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A Practical Guide to Polymeric Compatibilizers for Polymer Blends,
Composites and Laminates.
Jozef Bicerano, Ph.D.
Introduction
Fundamental Considerations
Overveiw of Available Compatibilization Technologies
Representative Examples of Vendors and their Technologies
Technology Outlook
Introduction
The development of polymer blends, composites and laminates is a very active area of
science and technology; of great economic importance not only for the plastics industry but
also for many other industries where the use of such products is becoming increasingly more
common.
Most pairs of polymers are immiscible with each other. Even worse is the fact that they also have
less compatibility than would be required in order to obtain the desired level of properties and
performance from their blends. Compatibilizers are often used as additives to improve the
compatibility of immiscible polymers and thus improve the morphology and resulting properties
of the blend. Similarly, it is often challenging to disperse fillers effectively in the matrix polymer
of a composite, or to adhere layers of polymers to each other or to other substrates (such as glass
or metals) in laminates. Continued progress in the development of compatibilization technologies
is, hence, crucial in enabling the polymer industry to reap the full benefits of such approaches to
obtaining materials with optimum performance and cost characteristics.
Term Definition
Additive Substance added to a polymer.
AdhesionHolding together of two bodies by interfacial forces or mechanical
interlocking on a scale of micrometers or less.
Adhesion promoter See Coupling agent.
Chemical adhesionAdhesion in which two bodies are held together at an interface by ionic
or covalent bonding between molecules on either side of the interface.
Compatibility
Capability of the individual component substances in either an
immiscible polymer blend or a polymer composite to exhibit interfacial
adhesion.
Compatibilization
Process of modification of the interfacial properties in an immiscible
polymer blend that results in formation of the interphases and
stabilization of the morphology, leading to the creation of a polymer
alloy.
Compatibilizer Polymer or copolymer that, when added to an immiscible polymer
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blend, modifies its interfacial character and stabilizes its morphology.
Compatible polymer blendImmiscible polymer blend that exhibits macroscopically uniform physical
properties throughout its whole volume.
Composite
Multicomponent material comprising multiple different (nongaseous)
phase domains in which at least one type of phase domain is a
continuous phase.
Co-continuous phase
domains
Topological condition, in a phase-separated, two-component mixture, in
which a continuous path through either phase domain may be drawn to
all phase domain boundaries without crossing any phase domain
boundary
Continuous phase domain
Phase domain consisting of a single phase in a heterogeneous mixture
through which a continuous path to all phase domain boundaries may
be drawn without crossing a phase domain boundary.
Coupling agent
Interfacial agent comprised of molecules possessing two or more
functional groups, each of which exhibits preferential interactions with
the various types of phase domains in a composite.
Degree of compatibilityMeasure of the strength of the interfacial bonding between the
component substances of a composite or immiscible polymer blend.
Discontinuous or discrete
or dispersed phase domain
Phase domain in a phase-separated mixture that is surrounded by a
continuous phase but isolated from all other similar phase domains
within the mixture.
Extender
Substance, especially a diluent or modifier, added to a polymer to
increase its volume without substantially altering the desirable
properties of the polymer.
Filler Solid extender.
Hard segment phase
domain
Phase domain of microscopic or smaller size, usually in a block, graft,
or segmented copolymer, comprising essentially those segments of the
polymer that are rigid and capable of forming strong intermolecular
interactions.
Immiscibility Inability of a mixture to form a single phase.
Immiscible polymer blend Polymer blend that exhibits immiscibility.
Interfacial adhesion
Adhesion in which interfaces between phases or components are
maintained by intermolecular forces, chain entanglements, or both,
across the interfaces.
Interfacial bondingBonding in which the surfaces of two bodies in contact with one another
are held together by intermolecular forces.
Interfacial region Region between phase domains in an immiscible polymer blend in
which a gradient in composition exists.
LaminateMaterial consisting of more than one layer, the layers being distinct in
composition, composition profile, or anisotropy of properties.
Matrix phase domain See Continuous phase domain.
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MiscibilityCapability of a mixture to form a single phase over certain ranges of
temperature, pressure and composition.
Miscible polymer blend Polymer blend that exhibits miscibility.
MorphologyShape, optical appearance, or form of phase domains in substances,
such as high polymers, polymer blends, composites and crystals.
Multiphase copolymer Copolymer comprising phase-separated domains.
NanocompositeComposite in which at least one of the phases has at least one
dimension of the order of nanometers.
Phase domainRegion of a material that is uniform in chemical composition and
physical state.
Polymer allloy
Polymeric material, exhibiting macroscopically uniform physical
properties throughout its whole volume, that comprises a compatible
polymer blend, a miscible polymer blend, or a multiphase copolymer.
Polymer blendMacroscopically homogeneous mixture of two or more different species
of polymer.
Polymer composite Composite in which at least one component is a polymer.
Soft segment phase
domain
Phase domain of microscopic or smaller size, usually in a block, graft,
or segmented copolymer, comprising essentially those segments of the
polymer that have glass transition temperatures lower than the
temperature of use.
Thermoplastic elastomer
Melt-processable polymer blend or copolymer in which a continuous
elastomeric phase domain is reinforced by dispersed hard (glassy or
crystalline) phase domains that act as junction points over a limited
range of temperature.
Table 1: IUPAC-recommended definitions1 of key terms.
Before proceeding any further, it is important to summarize the definitions of some key terms,
as recommended by the International Union of Pure and Applied Chemistry (IUPAC), in order
to avoid any confusion. These IUPAC definitions are listed in Table 1.
This report provides a practical guide to the science and technology of polymeric
compatibilizers for polymer blends, composites and laminates. This definition of its scope has
several important implications:
The report does not include any quantitative information regarding current or
projected market sizes and market segmentation by product type and geographical
region.
The focus of the report is on additives that are used as compatibilizers, rather than
being on polymer blends, composites, or laminates themselves. Consequently, while
many blends, composites and laminates are discussed as examples of the optimum
selection, use and effects of compatibilizers, we do not catalog and review the vast
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range of existing and developmental polymer blends, composites, laminates and their
applications. It suffices to state that automotive and electrical/electronic applications
provide the broadest range of opportunities for new compatibilizers. Significant
opportunities also exist in the packaging, major appliance, sports/recreation
equipment and medical device industries; as well as in the continued development of
plastics recycling technologies.
Since our focus is mainly on "polymeric compatibilizers" (additives that are polymers)
used in blends, composites and laminates, many types of compatibilization additives
(surfactants, most liquid or powder additives of low molecular weight, silane and
titanate coupling agents; and silane, phenolic, titanate and zirconate adhesion
promoters) are not discussed.
Our focus is on providing a "practical guide" consisting entirely of information that
specialty chemical and polymer producers and compounders can use. Consequently,
a lengthy review of the vast and rapidly growing academic literature on
compatibilization is avoided. We also avoid a lengthy review of the rapidly growing
patent literature, much of which consists of patents on technologies which (while they
may have significant merit) will never become commercially significant. The author
believes that these deliberate omissions are essential in order to help focus the
reader's attention on the information that will be most useful in practice by avoiding
lengthy digressions from the practical focus.
Section 2 presents the "practical fundamentals" of compatibilization. The five key factors that
every compatibilization additive developer must consider in order to improve the likelihood of
achieving technical and commercial success simultaneously are identified and discussed.
These five factors are (1) performance versus price, (2) the thermodynamic equilibrium phase
diagram, (3) metastable morphologies often induced by processing conditions, (4) practical
implications of kinetic barriers to equilibration and (5) morphology-property-connections.
Section 3 provides a brief overview of the commercially available polymeric compatibilizers.
The largest number of compatibilizers, by far, are modified polyolefins, most of which contain
polar groups enhancing the compatibility of polyolefins with polar polymers, their ability to
couple with (and thus disperse) inorganic fillers more effectively, and their ability to adhere to
substrates. Some modified polyolefins contain reactive groups that may further enhance their
effectiveness. Styrenic block copolymers constitute the second largest class of
compatibilizers. These thermoplastic elastomers have hard blocks that segregate into a
glassy glassy hard phase and soft blocks that segregate into a rubbery soft phase. Other
polymeric compatibilizers include methacrylate-based polymers, polycaprolactone polyesters,
polycaprolactone polyester / poly(tetramethylene glycol) block polyols, methacrylate-
terminated reactive polystyrene, and mixtures of aliphatic resins of low or medium molecular
weight.
