SPG Membrane Research Articles

Influence of process parameters on droplet size distribution in SPG membrane emulsification and stability of prepared emulsion droplets

SPG membranes were used to prepare monodispersed O/W and W/O/W emulsions over a wide range of membrane wall shear stress (0.37–40 Pa), dispersed phase content (1–20 vol.%) and transmembrane pressure. Although the most uniform droplets were prepared at the membrane wall shear stress of 30 Pa, a monodispersed O/W emulsion can be even obtained at the wall shear stress of 0.37 Pa, corresponding to laminar flow regime of continuous phase inside the membrane tube. The minimum droplet size somewhat decreased with time, probably due to gradual activation of smaller pores. There was no significant difference in the size distribution curve of pure oil droplets of O/W emulsions and W/O drops of W/O/W emulsions, if they were both prepared under the same conditions. No significant change in droplet size distribution of prepared O/W emulsions was observed during the storage time of up to 159 days.

Preparation of uniform titanium dioxide (TiO 2 ) polystyrene-based composite particles using the glass membrane emulsification process with a subsequent suspension polymerization

Uniform titanium dioxide (TiO(2))-polystyrene-based composite particles were prepared using the glass membrane emulsification process followed by a subsequent suspension polymerization. The oil phase, consisting of anatase TiO(2) fine powder, monomers, methyl laurate as the hydrophobic additive, Disperbyk-180 and the poly(styrene-co-2-ethyl hexylacrylate) were emulsified through the membrane pores into the aqueous phase containing stabilizers to form a (solid-in-oil)-in-water (S/O/W) emulsion of monomer droplets. The suspension polymerization was carried out at 343 K for 24 h under a nitrogen atmosphere. An SPG membrane with a pore size of 5.25 microm was employed and 20-25 microm TiO(2)-polystyrene based composite particles were obtained depending on the composition of polymerizing oil phase. The effects of the co-monomer, 2-ethylhexyl acrylate and the cross-linking agent, divinyl benzene on the dispersion stability of TiO(2) in the oil phase, the surface feature of the particle and the encapsulation loading were investigated in this study. The membrane emulsification process was capable of preparing the composite particles with approximately 5 wt% of TiO(2) encapsulated, which accounts for with at least 85 wt% of TiO(2) in the oil phase.

Preparation of uniform titanium dioxide (TiO2) polystyrene-based composite particles using the glass membrane emulsification process with a subsequent suspension polymerization

Uniform titanium dioxide (TiO2)-polystyrene-based composite particles were prepared using the glass membrane emulsification process followed by a subsequent suspension polymerization. The oil phase, consisting of anatase TiO2 fine powder, monomers, methyl laurate as the hydrophobic additive, Disperbyk-180 and the poly(styrene-co-2-ethyl hexylacrylate) were emulsified through the membrane pores into the aqueous phase containing stabilizers to form a (solid-in-oil)-in-water (S/O/W) emulsion of monomer droplets. The suspension polymerization was carried out at 343 K for 24 h under a nitrogen atmosphere. An SPG membrane with a pore size of 5.25 μm was employed and 20–25 μm TiO2-polystyrene based composite particles were obtained depending on the composition of polymerizing oil phase. The effects of the co-monomer, 2-ethylhexyl acrylate and the cross-linking agent, divinyl benzene on the dispersion stability of TiO2 in the oil phase, the surface feature of the particle and the encapsulation loading were investigated in this study. The membrane emulsification process was capable of preparing the composite particles with ∼ 5 wt% of TiO2 encapsulated, which accounts for with at least 85 wt% of TiO2 in the oil phase.

Mechanism of suspension polymerization of uniform monomer droplets prepared by glass membrane (Shirasu Porous Glass) emulsification technique

The mechanism of the unique suspension polymerization of uniform monomer droplets, without coalescence and breakup during the polymerization, was investigated using styrene (S) as a monomer mixed with water-insoluble hexadecane (HD). The glass membrane (Shirasu Porous Glass, SPG) emulsification technique was employed for the preparation of uniform droplets. Depending on the pore sizes of the SPG membranes (1.0, 1.4, and 2.9 μm), polymer particles of an average diameter ranging from 5.6 to 20.9 μm were obtained with the coefficient of variation (CV) being close to 10%. The role of HD was to prevent the degradation of the droplets by the molecular diffusion process. Sodium nitrite was added in the aqueous phase to kill the radicals desorbed from the droplets (polymer particles), thereby suppressing the secondary nucleation of smaller particles. Each droplet behaved as an isolated locus of polymerization. With the presence of HD, the initial polymerization rate was proportional to 0.24th power of the benzoil peroxide (BPO) concentration. This peculiar behavior as compared with the ordinary suspension polymerization was explained by introducing the assumption that each droplet was composed of isolated compartments (cells) in which active polymeric radicals were dissolved in an S-rich phase and surrounded by a rather incompatible S/HD (continuous) phase. The average number of radicals in the droplet increased initially due to the separate existence of polymeric radicals in compartments. As the polymerization progressed, the HD-rich phase gradually separated, eventually forming macrodomains, which were visible by an optical microscope. The phase separation allowed polystyrene chains to dissolve in a more favorable S phase, and the homogeneous bulk polymerization kinetics took over, resulting in a gradual decrease of the average number of radicals in the droplet until the increase of viscosity induced the gel effect. When no HD was present in the droplets, the polymerization proceeded in accordance with the bulk mechanism except for the initial retardation by the entry of inhibiting radicals generated from sodium nitrite in the aqueous phase. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1025–1043, 2000

Surface properties of monodisperse poly(acrylamide- co-acrylic acid) hydrogel microspheres prepared by a membrane emulsification technique

Monodisperse poly(acrylamide- co-acrylic acid) hydrogel microspheres of different average sizes were prepared using a membrane emulsification technique. The average diameters of the microspheres were dependent on the pore sizes (0.33, 0.73, 1.15, and 1.70 μm) of SPG membranes used in the preparation procedure. The surface properties of microspheres have been studied from their electrophoretic mobility values. The mobility values of poly(acrylamide- co-acrylic acid) microspheres were negative at pH 7.4 with ionic strengths between 0.005 and 0.154 at 25°C. More negative mobility values were obtained with smaller poly (acrylamide- co-acrylic acid) microspheres than with the larger ones. By analyzing the data with an electrokinetic theory for `soft' surfaces, it was found that copolymerization of acrylamide monomers and acrylic acid monomers does not proceed homogeneously within a microsphere. The density of polymer networks composed of both monomers is higher in the core region than in the surface layer of the microspheres. This is not the case for smaller microspheres, hence their electrophoretic mobility becomes more negative.

Novel Procedure for Monodispersed Polymeric Microspheres with High Electrifying Additive Content by Particle-Shrinking Method Via SPG Membrane Emulsification.

Novel Procedure for Monodispersed Polymeric Microspheres with High Electrifying Additive Content by Particle-Shrinking Method Via SPG Membrane Emulsification.