Polymer Colloids

Formation, Characterization and Applications

Rodney Priestley, Robert Prud'homme, Rodney Priestley, Robert Prud'homme

• Publisher: Royal Society of Chemistry
• Year: 2019
• Print ISBN: 9781788014175
• eBook ISBN: 9781839161216
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Physical & Theoretical Chemistry

Academic and industrial research around polymer-based colloids is huge, driven both by the development of mature technologies, e.g. latexes for coatings, as well as the advancement of new materials and applications, such as building blocks for 2D/3D structures and medicine. Edited by two world-renowned leaders in polymer science and engineering, this is a fundamental text for the field.

Based on a specialised course by the editors, this book provides the reader with an invaluable single source of reference. The first section describes formation, explaining basic properties of emulsions and dispersion polymerization, microfluidic approaches to produce polymer-based colloids and formation via directed self-assembly. The next section details characterisation methodologies from microscopy and small angle scattering, to surface science and simulations. The final chapters close with applications, including Pickering emulsions and molecular engineering for materials development.

A comprehensive guide to polymer colloids, with contributions by leaders in their respective areas, this book is a must-have for researchers and practitioners working across polymers, soft matter and chemical and molecular engineering.

Section I: Emerging Methods in Polymer Colloid Formation

CHAPTER 1

Development, Characterization, and Application of Novel High Temperature Thermoplastic and Thermosetting Dispersions

D. L. MALOTKY, D. L. DERMODY,* D. SCHMIDT, T. J. YOUNG AND M. KALINOWSKI

Dow Chemical Company, Michigan, USA

*Email: [email protected]

1.1 Introduction

Dow's HIPE (High Internal Phase Emulsion) process, also known as BLUEWAVE™ technology, has been practiced at Dow for over 20 years. It is a process and formulation approach for creating aqueous emulsions or dispersions of polymers, which cannot otherwise be made via polymerization of monomers in aqueous systems (i.e. by emulsion or suspension polymerization). Examples of such polymers include polyurethanes, epoxies, polyolefins, silicones, polyesters, and alkyds. Advantages of this process include:

• Controlled internal phase concentration (very dilute to >95% internal phase)
• Controlled particle or droplet size (200 nm–50 μm, although 500 nm–5 μm is most typical)
• Minimal surfactant requirements (typically 2–6% based on internal phase)
• Ability to process high viscosity materials (>100 000 cP)
• Solvent free

Compared to emulsion polymerization, BLUEWAVE™ technology generally requires slightly higher surfactant amounts and generates slightly larger particle size because it is a direct emulsification technique, as opposed to a polymer synthesis technique. The use of appropriate process equipment and surface active ingredients also allows for the creation of emulsions of polymer melts at temperatures above the boiling point of water. For example, an emulsion of high density polyethylene (HDPE, melting temperature=135 °C) in water can be generated at a process temperature of 150 °C and then cooled down to room temperature to give a stable HDPE in water dispersion.

Once the polymer is present in the form of a water-borne dispersion, it can be processed using standard emulsion application tools, such as printing or coating processes, dipping, spraying, and froth foaming. This provides a very different set of physical properties, such as the high crystallinity and melting temperature of a polyolefin, with the application convenience of an emulsion polymer. Compared with an extruder applied coating of the same polymer chemistry, water-borne submicron particles allow for significant down gauging of coating thickness.

There are a number of commercial products made with BLUEWAVE™ technology, including:

• CANVERA™ polyolefin dispersions for metal beverage packaging
• ECOSMOOTH™ polyolefin dispersions for skin and hair care
• HYPOD™ polyolefin dispersions for paper coating
• ProSperse™ epoxy dispersions
• ACCENT™ polyolefin co-polymer dispersions for oil and gas

Small particle size emulsions can be generated by a range of mechanical equipment or non-mechanical processes. Examples of mechanical emulsification techniques include rotor–stator mixing systems,^1,2 ultrasound,³ high pressure impingement systems,^4–6 and membrane emulsification.^7,8 The non-mechanical processes for emulsion formation include phase inversion,⁹ either by composition or temperature, as well as precipitation and solvent exchange.¹⁰ However, the ability of these standard processes to create very small (sub-micron) particle dispersed systems of very high viscosity materials, such as polyolefin elastomers, is limited. BLUEWAVE™ technology combines mechanical (process) and non-mechanical (formulation) approaches to generate challenging dispersions.

