the ultimate particle size and conversion were investigated for these two series of lattices. The modal diameters of these lattices were found to be in the range of 530 to 1550 nm for polystyrene lattices, and 140 to 270 nm for polymethyl methacrylate lattices. The surface charge densities were calculated from conductometric titration results for polymethyl methacrylate lattices and were found to increase almost linearly with increase of the concentration of potassium persulphate used.     

In situ mass-suspension polymerisation

In situ mass-suspension polymerisation of MMA was carried out in a single reactor. The mass polymerisation was carried out in a gently agitated monomer layer of a two stratified layers of monomer and water in the reactor. The degree of conversion at which mass polymerisation changed to suspension polymerisation, by increasing the rate of agitation, was altered systematically. The polymer content of the monomer/polymer solution, formed during the mass polymerisation stage, significantly affected the evolution of the particle size distribution. Mass-suspension polymerisation was found to be more vulnerable to drop coalescence and process failure than conventional suspension polymerisation. The results indicate the importance of the transition stage in a typical suspension polymerisation during which the rate of polymerisation is very low and the adsorption of stabiliser on the surface of drops is completed. The polymer beads from the mass-suspension polymerisation had a very broad size distribution with a large contribution from satellite particles.     

Characterisation of an anticorrosive phosphated surfactant and its use in water-borne coatings

The physicochemical features of a surfactant are quite important in the formulation of polymer water-borne coatings mainly due to the strong influence of the micelles on the nucleation and stability of dispersed polymer particles. In consequence, micellar transitions must be determined in order to obtain aqueous dispersions of spherical shaped particles with high monodispersion in size, which allows to obtain coatings with an improved performance. Besides, depending on its chemical structure, the surfactant could also have anticorrosive properties. In this work, a phosphate-based surfactant was characterised and its electrochemical properties were evaluated in order to use it as a stabiliser agent of a series of monodisperse styrene-acrylic lattices, synthesised by semi-continuous emulsion polymerisation. EIS was used to evaluate the anticorrosive properties of coatings obtained from polymeric dispersions.     

Effects of Particle Size and Molecular Weight of Polyethylenimine on Properties of Nanoparticulate Silicon Dispersions

The effect of particle size on the zeta potential and rheology of nanoparticulate SiO₂ dispersions stabilized with the polymer polyethylenimine (PEI) was investigated experimentally. The particle size and molecular weight of the polymer had only a small influence on the amount of PEI needed and the achieved zeta potential of the suspensions. The polymer concentration range within which a stable dispersion could be produced was very narrow for the smallest particle size. Higher-molecular-weight PEI was more suitable to stabilize small particle dispersions. Under optimum conditions, Newtonian flow behavior was achieved for dispersions of 20 nm particles with a solids content as high as 25 vol%.     

Vinyl acetate-ethylene copolymer dispersions

The function of ethylene as a plasticising comonomer for vinyl acetate is reviewed from the historical standpoint and in relation to alternative methods of plasticisation. Both chemical and physical effects are considered. Emulsion polymerisation and the use of aqueous dispersions are covered in some detail, and methods of polymer characterisation are summarised, with particular reference to i.r. and n.m.r. spectroscopy.     

Particle features and morphology of poly(vinyl chloride) prepared by living radical polymerisation in aqueous media. Insight about particle formation mechanism

The aim of this work is to evaluate PVC resins prepared by Single Electron Transfer Degenerative Chain Transfer Living Radical Polymerisation (SET-DTLRP) in a 150 L reactor under industrial conditions. The product features were analysed considering the standard resin features of PVC prepared by the conventional free radical polymerisation (FRP) method. It was proved that the FRP and SET-DTLRP have different particle growing mechanism and led to grains with completely different features (particle size, particle size distribution and morphology). It is critical for the PVC producers the preparation of PVC with a predetermined grain shape, particle size distribution and porosity which have an indubitable in?uence on polymer processing. It is presented a detailed study on the particle formation of the PVC synthesised by SET-DTLRP providing ?rst insights into PVC features associated with a new polymerisation technique taking into account the normal requirements of the PVC industry. A possible mechanism of the SET-DTLRP particle formation is proposed.     