Section 4 discusses selected products of specific vendors as representative examples. The
multiple roles that the same additive can perform (especially blend compatibilizer, filler
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coupling agent, adhesion promoter and impact modifier) are highlighted with many
examples
Section 5 provides an outlook on compatibilization technologies.
Fundamental Considerations
Performance Versus Price
As an empirical rule2 shown in Equation 1, if a polymeric product remains a commodity material
competing for use in commodity-type applications, the price that the average customer is willing
to pay will only increase proportionally to the logarithm of the improvement in its performance:
In this equation, Price2>Price1, Performance2>Performance1 are the corresponding performance
levels, "c" is a positive proportionality constant and "ln" is the natural logarithm. See Figure 1 for
a schematic illustration. This equation can be generalized readily to more complex cases where the
overall "desirability" for a particular application depends on several performance criteria that have
different levels of relative importance.
Figure 1:
Schematic
illustration of
the
"commodity
trap"; namely,
the empirical
rule2 that, if a
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polymeric
product
remains a
commodity
material
competing for
use in
commodity-
type
applications,
then the price
that the
average
customer is
willing to pay
for this
material will
only increase
proportionally
to the
logarithm of
the
improvement
in its
performance
The main implication of this equation is that whatever is done to improve the performance of a
polymer (blending, incorporation of fillers, lamination, processing in a different way, etc.) must
not be allowed to increase by much the sales price required to make a profit if its improved
performance remains in the commodity product range. We will refer to this fundamental
limitation on the price that the market will be willing to pay for a commodity polymer as the
"commodity trap". It is only if the performance can be increased sufficiently to make the
material competitive for higher-valued specialty applications (thus escaping the "commodity
trap") that a significant price increase can be allowed. A few examples will be provided below.
Car manufacturers are usually reluctant to pay a large price premium (sometimes any price
premium at all) for the improved performance of parts fabricated from engineering plastics
unless they are producing extremely expensive (and prestigious) vehicles such as Rolls
Royce or Ferrari. More generally, automotive consumers are often willing to pay for features
that are noticeable by their five senses (such as more attractive fascia, more comfortable
controls, high-intensity discharge headlights, advanced sound systems and a quiet interior),
as well as for major enhancements in vehicle quality and safety. On the other hand, if the
effects of a new feature or component of a vehicle cannot be "sensed" by the consumer and if
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it also has no implications in terms of significantly enhanced real or perceived quality and
safety, consumers will not be willing to pay any price premium for it and cost will be the
overriding consideration.
If an inexpensive polymer (such as a polyolefin) can be modified so that its properties become
competitive with those of an expensive engineering plastic, it can escape the "commodity trap"
since new potential applications become possible for it. It can then command a significant price
premium over the "ordinary" (commodity) grades of the polymer. It must, however, still remain
cheaper than the engineering plastic which it displaces in a higher-valued application. See Figure 2
for a schematic illustration.
Figure 2:
Schematic
illustration of
two situations
where
blending
and/or
compounding
are especially
attractive
from a
commercial
viewpoint.
The thick
vertical brown
line
represents
the minimum
acceptable
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performance
required to
qualify a
material for a
certain
application.
The ellipses
represent
regions on
the "price-
performance
plane". EP1 is
an expensive
engineering
polymer that
far exceeds
the
performance
requirements
of the
application.
EP2 is a
cheaper
blend or
composite of
EP1 with less
expensive
ingredients,
still exceeding
the minimum
performance
requirements.
CP1 is a
commodity
polymer that
does not
meet the
performance
requirements
of the
application.
CP2 is a
blend or
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composite of
CP1 that
exceeds the
minimum
performance
requirements
and can thus
be sold at a
substantially
higher price.
Most people agree about the desirability of recycling but are unwilling to pay any price
premium at all for plastic parts with enhanced recyclability. As a result, the growth rate of
post-consumer recycling enabled by the use of compatibilization additives has been
considerably slower than it would have been if its environmental benefits really outweighed
economic factors in most people's minds. This is clearly an area where new or improved
compatibilization technologies can make a significant impact.
The effects of market forces summarized above are sometimes modified (on some occasions
drastically) by governmental regulations. Such regulations are most often related to safety or
to environmental benefits. Regulations can involve international, national, or local governing
bodies. They can differ significantly between different regions of the world, such as the United
States and the European Union. They can modify the technologies and products that are
available, as well as the relative costs of the available choices. Examples include
governmental demands for increasing fuel economy and reducing tailpipe emissions in
vehicles and for increasing the amount of plastic recycling. When such changes are
mandated by governments, the cost-effectiveness of useful polymer compatibilization
technologies can change drastically.
Thermodynamic Equilibrium Phase Diagram
The latest edition of a book by Bicerano3 and illustrations of compatibilizer structure and
action posted on the website of SpecialChem were used as the main resources for this
subsection.
The rapid screening of possible compatibilizers by predicting how their molecular
architectures, chemical structures and concentrations affect the thermodynamic equilibrium
phase diagram is a challenging but useful starting point. ("Molecular architecture" refers to the
overall pattern of construction of a molecule. For example, a molecule that contains five
subunits of chemical structure A and five subunits of chemical structure B could have its A
and B subunits arranged randomly, or in an alternating fashion as in ABABABABAB, or in
"blocks" of A and B subunit as in AAAAABBBBB, etc.) At present, such relatively routine
predictive screening is only feasible for formulations without reactive components since the
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techniques for dealing with complexities introduced by chemical reactions in reactive
compatibilization are less developed.
The fundamentals of compatibilization have been studied for many years, especially for the
equilibrium (thermodynamic) properties. Methods for predicting the phasic behavior of
nonreactive mixtures have advanced tremendously in sophistication and accuracy (and hence
in reliabilty and practical utility) in recent years. It has been shown that, with the proper
selection of the material parameters describing the system components and their mutual
interactions, the same fundamental physical theory can give all observed types of phase
diagrams. Different simulation methods differ mainly in the details the calculation of how the
enthalpy (H) and the entropy (S) change upon mixing. Thermodynamic equilibrium is
determined by the drive towards minimum Gibbs free energy, G=H-TS, where T is the
absolute temperature.
The simplest example involves the calculation of the phase diagrams of binary amorphous
polymer blends. These phase diagrams can be predicted (or can at least be correlated) quite
easily as functions of the chemical structures and molecular weights of the component
polymers by using the Flory-Huggins solution theory. According to this theory, the enthalpy of
mixing ( Hmix) between mixture components A and B (and thus the deviation from ideal
mixing at thermodynamic equilibrium) is proportional to the "binary interaction parameter" AB.
The case of AB=0 indicates ideal mixing where Hmix=0. The very rare case of AB<0 indicates
an enthalpic driving force towards mixing ( Hmix<0). For the vast majority of mixtures, AB>0
(and hence Hmix>0), indicating that the components enthalpically prefer to be surrounded by
other molecules of their own kind. Larger positive AB indicates stronger enthalpic driving force
towards phase separation. Entropy always favors mixing. The total free energy of mixing,
Gmix, is the sum of enthalpic and entropic terms. For a binary blend of polymers A and B, it is
given by Equation 2, where R is the gas constant, Vtot is the total volume of the two
polymers, Vref is a reference volume (in practice, Vref=100 cm3/mole is often used), A and B
are the component volume fractions and n A and n B are their degrees of polymerization in terms
of Vref.
Phase separation occurs if AB has a sufficiently large positive value to overcome the entropic
effect. The entropic effect decreases rapidly in relative importance with increasing effective
degree of polymerization n, so that miscibility decreases with increasing n. The product AB?
quantifies the combined effects of degree of polymerization and intermolecular interactions on
miscibility. Equation 3, where d0, d1, d2 and d3 are fitting parameters, can produce all of the
observed types of binary amorphous polymer blend phase diagrams shown in Figure 3. This
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equation can be used either correlatively by fitting the theory to experimental data on phasic
behavior or predictively by fitting to the interaction energies predicted by atomistic simulations.
