Polymer Dispersions and Their Industrial Applications

Polymer Dispersions and Their Industrial Applications Edited by Dieter Urban and Koichi Takamura

Polymer Dispersions and Their Industrial Applications

edited by Dieter Urban and Koichi Takamura

IV

Editors Dr. Dieter Urban Dr. Koichi Takamura

BASF Corp. 11501 Steele Creek Road Charlotte, NC 28273, USA

This book was carefully produced. Nevertheless, editors, authors and publisher do not warrant the information contained therein to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate. Library of Congress Card No.:

applied for British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library. Die Deutsche Bibliothek – CIP Cataloguingin-Publication Data

A catalogue record for this publication is available from Die Deutsche Bibliothek © 2002 Wiley-VCH Verlag GmbH, Weinheim All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.

Scanning electron micrograph of a hollow sphere created by the deposition of 7.9 µm polystyrene particles on a nitrogen bubble during their preparation in the microgravity environment of the Space Shuttle Challenger (courtesy of the Emulsion Polymers Institute, Lehigh University, Bethlehem, PA, USA). Cover photograph

Printed in the Federal Republic of Germany Printed on acid-free paper Typesetting

TypoDesign Hecker GmbH,

Leimen Printing betz-druck GmbH, Darmstadt Binding Großbuchbinderei J. Schäffer

GmbH & Co. KG, Grünstadt ISBN 3-527-30286-7

V

Contents Preface

XIII

1

Introduction

1.1 1.2 1.3 1.4 1.5

Names and Definitions 1 Properties of Polymer Dispersions 3 Important Raw Materials 8 Commercial Importance of Polymer Dispersions Manufacturers of Polymer Dispersions 12 References 14

1

10

2

Synthesis of Polymer Dispersions 15

2.1 2.2 2.2.1 2.2.2 2.2.3 2.2.4 2.2.5 2.2.6 2.3 2.3.1 2.3.2 2.3.3 2.3.4

Introduction 15 Chemistry 17 Mechanism of Emulsion Polymerization 17 Major Monomers 23 Functional Monomers 26 Surfactants 27 Initiator Systems 30 Other Ingredients 32 Manufacturing Processes 34 Types of Process 34 Influence of Process Conditions on Polymer/Colloidal Properties Equipment Considerations 39 Safety Considerations 40 References 40

3

Characterization of Aqueous Polymer Dispersions 41

3.1 3.2 3.2.1 3.2.2 3.2.3 3.2.4

Introduction 41 Polymer Dispersions 42 General Characterization of Dispersions 42 Characterization of Polymer Particles 48 Residual Volatiles 56 Aqueous Phase Analysis 57

37

VI

Contents

3.3 3.3.1 3.3.2 3.3.3

Polymer Films 58 Film Formation 59 Macroscopic Characterization of Polymer Films Microscopic Characterization of Polymers 68 References 72

60

4

Applications in the Paper Industry 75

4.1 4.2 4.3 4.4 4.4.1 4.4.2 4.4.3 4.4.4 4.4.5 4.5

Introduction 75 The Paper Industry 76 Surface Sizing 79 Paper Coating 81 Coating Techniques 84 Pigments used in Coating Colors 86 Co-binders and Thickeners used in Coating Colors Binders used in Coating Colors 90 Test Methods 97 Concluding Remarks 100 Acknowledgments 100 References 101

5

Applications for Printing Inks 103

5.1 5.1.1 5.1.2 5.2 5.2.1 5.2.2 5.2.3 5.2.4 5.2.5 5.3 5.3.1 5.3.2 5.3.3 5.4 5.4.1 5.4.2 5.5 5.5.1 5.5.2 5.5.3 5.6 5.6.1 5.6.2 5.7

Introduction 103 Flexographic Ink 104 Gravure Ink 106 Ink Composition 106 Pigment Dispersion 108 Emulsion Vehicle 109 Solution Vehicle 112 Waterborne Wax Emulsions and Powders 113 Ink Additives 113 Physical Properties and Test Methods 114 Typical Properties 114 Application Tests 115 Test Method Abstracts 115 Inks for Flexible Substrates (Films) 117 Surface Print Film 118 Lawn and Garden Bags 118 Inks for Paper Board Substrates 118 Folding Cartons 118 Direct Print Corrugated Packages 119 Pre-print Corrugated Packages 119 Inks for Poly-coated Board 120 Milk Cartons 120 Cup and Plate 120 Inks for Paper Products 120

87

Contents

5.7.1 5.7.2 5.7.3 5.7.4

Multiple Wall Bags 121 Gift Wrap and Envelopes Newspapers 121 Towel and Tissue 122 References 122

121

6

Applications for Decorative and Protective Coatings 123

6.1 6.1.1 6.1.2 6.1.3 6.2 6.2.1 6.2.2 6.2.3 6.2.4 6.2.5 6.3 6.3.1 6.3.2 6.3.3 6.3.4 6.4 6.4.1 6.4.2 6.4.3 6.5 6.5.1 6.5.2 6.5.3 6.6 6.6.1 6.6.2 6.6.3 6.7 6.7.1 6.7.2 6.7.3 6.8 6.8.1 6.8.2 6.8.3 6.8.4 6.8.5 6.8.6