Fabrication and characterisation of polymer thin-films derived from cineole using radio frequency plasma polymerisation

The development of organic polymer thin-films is critical for the progress of many fields including organic electronics and biomedical coatings. This paper describes the fabrication of an organic polymer thin film produced from 1,8-cineole via radio frequency plasma polymerisation. A deposition rate of 55 nm/min was obtained under the polymerisation conditions employed. Infrared spectroscopic analysis demonstrated that some functional groups observed in the monomer were retained after the polymerisation process, while new functional groups were introduced. The refractive index and extinction coefficient were estimated to be 1.543 (at 500 nm) and 0.001 (at 500 nm) respectively. The polymers were shown to be optically transparent. AFM images of the polymer established a very smooth and uniform surface with average roughness of 0.39 nm. Water contact angle data demonstrated that the surface was stable while in contact with water.     

Hydroresin dispersions: new emulsifier free binders for aqueous coatings

Hydroresin dispersions are a new class of emulsifier free polyacrylate secondary dispersions. One advantage over conventional secondary dispersions is the fact that they are not only water dilutable but free of organic solvents. Another advantage is the extremely low content of hydrophilic salt groups in the polymer molecules, which leads to very hydrophobic films. The application properties of these aqueous systems are more similar to those of organic polymer solutions than to conventional emulsion polymers. Applications of these surfactant free binders are in areas such as road marking paints without solvents and corrosion protection coatings without active pigments. Hydroresin dispersions also show very interesting perspectives for applications in the field of solar energy conversion.     

Enhanced mechanical and thermal properties of polyurethane/functionalised graphene oxide composites by in situ polymerisation

ABSTRACT

Isocyanate-functionalised graphene (iGO) was prepared and incorporated into a thermoplastic polyurethane via an in situ polymerisation. Firstly, graphene oxide was successfully modified using a mixture of isocyanate- and diisocyanate-containing compounds, leading to the formation of good dispersions of resulting functional graphene oxide in organic solvents, such as N,N-dimethylacetamide and N,N-dimethylformamide. The addition of iGO into polyurethane matrix improved both mechanical and thermal properties in the polyurethane/iGO composites relative to neat polyurethane. An addition of only 0.03?wt-% of functionalised graphene into the polyurethane increased Young’s modulus by 1.4 times and tensile strength by two times. Meanwhile, the elongation at break was similar to that of the neat polymer. In addition, dynamic mechanical analysis also confirmed the improvement in storage modulus of the polymer composites especially at high-temperature range. We believe that the developed modification approach for graphene oxide and polyurethane/graphene composites presented herein could be useful in polymer/graphene composite development.     

Nanoencapsulation of Alpha-linolenic Acid with Modified Emulsion Diffusion Method

Nanocapsules of alpha-linolenic acid (α-LA) were prepared by a modified emulsion diffusion technique with encapsulation efficiency of 93%. Polylactic acid (PLA) was used as the encapsulating polymer with acetone and ethyl acetate as organic solvents, and Tween 20, gelatin and Pluronic-F68 in water as stabilizers. Two ratios of organic to aqueous phases were used with each solvent and stabilizer. Nanocapsule dispersions with a particle size less than 100 nm and a zeta potential as high as 33 mV were obtained as verified by scanning electron microscopy and the dynamic light scattering technique respectively. Both particle size and zeta potential were influenced by such preparation conditions as the type of stabilizer, type of organic solvent and the organic to aqueous phase ratio. Acetone was superior to ethyl acetate, and Tween 20 was superior to each of Pluronic-F68 and gelatin in obtaining smaller, less aggregated nanocapsules. An organic to aqueous phase ratio of 1:5 was shown to be more suitable for the formation of smaller nanocapsules, particularly when acetone was used as the organic solvent.     

Phosphated polyurethane-acrylic dispersions: synthesis, rheological properties and wetting behaviour

Phosphated polyurethane-acrylic dispersions were prepared by a new method that is free from organic solvents and requires a very low dispersion force. After the carboxylic acid groups of the phosphated polyurethane were neutralised by suitable bases, water was added to form the phosphated polyurethane seed dispersion. Polyurethane-acrylic dispersions were obtained from the phosphated polyurethane seed by emulsion copolymerisation. The polyurethane seed polymer was found to be stable over the initiator concentration used and the rheological properties of the polyurethane acrylics were found to follow Newtonian behaviour under the prescribed experimental conditions. This is a good indication that the dispersions may be used as pigment wetting media. The dynamic contact angle study showed the poor wettability of the phosphated polyurethane-acrylic dispersion films, indicating good hydrophobicity.     