Figure 3:
Schematic
illustration of
possible
types of
polymer blend
phase
diagrams, for
binary blends
where
additional
complications
that can be
introduced by
competing
processes
(such as the
crystallization
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of a
component)
are absent.3
The
coefficients
d1 and d2
refer to a
general
functional
form (see
Equation 3)
for the binary
interaction
parameter
AB.
While most commercially successful compatibilizers are random copolymers, block
copolymers consisting of dissimilar blocks (most commonly, blocks differing greatly in chain
rigidity) have always been viewed as obvious candidates for use as compatibilizers. Each
type of block interacts more favorably with a different polymeric component in the blend.
Since the blocks are connected to each other by covalent bonds, they cannot "get away" from
each other. Consequently, their favorable interactions with and penetration into the phase
domains of dissimilar polymers force these polymers to become more intimately mixed.
Compatibilization is considered to have occurred if the phase domains of the immiscible
polymers in the blend become small enough that the blend can be considered to manifest
"microphase" instead of "macrophase" separation. It is even better if the componenta can be
mixed at the nanoscale.4 The design of nanostructured blends creates opportunities to
develop novel materials whose property profiles can be tailored more precisely for specific
applications. The use of block copolymers as compatibilizers provides the ability to achieve
such nanoscale self-assembly.
The thermodynamics of blend compatibilization by block copolymers have been investigated
extensively by Leibler5 and by Balazs et al. 6,7 These researchers formulated models for
predicting the molecular architecture and composition of effective compatibilizers for any
given binary polymer blend. While Leibler's model can be applied equally to premade and
reactive compatibilizers, the latter have more complexity due to the intriguing interfacial
reaction kinetics. The role of such reaction kinetics in blend compatibilization has been
studied both theoretically (Fredrickson and Milner,8,9 O'Shaughnessy et al.10,11 ) and
experimentally (Macosko et al.12 ) in recent years, but much remains to be done before robust
models that can routinely be used to guide reactive blend design become available.
Preliminary data on the compatibilizing influence of fillers in polymer blends have been
reported by Rafailovich et al.13 (for organoclays) and by Lipatov et al. , 14,15,16 (for silica). This is
also an area where much further work is needed to develop robust models that can truly
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guide polymer blend as well as polymer composite design.
In addressing a specific set of problems via modeling, one can usually readily decide which
method is most appropriate. Once a choice is made, a particular experimental and/or
modeling capability to screen additives and processing conditions can generally be found.
The ability to predict the thermodynamic equilibrium mixing behavior in a blend, mixture, or
composite with reasonable reliability helps target experimental work towards the most
promising directions. This statement is valid regardless of the intended application of the
blend, mixture, or composite material. A recent review article on industrial applications of
polymer modeling 17 includes some examples of applications of thermodynamic equilibrium
mixing considerations.
The three major classes of compatibilizers can be distinguished from each other in terms of the
primary mechanism by which they reduce the interfacial tension between incompatible polymers
and thus favor finer dispersion with more regular and stable equilibrium morphologies:
Figure 4: Use
of a block
copolymer for
compatibilizati
on. The block
copolymer will
prefer to
migrate to the
interface to
reduce the
interfacial
tension. Red
blocks are
compatible
with Polymer
A (matrix).
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Blue blocks
are
compatible
with Polymer
B (dispersed
phase). The
consequence
will be lower
interfacial
tension,
better
interfacial
adhesion and
better
dispersion.
Block or graft copolymers (Figure 4).
Figure 5: Use
of an
nonreactive
polymer
containing
polar groups
for
compatibilizati
on by the
creation of
nonbonded
interactions
[in order of
increasing
strength,
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dispersive,
polar
cohesive and
hydrogen
bonding
(strongest
type of polar
cohesive)]. If
all else is kept
equal, the
stronger and
more
"specific" the
nonbonded
interactions,
the higher is
the
compatibilizati
on
effectiveness.
In general,
the
compatibilizer
must be
compatible
with one
phase
(generally
with the
nonpolar
phase) and
must create
specific
interactions
with the other
phase.
Nonreactive polymers containing polar groups (Figure 5).
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Figure 6: Use
of a reactive
functional
polymer for
compatibilizati
on. Reaction
at the
interface
between
functional
groups on the
different
polymers
creates, "in-
situ", a
grafted block
copolymer.
The
functionalized
copolymer is
miscible with
the matrix
and can react
with
functional
groups of the
dispersed
phase.
Reactive functional polymers (Figure 6). Many compatibilizers of this class also contain
nonreactive polar groups in addition to reactive groups. Maleic anhydride (MAH, see
Figure 7 for an example of how it works) is the most commonly used type of reactive
group in such polymers. The second most commonly used type of reactive group is
glycidyl methacrylate (GMA, see Figure 8 for an example of how it works) which
introduces epoxy functionalities.
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Figure 7:
Compatibilizat
ion by MAH-
grafted
reactive
functional
polymers.
Maleated
polymers can
be prepared
directly by
polymerizatio
n or by
modification
during
compounding
via the
reactive
extrusion
process.
Their
anhydride
groups can
react with
amine, epoxy
and alcohol
groups. In this
example, the
reaction
between a
maleated
polymer and
the -NH2 end
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groups of
Polyamide
6,6 (Nylon
6,6)
compatibilizes
a
polyamide/pol
yolefin blend.
Figure 8:
Compatibilizat
ion by GMA-
grafted
(epoxidized)
reactive
functional
polymers.
They react
with amine,
anhydride,
acid and
alcohol
groups,
making them
effective in
compatibilizin
g polar
polymers with
nonpolar
polymers
according to
the
mechanism
shown above.
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Some of these types of polymers (especially those containing polar functional groups and/or
reactive groups) are often also effective as coupling agents between polymers and inorganic fillers
in composites (Figure 9) and/or as adhesion promoters between incompatible polymers in a
laminate or between polymers and a substrate such as glass or a metal. In all cases, they owe their
effectiveness to the same fundamental underlying cause; namely, their favorable effect in
modifying the thermodynamic equilibrium state towards which the morphology of the system will
evolve unless its evolution is hampered by kinetic barriers as will be discussed next.
Figure 9: A
polymeric
coupling
agent
attaches an
inorganic filler
to the
polymer
matrix and
thus
compatibilizes
the filler with
the polymer
by
nonbonded
(physical)
interactions
and/or
chemical
bonds. It must
be compatible
with the
polymer
(ideally, it
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should have
the same
chemistry as
the polymer),
as well as
being able to
interact with,
react with, or
even better
"glue" to the
filler.
Metastable Morphologies Induced by Processing Conditions
The latest edition of a book by Bicerano3 was used as the main resource for this subsection.
The morphology of a polymer blend or composite is often not at thermodynamic equilibrium
but instead at a metastable state that the morphology is "frozen into" as a result of the
processing conditions used in fabrication. Metastability refers to the ability of a system to exist
indefinitely in a state separated by an energy barrier from a thermodynamically more stable
state. The "classic" example is that people often say that "diamonds are forever" although
graphite is thermodynamically more stable than diamond. A diamond will, in fact, become
transformed into graphite if it is heated for a sufficiently long time at a sufficiently high
temperature. In polymer blends and composites, factors that can cause and influence
deviations from thermodynamic equilibrium include the relative viscosities of polymeric
components during the blending process, details of mixing equipment and conditions and
post-fabrication physical aging by annealing.
High shear may produce morphologies that deviate strongly from thermodynamic equilibrium;
broadening greatly the volume fraction range over which phase co-continuity may occur in a
polymer blend. Such morphologies may be "frozen in" by kinetic barriers when the specimen
is cooled. A dramatic example is how the use of optimal melt processing conditions along with
appropriately chosen compatibilizers has led to lamellar co-continuous morphologies, thereby
producing blends whose solvent and gas barrier properties differed drastically from those of
ordinary blends of the same composition.18 In this example, kinetic barriers were used to help
design metastable morphologies with desirable properties. It is also possible to use high
shear to help disperse fillers in polymers and to create morphologies where stiff anisotropic
fillers (such as fibers and platelets) have a preferred orientation.
Annealing tends to coarsen the blend morphology, by reducing the total interfacial area per
unit volume so that the interfacial components of the Gibbs free energy G can be minimized.
