Science and Industrial Applications

If one considers that, worldwide, around 40% of all thermoplastics and 90% of elastomers are used as more or less complicated formulations with so-called fillers, it follows that approx

Science and Industrial Applications Filled Polymers

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Preface xi

Author Bio xv

1 Introduction 1

1.1 Scope of the Book 1

1.2 Filled Polymers vs Polymer Nanocomposites 3

References 8

2 Types of Fillers 11

3 Concept of Reinforcement 15

Reference 19

4 Typical Fillers for Polymers 21

4.1 Carbon Black 21

4.1.1 Usages of Carbon Blacks 21

4.1.2 Carbon Black Fabrication Processes 21

4.1.3 Structural Aspects and Characterization of Carbon Blacks 24

4.1.4 Carbon Black Aggregates as Mass Fractal Objects 30

4.1.5 Surface Energy Aspects of Carbon Black 44

4.2 White Fillers 49

4.2.1 A Few Typical White Fillers 49

4.2.1.1 Silicates 49

4.2.1.2 Natural Silica 52

4.2.1.3 Synthetic Silica 53

4.2.1.4 Carbonates 54

4.2.1.5 Miscellaneous Mineral Fillers 56

4.2.2 Silica Fabrication Processes 56

4.2.2.1 Fumed Silica 56

4.2.2.2 Precipitated Silica 58

4.2.3 Characterization and Structural Aspects of Synthetic Silica 62

4.2.4 Surface Energy Aspects of Silica 68

4.3 Short Synthetic Fibers 69

4.4 Short Fibers of Natural Origin 72

References 79

Appendix 4 82

A4.1 Carbon Black Data 82

A4.1.1 Source of Data for Table 4.5 82

A4.1.2 Relationships between Carbon Black Characterization Data 84

A4.2 Medalia’s Floc Simulation for Carbon Black Aggregate 85

A4.3 Medalia’s Aggregate Morphology Approach 86

A4.4 Carbon Black: Number of Particles/Aggregate 89

5 Polymers and Carbon Black 91

5.1 Elastomers and Carbon Black (CB) 91

5.1.1 Generalities 91

5.1.2 Effects of Carbon Black on Rheological Properties 95

5.1.3 Concept of Bound Rubber (BdR) 108

5.1.4 Bound Rubber at the Origin of Singular Flow Properties of Rubber Compounds 112

5.1.5 Factors Affecting Bound Rubber 114

5.1.6 Viscosity and Carbon Black Level 121

5.1.7 Effect of Carbon Black on Mechanical Properties 125

5.1.8 Effect of Carbon Black on Dynamic Properties 140

5.1.8.1 Variation of Dynamic Moduli with Strain Amplitude (at Constant Frequency and Temperature) 141

5.1.8.2 Variation of tan δ with Strain Amplitude and Temperature (at Constant Frequency) 142

5.1.8.3 Variation of Dynamic Moduli with Temperature (at Constant Frequency and Strain Amplitude) 142

5.1.8.4 Effect of Carbon Black Type on G′ and tan δ 144

5.1.8.5 Effect of Carbon Black Dispersion on Dynamic Properties 146

5.1.9 Origin of Rubber Reinforcement by Carbon Black 148

5.1.10 Dynamic Stress Softening Effect 151

5.1.10.1 Physical Considerations 151

5.1.10.2 Modeling Dynamic Stress Softening as a “Filler Network” Effect 152

5.1.10.3 Modeling Dynamic Stress Softening as a “Filler–Polymer Network” Effect 168

5.2 Thermoplastics and Carbon Black 172

5.2.1 Generalities 172

5.2.2 Effect of Carbon Black on Rheological Properties of Thermoplastics 173

5.2.3 Effect of Carbon Black on Electrical Conductivity of

Thermoplastics 175

References 179

Appendix 5 185

A5.1 Network Junction Theory 185

A5.1.1 Developing the Model 185

A5.1.2 Typical Calculations with the Network Junction Model 188

A5.1.3 Strain Amplification Factor from the Network Junction Theory 190

A5.1.3.1 Modeling the Elastic Behavior of a Rubber Layer between Two Rigid Spheres 190

A5.1.3.2 Experimental Results vs Calculated Data 191

A5.1.3.3 Comparing the Theoretical Model with the Approximate Fitted Equation 192

A5.1.3.4 Strain Amplification Factor 193

A5.1.4 Comparing the Network Junction Strain Amplification Factor with Experimental Data 194

A5.2 Kraus Deagglomeration–Reagglomeration Model for Dynamic Strain Softening 196

A5.2.1 Soft Spheres Interactions 196

A5.2.2 Modeling G′ vs γ0 197

A5.2.3 Modeling G″ vs γ0 198

A5.2.4 Modeling tan δ vs γ0 200

A5.2.5 Complex Modulus G* vs γ0 202

A5.2.6 A Few Mathematical Aspects of the Kraus Model 204

A5.2.7 Fitting Model to Experimental Data 206

A5.2.7.1 Modeling G′ vs Strain 207

A5.2.7.2 Modeling G″ vs Strain 209

A5.3 Ulmer Modification of the Kraus Model for Dynamic Strain Softening: Fitting the Model 212

A5.3.1 Modeling G′ vs Strain (same as Kraus) 213

A5.3.2 Modeling G′′ vs Strain 215

A5.4 Aggregates Flocculation/Entanglement Model (Cluster–Cluster Aggregation Model, Klüppel et al.) 218

A5.4.1 Mechanically Effective Solid Fraction of Aggregate 219

A5.4.2 Modulus as Function of Filler Volume Fraction 220

A5.4.3 Strain Dependence of Storage Modulus 221

A5.5 Lion et al Model for Dynamic Strain Softening 222

A5.5.1 Fractional Linear Solid Model 222

A5.5.2 Modeling the Dynamic Strain Softening Effect 223

A5.5.3 A Few Mathematical Aspects of the Model 226

A5.6 Maier and Göritz Model for Dynamic Strain Softening 227

A5.6.1 Developing the Model 227

A5.6.2 A Few Mathematical Aspects of the Model 229

A5.6.3 Fitting the Model to Experimental Data 230

A5.6.3.1 Modeling G′ vs Strain 231

A5.6.3.2 Modeling G″ vs Strain 232

6 Polymers and White Fillers 235

6.1 Elastomers and White Fillers 235

6.1.1 Elastomers and Silica 235

6.1.1.1 Generalities 235

6.1.1.2 Surface Chemistry of Silica 236

6.1.1.3 Comparing Carbon Black and (Untreated) Silica in Diene Elastomers 237

6.1.1.4 Silanisation of Silica and Reinforcement of Diene Elastomers 239

6.1.1.5 Silica and Polydimethylsiloxane 246

6.1.2 Elastomers and Clays (Kaolins) 257

6.1.3 Elastomers and Talc 260

6.2 Thermoplastics and White Fillers 262

6.2.1 Generalities 262

6.2.2 Typical White Filler Effects and the Concept of Maximum Volume Fraction 266

6.2.3 Thermoplastics and Calcium Carbonates 280

6.2.4 Thermoplastics and Talc 291

6.2.5 Thermoplastics and Mica 297

6.2.6 Thermoplastics and Clay(s) 300

References 302

Appendix 6 308

A6.1 Adsorption Kinetics of Silica on Silicone Polymers 308

A6.1.1 Effect of Polymer Molecular Weight 308

A6.1.2 Effect of Silica Weight Fraction 310

A6.2 Modeling the Shear Viscosity Function of Filled Polymer Systems 312

A6.3 Models for the Rheology of Suspensions of Rigid Particles, Involving the Maximum Packing Fraction Φm 315