Analysis of energy dissipation in stirred suspension polymerisation reactors using computational fluid dynamics

This work evaluates the spatial distribution of normalised rates of droplet breakage and droplet coalescence in liquid–liquid dispersions maintained in agitated tanks at operation conditions normally used to perform suspension polymerisation reactions. Particularly, simulations are performed with multiphase computational fluid dynamics (CFD) models to represent the flow field in liquid–liquid styrene suspension polymerisation reactors for the first time. CFD tools are used first to compute the spatial distribution of the turbulent energy dissipation rates (ε) inside the reaction vessel; afterwards, normalised rates of droplet breakage and particle coalescence are computed as functions of ε. Surprisingly, multiphase simulations showed that the rates of energy dissipation can be very high near the free vortex surfaces, which has been completely neglected in previous works. The obtained results indicate the existence of extremely large energy dissipation gradients inside the vessel, so that particle breakage occurs primarily in very small regions that surround the impeller and the free vortex surface, while particle coalescence takes place in the liquid bulk. As a consequence, particle breakage should be regarded as an independent source term or a boundary phenomenon. Based on the obtained results, it can be very difficult to justify the use of isotropic assumptions to formulate particle population balances in similar systems, even when multiple compartment models are used to describe the fluid dynamic behaviour of the agitated vessel. © 2011 Canadian Society for Chemical Engineering     

Emulsion polymerisation of styrene in the presence of hydrocarbon diluents

Results are given for the effects of four hydrocarbon diluents (benzene, toluene, ethylbenzene and cyclohexane) upon the rate of emulsion polymerisation of styrene at 50°C, upon the particle size of the resultant latex, and upon the intrinsic viscosity of the polymer produced. The aromatic diluents were found to have a much greater effect in reducing the rate of polymerisation than can be accounted for by mere dilution of the monomer. For these diluents, the rate of polymerisation is approximately third order in initial concentration of monomer in the oil phase as a whole. Cyclohexane is far less effective as a retarder of polymerisation, the rate being approximately first order in monomer concentration in the oil phase. Particle size determinations indicate that the reductions in rate are due primarily to a reduction in the rate of polymerisation at each locus, rather than to a reduction in the number of reaction loci. The intrinsic viscosity of the polymer produced tends to fall with the rate of polymerisation. These observations are consistent with the view that aromatic diluents cause severe retardation of polymerisation because they diminish the Trommsdorff ‘gel’ effect at the reaction loci. This view is in turn shown to be consistent with a reaction mechanism in which, in the case of styrene-rich systems at least, the growing polymer particles do not attain equilibrium with the monomer droplets.     

Characteristic intervals in suspension polymerisation reactors: An experimental and modelling study

Suspension polymerisation of methyl methacrylate was carried out as a model to elaborate on the evolution of particle size average and distribution in the course of polymerisation. Four characteristic intervals in the evolution of particle size were identified as: transition, quasi-steady-state, growth, and identification stages. The effects of stabiliser and initiator concentrations, monomer hold up, reaction temperature, and agitation speed on the characteristic intervals, as well as the kinetics of polymerisation, were examined. The transition stage, which has been totally ignored in the literature, was found to have significant effect on the evolution of particle size. The transition stage is shortened by increasing the rate of polymerisation in the drops (either by increasing initiator concentration or using a higher reaction temperature). Increasing the impeller speed and stabiliser concentration will also lead to a shorter transition period. However, the delayed adsorption of the stabiliser on the surface of drops will prolong the transition stage. It is shown that the occurrence of the quasi-steady state depends on the polymerisation conditions. The quasi-steady state occurs only if the balance between drop break up and coalescence can be maintained. This requires a high rate of drop break up within a period of time during polymerisation (i.e., a low rate of polymerisation in the drops by using a low initiator concentration and reaction temperature, a high agitation speed and a high stabiliser concentration). The mechanisms underlying the growth stage are explained in terms of the overall rates of drop break up and coalescence in the course of polymerisation reactions. It is also shown that the onset of growth stage cannot be defined in terms of a critical conversation or viscosity, and it depends on the polymerisation conditions including mixing. The growth stage occurs if drops are not sufficiently stable against both break up and coalescence. The onset of the growth stage is advanced with a decrease in the rate of drop break up (e.g., decreasing agitation speed and stabiliser concentration). The growth stage can be totally eliminated from a polymerisation process if dispersions with a static steady state can be formed. That requires a high concentration of stabiliser, or a low concentration of monomer, to be used. A population balance model, which included the transition stage and the delayed adsorption of the stabiliser, was developed that is capable of predicting the evolution of drop size in the suspension polymerisation.     