Introduction 123 Market Overview 123 Coating Industry Trends 124 Coatings Provide Decoration and Protection 124 Overview of Coating Formulations 125 Volume Solids and Pigment Volume Content 125 Polymer Matrix 127 Film Formation 128 Typical Polymer Compositions 129 Pigments, Extenders, and Additives 132 Decorative Coatings 137 Emulsion Polymers in Decorative Coatings 137 Polymer Compositions used for Emulsion-based Decorative Coatings 137 Regional Distinctions in Decorative Coatings 138 Market Size of Decorative Coatings 138 Interior Decorative Coatings 139 Key Performance Features 139 Interior Decorative Coating Formulations 140 Standard Application and Performance Tests 142 Exterior Decorative Coatings 146 Key Performance Features 146 Exterior Decorative Coating Formulations 147 Standard Application and Performance Tests 147 Elastomeric Wall Coatings 149 Key Performance Features 149 Typical Elastomeric Wall Coating Formulations 150 Standard Application and Performance Tests 151 Primer Coatings 151 Key Performance Features 152 Primer Formulations 152 Standard Application and Performance Tests 153 Protective and Industrial Coatings 154 Copolymers used in Protective and Industrial Coatings 154 Market Size 155 Industrial Maintenance Coatings 155 Key Performance Features 155 Formulation Characteristics for Industrial Maintenance Coatings 156 Standard Application and Performance Tests 156

VII

VIII

Contents

6.9 6.9.1 6.9.2 6.9.3 6.9.4

Traffic Marking Paints 158 Description of Traffic Paint Market 158 Key Performance Features 159 Typical Traffic Paint Formulation 159 Standard Application and Performance Tests 159 References 161

7

Applications for Automotive Coatings 163

7.1 7.1.1 7.2 7.2.1 7.2.2 7.2.3 7.3 7.3.1 7.3.2 7.3.3 7.3.4 7.3.5 7.3.6 7.4 7.5 7.6 7.6.1 7.7

Introduction 163 History of Automotive Coating 164 Automotive Coating Layers 166 Electrocoat 170 Primer 172 Basecoat 173 Properties of Water-borne Binders used for Automotive Coatings Emulsion Polymers 176 Microgels 177 Miniemulsions 177 Selection of Monomers, Initiators, and Surfactants 178 Secondary Acrylic Dispersions 179 Secondary Polyurethane Dispersions 179 Rheology 181 Crosslinking 183 Application Properties 185 Metallic Effect 186 Environmental Aspects and Future Trends 186 References 187

8

Applications in the Adhesives and Construction Industries 191

8.1 8.2 8.2.1 8.2.2 8.2.3 8.3 8.3.1 8.3.2 8.3.3 8.4 8.4.1 8.4.2 8.4.3 8.4.4 8.4.5 8.4.6

Introduction 191 Pressure-sensitive Adhesives 193 Self-adhesive Labels 194 Self-adhesive Tapes 207 Test Methods 210 Laminating Adhesives 217 Flexible Packaging 217 Glossy Film Lamination 219 Furniture and Automotive 222 Construction Adhesives 224 Floor-covering Adhesives 224 Sub-floor and Wall Mastics 231 Sealants 233 Ceramic Tile Adhesives 238 Polymer-modified Mortars 241 Waterproofing Membranes 244

176

Contents

8.4.7

Elastomeric Roof Coatings Acknowledgments 250 References 251

247

9

Applications in the Carpet Industry 253

9.1 9.2 9.3 9.4 9.5 9.5.1 9.5.2 9.5.3 9.5.4 9.5.5

Introduction 253 History of Carpet 253 Present Day Carpet Business 255 Carpet Backing Binders 256 Carpet Laminating 259 Background 259 Carpet Terminology 260 Back-coating Applications 261 Back-coating Formulations and Ingredients 262 Industry Issues 264 References 266

10

Non-wovens Application 267

10.1 10.2 10.2.1 10.2.2 10.3 10.4

Introduction 267 Manufacturing Systems 270 Web Formation 271 Web Consolidation 272 Polymer Dispersions for Chemical Bonding Application Test Methods 275 References 281

11

Applications in the Leather Industry 283

11.1 11.2 11.3 11.3.1 11.3.2 11.3.3 11.3.4 11.3.5 11.3.6 11.3.7 11.4 11.4.1 11.4.2 11.4.3 11.5 11.5.1 11.5.2 11.5.3

Introduction 283 Market Situation 284 Leather Finishing 286 Modern Finishing 287 General Construction of Finishing Coats Spray Dyeing 287 Grain Impregnation 287 Base Coat 287 Pigment Coat 288 Top Coat 288 Application Methods 288 Spraying 289 Roll Coating 289 Curtain Coater 289 Binders 291 Polyacrylate Dispersions 291 Polybutadiene Dispersions 291 Polyurethane Dispersions 292

273

287

IX

X

Contents

11.6 11.6.1 11.6.2 11.6.3 11.6.4 11.7 11.7.1 11.7.2 11.7.3 11.7.4 11.7.5 11.7.6 11.7.7 11.7.8 11.7.9

Production of Selected Leather Articles 292 Shoe Upper Leather 292 Apparel Leather 293 Automotive Leather 294 Furniture Leathers 295 Test Methods in Leather Finishing 296 Flexing Endurance 297 Rub-fastness 298 Dry and Wet Adhesion 299 Fastness to Ironing 299 Hot Air Fastness 299 Aging resistance 299 Fogging test 300 Light-fastness 300 Hot light aging 300 References 300