A6.4 Assessing the Capabilities of Model for the Shear Viscosity Function of Filled Polymers 319

A6.4.1 Effect of Filler Fraction 320

A6.4.2 Effect of Characteristic Time λ 0 320

A6.4.3 Effect of Yasuda Exponent a 321

A6.4.4 Effect of Yield Stress σc 321

A6.4.5 Fitting Experimental Data for Filled

Polymer Systems 322

A6.4.6 Observations on Experimental Data 323

A6.4.7 Extracting and Arranging Shear Viscosity Data 324

A6.4.8 Fitting the Virgin Polystyrene Data with the Carreau–Yasuda Model 324

A6.4.9 Fitting the Filled Polystyrene Shear Viscosity Data 326

A6.4.10 Assembling and Analyzing all Results 332

A6.5 Expanding the Krieger–Dougherty Relationship 335

7 Polymers and Short Fibers 339

7.1 Generalities 339

7.2 Micromechanic Models for Short Fibers-Filled Polymer Composites 344

7.2.1 Minimum Fiber Length 344

7.2.2 Halpin–Tsai Equations 345

7.2.3 Mori–Tanaka’s Averaging Hypothesis and Derived Models 351

7.2.4 Shear Lag Models 353

7.3 Thermoplastics and Short Glass Fibers 358

7.4 Typical Rheological Aspect of Short Fiber-Filled Thermoplastic Melts 368

7.5 Thermoplastics and Short Fibers of Natural Origin 370

7.6 Elastomers and Short Fibers 375

References 383

Appendix 7 389

A7.1 Short Fiber-Reinforced Composites: Minimum Fiber Aspect Ratio 389

A7.1.1 Effect of Volume Fraction on Effective Fiber Length 389

A7.1.2 Effect of Matrix Modulus on Effective Fiber Length 390

A7.1.3 Effect of Fiber-to-Matrix Modulus Ratio on Effective Fiber Length/Diameter Ratio 391

A7.2 Halpin–Tsai Equations for Short Fibers Filled Systems: Numerical Illustration 391

A7.2.1 Longitudinal (Tensile) Modulus E11 392

A7.2.2 Transversal (Tensile) Modulus E22 393

A7.2.3 Shear Modulus G12 393

A7.2.4 Modulus for Random Fiber Orientation 394

A7.2.5 Fiber Orientation as an Adjustable Parameter 394

A7.2.6 Average Orientation Parameters from

Halpin–Tsai Equations for Short Fibers

Filled Systems 394

A7.2.6.1 Longitudinal (Tensile) Modulus E11 395

A7.2.6.2 Transversal (Tensile) Modulus E22 396

A7.2.6.3 Orientation Parameter X 396

A7.3 Nielsen Modification of Halpin–Tsai Equations with Respect to the Maximum Packing Fraction: Numerical Illustration 396

A7.3.1 Maximum Packing Functions 397

A7.3.2 Longitudinal (Tensile) Modulus E11 398

A7.3.3 Transverse (Tensile) Modulus Ey 398

A7.3.4 Shear Modulus G 398

A7.4 Mori–Tanaka’s Average Stress Concept: Tandon–Weng Expressions for Randomly Distributed Ellipsoidal (Fiber-Like) Particles: Numerical Illustration 399

A7.4.1 Eshelby’s Tensor (Depending on Matrix Poisson’s Ratio and Fibers Aspect Ratio Only) 399

A7.4.2 Materials’ Constants (i.e., Not Depending on Fiber Volume Fraction) 400

A7.4.3 Materials and Volume Fraction Depending Constants 401

A7.4.4 Calculating the Longitudinal (Tensile) Modulus E11 402

A7.4.5 Calculating the Transverse (Tensile) Modulus E22 402

A7.4.6 Calculating the (In-Plane) Shear Modulus G12 403

A7.4.7 Calculating the (Out-Plane) Shear Modulus G23 404

A7.4.8 Comparing with Experimental Data 404

A7.4.9 Tandon–Weng Expressions for Randomly Distributed Spherical Particles: Numerical illustration 406

A7.4.9.1 Eshelby’s Tensor (Depending on Matrix Poisson’s Ratio Only) 406

A7.4.9.2 Materials’ Constants (i.e., Not Depending on Filler Volume Fraction) 406

A7.4.9.3 Materials and Volume Fraction Depending Constants 407

A7.4.9.4 Calculating the Tensile Modulus E 408

A7.4.9.5 Calculating the Shear Modulus G 408

A7.5 Shear Lag Model: Numerical illustration 409

Index 411

This book is an outgrowth of a course I have taught for several years to

master and doctorate students in polymer science and engineering at the

Université Pierre et Marie Curie (Paris, France) It is also based on around 30

years of interest, research and engineering activities in the fascinating field

of so-called complex polymer systems, i.e., heterogeneous polymer based

materials with strong interactions between phases Obviously, rubber

com-pounds and filled thermoplastics belong to such systems If one considers

that, worldwide, around 40% of all thermoplastics and 90% of elastomers

are used as more or less complicated formulations with so-called fillers, it

follows that approximately 100 million tons/year of polymers are indeed

“filled systems.” Quite a number of highly sophisticated applications of

polymers would simply be impossible without the enhancement of some of

their properties imparted by the addition of fine mineral particles or by short

fibers, of synthetic or natural origin

The idea that, if a single available material cannot fulfill a set of desired

properties, then a mixture or a compound of that material with another one

might be satisfactory is likely as old as mankind Adobe, likely the oldest

building material, is made by blending sand, clay, water and some kind of

fibrous material like straw or sticks, then molding the mixture into bricks

and drying in the sun It is surely one of the oldest examples of

reinforce-ment of a “plastic” material, moist clay, with natural fibers that was already