Emulsion polymerisation of vinyl acetate in relation to the chemical structure of polyvinyl alcohol

The effects of content and sequence distribution of residual acetyl groups in the polymer chain, and carbonyl content of polyvinyl alcohol, on the emulsion polymerisation of vinyl acetate in the presence of polyvinyl alcohol were investigated. Properties of modified polyvinyl alcohol grades as a protective colloid were also studied. Results show that the viscosity, particle size, stability and the freeze-thaw stability of the emulsion are determined largely by the fine chemical structure of the polyvinyl alcohol used in the polymerisation.     

Preparation of nanocomposite dispersions based on cellulose whiskers and acrylic copolymer by miniemulsion polymerization: Effect of the silane content

A one‐step method was used to prepare stable aqueous nanocomposite dispersions based on cellulose whiskers extracted from the rachis of the date palm tree and a poly(styrene‐co‐2‐ethyl hexylacrylate) copolymer via miniemulsion polymerization. A reactive silane, i.e., methacryloxypropyl triethoxysilane was added to stabilize the dispersion and favor the anchoring of the whiskers on polymer particles. Dynamic light scattering was used to study the effect of the silane and whiskers contents on the average particle size of the polymer. Nanocomposites materials were prepared from these dispersions using a casting/evaporation method. The effect of the silane and whiskers contents on the thermal and mechanical properties were studied using differential scanning calorimetry and dynamic mechanical analysis. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Recast Nafion‐117 thin film from water solution

Perfluorosulfonated ionomer (PFSI) dispersions in various solvents, usually mixtures of organic compounds and water, were used to prepare the membrane‐electrode system in polymer electrolyte membrane fuel cells (PEMFC), the aim being to increase performance by improving the triple contact of graphite (electron conducting material), Pt (hydrogen dissociation catalyst) and ionomeric membrane (proton conducting). When using PFSI dispersions in water‐organic solvent mixture, care must be taken not to poison the Pt catalyst through organic decomposition products, a consequence of the thermal treatment of the electrode‐polymer system bonded with PFSI dispersion. In the present study some procedures for preparing Nafion water dispersion, starting from a Nafion‐117 membrane, are described. The morphological characteristics of the prepared dispersions were compared with Nafion commercial dispersion (NCD). Moreover, membranes with a thickness of 5–20 μm were prepared and characterised, using both the obtained and the NCD dispersions. The obtained data showed that Nafion water dispersion, which can be used to prepare the membrane/electrode system, results in thin membranes that absorb more water than NCD membranes, and have equal and/or higher proton conduction than the NCD.     

Synthesis of poly(styrene-co-maleimide) and poly(octadecene-co-maleimide) nanoparticles and their utilization in paper coating

Aqueous polymer dispersions comprising of poly(styrene-co-maleimide) (SMI) or poly(octadecene-co-maleimide) (OMI) nanoparticles were synthesized by thermal imidization of the corresponding maleic anhydride copolymer precursors with ammonia using an organic solvent free process. Different reaction parameters such as temperature, time, agitation speed and stirrer geometry, and molar ratio of ammonia-to-anhydride were investigated in order to find optimal conditions. The obtained copolymer nanoparticles exhibited glass transition temperatures (T_g's) between 140 and 170 °C with particle sizes ranging from 50 to 230 nm. The compositional analysis was conducted by recording ¹H NMR and ATR-FTIR spectra. In addition, SMI dispersions were successfully spray dried and analyzed by SEM. Finally, the polymer dispersion's utility as auxiliary organic pigment in paper coating formulations was evaluated.