Science and Industrial Applications

Filled
Polymers
Science and
Industrial
Applications



Filled
Polymers
Science and
Industrial
Applications
Jean L. Leblanc

Boca Raton London New York

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Contents
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

v

vi

Contents

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
5.1.4Bound 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


Contents

vii

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


viii

Contents

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 λ0...................................... 320
A6.4.3 Effect of Yasuda Exponent a............................................ 321
A6.4.4 Effect of Yield Stress σc................................................... 321


Contents

ix

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


x

Contents

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


Preface
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 compounds 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 reinforcement 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 support 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 somewhat 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 ­t wentieth
century. Today, some light has been shed on certain aspects of polymer reinforcement, 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 techniques or theoretical views about polymer–filler interactions, or (and most
likely) both.
xi


xii

Preface

One of the starting points of my deep interest for filled polymers is the
simple observation that, whilst having different chemical natures, a number of filled polymers, either thermoplastics or vulcanizable rubbers, 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 sufficient 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 carbonate particles or short glass fibers on the tensile and flexural moduli of polypropylene 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 technology of filled polymers, once the basic relationships between reinforcement 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 experience, nothing must be left in the shadow when teaching a complex subject 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 measuring. 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 (commercial) 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


Preface

xiii

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 scientistwriter 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



Author Bio
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 AcrylonitrileButadiene-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 collaboration 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.

xv



1
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 (polymer) 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, mechanical, 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 modulus, 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 calcium 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 polymers. 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,
1


2

Filled Polymers

Table 1.1
Relative Cost of Mineral Fillers and Polymers
Type of Filler or Polymer
Grinded calcium carbonate
Grinded clays
Polyvinyl chloride
Carbon black
Polypropylene
Talc
Polyethylene
Calcined clays
Wollastonite (not treated)
Natural rubber
Ethylene-propylene rubber
Treated calcined clays
Styrene-butadiene rubber
Silica

Precipitated CaCO3
Polyamides

Relative Weight Cost
(Polypropylene = 1.0)
0.3–0.6
0.4–0.7
0.7
0.7–1.2
1
1.1–1.4
1.1
1.5–1.7
1.6
1.6
1.6–1.9
1.7–1.9
1.7
1.7–1.9
1.9
3.0–6.0

Note: Table assembled using prices and quotations on the
European market during the first sem­ester of 2008.

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 accounting 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% volume). 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 engineering aspects associated with the preparation, the development and the applications 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)


Introduction

3

and it is only the recent development of advanced investigation means that
really boosted research and development work in this area, obviously connected 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, eventually 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 (volume) of a small size foreign rigid (or at least less flexible) material, e.g., powdered minerals, short glass fibers, etc., has been well dispersed in order to

improve certain key properties of engineering importance, for instance modulus, stiffness, or viscosity. The reinforcing effect of carbon black in rubber is
known for one century (1907, Silvertown, UK) and the mastering and understanding of its scientific aspect has led to the development of many high engineering 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 automotive 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. patent 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


4

Filled Polymers

polymer properties and the specific weight. Several types of polymeric
nanocomposites can in principle be obtained with different particle nanosize, 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 nanostructures, essentially through an intercalation process. In the case of hydrophilic

­polymers (typically polyamides) and silicate layers, pretreatment is not necessary; 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 phosphonium solutions, to name a few reported techniques. Established methods
are: solution induced intercalation, in situ polymerization, and melt processing. 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 layers into a matrix before polimerization, i.e., mixing the silicate layers 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, previously 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, providing mixing/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 fabrication. 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: composites (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 justifies fundamental research in this area, even if large scale industrial applications are not yet in sight. Certain thermoplastics, filled with nanometer-size

Introduction

5

materials, have indeed different properties than systems filled with conventional mineral materials. Some of the properties of nanocomposites, such as
increased tensile strength, are routinely achieved by using higher conventional 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 nanocomposites such as clarity or improved barrier properties cannot be duplicated
by filled resins at any loading.
One may indeed consider that polymer nanostructured materials represent 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 component 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 crystallites 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 thermoplastics, essentially because certain polymer nanocomposites allow the
substitution of more expensive engineering resins with less expensive commodity 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 composites. With respect to the improved barrier, strength and conductive properties 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.,


6

Filled Polymers

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 (equivalent) 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 technology 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 rubber 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 industrial 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 nanocomposites6–8 and elastomer nanocomposites.9,10 The present book is definitely not addressing the same subject, but rather so-called
“filled polymer systems” that are nowadays used yearly in quantities of hundred 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 wellsupported 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 characteristic 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 mesocomposites 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


7

Introduction

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 elaborated 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 modeling 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 hypothesized 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 compounds, 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 rubbers 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 reinforcement has indeed been demonstrated with such exfoliated nanoparticles
but, generally with very specific rubber systems and/or at a cost of preparation that is hardly compatible with reasonable chances of commercialization.

Table 1.2
Classification of Filled/Composite Polymer Systems
Designation

Characteristic
Dimension (nm)

Nanofiller/particle composite

1–10

Mesofiller/particle composite

10–100

Microfiller/particle composite

100–10,000

Macrofiller/particle composite

 > 104

Example
Polyamide/exfoliated montmorillonite
Rubber compounds with highly
reinforcing carbon blacks
Polypropylene/grinded calcium
carbonate
Polymer concrete


8

Filled Polymers

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

systems is not even comparable with what is practically achieved with conventionally 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 conventional carbon black filled compounds. One can nevertheless expect that,
owing to their special geometries (plates or scales), properly dispersed exfoliated clays might enhance certain properties, such as gas impermeability,
through barrier effects, or thermal or electrical conductivity, through appropriate 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.
Polym. Sci., 28 (11), 1539–1641, 2003; H. Fischer. Polymer nanocomposites: from
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 fullerene 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.