Economic value can be gained by the development of combinations of blend or composite
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formulations and processing conditions that enable the components to mix well at lower shear
rates. Less sophisticated (and hence less expensive) mixing equipment can then be used to
attain the desired morphology, reducing equipment costs. Energy costs can sometimes also
be reduced, provided that the ability to process at a lower shear rate can be attained without
requiring a substantial increase in the processing temperature. It is also valuable to design
processing conditions that can shorten cycle times and/or enable thin or complex-shaped
objects to be manufactured faster and with better quality. Metastable morphologies induced
by the processing conditions are important in making any of these process improvements.
It is crucial, for promising blend and composite formulations, to explore how the phase
structure depends on the processing conditions. Physical phenomena in polymers take place
over a vast range of length and time scales. Atomistic simulations describe physical
processes whose trea™ent requires the explicit consideration of the atoms. Simulations at the
continuum level describe the behavior of the bulk material. Mesoscale simulation methods
(such as dissipative particle dynamics and dynamic density functional theory) bridge between
these two scales. They describe phenomena taking place at length and time scales that are
larger than atomistic but smaller than macroscopic, such as the collective behavior of chain
segments consisting of several repeat units lumped together into "beads" connected to
adjacent "beads" by "springs". They provide valuable insights on morphology evolution over
time in heterophasic polymer systems. There is, therefore, intense ongoing research to
improve their abilities to predict the dynamic pathway along which the morphology evolves
from an initial state towards thermodynamic equilibrium. Nonetheless, much additional work is
needed to develop reliable rules for predicting (even at a merely qualitative level) kinetic
effects on the phase structure. An empirical "statistical design-of-experiments" approach is,
hence, currently (and possibly for the foreseeable future) most often the best approach for
optimizing such effects.
Practical Implications of Kinetic Barriers to Equilibration
The compatibilization of immiscible polymers is one of the most important, widespread and
difficult problems in contemporary applied polymer science. In investigating various methods
of compatibilizing immiscible blends, one can roughly distinguish two broad types of
approaches:
1. Modification of Processing Conditions. These methods could include:
(a) Increasing the processing temperature.
(b) Increasing the motor speed and/or improving the mixing by some other means.
2. Modification of Polymer Formulation. The additives could include:
(a) "Standard" (premade) compatibilizers.
(b) Reactive compatibilizers.
(c) Other substances (such as silica, carbon, or clay nanoparticles) that may manifest a
compatibilizing effect under some conditions.
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Some techniques [such as 1(a), 2(a) and 2(b) and perhaps in many cases also 2(c)] rely on
thermodynamics to "break up" macrodomains and ensure "true" homogeneity of the system.
Other methods [1(b) and 2(c)] rely on kinetics to "break up" domains constantly and force the
system to remain "approximately" homogeneous in metastable morphologies with domain
sizes not exceeding ~1 micron. Several of these techniques are often combined in practice.
For example, it is quite common to increase both the temperature and the shear rate during
processing, while also including both a compatibilizer and other substances in the formulation.
It is difficult to prescribe a priori which method should be used for any particular problem.
Each method has its own advantages and disadvantages. For example:
If it were practically feasible, increasing the processing temperature to the point
where two polymers become miscible would certainly solve thermodynamic
incompatibility problems. However, this solution is impractical for many realistic
systems in which the transition from a two-phase system to a one-phase system
occurs far above the decomposition temperature of one or both components.
Improving mixing can be relatively easy and straightforward, but the mixture can
quickly phase separate into large droplets once shear (a kinetic factor) is removed.
Compatibilizers (such as short chains of block copolymers or random copolymers)
can reduce the interfacial tension to near-zero levels and promote mixing on the
nanoscale. However, this effect is limited by the migration knietics of compatibilizer
molecules towards interfaces and can thus be very slow,.
Reactive compatibilizers rely on chemical reactions that take place during processing
to attach themselves to the polymers that are being blended and thus compatibilize
immiscible polymers with each other. In practice, they can be either more effective or
less effective than standard compatibilizers, depending on the choices of reactive
groups and catalysts.
The addition of lower molecular weight molecules (compatibilizers) sometimes leads
to a dramatic worsening of various properties (such as stiffness, toughness, or flame
retardancy) even if these additives improve the compatibility of the polymers in the
blend.
The addition of nanoparticles may be a useful and interesting method of
compatibilization, but its mechanism is not well-understood and so far there have
been only a few studies describing this effect which is at the frontiers of
compatibilization science and technology.
Morphology-Property Connections
The latest edition of a book by Bicerano3 was used as the main resource for this subsection.
The qualitative connections between polymer blend or composite morphology and mechanical
properties, as well as the mechanisms by which an additive can improve the mechanical
properties, are known. Many additives can often perform multiple roles and sometimes do so
Page 23
simultaneously in a given polymeric system. Here is a summary of the most commonly found
multiple roles. These roles will be illustrated with many examples in later pages of this report.
A "blend compatibilizer" often also functions as an "impact modifier". The
morphological changes resulting from enhanced compatibility can increase the impact
strength at ambient temperature and also help retain acceptable impact strength at
lower temperatures than is possible in the absence of the additive. These
morphological changes typically are the development of much smaller (in some
instances, interpenetrating) phase domains that are better connected to each other,
enabling improved load transfer across phase boundaries.
If a polymer (or blend) contains reinforcing fillers (such as inorganic fibers), an
additive that can compatibilize the polymers in a blend may also act as a "coupling
agent" between the polymer(s) and inorganic fillers, helping disperse the fillers and
bond them to the polymer(s) and thus increase the stiffness (modulus), strength and
impact toughness of the composite.
A compatibilizer may often also act as an "adhesion promoter" between a polymer (or
blend) and a substrate, or between adjacent layers consisting of dissimilar polymers
in a multilayer structure. Better interlayer adhesion results in better mechanical
properties.
Both analytical (micromechanical) and numerical simulation (most commonly, finite element)
methods for the semi-quantitative prediction of such effects are still under development. For
multilayer systems with good interlayer adhesion and known layer properties, the equations of
lamination theory or numerical simulations can often be used to predict some key properties
quantitatively as a function of the properties and the arrangement of the layers in the
laminate. More generally, the ability to make reliable quantitative predictions remains further
in the future.
In a practical blend or composite design project, it will generally be useful to use the
qualitative and semi-quantitative insights that can be gained from theory and simulations to
provide some guidance to experimental work intended to link the formulations of products of
interest to their final mechanical properties. It will, however, be essential both to verify the
qualitative validity of anticipated connections between morphology and mechanical properties
and to quantify these connections as a part of product design and optimization, by means of
careful experiments.
In relation to the mechanical and other properties, it is important to keep in mind when blends
and composites can provide the most value and thus offer the greatest profit potential. It is
when their properties are not simple weighted averages of the properties of their components,
with all of the compromises and tradeoffs inherent in such an average. The best blends and
composites offer far more than just a compromise between the properties of their
components. Instead, they offer synergies whereby the product can provide combinations of
performance characteristics that are unattainable by using any single polymer, at a
Page 24
reasonable price. If an additive supplier is able to provide compatibilizers that enables certain
polymers to blend better or certain fillers to be incorporated more effectively into polymers
and thus provide such synergistic combinations of properties, it will be rewarded by the
market.
Here is an example of what is meant by a synergistic combination of properties. Polymers
(just like other materials) become embrittled as the temperature is lowered. It is highly
desirable for exterior body panels in cars to have high impact strength at very low
temperatures. A car producer would want to be able to sell the same car in Alaska, with
comparable safety and quality attributes, as it is able to sell in Texas. On the other hand,
plastic parts used in exterior body panels are normally painted by the "e-coat" electrostatic
painting process where they are subjected to elevated temperatures for a prolonged period in
a baking oven. One needs to avoid warpage and/or other dimensional changes of a panel
during this manufacturing step so that the polymer must be able to maintain its high stiffness
("modulus") up to very high temperatures and thus avoid "creep". In other words, the polymer
needs to have a very high "heat distortion temperature". An empirical trend (with fundamental
underlying physical causes) is that the low-temperature fracture toughness (resistance to
brittle fracture under impact) of a polymer decreases with increasing high-temperature
stiffness (elastic modulus). One reason why General Electric's NORYL™ GTX blends have
been successful in this application is that they are able to provide a desirable combination of
adequate low-temperature toughness and high-temperature stiffness, while still remaining at a
reasonable price.