A general schematic of the continuous process used in BLUEWAVE™ technology is shown in Figure 1.1. The particular equipment that is used for the primary mixer and dilution mixer unit operations depends upon the material properties of the polymer being fed into the process. For example, a thermoplastic polyolefin may have both mixing operations performed in series in a single twin screw extruder. For an amorphous polymer feed, such as an alkyd or high molecular weight polydimethylsiloxane, it may be more effective to use separate rotor stator mixers as the primary and secondary mixers.

Figure 1.1 General schematic for BLUEWAVE™ technology process.

In the BLUEWAVE™ technology, a polymer melt phase, a surfactant, and a small amount of initial water are combined in a primary mixing device at a temperature above the glass transition temperature (T_g) and melting temperature (T_m) of the polymer to create a polymer melt in water High Internal Phase Emulsion (HIPE). The HIPE can be thought of as a liquid/liquid foam, and is, by definition, an emulsion where the internal phase is greater than 74.5% of the total volume, which is the limit for close packed mono-dispersed spheres. Figure 1.2 shows a scanning electron micrograph of a polyolefin high internal phase ratio emulsion that has been allowed to cool below the polymer T_m without dilution. The polyhedral nature of the solid internal phase particles, as well as their high volume fraction, is clear.

Figure 1.2 SEM of cooled polyolefin co-polymer in water HIPE.

With the BLUEWAVE™ technology, the particle size of the internal phase droplet is set with the creation of this HIPE, which is then combined with additional dilution water to yield the final dispersion product at the desired internal phase volume concentration. For some applications, such as cosmetic emollient concentrates,¹¹ the final product may itself be a HIPE, as it is desirable that it contains as little water as possible. In other applications where a low viscosity dispersion is desired for spray coating, the final solids level may be in the range of 50% by volume. Internal phase polymers that solidify above room temperature must be diluted down below ∼60% by volume before the polymers cool and solidify to avoid mechanical interlocking of the HIPE, which makes further dilution of the dispersion impossible.

The rest of this chapter is separated into two sections. In Section 1.2, we will discuss the advantages, in the context of droplet breakup theory, of passing through this HIPE phase to produce small, mono-disperse emulsion particles. The mechanism of droplet breakup in the concentrated (concentrated internal phase) system differs from the droplet breakup in the conventional (dilute internal phase) system. These differences result in the production of the small, monodisperse droplets generated by our process. We will also discuss the complications of finding a stabilizing agent that is effective at helping to form this polymer melt/water interface at high temperatures. In Section 1.3, we will discuss the applications that are enabled by the BLUEWAVE™ technology.

1.2 Droplet Breakup Theory

In the following sections we will discuss classical droplet breakup theory, and how it has been extended to more concentrated systems in order to gain insight into the mechanisms that allow for the formation of small, monodisperse particles with our BLUEWAVE™ mechanical dispersion process technology.

1.2.1 Classical Droplet Breakup Theory

The particle or droplet size of an aqueous emulsion depends upon how the internal oil phase breaks up during mixing. Promoting drop deformation and breakup is the shear stress, τ, caused by the flow field within the mixer, which is generally defined as τ=η_c

where η_c is the continuous phase viscosity and

is the shear rate. Counteracting that force is the interfacial stress σ/R, where σ is the oil–water interfacial tension and R is the drop radius. The ratio of these values is the dimensionless capillary number Ca:

(1.1)

Taylor¹² was the first to provide a theoretical analysis of droplet deformation and breakup. Within the constraints of his system (simple steady-state shear flow, no droplet–droplet interactions, small drop deformation, and zero inertial effects), Taylor showed that the drop behavior depends on only the capillary number and the viscosity ratio, λ, defined as follows, where η_i is the internal phase viscosity:

(1.2)

For a given flow field and viscosity rati...

Table of contents

• Cover
• Title
• Copyright
• Preface
• Contents
• Section I: Emerging Methods in Polymer Colloid Formation
• Section II: Recent Advances in Colloid Characterization
• Section III: Advanced Applications of Polymer Colloids
• Subject Index