12

Applications for Asphalt Modification 301

12.1 12.2 12.2.1 12.2.2 12.3 12.3.1 12.3.2 12.3.3 12.3.4 12.3.5 12.4 12.5

Introduction 301 Hot Mix Asphalt Paving 303 Asphalt Specification 304 In-line Injection (Pump-in) 311 Paving with Asphalt Emulsion 313 Applications of Asphalt Emulsions 314 Asphalt Emulsion Tests 317 Polymer Honeycomb Structure in Cured Asphalt Emulsion 317 Asphalt Emulsion Residue Characterization 319 Application Tests for Chip Seal and Microsurfacing 321 Eco-efficiency Analysis 323 Concluding Remarks 326 Acknowledgement 326 References 326

13

Applications of Redispersible Powders

13.1 13.2 13.3 13.4 13.4.1 13.4.2 13.4.3 13.4.4 13.4.5 13.4.6 13.5

Introduction 329 Manufacturing of Redispersible Powders 330 Dry Mortar Technology 332 Markets and Application Areas of Redispersible Powders 333 Adhesives for Ceramic Tiles 334 Tile Grouts 340 Exterior Insulation and Finish Systems and Top Coats 341 Self-leveling Underlayments 345 Patch and Repair Mortars 346 Waterproof Membranes 350 Summary 353

329

Contents

References

354

14

Applications for Modification of Plastic Materials 355

14.1 14.2 14.2.1 14.3 14.3.1 14.3.2 14.4 14.4.1 14.4.2

Introduction 355 Emulsion Polymerization and Isolation Technology 356 Isolation Technology 357 Processing Aids 358 Processing Aids for PVC 359 Processing Aids for Other Resins 366 Impact Modifiers 367 Impact Modifiers for PVC 368 Engineering Resins 375 Acknowledgment 378 References 379

15

Applications for Dipped Goods 383

15.1 15.2 15.3 15.4 15.4.1 15.4.2 15.4.3 15.4.4 15.5 15.5.1 15.5.2

Introduction 383 Polymers Used by the Dipping Industry 384 Principles of Dipping 385 Dipping Synthetic Polymer Emulsions in Practice 386 Former Design 386 Mix Design 388 Coagulant 390 The Dipping Process 390 The Testing of Synthetic Gloves 395 Non-safety-critical Gloves 395 Safety-critical Gloves 396 References 398 Index 399

XI

XIII

Preface Aqueous polymer dispersions are important raw materials used in a variety of industrial processes. They consist of very small polymer particles dispersed in water and appear as milky fluids. When finally processed and providing the function for which they were selected, they are barely visible. Polymer dispersions are used to protect metal, wood, and leather against water and microorganisms, and are used as binders for pigments, fillers, and fibers and to finish the surfaces of metal, wood or paper. Protecting, binding, and finishing are the essential effects achieved by use of polymer dispersions. In most applications the water will be evaporated and a functional polymer remains. This can be hard or tacky, plastic or elastic, transparent or opaque. Accordingly, they are used for coatings or as adhesives, for binders or foams, for clear coat varnishes or opacifiers. It is even possible to reconcile these classically contradictory properties by proper design of a single dispersion or by mixing several. Even small amounts of polymer dispersion are able to improve considerably the properties of different binders, e.g. starch, bitumen, or cement. The huge variety of applications continues into the area of solid plastic materials – impact modifiers are added to improve the properties of plastic materials. Dipping goods, e.g. gloves, and latex foams for mattresses are polymeric materials which are made directly from polymer dispersions. Finally, there are also applications in which polymer dispersions remain in their liquid form – they are used as drug carriers, in medical diagnosis, and in liquid soap. This book focuses on the applications of aqueous polymer dispersions. The chapters on synthesis and characterization should be regarded as an introduction and should aid understanding of the applications. The applications of aqueous polymer dispersions have developed differently, both historically and regionally. Regulatory issues have contributed to these differences. The strongest development of polymer dispersions occurred in Europe and North America in the middle of the 20th century. The differences between these two regions are emphasized. We are specially grateful to all the authors who helped us make this global comparison and acknowledge the authors’ companies, for approving and supporting this work. Charlotte, North Carolina, USA

Dieter Urban Koichi Takamura

XV

List of Authors Peter Blanpain

Dr. Christoph Hahner

7834 Covey Chase Drive Charlotte, NC 28210, USA

Wacker Polymer Systems, L. P. 3301 Sutton Road Adrian, MI 49221, USA

Dr. Mary Burch

Rohm & Haas Company 727 Norristown Road Spring House, PA 19477, USA Dr. Chuen-Shyong Chou

Rohm & Haas Company Rt. 413 and Old Rt. 13 Bristol, PA 19007, USA Dr. Dieter Distler

BASF Aktiengesellschaft GKD - B1 D-67056 Ludwigshafen, Germany Dr. Johannes Peter Dix

BASF Aktiengesellschaft EVL/I – G100 D-67056 Ludwigshafen, Germany Dr. Luke Egan

BASF Corporation 11501 Steele Creek Road Charlotte, NC 28273, USA Dr. Onno Graalmann

BASF Nederland B.V. Westervoortsedijk 71 NL-6827 AV Arnhem, The Netherland Dr. Sunitha Grandhee