in use in the Late Bronze Age, nearly everywhere in the Middle East, North

Africa, South Europe and southwestern North America In a sense, the basic

principle of reinforcement, i.e., to have a stiffer dispersed material to

sup-port the load transmitted by a softer matrix, is already in the adobe brick

Therefore, the “discovery” of natural rubber reinforcement by fine powdered

materials, namely carbon black, in the dawn of the twentieth century surely

proceeded from the same idea

At first, mixing rubber and carbon black was pragmatic engineering, it

gave a better and useful set of properties, and the technique could be

some-what mastered, thanks to side developments, such as the internal mixer The

very reasons for the reinforcing effect remained unclear for a long time and

the question only started to be seriously considered by the mid twentieth

century Today, some light has been shed on certain aspects of polymer

rein-forcement, as will be reviewed through the book But the story is surely

not complete because any progress in the field is strongly connected with

either the availability of appropriate experimental and observation

tech-niques or theoretical views about polymer–filler interactions, or (and most

likely) both

One of the starting points of my deep interest for filled polymers is the

simple observation that, whilst having different chemical natures, a

num-ber of filled polymers, either thermoplastics or vulcanizable rubnum-bers, exhibit

common singular properties This aspect will be thoroughly documented

throughout the book but a few basic observations are worth highlighting

here Let us consider for instance the flow properties of systems that are as

(chemically) different as a compound of high cis-1,4 polybutadiene with a

suf-ficient level of carbon black and a mixture of polyamide 66 with short glass

fibers They share the same progressive disappearance with increasing filler

content of the low strain (or rate) linear viscoelastic behavior Regarding the

mechanical properties, the effect of either fine precipitated calcium

carbon-ate particles or short glass fibers on the tensile and flexural moduli of

poly-propylene are qualitatively similar but by no means corresponding to mere

hydrodynamic effects So, many filled polymer systems are similar in certain

aspects and different in others Understanding why is likely to be the source

of promising scientific and engineering developments

The possibilities offered by combining one (or several) polymer(s) with one

(or several) foreign stiffer component(s) are infinite and the just emerging

nanocomposites science is an expected development of the science and

tech-nology of filled polymers, once the basic relationships between

reinforce-ment and particle size had been established For reasons that are given in

Chapter 1, nanofillers have been excluded from the topics covered by the

book, whose objectives are to survey quite a complex field but by no means

offer the whole story

As stated above, teaching the subject is the origin of the book In my

expe-rience, nothing must be left in the shadow when teaching a complex

sub-ject and all theories and equations found in the literature must be carefully

checked and weighed, particularly if engineering applications are foreseen

I am not a theoretician but an experimentalist with an avid interest for any

fundamental approach that might help me to understand what I am

measur-ing Therefore, whilst theoretical considerations that lead to proposals such

as “property X is proportional to (or a function of) parameter Y,” i.e., X∝ Y or

X ∝ F(Y), may be acceptable in term of (scientific) common sense, they are of

very little use for the engineer (and less so for the student) if the coefficient of

proportionality (or the function) is not explicitly given This is the reason why

all equations displayed in the book have been carefully tested, using

(com-mercial) calculation software When one loads theoretical equations with

parameters expressed in the appropriate units, then either the unit system

is inconsistent and the software gives no results because the unit equation

is considered, or the right units are used and the results of the theory can be

weighed, at least in terms of “magnitude order.” If the results have the right

order of magnitude, then the theoretical considerations are likely acceptable

If not… Such an exercise is always useful and I am grateful to my editor

for having accepted, as appendices, a selection of calculation worksheets

(obviously inactive in a printed book) that offer numerical illustrations of

several of the theoretical considerations discussed in the book Readers who

are familiar with the calculation software I use will have no difficulties in

implementing these appendices in their own work

As a last word, it is worth noting that writing a science book on an active

field is (by essence) a never ending task since new interesting contributions

are published every day But working with an editor forces the

scientist-writer to accept a deadline, in other words to make choices, to develop more

certain subjects and drop other ones, and eventually to bring an end point,

not final but temporary as always in science and industrial applications

Jean L Leblanc

Bois-Seigneur-Isaac

Born in 1946, Jean L Leblanc studied physico-chemistry at the University of Liège, Belgium, with a special emphasis

on polymer science and received his PhD

in 1976, with a thesis on the rheological properties on SBS bloc copolymers He then joined Monsanto Company where, from

1976 to 1987, he held various positions in the Rubber Chemicals, the Acrylonitrile-Butadiene-Styrene plastics (ABS), and the Santoprene• divisions He left Monsanto in

1987 to join the italian company Montedison

as manager, technical assistance and applied research, then moved to the position of manager applied research

when Enichem took over Montedison in 1989 In 1988, he became fellow of

the Plastics and Rubber Institute (U.K.) and in 1993 he qualified as European

Chemist (EurChem) In 1993, he was elected Professeur des Universités in France

and joined the Université Pierre et Marie Curie (Paris, France), as head of the

then newly developed polymer rheology and processing laboratory, in

col-laboration with the French Rubber Institute He is still in this position today

and, since 1997, also teaches polymer rheology and processing at the Free

University of Brussels (Belgium), as a visiting professor He has written two

books and more than 100 papers

Introduction

1.1 Scope of the Book

This book deals with the properties of filled polymers, i.e mixtures of

macromolecular materials with finely divided substances, with respect to

established scientific aspects and industrial developments So-called

(poly-mer) composites, that consist of long fibers impregnated with resins, such as

glass fibers reinforced polyesters or carbon fibers reinforced epoxy resins, are

not within the subject of this book Filled polymers discussed hereafter are

heterogeneous systems such that, during processing operations, the polymer

and the dispersed filler flow together In other words, filled polymers are

macroscopically coherent masses that exhibit interesting physical,

mechani-cal, and/or rheological properties, often peculiar, but always resulting from

interactions taking place between a matrix (the polymer) and a dispersed

phase (the filler) It follows obviously that filled polymers have to be prepared

through mixing operations, generally complex and requiring appropriate

machines, in such a manner that a thorough dispersion of filler particles is

achieved

Why does one prepare filled polymers? There are many reasons, all of

them related to engineering needs Generally one mixes fillers into polymers

in order to modify properties of the latter, either physical properties, such

as density or conductivity, or mechanical properties, for instance

modu-lus, stiffness, etc., or rheological properties, i.e., viscosity or viscoelasticity

