Two-Stage Stabiliser Addition Protocol as a Means to Reduce the Size and Improve the Uniformity of Polymer Beads in Suspension Polymerisation

A 2-stage stabiliser addition protocol is suggested for reducing the size and improving the uniformity of polymer beads resulting from conventional suspension polymerisation. The stabiliser load was divided into an initial charge and a secondary addition. The use of a low concentration of stabilizer in the initial charge served to assist drop rupture while avoiding significant reduction in drop size and production of too many satellite droplets. The secondary addition time of stabiliser occurred just before the onset of the growth stage when drops were vulnerable to coalescence but were robust against break up due to their high viscosity. The secondary addition of stabiliser served to provide stability to monomer drops during the growth stage and as a result the drops underwent limited coalescence. This resulted in the formation of smaller and more uniform polymer beads in comparison to beads obtained by conventional suspension polymerisation at the same overall concentration of stabiliser

“On-The-Fly” Fabrication of Highly-Ordered Interconnected Cylindrical and Spherical Porous Microparticles via Dual Polymerization Zone Microfluidics

A microfluidic platform with dual photopolymerization zones has been developed for production of novel uniform interconnected porous particles with shapes imposed either by the geometry of the external capillary or by the thermodynamic minimisation of interfacial area. Double w/o/w drops with well-defined internal droplet size and number were produced and then exposed to online photopolymerization to create the porous particles. Cylindrical interconnected porous particles were produced in a segmented flow where the drops took the shape of the capillary. The microfluidic set up included an extension capillary where the drops relaxed and conformed to their thermodynamically favoured morphology. Window opening of the particles occurred “on-the-fly” during UV polymerization without using any offline auxiliary methods. A distinction was made between critically and highly packed arrangements in double drops. The window opening occurred consistently for highly packed spherical drops, but only for critically packed drops containing more than 6 internal cores at internal phase ratio as low as 0.35. The size and number of cores, shape and structure of double drops could be precisely tuned by the flowrate and by packing structure of the inner droplets

Preparation and characterization of tunable oil-encapsulated alginate microfibers

© 2017 Elsevier LtdA single-step microfluidic approach was developed which allowed a wide range of oil-loaded calcium-alginate microfibers to be fabricated at the same compositions but with different morphologies. A framework for characterization of wavy fibers was developed which linked the fiber morphology and tensile strength to the encapsulation type and geometry. The geometry of oil encapsulates as well as the fibers surface morphology were conveniently tuned via the gelation reaction dynamics and phase flow rates. A 2D mathematical reconstruction of the fiber's surface revealed that fibers having spherical and ellipsoid encapsulates enjoyed the highest surface roughness. Tubular fibers endured the highest tensile force before failure, compared to fibers with other encapsulate geometries at a fixed alginate phase ratio (ϕalg). Fibers with increased ϕalg withstood a higher tensile force. However, the strength of fibers reduced if the increase in ϕalg altered the encapsulate geometry from tubular to discrete oil segments. Tubular fibers also underwent maximum elastic and plastic deformation prior to failure, among all fibers

Ultrafine Nanolatexes Made via Monomer-Starved Semicontinuous Emulsion Polymerization in the Presence of Water-Soluble Chain Transfer Agents

Ideal chain transfer agents are usually water insoluble as they do not affect the kinetics of polymerisation reactions occurring in the water phase. Water-soluble chain transfer agents act non-ideally by easily crossing the water phase and affecting the kinetics of polymerisation including nucleation. In this research, a partially water-soluble chain transfer agent (CTA), 2-Butanethiol, was used in the monomer-starved semicontinuous emulsion polymerisation of styrene as a means to affect the kinetics of water phase and synthesise ultrafine nanolatexes. Batch emulsion polymerisations were also carried out for comparison. In the batch process, the termination of chain transferred radicals in the water phase was found to be quite dominant, resulting in the formation of large polymer particles with polydisperse molecular weights and slow rate of reaction. By contrast, for the semicontinuous process, the application of the CTA reduced the average size of particles, by enhancing the rate of nucleation via increasing the rate of radical entry into micelles, and provided a good controllability over molecular weight distribution as well as the rate of polymerisation

Flexible microfluidic fabrication of oil-encapsulated alginate microfibers

A unified microfluidic approach is presented for flexible fabrication of oil-encapsulated calcium alginate microfibers. The oil encapsulate phase was directly injected into the gelling alginate fiber, thus allowing the adjustable tuning of the encapsulate geometry ranging from spherical to prolate ellipsoid, plug-like and tubular shapes. Phase maps were developed that show the conditions required to achieve desired fiber morphologies with intended encapsulate phase ratio. We also show for very first time how oil encapsulates can be selectively grouped across the microfibers. A force-balance model, validated against a non-gelling system, was introduced to predict the size of spherical encapsulates

Supressing Coalescence and Improving Uniformity of Polymer Beads in Suspension Polymerisation using a Two-Stage Stirring Protocol

In a typical suspension polymerisation, both emulsification and polymerisation occur simultaneously in a single stirred vessel reactor using a constant stirring speed and stabiliser concentration. This work introduces a novel two-stage stirring protocol for improving the uniformity of polymer beads produced in suspension polymerisation reactions. In the two-stage stirring protocol proposed, the polymerisation stage was carried out at a reduced stirring speed. This policy, confirmed by mathematical modelling, led to the drops coalescence being suppressed and as a result drops average size and size distribution being maintained in the course of polymerisation. The particle size distribution narrowing was more significant if the emulsification stage was carried out at room temperature, the stabiliser concentration was low, and the difference between the stirring speeds used in the two stages was large. The two-stage stirring protocol was extended to include a two-stage stabiliser-addition protocol, which further improved the quality of the beads