Another interesting example of a synergistic combination of properties comes from the
frontiers of composite materials development, in nanocomposites where the "exfoliation" and
dispersion of highly anisotropic clay platelets with a thickness of ~1 nanometer in
polypropylene is improved by using MAH-grafted polyropylene. For low clay loadings (up to
2.5% by weight), it is observed that the tensile strength, modulus and fracture toughness all
increase substantially. 19
It should be clear by now that any polymeric compatibilizer can potentially also serve as an
impact modifier, if incorporated in the right amount, into an appropriate polymeric system, by
using a suitable processing technique. It is important to emphasize, next, that while all
polymeric compatibilizers thus have the potential to serve as impact modifiers, all polymeric
impact modifiers are not necessarily compatibilizers. It is possible for some polymeric
additives to serve as highly effective impact modifiers in certain polymeric systems without
also playing the role of a compatibilizer. In order to understand this subtle but important
distinction, we must delve deeper into the mechanisms of toughening a polymer by
incorporating another phase in it.
Rubber particle incorporation is a common toughening method. However, voids and even
rigid particles are sometimes used as tougheners. Toughening occurs by imparting either the
ability to craze (in brittle matrix polymers such as polystyrene) or the ability to undergo shear
Page 25
yielding (in pseudoductile matrix polymers such as Polyamide 6,6) more effectively. It has
also been shown, in work on rubber-toughened polypropylene, that energy dissipation due to
viscoelastic relaxation may sometimes be an additional toughening mechanism. The main
initial role of the inclusion (whether it is a rubber particle, a void, or a rigid particle such as
CaCO3) is to act as a stress concentrator in its vicinity because of the difference between its
stiffness and the stiffness of the surrounding matrix material. The local initiation and then the
propagation of many crazes or shear bands (or both, in polymers which exhibit mixed failure
modes) increases the energy dissipation required to cause failure so that the polymer
becomes "tougher". The optimum rubber phase morphology correlates with the nature of the
matrix phase. The extent to which a polymer can be toughened at a given rubber volume
fraction depends on its intrinsic toughness:
For brittle (crazing) thermoplastic matrix polymers, the controlling parameter is the
optimum rubber particle size. This parameter decreases with increasing matrix
ductility, so that if the matrix polymer is less brittle then smaller rubber particles may
be able toughen it.
For pseudoductile (shear yielding) thermoplastic matrices, the controlling parameter
is the critical average distance between the surfaces of two neighboring rubber
particles. This parameter increases with increasing matrix ductility, so that if the
matrix polymer is more ductile then rubber particles that are further apart from each
other may be able to toughen it.
Much work has been reported on the quantification of these trends in terms of
intrinsic characteristics of polymers (such as characteristic ratio and entanglement
density), the morphologies of polymers (such as the effects of crystallinity), and
characteristics of the particles of the second phase (volume fraction, size distribution
and spatial distribution).
It has also been found that rubber-toughenable thermosets with high glass transition
temperature (Tg) are more readily obtained if the high Tg is attained by enhancing the
chain stiffness than if it is attained by increasing the crosslink density.
It should be clear from the paragraph above that many entities can act as impact modifiers
without serving as compatibilizers. These entities include rubber particles (which are
polymers), and in some instances voids or even rigid particulate fillers. Such entities can
"toughen" a polymer without playing any role in compatibilizing immiscible polymers, in
coupling polymers to fillers, or in helping enable the adhesion of dissimilar materials in
laminates. The focus of this report is on compatibilization technologies. Consequently, while
many examples of impact modification by compatibilizers will be highlighted to provide a
complete perspective of their versatility as additives, we will not discuss impact modifiers
which are not also compatibilizers.
Overveiw of Available Compatibilization Technologies
Page 26
The information provided in this section was assembled through extensive searches on the
worldwide web which has become the best available source of product information. Most
companies provide detailed information online regarding their products, often including case
studies describing the use of their products and/or citations to relevant articles in the open
literature. There are also many online databases [such as SpecialChem (which contains a
very extensive additives database), Omnexus, MatWeb, CAMPUS and IDES Prospector] of
commercial polymers, blends and additives. These databases all provide free access to their
compilations, but some require the payment of fees to gain access to their "premium content".
The author considered whether to list the URLs of the many worldwide web pages from which
information was extracted and decided not to list them. Unlike a book or a journal article,
URLs are quite ephemeral. They can change and/or be removed at any time, potentially
resulting in considerable frustration and waste of time for a person looking for them a year or
two after they were cited. Readers interested in more detailed information about the products
discussed in this section are recommended, instead, to visit the most current websites of the
online databases named above and of the companies named below.
Companies sometimes change identity because of events such as mergers and acquisitions.
Furthermore, product lines are sometimes sold from one company to other. Trademarks generally
outlive such events. Consequently, searching the worldwide web by using the tradename of a
product as a keyword may also be a good strategy to find the most recent information about a
product line a few years after the completion of this report.
Company Product Tradename
MODIFIED POLYOLEFINS
DuPont
Ethylene-VAc-CO (CO denotes carbon monoxide), ethylene-BA-
CO and ethylene-BA-GMA terpolymers; ethylene-MA, ethylene-EA
and ethylene-BA copolymers.
Use of CO as a comonomer results in the incorporation
of -C(O)- (ketone) groups along the chain backbone.
Elvaloy
DuPont A very broad range of MAH-grafted polyolefins. Fusabond
DuPont
Ethylene-methacrylic acid (MAA) ionomers. Zn2+ or Na+ is used as
the counterion in the different product grades.
MAA repeat unit: -CH2-C(CH3)(COOH)-.
Anionic MAA repeat unit: -CH2-C(CH3)(COO-)-.
Surlyn
DuPont Poly(vinyl alcohol), repeat unit: -CH2-CH(OH)-. Elvanol
STYRENIC BLOCK COPOLYMERS
BASF Styrene-butadiene (SB) diblock copolymers.
B repeat unit: -CH2-CH=CH-CH2-. Styrolux
BASF Styrene-butadiene-styrene (SBS) triblock copolymers. Styroflex
Page 27
Dexco Polymers
Styrene-butadiene-styrene (SBS) and styrene-isoprene-styrene
(SIS) triblock copolymers.
I repeat unit: -CH2-CH=C(CH3)-CH2-.
VECTOR
Kraton Polymers
SBS and SIS triblock copolymers, their hydrogenated midblock
versions and their hydrogenated midblock versions grafted with
functional groups such as MAH. .
KRATON
Kuraray SBS and SIS triblock copolymers (hydrogenated B or I block).
See Figure 22 for the chemical structures.SEPTON
OTHER TYPES OF COMPATIBILIZERS
Degussa Methacylate-based polymeric compatibilizers. DEGALAN
Dow Chemical
Polycaprolactone (PCL) polyesters, PCL polyester /
poly(tetramethylene glycol) (PTMEG) block polyols.
PCL repeat unit: -(CH2)5-COO-.
PTMEG repeat unit: -(CH2)4-O-.
TONE
Polymer
Chemistry
Innovations
Methacrylate-terminated reactive polystyrene.
See Figure 27 for the chemical structure. Methacromer
Struktol Mixture of aliphatic resins with a molecular weight below 2000
g/mole, blend of medium molecular weight resins.STRUKTOL
Table 2: A representative (but not comprehensive) selection of polymeric compatibilizer suppliers and
their products, some acronyms used in this report, and trade names for the products. The products
listed below will be discussed further in Section 4.
Table 2 lists the companies and products that will be discussed further in providing examples
of the use of polymeric additive technologies. The information provided in Table 2 is intended
to constitute a representative sampling of the types of additive technologies and is not (nor
was it intended to be) a comprehensive listing. The suppliers of polymeric compatibilizers
cited in Table 2 will be discussed in the next section, in alphabetical order. It is hoped that
sufficient detail will have been provided in this broad survey to give the reader a good idea of
the type of additive product that may be most appropriate for his/her needs and thus focus
further effort.
The largest number of polymeric compatibilizers, by far, are the modified polyolefins.