Occasionally, fillers are also used for economical reasons, as cheap additives

that reduce material costs in polymer applications Table 1.1 gives the relative

volume costs of a few common mineral fillers in comparison with several

polymers, using polypropylene (PP) as a reference Clearly, only grinded

cal-cium carbonate and finely divided clays can be considered as “economical”

fillers; in all other cases, specific property improvements are sought when

mixing the filler and the polymer

A few numbers allow underlining the economical importance of filled

poly-mers According to recently published market research reports (2007), the

worldwide consumption of fillers is more than 50 million tons with a global

value of approximately €25 billion Many application areas are concerned,

such as paper, plastics, rubber, paints, and adhesives Fillers, either synthetic

or of natural origin are produced by more than 700 companies all over the

globe In Western Europe, 17 millions tons of thermoplastics were consumed

in 2005 with a significant part in association with 1.7 millions tons of mineral

fillers Polyvinyl chloride (PVC) and polyolefins (polyethylene PE, PP) are

the main markets for mineral fillers, with calcium carbonate CaCO3

account-ing for more that 80% of the consumption (in volume) In rubber materials,

more that 90% of the applications concern “compounds”, i.e quite complex

formulations in which fillers are used at around 50% weight (some 30%

vol-ume) The Western Europe consumption of rubbers was 3.79 millions tons

in 2006 (1.28 MioT natural rubber; 2.51 MioT synthetic elastomers) and some

2.25 millions tons carbon black were used in the interim

Preparing and using filled polymers is consequently a well established

practice in the polymer field, particularly in the rubber industry where the

first use of carbon black as a reinforcing filler can be traced back to the early

twentieth century There are consequently a number of pragmatic

engineer-ing aspects associated with the preparation, the development and the

appli-cations of filled polymers, not all yet fully understood, despite considerable

progresses over the last 50 years As usual, scientific investigations on filled

polymer systems started later than empirical engineering (trial-and-error)

Table 1.1

Relative Cost of Mineral Fillers and Polymers

Type of Filler or Polymer

Relative Weight Cost (Polypropylene  = 1.0)

Grinded calcium carbonate 0.3–0.6

and it is only the recent development of advanced investigation means that

really boosted research and development work in this area, obviously

con-nected with the contemporary physico-chemistry research on interfaces and

interphases

Polymers, either elastomers or thermoplastics, offer a great variety of

chemical natures, as well as the fillers, but curiously common effects and

properties are (at least qualitatively) observed whatever is the chemistry of

the polymer matrix and of the filler particles This striking observation is the

very origin of this book that intends to offer a survey of a quite complex field,

with the objectives to highlight what most filler–polymer systems have in

common, how proposed theories and models suit observations and,

eventu-ally what are the specificities of certain filled polymers

1.2 Filled Polymers vs Polymer Nanocomposites

A filled polymer system is thus a polymer in which a sufficient quantity

(vol-ume) of a small size foreign rigid (or at least less flexible) material, e.g.,

pow-dered minerals, short glass fibers, etc., has been well dispersed in order to

improve certain key properties of engineering importance, for instance

mod-ulus, stiffness, or viscosity The reinforcing effect of carbon black in rubber is

known for one century (1907, Silvertown, UK) and the mastering and

under-standing of its scientific aspect has led to the development of many high

engi-neering performance products, for instance the automobile, truck, or aircraft

tires Starting in 1984, a series of patents obtained by Toyota1 described the

use of organoclay additives for plastics as well as various plastic structures

that could replace traditional components (e.g., aluminium parts) in

automo-tive applications Typically U.S patent No 4,810,734 described a production

process for a composite material by firstly treating a layered smectite mineral

having a cation exchange capacity (e.g., a phyllosilicate) with a swelling agent

having both an onium ion and a functional group capable of reacting with a

polymer and secondly forming a complex with a molten polymer U.S

pat-ent No 4,889,885 described a composite material made with at least one resin

selected from the group consisting of a vinyl-based polymer, a thermosetting

resin and a rubber, and a layered bentonite uniformly dispersed in the resin

The layered silicate has a layer thickness of about 0.7–1.2 nm and an interlayer

distance of at least about 3 nm, and at least one polymer macromolecule has

to be connected to the layered silicate Such patents prompted, over the last

20 years, a kind of cult research area for so-called polymer nanocomposites,

whose origin of reinforcement is on the order of nanometers, but with the

capability to deeply affect the final macroscopic properties of the resulting

material In certain cases, such materials exhibit properties not present in the

pure polymer resin, whilst keeping the processibility, the other mechanical

polymer properties and the specific weight Several types of polymeric

nanocomposites can in principle be obtained with different particle

nano-size, nature and shape: clay/polymer, carbon nanotubes, and metal/polymer

nanocomposites

Let us consider the case of clay/polymer nanocomposites The key aspect

is obviously the successful formation of suitable clay/polymer

nanostruc-tures, essentially through an intercalation process In the case of hydrophilic

polymers (typically polyamides) and silicate layers, pretreatment is not

nec-essary; but most polymers are hydrophobic and are not compatible with

hydrophilic clays Complicated and expensive pretreatments are thus required

For instance organophilic clays can be obtained from normally hydrophilic

clay by using amino acids, organic ammonium salts, or tetra organic

phos-phonium solutions, to name a few reported techniques Established methods

are: solution induced intercalation, in situ polymerization, and melt

process-ing Solution induced intercalation consists of solubilizing the polymer in an

organic solvent, then dispersing the clay in the solution and subsequently

either evaporating the solvent or precipitating the polymer Such a technique

is obviously expensive, raises a number of environmental, health, and safety

problems (common to all organic solution techniques), and in fact leads to

poor clay dispersion In situ polimerization consists of dispersing clay

lay-ers into a matrix before polimerization, i.e., mixing the silicate laylay-ers with

the monomer, in conjunction with the polymerization initiator and/or the

catalyst This technique is obviously limited to polymers whose monomers

are liquids, and therefore excludes most of the general purpose (GP) resins,

namely polyolefins In the melt processing technique the silicates layers,

pre-viously surface treated with an organo-modifier, are directly dispersed into

the molten polymer, using the appropriate equipment and procedure A priori,

this technique would be the preferred route with most GP polymers,

provid-ing mixprovid-ing/dispersion problems are mastered

In theory, extraordinary improvements of material properties are expected

with polymer nanocomposites but, in reality, the overall balance of usage

properties (i.e., mechanical, hardness, wear resistance, to name a few) in the

best clay/polymer nanocomposites are much lower than in conventional fiber

reinforced composites, or even in certain traditional filled compositions It is

indeed only in the low filler range, typically 4–5 wt%, and providing the

dispersion of nanoparticles is nearly ideal, that nanocomposites show better

mechanical performances, but at the cost of major difficulties in mass

fabrica-tion At higher loading, the surface area of the silicate-filler increases, which

leads to insufficient polymer molecules adsorbed on the clay surface One

may consider that polymer nanocomposites combine two concepts:

compos-ites (i.e., heterogeneous systems) and nanometer-size materials; the hope that

manufacturing composites polymer material could eventually be achieved

with a tight control at molecular level (i.e., the nanometer range) surely

justi-fies fundamental research in this area, even if large scale industrial

applica-tions are not yet in sight Certain thermoplastics, filled with nanometer-size

materials, have indeed different properties than systems filled with

conven-tional mineral materials Some of the properties of nanocomposites, such as

increased tensile strength, are routinely achieved by using higher

conven-tional filler loading, but of course at the expense of increased weight and

sometimes with unwanted changes in surface aspects, i.e., gloss with certain

polymers Obviously other typical properties of certain polymer

nanocom-posites such as clarity or improved barrier properties cannot be duplicated