BASF Corporation 26701 Telegraph Road Southfield, MI 48034, USA Richard Groves

Synthomer LTD Central Road, Templefields, Harlow, Essex, CM20 2BH, UK

Dr. Do Ik Lee

The Dow Chemical Company 1604 Building Midland, MI 48674, USA Dr. Hermann Lutz

Wacker Polymer Systems GmbH&CoKG Johannes-Hees-Str. 24 D-84489 Burghausen, Germany Dr. Werner Kirchner

BASF Aktiengesellschaft EV/CS – H201 D-67056 Ludwigshafen, Germany Andrew Lanham

Synthomer Ltd. Central Road, Templefields, Harlow, Essex, CM20 2BH, UK Dr. Brough Richey

Rohm & Haas Company 727 Norristown Road Spring House, PA 19477, USA Dr. Jürgen Schmidt-Thümmes

BASF Aktiengesellschaft GKD/S – B1 D-67056 Ludwigshafen, Germany Dr. Elmar Schwarzenbach

BASF Aktiengesellschaft EDP/MB – H201 D-67056 Ludwigshafen, Germany Richard Scott

BASF Corporation 475 Reed Road NW Dalton, GA 30720, USA

XVI

J. Arthur Smith

BASF Nederland B.V. Westervoortsedijk 71 NL-6827 AV Arnhem, The Netherland K. Spenceley

Synthomer Ltd. Central Road, Templefields, Harlow, Essex, CM20 2BH, UK Barna Szabo

Flint Ink Corporation 4600 Arrowhead Drive Ann Arbor, MI 48105, USA Dr. Koichi Takamura

BASF Corporation 11501 Steele Creek Road Charlotte, NC 28273, USA Jim Tanger

BASF Corporation 11501 Steele Creek Road Charlotte, NC 28273, USA Michael A. Taylor

BASF Corporation 11501 Steele Creek Road Charlotte, NC 28273, USA Dr. Dieter Urban

BASF Corporation 11501 Steele Creek Road Charlotte, NC 28273, USA Dr. Jane E. Weier

Rohm & Haas Company Rt. 413 and Old Rt. 13 Bristol, PA 19007, USA Dr. Harm Wiese

BASF Aktiengesellschaft GKD/N – B1 D-67056 Ludwigshafen, Germany Marilyn Wolf

BASF Corporation 11501 Steele Creek Road Charlotte, NC 28273, USA

Color Plates

Color Plates Fig. 1-3

Particle morphologies.

Raspberry structure

Core/shell structure

Acorn structure

Uncoated grade, supercalendered

Coated grade, supercalendered

Fig. 4-7

Effect of coated paper on offset printing.

XVII

XVIII

Color Plates

Coated gravure paper

Uncoated gravure paper

Fig. 4-8

Effect of coated paper on rotogravure printing.

Coating head

Steam Dryer Laminating station Release liner

Schematic representation of PSA label coater.

Backing

Fig. 8-9

Unwind

Rewind

Latex Polymer Network

Photomicrograph demonstrating spontaneous formation of polymer network upon curing of the CRS-2 asphalt emulsion modified with 3 % cationic SBR latex.

Fig. 12-15

50 µm

1

1

Introduction Dieter Urban and Dieter Distler

1.1

Names and Definitions

Most precisely the subject of this book is called “aqueous synthetic organic polymer colloids”. The term “polymer colloid” defines a state of subdivision in which polymolecular particles dispersed in a medium have at least in one direction a dimension of roughly between 1 nm and 1000 nm [1]. The term “organic” needs to be added to exclude inorganic polymers like silica. To be more precise the term “synthetic” will be added, if organic polymers of natural origin like natural rubber should be excluded. Finally, the term “aqueous” ensures that the continuous medium is only water, excluding e.g. organic solvents. However, depending on the language, the geographical region and the field of application there are many other names commonly used (Fig. 1-1). In general the term “dispersion” characterizes a two phase system consisting of finely dispersed solid particles in a continuous liquid phase. An example of a dispersion is whitewash, calcium hydroxide above the solubility limit in water. If the finely dispersed phase and the continuous phase, both are liquid, the term “emulsion” will be used. An example is milk, which essentially consists of fat droplets in water; the droplets are stabilized by proteins. In both cases, in dispersions and emulsions, the continuous phase is therefore a liquid; in all of our examples, the liquid is water. In dispersions, the finely disperse substance is solid, while in emulsions it is liquid. Dealing with organic polymers being the dispersed substance it is difficult to define precisely whether they are solid or liquid. Depending on the glass transition temperature (Tg) and chain length, polymers are viscous liquids at low Tg and low molecular weight or they will be tough to brittle solids, if Tg and molecular weight are high. The temperature and stress duration are other important factors. At temperatures below the glass transition temperature or in the case of very short stress duration, polymers behave like glasses, while above this temperature or in the case of long stress times, they are viscous or elastic materials. This behavior of polymers between liquid and solid is one reason why aqueous synthetic organic polymer colloids are referred to as dispersions (Danish, Dutch, Finnish, German, Greek, Hungarian, Japanese, Korean, Norwegian, Polish, Portuguese, Romanian, Russian, Spanish,

2

1 Introduction

Fig. 1-1

colloids.