Polymeric additives manufactured by DuPont are used in this review to provide illustrative
examples of such additives and their utility. Most types of modified polyolefins contain polar
groups that enhance their compatibility with polar polymers, and their abilities to couple to
(and disperse) inorganic fillers more effectively and to adhere to substrates. In some modified
polyolefins, some or all polar functional groups are reactive. Reactive functionalities may
further strengthen the effectiveness of an additive by creating chemical bonds to a polar
polymer, filler, or substrate. The abundance of competing modified polyolefin additive
Page 28
technologies from many vendors reflects the tremendous commercial importance of the
polyolefins as inexpensive commodity polymers that can be used for a wide range of
applications. The importance of polyolefins has been growing in recent years. This trend is
driven both by advances in catalyst technology that have made it possible to "tailor"
polyolefins more precisely than was possible in the past and by the desire to expand the use
of polyolefins in applications where the incumbent materials are much more expensive
engineering thermoplastics.
Styrenic block copolymers constitute the second largest general class of compatibilizers.
These thermoplastic elastomers have hard blocks that segregate into a glassy glassy hard
phase and soft blocks that segregate into a rubbery soft phase. The growth of this technology
(as illustrated here in the context of products from BASF, Dexco Polymers, Kraton Polymers
and Kuraray) is a result of the synergistic superposition of three key factors that encourage
intense research and development activity towards its continued development:
1. These types of block copolymers have many important applications on their own right, in
addition to their use as additives.
2. Polystyrene is a relatively inexpensive commodity polymer that has a very broad range of
applications. Consequently, new additives that improve its properties and/or allow it to be
blended with a broader range of polymers will be valuable.
3. Advances in anionic polymerization technology, as well as in the ability to predict the
effects of molecular architecture on the properties of a block copolymer, have resulted in the
ability to "tailor" styrenic block copolymers increasingly more precisely for targeted
applications.
Other types of commercially available polymeric compatibilizers include methacrylate-based
polymers (Degussa), polycaprolactone polyesters and polycaprolactone / poly(tetramethylene
glycol) block polyols (Dow Chemical), methacrylate-terminated reactive polystyrene (Polymer
Chemistry Innovations), and mixtures of aliphatic resins of low or medium molecular weight
(Struktol).
Automotive and electrical/electronic applications provide the broadest range of opportunities
for new polymeric compatibilizers; as blend compatibilizers, coupling agents, adhesion
promoters and/or impact modifiers. Significant opportunities also exist in the packaging, major
appliance, sports/recreation equipment and medical device industries; and in the
continued development of plastics recycling technologies.
Representative Examples of Vendors and Their Technologies
BASF
Page 29
Figure 10:
Characteristic
s and
applications
of BASF's
Styroflex SBS
triblock
copolymers.
BASF makes the Styrolux™ styrene-butadiene (SB) diblock and Styroflex™ styrene-
butadiene-styrene (SBS) triblock copolymers. These polymers have many important
applications on their own right, in addition to being useful as polymer blend compatibilizers
and as impact modifiers in polymers (especially polystyrene) and blends. See Figure 10 for
the characteristics and applications of Styroflex. Such versatility is also shared by the styrenic
block copolymers (SBCs) of other manufacturers (discussed later) and enhances the growth
of SBC technology.
Degussa
The DEGALAN™ products of Degussa are specially-designed thermoplastic methacylate-
based polymeric compatibilizers for polymer blends. Acrylic polymers typically manifest
excellent resistance to UV light and saponification, colorfastness and durable gloss and good
chemical resistance. The selection of suitable methacrylic comonomers makes it possible to
obtain coating systems with excellent resistance, especially to outdoor exposure. Coatings
manufactured according to standard formulations do not yellow even after prolonged
weathering and show no change in color. They are also remarkable for their durable high
gloss and very low tendency to chalking. Applications include heat-seal lacquers, PVC
finishes, concrete coatings, marine and container paints, low-odor interior paints, metal
Page 30
coatings, printing inks, exterior paints, ceramic transfer lacquers and halogen-free plastisols.
Dexco Polymers
Dexco Polymers is a joint venture between Dow Chemical Company and ExxonMobil
Chemical Company. It makes VECTOR™ styrene-butadiene-styrene (SBS) and styrene-
isoprene-styrene (SIS) triblock copolymers, which are thermoplastic elastomers, via anionic
polymerization.
Different VECTOR polymer grades differ in their relative amounts of rigid (polystyrene) and
soft (polybutadiene or polyisoprene) blocks, molecular weights, molecular architecture
(whether the arrangement of the blocks is linear or radial), whether any residual diblock
copolymer is present, whether any other component is present and/or the physical form in
which the product is supplied (pellet or powder). These differences cause variations in
properties and processing characteristics. For example, increasing molecular weight generally
improves mechanical properties but reduces the ease of melt processing. Increasing the
relative amount of the rigid blocks results in a stiffer (higher modulus) polymer. Any change in
the composition or molecular architecture can also alter the thermodynamics and kinetics of
mixing with other polymers and thus affect the action of these polymers as blend
compatibilizers and/or impact modifiers.
VECTOR block copolymers are used by producers and compounders of olefinic and styrenic
thermoplastics, engineering resins, thermosets, blends and alloys, to enhance the toughness
and impact strength of such materials at ambient and low temperature. When used in blends,
they enhance the compatibility between appropriate types of dissimilar polymers (such as
styrenic polymers and olefinic polymers). Diblock-free grades also extend the high-
temperature performance range of the modified base resin compared to conventionally
polymerized styrenic block copolymers containing diblock residues. Some grades can be
used as base feedstocks for the manufacture of more advanced engineering resins. Others
are tailored to overcome the deleterious effects of additives such as flame retardants. The
superior heat resistance of halide-free VECTOR grades manifests itself in in the improved
color stability of the base resin and is especially evident after multiple-heat exposures of in-
plant recycle. Some VECTOR grades may be qualified for certain food contact and/or medical
applications. The recycling of plastics (where compatibilization of dissimilar polymers is of
crucial importance) is another focus of product development activities. For homogeneous
recovered plastics, VECTOR block copolymers can renew the properties, resulting in near-
virgin product performance.
The VECTOR grades available as of the date of this report are 2411, 2411P, 2518, 2518P,
4461, 6241, 6507, 7400 and 8508 (SBS); and 4111A, 4113A, 4114A, 4211A, 4215A, 4230
and 4411A (SIS). The product grades containing the letter "P" (2411P and 2518P) are
provided as powders while the other grades are provided as pellets. The following grades
include a diblock copolymer component: 2411, 2411P, 4113A, 4114A, 4215A and 4230. In
Page 31
VECTOR 7400, a linear, pure SBS triblock copolymer is extended with 33% mineral oil. The
molecular architecture is radial in VECTOR 2411, 2411P and 4230; and linear in the other
grades.
Dow Chemical Company
The TONE™ polycaprolactones are truly biodegradable when composted and thus of special
interest when biodegradability is desired. TONE P-767 and P-787 are linear polycaprolactone
polyesters with high crystallinity and a low melting temperature, used in various thermoplastic
blend applications. They have broad miscibility or mechanical compatibility with many polymers
(see Table 3), resins and pigments. Applications include use as dispersants, compatibilizers and
reactive modifiers for other polymers such as polyesters and nylon fibers. TONE P-767 can be
injection molded, extruded, slot-casted into films, or blended with other polymers. It is available
in pellet or powder form. TONE P-787 can be extruded or blended with other polymers. It was
specially formulated for use in high melt strength thermoplastic applications.
Miscible
Poly(vinyl chloride) (PVC), poly(styrene-co-acrylonitrile) (SAN, 24 % to 29 %),
poly(acrylonitrile-co-butadiene-co-styrene) (ABS), polydroxyether of bisphenol-A,
phenoxy resin, polycarbonate, nitrocellulose, cellulose butyrate, cellulose propionate,
chlorinated polyether, polyepichlorohydrin, poly(vinylidene chloride), styrene/allyl
alcohol copolymers.