by filled resins at any loading

One may indeed consider that polymer nanostructured materials

repre-sent a radical alternative to the conventional filled polymers and polymer

blends, because the utility of inorganic nanoparticles as additives to enhance

polymer performance has been well established at laboratory level The

incorporation of low volume (1–5 wt%) of highly anisotropic nanoparticles,

such as layered silicates or carbon nanotubes, results in the enhancement of

certain properties with respect to the neat polymer that are comparable with

what is achieved by conventional loadings (15–40 wt%) of traditional fillers.2

In principle the lower loadings would facilitate processing and reduce

com-ponent weight, and in addition, certain value added properties not normally

possible with traditional fillers are also observed, such as higher stiffness,

reduced permeability, optical clarity, and electrical conductivity But the

chemical and processing operations to disrupt the low-dimensional

crystal-lites and to achieve uniform distribution of the nanoelement (layered silicate

and single wall carbon nanotube, respectively) continue to be a challenge

Most commercial interest in nanocomposites has so far focused on

ther-moplastics, essentially because certain polymer nanocomposites allow the

substitution of more expensive engineering resins with less expensive

com-modity polymer nanocomposites, to yield overall cost savings But such

favorable cases are rare and restricted to very specific applications A recent

study by a market research company claims that, by 2010, nanocomposites

demand will grow to nearly 150,000 tons, and will rise to over 3 million tons

with a value approaching $15 billion by 2020.3 So far however the market for

these new materials has not developed as expected and if, indeed, exfoliated

(or surface treated) nanoclays are commercially available,4 their uses seem

restricted to very specific cases Packaging and parts for motor vehicles are

nevertheless expected to be key markets for nanoclay and nanotube

compos-ites With respect to the improved barrier, strength and conductive

proper-ties that they can offer, polymer nanocomposites should somewhat penetrate

certain food, beverage, and pharmaceutical packaging applications, as well

as specific parts for electronics In motor vehicles, automotive manufacturers

are expected to consider polymer nanocomposites either as replacement for

higher-priced materials, or to increase the production speed of parts and to

reduce motor vehicle weight by lightening a number of exterior, interior, and

underhood applications The future will weigh such expectations

Over the last decades, a considerable number of research papers have been

published whose main subject is so-called polymer nanocomposites,5 i.e.,

mixtures or preparations involving macromolecular materials and small

particles with dimensions in the nanometer range, with however a great deal

of confusion in the author’s opinion Indeed, a careful reading of published

papers reveals that for certain authors, nanoparticles are entities with

(equiv-alent) diameters up to a few tens nanometers, whilst others title their works

with the heading nanocomposites but consider mixtures with particles in

the micron range It is also worth underlining that nanoparticles

technol-ogy implies that individual representatives particles (i.e., spheres, platelets,

etc.) are ideally dispersed in the polymer matrix, without agglomeration or

flocculation This aspect of polymer nanocomposites appears thus in sharp

contrast with conventional filled polymer technology where elementary

particles must be suitably clustered in complex tri-dimensional structures

called “aggregates” to yield reinforcing properties As will be extensively

described in this book, this is the key aspect of the reinforcement of

rub-ber with carbon black and high structure silica In many published papers

this ideal dispersion of nanoparticles is neither documented nor granted by

the preparation (mixing) process, and therefore the reference to polymer

nanocomposites is dubious Despite the lack—so far—of significant

indus-trial applications, polymer nanocomposites seem to be a fashion subject for

fundamental research, with sometimes an unfortunate lack of reference to

earlier works on more classical filled polymer systems, namely filled rubber

materials, surely the oldest class of complex polymer materials of industrial

importance There are a number of recent books, reviews, and treatises on

so-called polymer nanocomposites6–8and elastomer nanocomposites.9,10 The

pres-ent book is definitely not addressing the same subject, but rather so-called

“filled polymer systems” that are nowadays used yearly in quantities of

hun-dred thousands to million tons worldwide

In order to avoid confusion it is thus necessary to clearly define what are

filled polymer systems, the very subject of the present book, in contrast with

polymer naonocomposites It is clear that industrial use is not a sufficient

criterion to distinguish both classes of materials Whilst mainly concerned

with rubber reinforcement, Hamed offered recently quite a clear and

well-supported proposal to distinguish filled polymer systems, with respect to the

smallest size d of the dispersed phase.11 The characteristic smallest dimension

d depends of course of the actual geometry of the particles, the diameter for

spheres and rods, the thickness for plates and scales There are a number of

available materials whose characteristic particle dimension is in the 1–100 nm

range and therefore the prefix nano is ambiguously used in the literature We

will consequently somewhat follow the Hamed’s proposal: when the

charac-teristic dimension d of the dispersed phase is between 1 and 10 nm, then one

is dealing with nanocomposites, when 100 nm > d > 10 nm, then

mesocom-posites are involved, with d above 100, composite materials are referred with

the prefix micro, and the prefix macro when very gross (d > 104 nm) rigid

“entities” are dispersed in a polymer Further to this basic characterization,

Hamed considers that the dispersed entities can be structured, either a priori

by their nature or through their manufacturing process, or as a result of the

kinetics and thermodynamics of phase separation that may occur during the

preparation of the complex polymer system The proposal is further

elabo-rated in Table 1.2., with typical examples of concerned materials

With respect to Table 1.2, all filled polymer systems discussed in this book

are either meso or microcomposites, and most of them have a considerable

industrial importance The proposal by Hamed is based on well sounded

arguments on the mechanical properties of filled rubbers and is further

reinforced by very recent observations on the likely origin of the unusual

properties of (true) nanocomposites Indeed as demonstrated by a number

of authors, so-called anomalous rheological and mechanical properties of

polymer nanocomposite systems are observed when the characteristic

dimensions of (ideally) dispersed particles are in the 1–10 nm range, in fact

commensurable with some typical dimensions of polymer dynamics, namely

the reptational tube diameter (a few nanometers), as considered when

mod-eling the behavior of entangled polymers In fact polymer nanocomposites

are distinguished by the convergence of length scales corresponding to the

radius of gyration of the polymer chains, a dimension of the nanoparticle

and the mean distance between the nanoparticles.12 It was therefore

hypoth-esized that, when nanoparticles have such small dimensions, they have the

capability to participate in the local polymer dynamics.13

Filled polymer systems of industrial importance, e.g., filled rubber

com-pounds, filled thermoplastics are thus meso or microcomposites, possibly

with a structuration (of the dispersed phase) at the nano or meso scale

Whilst no sizeable commercial application yet exist for nanocomposites

rub-bers or thermoplastics (to the author’s knowledge), considerable research has

been made since 1984 with so-called ex-foliated layered silicate “nano-clays.”

