Comparisons between membranes for use in cross flow membrane emulsification

Mapping Bubble Formation and Coalescence in a Tubular Cross-Flow Membrane Foaming System

Membrane foaming is a promising alternative to conventional foaming methods to produce uniform bubbles. In this study, we provide a fundamental study of a cross-flow membrane foaming (CFMF) system to understand and control bubble formation for various process conditions and fluid properties. Observations with high spatial and temporal resolution allowed us to study bubble formation and bubble coalescence processes simultaneously. Bubble formation time and the snap-off bubble size (D0) were primarily controlled by the continuous phase flow rate (Qc); they decreased as Qc increased, from 1.64 to 0.13 ms and from 125 to 49 µm. Coalescence resulted in an increase in bubble size (Dcoal>D0), which can be strongly reduced by increasing either continuous phase viscosity or protein concentration-factors that only slightly influence D0. Particularly, in a 2.5 wt % whey protein system, coalescence could be suppressed with a coefficient of variation below 20%. The stabilizing effect is ascribed to the convective transport of proteins and the intersection of timescales (i.e., μs to ms) of bubble formation and protein adsorption. Our study provides insights into the membrane foaming process at relevant (micro-) length and time scales and paves the way for its further development and application.

Manufacture of poly(methyl methacrylate) microspheres using membrane emulsification

Accurate control of particle size at relatively narrow polydispersity remains a key challenge in the production of synthetic polymer particles at scale. A cross-flow membrane emulsification (XME) technique was used here in the preparation of poly(methyl methacrylate) microspheres at a 1-10 l h(-1) scale, to demonstrate its application for such a manufacturing challenge. XME technology has previously been shown to provide good control over emulsion droplet sizes with careful choice of the operating conditions. We demonstrate here that, for an appropriate formulation, equivalent control can be gained for a precursor emulsion in a batch suspension polymerization process. We report here the influence of key parameters on the emulsification process; we also demonstrate the close correlation in size between the precursor emulsion and the final polymer particles. Two types of polymer particle were produced in this work: a solid microsphere and an oil-filled matrix microcapsule.This article is part of the themed issue 'Soft interfacial materials: from fundamentals to formulation'.

Advances in membrane emulsification. Part B: recent developments in modelling and scale-up approaches

Membrane emulsification is a promising process for formulating emulsions and particulates. It offers many advantages over conventional 'high-shear' processes with narrower size distribution products, higher batch repeatability and lower energy consumption commonly demonstrated at a small scale. Since the process was first introduced around 25 years ago, understanding of the underlying mechanisms involved during microstructure formation has advanced significantly leading to the development of modelling approaches that predict processing output; e.g. emulsion droplet size and throughput. The accuracy and ease of application of these models is important to allow for the development of design equations which can potentially facilitate scale-up of the process and meet the manufacturer's specific requirements. Part B of this review considers the advantages and disadvantages of a variety of models developed to predict droplet size, flow behaviour and other phenomena (namely droplet-droplet interactions), with presentation of the appropriate formulae where necessary. Furthermore, the advancement of the process towards an industrial scale is also highlighted with additional recommendations by the authors for future work.

Advances in membrane emulsification. Part A: recent developments in processing aspects and microstructural design approaches

Modern emulsion processing technology is strongly influenced by the market demands for products that are microstructure-driven and possess precisely controlled properties. Novel cost-effective processing techniques, such as membrane emulsification, have been explored and customised in the search for better control over the microstructure, and subsequently the quality of the final product. Part A of this review reports on the state of the art in membrane emulsification techniques, focusing on novel membrane materials and proof of concept experimental set-ups. Engineering advantages and limitations of a range of membrane techniques are critically discussed and linked to a variety of simple and complex structures (e.g. foams, particulates, liposomes etc.) produced specifically using those techniques.