Mechanically
Compatible
Polypropylene, poly(1-butene), polyethylene, natural rubber, styrene/butadiene
elastomers, styrene/butadiene block copolymers, unsaturated polyesters, epoxies,
phenolics, poly(vinyl acetate), poly(vinyl butyral), polybutadiene, ethylene/propylene
rubber, polyisobutylene, polyoxymethylene, polyoxyethylene.
Table 3: Miscibility and compatibility of polymer blends containing poly( -caprolactone).
The TONE polyol-based urethane product family consists of grades which are either liquids at
room temperature (25°C) or have melting temperatures not too far above it. They can be
formulated for adhesion to various substrates at ambient and at elevated temperatures. The
applications of TONE 7241, a linear polycaprolactone polyester / poly(tetramethylene glycol)
(P™EG) block polyol designed for use in elastomers and microcellular systems with
enhanced flex-fatigue performance and hydrolytic stability, include polyol blend
compatibilization.
DuPont
DuPont makes four product lines of functionalized polyolefins. The many applications of these
materials include polymer blend compatibilization, coupling of polymers to fillers, promotion of
adhesion of polymers to substrates as well as to dissimilar polymers in multilayer structures
and impact modification of polymers. Different grades of each product line are optimum
Page 32
choices for use in different applications. Many of these polymers meet the requirements of the
Food and Drug Administration of the USA for use in a number of regulated applications.
Elvaloy™ ethylene-VAc-CO (VAc: vinyl acetate, CO: carbon monoxide), ethylene-BA-CO and
ethylene-BA-GMA terpolymers; and ethylene-MA, ethylene-EA and ethylene-BA copolymers,
can toughen (impact modify) and flexibilize (plasticize) other polymers. Because of their high
molecular weights, unlike conventional plasticizers, they do not migrate to the surface and
hence are not lost through evaporation or extraction. They can flexibilize and toughen many
polymers; such as PVC, ABS, polypropylene, PET, PBT and polyamides. They also serve as
compatibilizers in polymer blends and coupling agents between polymers and fillers.
Fusabond™ MAH-grafted polyolefins include modified conventional as well as metallocene
polyethylenes, ethylene propylene rubbers, polypropylenes, ethylene-BA-CO terpolymers and
ethylene-VAc copolymers. They are used as coupling agents between polymers and fillers
and as high-performance impact modifiers for engineering polymers. Each grade offers its
own specific interpolymer adhesion characteristics. Their functionalization makes them
effective in helping bond together polymers used in toughened, filled and blended
compounds. For example, MAH-grafted polyolefins can compatibilize and thus help blend,
polyamides with polyolefins. Polyamide-polypropylene blends that can be made by using such
compatibilizers can be used in applications such as parts for automotive cooling systems.
Such applications require the high-temperature properties of the polyamide. However, since
moisture absorption can degrade the polyamide, polypropylene is also needed to reduce
moisture absorption. The Fusabond coupling agents can also provide new levels of
functionality in polymer-wood composites and in other wood alternatives.
Surlyn™ ethylene-methacrylic acid ionomers (with Zn2+ or Na+ used as the counterion in the
different product grades) provide impact toughness, abrasion resistance and chemical resistance
various consumer and industrial products. They can either be used by themselves or blended with
other polymers. They can be injection-molded, extruded, foamed, thermoformed, or used as a
powder-coatings or resin modifiers. The resulting applications range from tough, cut-resistant golf
ball and bowling pin covers, to footwear components, glass coatings, abrasion resistant surfaces
and buoys. Their high resistance to chemicals and oils enables them to provide unique packaging
options for perfumes and cosmetics.
Polymer Blend Compatibilizer DuPont's Recommendations
PA6/PE PE-g-MAH, E-MAA (Zn) Fusabond E, Surlyn 1652
PA6/PP PP-g-MAH Fusabond P
PBT/PP Ethylene-BA-GMA Elvaloy PTW
PBT/PA Ethylene-BA-GMA Elvaloy PTW
PET/Polyolefin Ethylene-BA-GMA Elvaloy PTW
PC/ABS Ethylene-Acrylate Elvaloy AC, Elvaloy PTW
Page 33
PC/PBT Ethylene-Acrylate Elvaloy AC, Elvaloy PTW
Table 4: Some important types of polymer blends and both the best generic compatibilizer
chemistries and the compatibilizers recommended by DuPont for each of them. PA6 denotes
Polyamide 6 (Nylon 6). PC denotes polycarbonate.
Figure 11:
Example
showing the
finer
dispersion
and more
regular and
stable
morphologies
that can result
from
compatibilizati
on. Both
micrographs
show the
morphology
of a blend of
30%
Polyamide 6
with 70%
linear low-
density
polyethylene.
A grade of
Fusabond
has been
used at a
level of 10%
Page 34
as a
polymeric
compatibilizer
in one of the
two samples.
Table 4 lists some important types of polymer blends and provides both the best generic
compatibilizer chemistries and the compatibilizers recommended by DuPont for each of them.
Compatibilization reduces the interfacial energy between two polymers and thus increases the
adhesion between them. Compatibilizers also generally provide finer dispersion, more regular and
stable phase morphology, better mechanical properties, improved surface characteristics and
enhanced recyclability. Figure 11 shows a dramatic example of the finer dispersion and more
regular morphologies that can result from the addition of a suitable compatibilizer.
Figure 12:
Effects of
using a small
amount of
Elvaloy as an
impact
modifier in
polymers. (a)
PC(50)/PBT(5
0)/Additive(10
) blend
compared
with
PC(50)/PBT(5
0). Effect the
choice of
impact
modifier on
notched Izod
Page 35
impact
strength at
room
temperature
(23 °C) and at
0 °C. (b)
Great
increase in
impact
strength of
PVC, with
negligible
reduction in
heat distortion
temperature.
Figure 12 shows the effects of using a small amount of Elvaloy as an impact modifier. Figure
12(a) illustrates how an additive can often perform more than one role in a blend. Various grades
of Elvaloy, which compatibilize polycarbonate (PC) with poly(butylene terephthalate) (PBT), also
serve as impact modifiers in PC/PBT blends. It can also be seen that, while the use of any of these
additives improves the impact strength compared with the uncompatibilized blend, various grades
differ drastically in the magnitude of their effectiveness. This example thus also illustrates the
need to select the specific product grade within a given additive product line very carefully to
obtain the desired level of properties at the lowest possible cost. Figure 12(b) shows that a small
amount of suitable grade of Elvaloy can improve the impact strength of poly(vinyl chloride)
(PVC) drastically with very small reduction in the heat distortion temperature.
Figure 13:
General
structure of a
multilayer film
(laminate).
Multilayer structures ("laminates", see Figure 13) are used in many packaging applications.
The combination of layers generally provides a mix of the individual performances of the
polymers involved (such as barrier, sealability, moisture or chemical resistance and stiffness)
Page 36
that is usually impossible to achieve with a single polymer. The recyclability of the resulting
multilayer material is also desired. The interlayer compatibilization of multilayer.polymeric
materials (such as Polyamide/PE, Polyamide/EVOH/PE, PE/EVOH/PP, PE/EVOH/PE and
PET/PE) is, hence, crucial. Functionalized polyolefins are very useful in such "adhesion
promoter" applications.
Elvanol™ 71-30 is poly(vinyl alcohol). It is prepared in aqueous solutions. Transparent films
with high tensile strength, tear resistance and barrier properties are formed upon evaporation
of water. Elvanol 71-30 provides excellent adhesion to porous, water-absorbent surfaces. It
also provides a combination of excellent film forming and binder characteristics. Its
applications are in adhesives, paper and paperboard sizing and coatings, textiles, films and
building products.
Kraton Polymers
KRATON Polymers makes both clear and oil-extended grades of its styrenic block
copolymers, which are thermoplastic elastomers.
KRATON D polymers are elastic and flexible. The choice of soft block influences the
properties. For example, styrene-butadiene-styrene (SBS) is especially suitable for footwear
and for the modification of bitumen/asphalt, while styrene-isoprene-styrene (SIS) is preferred
for the production of pressure-sensitive adhesives.
The middle blocks of SBS and SIS can be hydrogenated to make KRATON G block
copolymers. These polymers include styrene-ethylene/butene-styrene (SEBS) and styrene-
ethylene/propylene-styrene (SEPS). KRATON G block copolymers have the added benefits of
enhanced oxidation and weather resistance, higher service temperatures and increased
stability during processing by common thermoplastic processing technology. Their
applications include use as sealants and high performance adhesives.