Exfoliation means that individual clay sheets, of around 1 nm thickness,

have been separated and adequately dispersed in the matrix Some

rein-forcement has indeed been demonstrated with such exfoliated nanoparticles

but, generally with very specific rubber systems and/or at a cost of

prepara-tion that is hardly compatible with reasonable chances of commercializaprepara-tion

Nanofiller/particle composite 1–10 Polyamide/exfoliated montmorillonite

Mesofiller/particle composite 10–100 Rubber compounds with highly reinforcing carbon blacks

Microfiller/particle composite 100–10,000 Polypropylene/grinded calcium carbonate

Macrofiller/particle composite  > 10 4 Polymer concrete

It can further be commented that the level of reinforcement obtained in such

systems is not even comparable with what is practically achieved with

con-ventionally filled mesocomposite polymers, namely rubbers No amorphous

vulcanized rubber reinforced only with exfoliated clay has been reported to

have a tensile strength in the 30 MPa range, as currently obtained with

con-ventional carbon black filled compounds One can nevertheless expect that,

owing to their special geometries (plates or scales), properly dispersed

exfo-liated clays might enhance certain properties, such as gas impermeability,

through barrier effects, or thermal or electrical conductivity, through

appro-priate orientation effects, and therefore find niche markets

References

1 U.S Patents: 4,472,538 (Composite material composed of clay mineral and

organic high polymer and method for producing the same, September

18, 1984); 4,739,007 (Composite material and process for manufacturing

same, April 19, 1988); 4,810,734 (Process for producing composite material,

March 7, 1989); 4,889,885 (Composite material containing a layered silicate,

December 26, 1989); 5,091,462 (Thermoplastic resin composition, February

25, 1992).

2 Q Yuan, R.D.K Misra Polymer nanocomposites: current understanding and

issues Mater Sci Technol., 22 (7), 742–755, 2006.

3 Nanocomposites The Freedonia Group, Inc., Cleveland, OH, 2006.

4 For example, Nanomer® nanoclays from AMCOL Intern Corp., Arlington

Heights, IL; Cloisite® and Nanofil® from Southern Clay Products, Inc.,

Gonzales, TX; Bentone® from Elementis plc, Hightstown, NJ.

5 See for instance the following recent reviews: S.S Ray, M Okamoto Polymer/

layered silicate nanocomposites: a review from preparation to processing Prog

fundamental research to specific applications Mater Sci Eng C, 23 (6–8), 763–

772, 2003; Wang, Z.-X Guo, S Fu, W Wu, D Zhu Polymers containing

fuller-ene or carbon nanotube structures Prog Polym Sci., 29 (11), 1079–1141, 2004;

J Jordan, K.I Jacob, R Tannenbaum, M.A Sharaf, I Jasiuk Experimental trends

in polymer nanocomposites—a review Mater Sci Eng A, 393 (1–2), 1–11, 2005.

6 P.M Ajayan, L.S Schadler, P.V Braun Nanocomposite Science and Technology

Wiley, New York, NY, 2003 ISBN: 9783527303595.

7 Y.-W Mai, Z.-Z Yu Ed Polymer Nanocomposites CRC Press, Baton Roca, FL,

USA; 2006 ISBN 9780849392979; a review by an international team of authors

with 13 papers on layered silicates/polymer compositions and eight papers on

nanotubes, nanoparticles and inorganic-organic hybrid systems.

8 J.H Koo Polymer Nanocomposites McGraw-Hill Prof., New York, NY, 2006 ISBN

13: 978-0071458214.

9 S.D Sadhu, M Maiti, A.K Bhowmick Elastomer-clay nanocomposites

Chapter 2, 23–56 In Current Topics in Elastomer Research, A.K Bhowmick Ed

CRC Press, Taylor & Francis Group, Boca Raton, FL, 23–562008 ISBN-13:

13 M.E Mackay Anomalous rheology of polymer-nanoparticle suspensions

KL.11.

Types of Fillers

In polymer technology, there are essentially two major classes of fillers,

either extracted or fabricated Minerals such as talc and clays (Al2O3, 2SiO2,

2H2O) are extracted, grinded, and possibly treated and therefore belong to

the first class Calcite (CaCO3) belongs to both classes, as it can be either

extracted and grinded or obtained through a chemical process that involves

precipitation Carbon blacks result from the incomplete combustion of

hydrocarbon feedstock, and are consequently fabricated fillers, as well as

synthetic silica that are obtained through more or less complex chemical

operations Short fibers made either of glass, or of carbon, are fabricated

products, and we arbitrarily include cellulose fibers also in the second class,

because quite complex treatments are required before they can be used as

a polymer reinforcing material Moreover, many types of natural fibre have

been considered for use in polymers as reinforcing materials including

flax, hemp, jute, straw, wood flour, rice husks, sisal, raffia, green coconut,

banana, and pineapple leaf fibre to name a few, but technical problems such

as moisture absorption and low impact strength have sometimes restricted

their development Wood flour nowadays used to prepare so-called wood–

polymer composites (WPC), which represents a growing market over the

last decades,* can also be considered as a fabricated filler with respect to its

preparation mode

Fillers for polymers exhibit in fact a stunning variety of chemical natures,

particle sizes and shapes Essentially three basic shapes can be distinguished:

either spheres, or plaques (disks, lamellas) or rods (needles, fibers), as

illus-trated in Figure 2.1 Such basic shapes can be further combined to result in

quite complex geometrical objects to which specific (reinforcing) properties

can be associated Carbon black aggregates offer typical examples of

com-plex tri-dimensional structures whose shape specifically affects the

reinforc-ing properties, as will be discussed hereafter Most fillers, either extracted or

fabricated, have a mineral origin, with the notable exception of carbon blacks

that result from the thermal degradation of hydrocarbons There are also a

* In North America the WPC market amounts today to around 300,000 tons/year,

essen-tially for building and garden applications, particularly decking and associated

prod-ucts Estimated over $600 Mio in 2002, the USA and Canada segment is nowadays worth

over $2 billion and worldwide estimates are in the $3 billion range Market growth is

slower in West Europe with a consumption of around 140,000 tons in 2002, over 200,000

tons in 2005 and estimated to reach some 270,000 tons in 2010 (source: A Eder WPCs – an

updated worldwide market overview including a short glance at final consumers 3rd Wood

Fibre Polymer Composites Symposium, Bordeaux, France, March 21–27, 2007).

number of filler materials that have a vegetal origin, for instance wood flour,

sisal, coco, or jute fibers

It is tempting to consider a classification scheme for polymer fillers but

no overall system is available and the analysis of existing proposals reveal

that their validity and interest strongly reflect the application considered We

will nevertheless consider a few logical possibilities, which underline certain

specific aspects of the common property considered

Considerations based on the refractive index allow to draw a clear

dis-tinction between a filler and a pigment, whilst if certain fillers can be used

to modify the color of a polymer (e.g., carbon black in polyolefin), not all

pigmenting materials have reinforcing capabilities Let us consider various

materials and their respective refractive indices (Table 2.1) The refractive

index of vacuum is (by definition) equal to 1, and most polymers exhibit

indices around 1.5 One would consider that any given material has no

capa-bility to modify the color of another one if the respective refractive indices

of both materials do not differ by more than 0.2 It follows that materials

with refractive indices either above 1.3 or below 1.7 have practically neither

clearing nor darkening effects on polymers Consequently, a mineral whose

refractive index is above 1.7 can potentially be used as a pigment (but can

also have reinforcing capabilities), whilst materials whose refractive index is

below 1.7 would be essentially considered as fillers.*

A logical and broader approach would associate the origin, the

produc-tion process and the reinforcing capabilities (Figure 2.2) In this manner,

essentially four types of filler are considered: organic fillers of natural

ori-gin (liege, wood flour, vegetal fibers), organic fillers obtained by chemical

* One notes however that such a classification makes no sense for “dark” fillers, such as carbon

blacks, which do not refract light.