Commonly used names for aqueous synthetic organic polymer

1.2 Properties of Polymer Dispersions

Swedish, Turkish) and emulsions (Arabic, Chinese, English, Indonesian, Italian, Malay). Another reason for the use of emulsion or emulsion polymer comes from the most important production process for these products, the emulsion polymerization. The products are referred to as emulsion polymers or simply emulsions. In contrast to this the name latex (Latin: latex, liquid; Greek: λαταξ, droplet) is derived from the naturally occurring rubber milk and is most widely used for aqueous synthetic organic polymer colloids, especially for the substitution products of natural latex, butadiene-styrene copolymer emulsions. The Union for Pure and Applied Chemistry recommends two names: Latex and polymer dispersion [2]. Latex is defined as “A colloidal dispersion of polymer particles in an aqueous medium. The polymer may be organic or inorganic.” Since we will not cover inorganic dispersions, this book should have been called “Organic Latices and Their Industrial Applications”, which seems to be a pleonasm because the use of latex is generally associated with organic material. Polymer dispersion is defined as “A dispersion in which the disperse phase consists of polymer particles.” The continuous phase can be a liquid, solid or gas. If we want only water to be the continuous phase, aqueous is added. In industrial applications non-aqueous polymer dispersions are negligible. Therefore this book has been called “Polymer Dispersions and Their Industrial Applications”. However, according to the preference of the authors the terms “polymer dispersion”, “dispersion”, “emulsion polymer”, “emulsion” and “latex” are used synonymously.

1.2

Properties of Polymer Dispersions

The aggregate state of a polymer dispersion is thermodynamically unstable. The very large internal surface area of up to 100 m2 mL–1 of dispersion requires stabilization of the particle surfaces in order to suppress phase separation and coagulation. Driving force for the agglomeration of particles is the gain of energy by reducing the internal surface. Finally a polymer block and a substantially polymer-free water phase will be formed. This coagulation can be accelerated by salts, acids, solvents, freezing, shear, etc. To obtain highly stable polymer dispersions, the particles are usually provided with ionic groups, for example by adsorption of anionic or cationic surfactants, or by incorporation of ionic groups into the polymer. Another, nonionic type of stabilization takes place via hydrophilic groups on the particle surface, for example by aminoor hydroxyl-containing monomers or protective colloids. Polymer dispersions used in industry usually are stabilized by both mechanisms (ionic and nonionic). The special nature of the particle surface, which differs from the particle interior, plays an important role in all applications. Industrially important polymer dispersions usually contain 40–60 % of polymer in water. Each mL of dispersion contains about 1015 particles with diameters of 50–500 nm. One particle contains 1–10 000 macromolecules, and each macromolecule contains about 100–106 monomer units (Fig. 1-2).

3

4

1 Introduction

Fig. 1-2

What is a polymer dispersion?

These figures give an impression of the possible variation, if just the molecular weight (or molecular weight distribution) and particle size (or particle size distribution) of homo-polymers will be considered. The random incorporation of various monomers in the chains, the possibility of cross-linking between the polymer chains and finally separated phases of different polymers in a particle allow a virtually unlimited variety in this product class. Polymer dispersions normally consist of spherical particles. The dispersed particles scatter the light and are the cause of the milky appearance. This Mie scattering is utilized for particle size measurement. Very small polymer particles hardly scatter visible light at all, those polymer dispersions have a translucent appearance. If all the particles are of the same size, the term “monodisperse dispersions” will be used. They are frequently recognized from a certain particle size merely from the iridescent appearance, which is caused by Bragg scattering at a crystalline superstructure of close packing of the particles. Polymer dispersions with a heterogeneous particle structure – a special particle morphology consisting of a number of phases – have recently become of interest. Examples are particles with a core/shell structure or two coexistent polymer phases, particles with a raspberry structure, etc. The particle morphology may be thermodynamically preferred; in the case of polymers with reduced chain mobility or even in the case of relatively low cross-linking, it is mostly kinetically controlled morphologies that are frozen. This enables product properties with even contradictory requirements to be achieved better, for example low film formation temperature, but maximum blocking resistance or hardness of the polymer (Fig. 1-3). The flow behavior is also an important parameter. The flow property of polymer dispersions is a particular advantage of this aggregate state. Dispersions can have a polymer content which is a multiple higher than polymer solutions, yet still be freeflowing. Besides the polymer content, particle size, particle size distribution and electrolyte content, the viscosity is also affected by dissolved constituents in the aqueous phase. The water phase of many polymer dispersions contains a whole range of water-soluble oligomers, auxiliaries and additives which contribute to the application properties as well.

1.2 Properties of Polymer Dispersions Fig. 1-3

Particle morphologies.

Raspberry structure

Core/shell structure

Acorn structure

To obtain readily free-flowing dispersions with low viscosity at high polymer contents of >60 % by volume, very broad or bimodal particle size distributions are needed (Fig. 1-4).

Fig. 1-4 Electron photomicrograph of a bimodal polymer dispersion.