Spheres

Partial fusion elementary particles => aggregates

Complex tri-dimensional object

=> structural effect of the filler

Scales, flakes lamellas Cylinders, rods,needles, fibers

Figure 2.1

Fillers basic shapes and structure.

synthesis (synthetic resins, cellulose derivatives), mineral fillers of natural

origin (essentially all extracted fillers) and mineral fillers obtained through

chemical processes in the broad sense (carbon blacks, fumed and

precipi-tated silica) Furthermore, for each type, one might distinguish materials as

active, semiactive, or inert filler, depending how they boost, improve or do

not affect certain mechanical properties of interest, for instance stiffness,

tensile or flexural strength, and abrasion resistance, to name a few

Another approach, maybe less subjective, consists of paying attention to

particle size because, as illustrated in Figure 2.3, there is a clear

relation-ship between this characteristic and the reinforcing capabilities Essentially

Wood flour Fibres (jute, sisal, )

Synthetic

Synthetic resins Cellulose derivatives

Natural

Minerals (CaCO3, talc, clays, )

Synthetic

Carbon blacks Silicas (fumed, precipitated) Metal oxides (TiO2, ZnO, ) Metal salts (BaSO4, )

no reinforcement is obtained when particles are larger than 103

nanome-ter (nm) and too large particles denanome-teriorate mechanical properties of

poly-mer materials The wide range of particle sizes (and structures) offered

by the manufacturing of carbon blacks and synthetic silica clearly reflect in

the semireinforcing and reinforcing character of these fillers The general

relationship between reinforcing capabilities and particle size suggests

obvi-ously that a poorly dispersed mineral, whatever its ultimate particle size, is

likely to deteriorate ultimate mechanical properties, for instance by reducing

the elongation at break of vulcanized rubbers and thermoplastics Indeed,

large and badly dispersed particles are fracture initiation sites

Grinded CaCO3 mica, talc

Clays

Precipitated CaCO3TiO2, ZnO

Si aluminates

Ca silicates Hydrated silica Anhydrous silica Carbon blacks

Degradative fillers

Dilution fillers

Semireinforcing fillers

Reinforcing fillers

Figure 2.3

Classifying fillers with respect to particle sizes.

Concept of Reinforcement

Whilst they can be added to polymers for other purposes, it is mainly for their

reinforcing capabilities that certain fillers offer the largest interest When

compared to polymers, any mineral exhibits mechanical properties, such

as modulus, stiffness, hardness, that are several order of magnitudes larger

Therefore, one may reasonably expect that mixing the latter with the former

will result in a heterogeneous mixture that exhibits macroscopic mechanical

properties, at least intermediate between those of the polymer and those of

the filler Reinforcement of elastomers by carbon black, discovered in 1907

in Silvertown, UK, is likely the most significant example of this effect, that

really permitted the development of the emerging tire technology, strongly

connected of course with the automotive industry

Essential in rubber technology, the concept of reinforcement is however

very complex, even if relatively easy to capture at first sight Indeed, when a

filler is added to a polymer, practically all properties are affected, some in a

positive manner, others negatively with respect to a given application There

has been much debate about which particular property should be considered

as the most expressive in terms of reinforcement In this respect, it is worth

quoting here the opinion expressed by G Kraus:1

A precise definition of the term «reinforcement» is difficult because it depends somewhat on the experimental conditions and the intended effects of the filler addition…it appears preferable to regard reinforce- ment broadly as the modification of the viscoelastic and failure proper- ties of a rubber by a filler to produce one or more favorable results…

The reinforcing capabilities of a filler must consequently be appreciated

with respect to a balance of properties, whose choice depends on the

applica-tion considered Let us consider the general trends exhibited by a rubber

compound in which increasing quantities of active (e.g., carbon black) or

inert (e.g., finely divided clay) have been added

As shown in Figure 3.1, certain properties will only either increase or

decrease, for instance viscosity, hardness, but other ones will pass through

extremes in the case of the reinforcing filler This immediately suggests that

there will be optimum loadings, for a given filler, in a given polymer, for

a specific application To establish the optimum filler level is therefore the

most important task for the compounder, further complicated by the

obvi-ous requirement that the compound must remain processible at reasonable

energy and labor costs; sometimes the excessive viscosity increase imparted

by very active fillers, either limits their practical level in certain elastomers or

requires additional modification in formulation, for instance higher levels of

processing oils, or plasticizers, which generally have a penalizing effects on

certain mechanical properties of the vulcanized part

In general, the reinforcing activity of a filler depends on at least four

The structure of the filler material refers to the fact that, during their

man-ufacturing process, reinforcing fillers develop very complex tri-dimensional

shapes, which are called aggregates in the case of carbon black Aggregate

structure appears thus as one of the most important aspect of reinforcement

and is obviously related with the specific area The quantification of structure

and the measure of specific area are somewhat related, essentially because

the adsorption of molecules of known size is used to assess both

charac-teristics The well-known BET (Brunauer, Emmet, Teller) method is used to

measure the adsorption isotherm of nitrogen (N2) absorbed by powdery

fill-ers, whilst the aggregate complexity is assessed by evaluating the maximum

quantity of larger molecules (for instance di-butylphthalate DBP, or

cetyl-triethylammonium bromide CTAB) than can be adsorbed on the external

surface As might be expected, there is a (loose) correlation between the

so-called BET surface and the activity (or reinforcing capability) of a filler:

BET < 10 m2/g: inert fillerBET = 10–60 m2/g: semiactive fillerBET > 60 m2/g: active filler

BET > 100 m2/g: very active filler

In fact, relationships between the reinforcing abilities and the

character-istics of the filler are very complicated and, in general, one has to consider

more than one criterion to make valid comparisons, useful for a given filler

in a given polymer, for a given application

It is worth underlining that the concept of reinforcement has been more

debated in the field of rubber science and technology than in the field of

thermoplastics The fact that, without suitable reinforcement, most

elasto-mers exhibit so low mechanical properties that no interesting applications

are possible is surely a reason Another one is that most general purpose

thermoplastics have known their tremendous development in the second

half of the twentieth century, in parallel with the expansion of

petro-chemistry, and have found immediately interesting applications “as such,”

nearly without additives except a few protective chemicals Polyethylene

and polypropylene for instance are used to fabricate sheets and films by

essentially exploiting their capabilities as semicrystalline polymers No

filler is needed to obtain the high mechanical properties that develop when

crystalline structures are properly established and oriented Polystyrene,

ABS and other styrenics exhibit properties directly used in a number of

applications, without the need of reinforcing fillers Of course, in their

usages, most thermoplastics must also meet a balance of properties but,

except maybe polyvinyl chloride (PVC), the right material for a given

appli-cation is obtained by controlling the macromolecular size and structure,

essentially through a suitable adaptation of the polymerization process

The key role played by polymerization catalysts in the developments of

polyolefins clearly supports this point PVC is an exception because when

suitably compounded with stabilisers, plasticizers, and other ingredients, a

whole range of products can be obtained, essentially by changing the glass

transition temperature of the material It is quite symptomatic that the

so-called “plastograph,” a small laboratory mixer, was specifically developed

in the 1950s as a convenient tool to document the “plasticization” of PVC

The addition of fillers to thermoplastics polymers is thus quite a recent

practice, around three decades old, whilst filled rubber compounds are

used for more than a century

There is nevertheless another important, more technical reason for the

different meaning of reinforcement in the rubber and plastics fields In

most of their applications, thermoplastics are used within the limits of

their elastic behavior, generally below 10% strain Indeed, once the yield

strength limit is exceeded, permanent deformation occurs It follows that

most applications of thermoplastics are first concerned by the elastic

behav-ior of the material; the viscoelastic character plays a secondary role, namely

in what the long term variation of modulus is concerned through the creep

phenomenon for instance The situation is totally different with rubber

materials, whose performance are controlled by their viscoelastic

charac-ter, in a strain range that is substantially larger than for thermoplastics

For instance, with rubber materials, the tensile (Young) modulus is far less

significant than the 100 or 200% modulus in most applications It follows

that the role played by fillers in “reinforcing” rubbers and thermoplastics

is substantially different, as well as the balance of properties, as will be

largely underlined throughout the book A direct consequence is that the

modeling of the filler’s effects in thermoplastics and in elastomers, whilst

sometimes based on a similar theoretical background, is generally

substan-tially differing in the supporting reasoning and therefore in the

applicabil-ity It is one of the objectives of this book to identify both the similitudes

and the differences in those theoretical approaches, with respect to the

class of polymer matrix considered

1 G Kraus Reinforcement of elastomers by carbon black Adv Polym Sci.,

8, 155–231, 1971.

Typical Fillers for Polymers

4.1 Carbon Black

4.1.1 usages of Carbon blacks

Essentially, carbon black is the soot that results from the incomplete

combus-tion of hydrocarbon materials, i.e., gas and oils This definicombus-tion does not pay

tribute however to the high degree of development and control in use today

in most industrial processes The uses and the basic production principles

of carbon black are lost in antiquity, but the development of controlled

fab-rication processes dates back to the previous century, resulting nowadays in

highly sophisticated technologies with the capability to produce very fine

and structurally complex materials, in accordance with the most recent

stan-dards of quality

As we will briefly see below, the term “carbon blacks” covers a very broad

range of filler materials, with numerous applications, as outlined in Table 4.1

Except elastomer reinforcement, printing inks and several uses in the

electri-cal industry, most application concern relatively low fraction of carbon black,

typically below 5% volume

4.1.2 Carbon black Fabrication Processes

Fabrication processes of carbon blacks all share the same principle:

con-trolled heat decomposition of hydrocarbon products Such processes are

essentially chemical, either thermo-oxidative or mere thermal

decomposi-tion, as described in Table 4.2

Amongst the thermo-oxidative processes, the furnace black one is the most

recent and nowadays the most important As illustrated in Figure 4.1, the

liquid combustible (either oil or gas) is sprayed in a flame of natural gas and

hot air Black smoke is produced that is a mixture of gas and carbon particles,

initially nearly spherical elementary particles that partially fuse together to

produce complex tri-dimensional objects called aggregates Carbon black

aggregates are quenched through water spraying that stops the pyrolysis

and aggregation processes and cools down smoke, which is then filtered to

recover solid particles Unburned gas is treated and recycled in the process

Table 4.1

Important Uses of Carbon Blacks

Elastomers Reinforcing filler in tires and mechanical rubber goods

Printing inks Tinting, rheology modifier

Enduction Black and gray tinting, color enhancement

Thermoplastics Black and gray tinting, color enhancement, anti-UV protection of

polyolefins, high voltage cable shielding, application in semiconductors, static electricity dissipation

Paper Black and gray tinting, photograph protective paper

Electrical industry Electrodes, dry batteries and cells

Table 4.2

Fabrication Methods of Carbon Blacks

Thermo-oxidative

decomposition Furnace black

Gas black (Degussa process) Lamp black

Aromatic oils from coal tar or petrol distillates, natural gas Coal tar distillates, natural gas Aromatic oils from coal tar or petrol distillates

Thermal decomposition Thermal black

Acetylene black Natural gas (or oils)Acetylene

Oil Gas

Water quench (stops pyrolysis)

Smoke gas

Air

Thermo-oxidative process : furnace black

Liquid feedstock atomized and sprayed into the flame

Smoke treatment for carbon black recovery

Flame from combustion

of gas combined with preheated air

Figure 4.1

Carbon black manufacturing process for furnace black.

After filtration, carbon black aggregates are first packed into agglomerates

then into pellets (of millimeter dimensions) in order to produce roughly

spherical grains that are easy to handle The process has several advantages:

first it is a totally sealed, so that full respect of environment is obtained

sec-ond a precise control of elementary particle size (from 10 to 100 nm) and of

aggregate structures is achievable.1

The lamp black process is likely the oldest industrial process and has

consequently been the object of numerous engineering variants Figure 4.2

describes the principle of a typical modern plant The partial combustion of

a feedstock (oil generally) in an atmosphere purposely poor in oxygen

pro-duces smoke, which is cooled down and filtered to recover carbon black

par-ticles that are subsequently flocculated The control of the pyrolytic process

is loose and results in a large distribution of elementary particle sizes (from

60 to 200 nm) This fabrication process tends to be abandoned today in favor

of the much cleaner and more versatile furnace one

Degussa (now EVONIK), in Germany, developed the so-called gas black

process in the 1930s Initially coal tar was used, quite a common feedstock

at that time, when carbochemistry was very important in a country that

had limited access to petrol Today, any kind of hydrocarbon feedstock

may be used in the process As shown in Figure 4.3, a carrying gas is flown

over preheated oil, then the oil–rich gas feeds a burner Smoke is in part

captured on the wall of water-cooled rotating cylinders and removed with

scrapers, and in part recovered through filtration Very fine elementary

Smoke treatment for carbon black recovery

Figure 4.2

Carbon black manufacturing process for lamp black.