This can be achieved during the polymerization or by partial agglomeration, for example, by means of a shear gradient, by freezing or by addition of an agglomeration aid, so that significantly larger agglomerates are present alongside the small primary particles. The viscosity of polymer dispersions is usually dependent on the shear rate. A distinction is made between pseudoplastic behavior (viscosity decreases with increasing shear), possibly with a flow limit, thixotropic behavior (viscosity decreases with in-

5

6

1 Introduction

creasing shear time) and dilatant behavior (viscosity increases with increasing shear). The rheology of concentrated polymer dispersions is complex, often being dependent on the shear rate and previous history. Owing to the content of surface-active substances, the foaming behavior is an important property for many applications. Antifoam agents reduce foaming, while further emulsifiers and rheology modifiers increase the foaming or stabilize the foam once formed. The biodegradability of many additives makes the dispersions susceptible to attack by microorganisms (bacteria, yeast). Most dispersions are therefore provided with biocides. In most applications, the water is evaporated from the dispersions. Depending on the composition and/or processing temperature, a polymer film or powder is formed. The properties of the polymer now come into play: strength, elongation at break, elasticity, transparency, solvent and environmental resistance, glass transition temperature, tack, etc. These properties are determined by the chemical composition of the copolymers, the molecular weight and the molecular weight distribution, by the morphology of the polymer particles and by the morphology of the polymer film. Important polymer classes are: Styrene/butadiene dispersions are used for their elastic properties since molecular weight and cross-linking of the polymer can be adjusted widely by choosing the degree of conversion and the amount of chain transfer agents. They are used as synthetic rubber for tires and molded foam. When styrene is replaced by acrylonitrile, elastic and solvent resistant polymers are obtained, which are used for dipping goods. Carboxylated styrene/butadiene (XSB) dispersions contain acrylic, methacrylic, maleic, fumaric or itaconic acid. The carboxylic groups provide stabilization of the polymer particles and a good interaction with fillers (calcium carbonate, clay) and pigments. The main applications are paper coating and carpet backing. The remaining 1,2 and 2,3 double bonds of butadiene favor autoxidation of the polymer, it becomes yellow and brittle. This is prevented by adding antioxidants. This polymer class is resistant to hydrolysis at all pH values since it does not contain ester units which tend to hydrolyze especially at very high pH. Acrylic dispersions (pure acrylics and styrene acrylics) are extremely versatile. The big variety of available acrylic and methacrylic esters together with styrene offer almost unlimited opportunities to choose for the glass transition temperature and the hydrophilic/hydrophobic properties. Acrylic esters tend to form cross-linked polymers by abstraction of the α-hydrogen atom, methacrylic esters in contrast form polymer chains which are not cross-linked. Acrylics are resistant against oxidation by air and degradation by light. The main application areas are coatings and adhesives. Vinyl acetate dispersions are widely used for coatings and adhesives as well. To stabilize the polymer particles often polyvinyl alcohol is used as protective colloid. Most common co-monomers are ethylene, versatic esters, vinyl chloride or acrylic esters. The polymer dispersions are spray dried to obtain a polymer powder, which is widely used in construction industry. Ethylene/vinyl acetate copolymers form elastic films and are fairly resistant to oxygen and light.

1.2 Properties of Polymer Dispersions

Polymer dispersion with a high content of vinylidene chloride form polymer films with crystalline areas. These PVDC films are highly impermeable for both, oxygen and water vapor, and are used as barrier coatings in packaging materials, especially for food packaging (Fig. 1-5).

Fig. 1-5 Permeability of polymer films.

Polymer dispersions with a high amount of acrylic/methacrylic acid convert to aqueous solutions or gels when pH is increased. They are used as thickeners. Films made from polyurethane dispersions combine elastic properties with high tensile strength. Polystyrene dispersions have a glass transition temperature of 105 ºC. They are used in paper coating to improve gloss, in liquid soaps to provide opacity and in medical diagnosis as carrier for active ingredients. Films of acrylic dispersions, which are cross-linked with metal ions and re-dispersible with an aqueous solution of ammonia, are used as temporary protective films. All those examples elucidate that polymer dispersions are used in both big volume and small volume applications. They are both commodities and specialties. And the use of polymer dispersions is increasing worldwide. The main reasons for this are: the variety of polymer properties achievable by emulsion polymerization is virtually unlimited, emulsion polymerization is an inexpensive production process for these products, the fluid form of polymer dispersions is easy to handle, and water is environmentally friendly. The complex colloidal and chemical behavior of polymer dispersions is an interesting working area for many scientific disciplines and is important for many applications. In addition to excellent reviews [3–13], a whole range of periodicals focuses on polymer dispersions [14–18].

7

8

1 Introduction

1.3

Important Raw Materials

The most important production process for polymer dispersions is emulsion polymerization [19]. This process is started by preparing a monomer emulsion consisting of monomer droplets in water. The monomer droplets are stabilized by emulsifiers and/or protective colloids. When adding an initiator polymerization is started converting the monomers into polymer particles (Chapter 2). The production of polymer dispersions by emulsion polymerization requires deionized water, free-radical-polymerizable monomers, emulsifiers and/or protective colloids and initiators. Further auxiliaries, such as chain transfer agents, buffers, acids, bases, anti-aging agents, biocides, etc., can be used. The most important source of the main monomers used or their precursors is petroleum chemistry, with the steam cracker as reactor. Liquid hydrocarbons (naphtha or liquefied natural gas LNG) are broken down (“cracked”) into short-chain hydrocarbons at 800–850 °C with addition of steam as diluent (Fig. 1-6) [20].

Fig. 1-6

Steam cracker products.

There are currently about 200 steam crackers worldwide. In Europe, Latin America and South-East Asia, the starting material is mostly naphtha, while in North Africa, the Middle East and North America, predominantly ethane and propane from natural gas are used. The largest plants have an annual capacity of more than 800 000 tons of naphtha. Ethene, the most important petrochemical feedstock today, reached a world capacity of about 80 million tons per year in 1995. Almost half is polymerized to give polyethylene. It plays only a secondary role for emulsion polymerization in vinyl acetateethene copolymers and in polyethylene waxes. It is important, however, in this connection as a feedstock for the production of vinyl chloride, styrene and vinyl acetate.

1.3 Important Raw Materials

Propene cannot be polymerized by means of free radicals. It is, however, a feedstock for acrylic acid, acrylates and acrylonitrile. Butadiene is extracted from the C4 fraction from the steam cracker, and can be used directly for emulsion polymerization. The principal monomers butadiene, styrene, vinyl acetate, (meth)acrylates and acrylonitrile essentially determine the material properties of films made from the corresponding dispersions: the glass transition temperature, the water absorption capacity, the elasticity, etc. Auxiliary monomers, which are only used in a small proportion, usually 150 16 44 0.086

69 –29 –24 67 –34 64–34 >150 11 56 0.34

65 –14 –17 63 –24 64–22 28 6.7 49 0.33

78 –19 –14 78 –24 76–22 86 4.5 63 1.6

The results of modifying asphalt with additives are highly dependent upon the concentration, the molecular mass, the chemical composition, and microscopic morphology of the additive as well as the crude source, the refining process and the grade of the base asphalt used. Superpave binder specifications are successful in predicting the rutting resistance and cold fracture resistance of the unmodified asphalt. A new DSR procedure is under development for the better prediction of fatigue resistance. Integration of the bending beam rheometry data and direct tension measurement in the near future will provide a better description of the benefits of the polymer-modified asphalt. One of the primary benefits of polymer modified asphalt binders is a reduced susceptibility to temperature variation [13]. Because many Performance Grade asphalt specifications can only be met with polymer modification, it is expected that the use of polymer modified binders will increase as these specifications are implemented during the late 1990s and the early 2000s. A 1997 survey of state highway agencies found that 35 agencies reported that they will be using greater quantities of modified binders; 12 agencies reported they will be using the same amount of modified binders; and no agency reported they will be using less modified binder [14]. Storage Stability A polymer-modified asphalt is a two phase system, forming a continuous fine polymer network, that is highly swollen with aromatic components in the asphalt. The polymer is mixed in the asphalt and stored at elevated temperature, which could cause chemical reaction within polymer chains and with some components in the asphalt. The degree of swelling, and thus the microscopic morphology of the polymer phase, varies widely dependent on the crude source, the refining process and the grade of the base asphalt [15–17].

309

310

12 Applications for Asphalt Modification

When the chemical and physical properties of the polymer and asphalt are not matched to each other, a polymer rich phase could develop near the surface of the asphalt when stored at 160–170 °C for a few days without agitation as reported by Brûlé et al. with SBS modified asphalts [16]. The asphalt composition in the polymer rich phase is vastly different from the original asphalt. One of their results with Asphalt E modified with 5 % SBS polymer is shown in Fig. 12-4. The aromatic and saturate components preferentially partition to the polymer phase, thus concentrating the asphaltenes and polar resin fractions in the asphalt phase. The majority of asphaltenes are retained in the asphalt phase, resulting in an increase in the asphaltenes/aromatic ratio. This potentially leads to reduced swelling of asphaltenes, which would have negative effects on low temperature flexibility of asphalt. Polymer phase

Original Asphalt E Asphaltene Saturate

Resin

Asphalt phase

Aromatic

Difference in asphalt composition among original asphalt and the polymer rich and asphalt phases developed during storage.

Fig. 12-4

The phase separation during storage can be visualized with hot stage optical microscopy, which allows us to observe changes in the polymer morphology at the mixing and storage conditions. Here, the other MRL asphalt, AAB-1 (Wyoning Sour), was modified with 3 % Butonal NS175. Photomicrographs shown in Fig. 12-5 illustrate the presence of a fine polymer network in the freshly mixed sample observed at 110 °C at ×200 magnification. The polymer phase transfers to macroscopic polymer globules without agitation when the sample is slowly heated to 170 °C. These polymer blobs migrate to the top due to the density difference.

12.2 Hot Mix Asphalt Paving

Photomicrographs of conventional SBR modified asphalt taken at 110 and 170 °C.

Fig. 12-5

Wegan et al. [17] reported observing similar macroscopic polymer globules and/or a polymer layer surrounding the aggregate surface in the paved asphalt mixtures, even though only fine structures existed in the modified binder observed at room temperature using fluorescence microscopy, which is the traditional method of studying polymer morphology [15–17]. The photomicrograph shown here (Fig. 12-5) demonstrates that polymer modified asphalt behaves as a dispersion consisting of two immiscible fluids; a highly viscoelastic fluid dispersed in a less viscous one. The dispersed phase elongates to fine fluid columns under agitation. When the agitation is removed, these elongated columns transfer to a series of spherical droplets as minimizing the total surface area and thus the total energy. Numerous inventions are reported in the literature to overcome the polymer incompatibility in the modified asphalt, which often involve introduction of a controlled cross-link reaction in the polymer phase. Cross-linking reduces solvent swelling and increases the visco-elasticity of the polymer phase. Butonal NX1129 is an example of the new type of SBR latex. As shown in Fig. 12-6, a fine polymer network remains even when the modified asphalt is observed at 170 °C for 10 min. Stable polymer structures of this latex also extend the low temperature limits of certain modified asphalts, as determined by the direct tension measurement. 12.2.2

In-line Injection (Pump-in)

Pre-blending infers that the latex and asphalt have been mixed at a central location using a batch process as discussed above. In-line injection (also known as pump-in) implies that the latex and asphalt are blended immediately before being applied to the aggregate at the hot-mix plant. This process eliminates potential separation of

311

312

12 Applications for Asphalt Modification

Fig. 12-6

Butonal NX1129 maintains stable, fine polymer network even

at 170 °C.

polymer and asphalt during transportation and storage of incompatible materials, and the need for an asphalt storage tank for the polymer modified asphalt, thus reducing handling costs. With the pre-blending process, polymer and asphalt are thoroughly mixed and the binders can be tested and certified before application to the aggregates. Recent advancement in quality control at the mixing process guarantees adequate mixing and performance of the asphalt produced by the in-line injection process. An optical photomicrograph demonstrating polymer networks in the asphalt prepared by the direct injection process is shown in Fig. 12-7.

Photomicrograph demonstrating the presence of polymer networks in the asphalt prepared by the in-line injection (pump-in) process.

Fig. 12-7

12.3 Paving with Asphalt Emulsion

12.3

Paving with Asphalt Emulsion

Asphalt emulsions used in road construction and maintenance are either anionic or cationic, based on the electrical charge of the asphalt particles, which is determined by the type of the emulsifying agent used. The asphalt contents of these emulsions are, in most cases, from 55 to 75 % and prepared using a high shear mechanical device such as a colloid mill. The colloid mill has a high-speed rotor that revolves at 1000–6000 rpm with mill-clearance settings in the range of 0.2 to 0.5 mm. A typical asphalt emulsion has a mean particle size of 2–5 µm in diameter with distribution from 0.3 to 20 µm. A photomicrograph and typical size distribution of an asphalt emulsion are shown in Fig. 12-8. Asphalt emulsion properties depend greatly upon the emulsifier used for their preparation.

Particle size distribution and photomicrograph of a typical asphalt emulsion.

Fig. 12-8

A latex modified asphalt emulsion can be prepared using several methods: addition of the latex in the aqueous emulsifier solution, direct injection in the asphalt line just ahead of the colloid mill or post-addition to the pre-manufactured emulsion, as schematically shown in Fig. 12-9. Addition to the aqueous phase is the most commonly used method. The direct injection process often helps to produce an emulsion with a desired high viscosity for chip seal application (Sect. 12.3.1). This is due to the narrow particle size distribution of the asphalt emulsion produced with this process. Asphalt emulsions are classified with their charge and on the basis of how quickly the asphalt will coalesce, which is commonly referred to as breaking, or setting. The terms RS, MS and SS have been adopted to simplify and standardize this classification. They are relative terms only and mean rapid-setting, medium-setting and slowsetting. An RS emulsion has little or no ability to mix with an aggregate, an MS emulsion is expected to mix with coarse but not fine aggregate, and an SS emulsion is designed to mix with fine aggregate. The emulsions are further subdivided by a series of numbers and letters related to the viscosity of the emulsions and the hardness of the base asphalt cements. The letter “C” in front of the emulsion type denotes

313

314

12 Applications for Asphalt Modification Schematic illustration for latex modified asphalt emulsion production.

Fig. 12-9

Latex Asphalt

Water Emulsifier Acid or Base

Latex Storage

Colloidal Mill Latex

cationic. The absence of the “C” denotes anionic. For example, CRS-2 is a cationic rapid setting emulsion typically used for chip seal application. ASTM and the American Association of State Highway and Transportation Officials (AASHTO) have developed standard specifications for the grades of emulsions, shown in Tabs 12-4 and 12-5 for anionic and cationic emulsions, respectively. The “h” that follows certain grades means that harder base asphalt is used. The “HF” preceding some of the MS grades indicates high-float, as measured by the Float Test (ASTM D139 or AASHTO T 50). High float emulsions have a specific quality that permits a thicker asphalt film coating on the aggregate particles. 12.3.1

Applications of Asphalt Emulsions

The Cold-mix recycling operation, which utilizes milled old asphalt pavement mixed with asphalt emulsion, is gaining popularity for rehabilitating deteriorating roadways. In this method, the old asphalt pavement is crushed, often in place. An inplace aggregate base can also be incorporated or new aggregates can be added to the old materials and asphalt emulsion added. Then, materials are mixed together, spread to a uniform thickness, and compacted. Slow setting SS and CSS asphalt emulsions are used currently without polymer modification. Surface treatments applied to an existing pavement for preventive maintenance are the most significant application of polymer modified asphalt emulsion. They are economical, easy to place, resist traffic abrasion and provide a long lasting waterproof cover over the underlying structure. There are several types of surface treatment, but in this chapter, we will limit our discussion to chip seal and slurry surfacing. Detailed descriptions as well as recommended performance guidelines of various paving technologies using asphalt emulsions can be found elsewhere [18, 19].

75–400 63

75–400 63 65

100+

100–250