KRATON FG polymers are KRATON G polymers that have been grafted with functional
groups such as maleic anhydride. KRATON FG polymers can manifest improved adhesion to
polar substrates such as metals and polyamides. They can be used as impact modifiers for
polar polymers such as polyesters, polyamides and epoxies. They can also help compatibilize
polyamides and thermoplastic polyesters with polyolefins.
Kuraray
Page 37
Figure 14:
Four types of
SEPTON
block
copolymers:
(Top left)
Hydrogenated
poly(styrene-
b-isoprene)
[polystyrene-
b-
poly(ethylene/
propylene)
(SEP)]. (Top
right)
Hydrogenated
poly(styrene-
b-isoprene-b-
styrene)
[polystyrene-
b-
poly(ethylene/
propylene)-b-
polystyrene
(SEPS)].
(Bottom left)
Hydrogenated
poly(styrene-
b-butadiene-
Page 38
b-styrene)
[polystyrene-
b-
poly(ethylene/
butylene)-b-
polystyrene
(SEBS)].
(Bottom right)
Hydrogenated
poly(styrene-
b-isoprene/bu
tadiene-b-
styrene)
[polystyrene-
b-
poly(ethylene-
ethylene/prop
ylene)-b-
polystyrene
(SEEPS)]4 .
Each type of
polymers has
its own
unique set of
properties.
Kuraray uses its isoprene technology to make the SEPTON™ hydrogenated styrenic block
copolymers (Figure 14), which are thermoplastic elastomers.
Figure 15:
Main
Page 39
structural and
morphological
features of
the SEPTON
hydrogenated
styrenic block
copolymers
made by
Kuraray. The
styrenic block
copolymers
made by
other
companies
(such as
BASF, Dexco
Polymers and
Kraton
Polymers)
also possess
similar
general
features.
Prior to processing, the polystyrene end blocks are associated in rigid domains. In the presence of
heat and shear (such as the shear imposed during processing), the polystyrene domains soften and
permit flow. After cooling, the polystyrene domains reform and harden, locking the rubber
network in place. This physical phenomenon provides SEPTON its high tensile strength and its
elasticity. These general features are illustrated in Figure 15.
Figure 16:
Scanning
Electron
Micrographs
Page 40
(×1000),
illustrating
compatibilizati
on by
SEPTON.
When blended with polyolefins, SEPTON improves various properties, including the impact
strength. It can also compatibilize polyolefins with polystyrenes. In the Kuraray product literature,
examples are given of the use of SEPTON as a polypropylene impact modifier and as a
compatibilizer in blends of polypropylene with ABS. The much better mutual dispersion of ABS
and polypropylene in the blends using a SEPTON compatibilizer can be seen from the
micrographs shown in Figure 16.
Property ABS(70)/PP(30) ABS(70)/PP(30)/SEPTON(5)
Notched Izod (J/m) 49 88
Unnotched Izod (J/m) 167 549
Flexural Modulus (MPa) 2040 1980
Table 5: Data from Kuraray, showing how its SEPTON 2104 compatibilizer, when added at a level of
5% by weight, improves the impact strength of a 70/30 blend of ABS and polypropylene (PP) at room
temperature (25 °C) drastically while causing only negligible loss in stiffness.
The data listed in Table 5 show that the notched and unnotched Izod impact strength both increase
drastically as a result of the improved morphology resulting from compatibilization, while the loss
in stiffness (as measured by the flexural modulus) is negligible. This example, therefore, also
illustrates how an additive can perform multiple roles. SEPTON clearly serves both as a
compatibilizer (Figure 16) and as an impact modifier (Table 5) in this particular blend.
Polypropylene 100 80 80 80
SEPTON 2004 0 20 0 0
SEPTON 2007 0 0 20 0
Ethylene-Propylene Rubber 0 0 0 20
Izod Impact Strength (J/m, at 25 °C) 117 614 547 164
Izod Impact Strength (J/m, at -20 °C) 38.5 141 122 90
Flexural Modulus (MPa) 752 572 671 656
Flexural Strength (MPa) 23.3 18.3 19.3 18
Table 6: Data from Kuraray, showing tremendous improvements in the Izod impact strength of
polypropylene at both ambient and low temperatures with the use of SEPTON 2004 or SEPTON 2007
as an impact modifier. Formulations are indicated in terms of the percentages of their ingredients by
Page 41
weight. There are only small reductions in flexural modulus and strength. Note that SEPTON is far
more effective than ethylene-propylene rubber as an impact modifier.
Table 6 shows tremendous improvements in the Izod impact strength of polypropylene at both
ambient and low temperatures, with only small reductions in flexural modulus and strength.
Polymer Chemistry Innovations Inc.
Figure 17:
Chemical
structure of
Methacromer
™ PS12
reactive
polystyrene.
More than
85% of the
polymer
chains are
terminated
with a
methacrylate
group.
Polymer Chemistry Innovations Inc. makes the Methacromer™ PS12 methacrylate-
terminated reactive polystyrene. The chemical structure of this polymer is shown in Figure 17.
Its physical properties resemble those of polystyrene woth a low molecular weight. It allows
formulators to modify polymers with a high degree of control. It is especially attractive to
adhesive manufacturers since it can be used to increase the shear strength with only minor
effects on the peel strength. It is available in a standard molecular weight range of 11,000 to
Page 42
15.000 g/mole, with 12,000 g/mole as the target molecular weight. The molecular weight can
be modified to meet individual specifications. The polydispersity is low: [(Mw/Mn)<1.1]. More
than 85% of the polymer chains are terminated with a methacrylate group. It reacts readily
with the acrylates and acrylamides, imparting toughness while keeping the polymer
thermoplastic.
Struktol
Struktol's product line of STRUKTOL™ polymer additives includes the STRUKTOL TR
product grades (among which TR 060 and TR 065 can be considered primarily as
compatibilizers), as well as the more recently developed STRUKTOL TPW product grades.
TR 060 and TR 065 are normally incorporated at low levels (0.5% to 1 %) into a formulation.
They both meet the requirements of the Food and Drug Administration of the USA for use in a
number of regulated applications.
TR 060 is a mixture of light-colored aliphatic resins with a molecular weight below 2000
g/mole. It has good solubility in aliphatic, aromatic and chlorinated hydrocarbons. It is a
compatibilizer and blending aid that reduces splay in colored and/or filled polyolefins. It is very
compatible with the polyolefins. It can be used to increase extrusion output rates. It has a
natural tackiness at process temperatures. This "adhesive" nature enables it to act as an
effective binder. This is especially important in polymers where high filler levels require the
most uniform blending in order to maintain or improve the physical properties. In addition, its
low molecular weight provides some viscosity reduction during processing, improving the flow
characteristics. TR 060 has been shown to improve the blending of thermoplastic olefin (TPO)
compounds, flame retardant formulations and filled polymer systems. In general, it is
recommended for use with polyolefins, ABS, styrene-acrylonitrile (SAN) copolymers, general-
purpose polystyrene, high-impact polystyrene, rigid poly(vinyl chloride) (PVC) and polyesters
such as poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT).
TR 065 is a blend of medium molecular weight resins designed as a high temperature
process aid and blending agent. It works up to process temperatures of 370°C. Its
compatibilizing action is useful in blending polymers, processing recycle materials and
incorporating impact modifiers. It is effective in binding filler materials to the polymer system
by virtue of its adhesive nature at process temperatures. In many cases, especially when high
filler levels are involved, this more homogenous blend results in better physical properties and
fewer processing problems. Its components make it compatible with many polymers, whether
polar or nonpolar in nature. In general, it is recommended for use with polyesters such as
PET and PBT, polyamides, nitriles, PVC, ABS, SAN and general-purpose or high-impact
polystyrene.
The new STRUKTOL TPW product grades are polymeric additives that have been developed
specifically for the improved processing of wood-filled thermoplastics. While they can be
Page 43
viewed primarily as lubricants, their roles also include compatibilization. For example, the
general purpose grade (TPW 101), which consists of a mixture of zinc stearate and waxes,
can improve the processing characteristics of highly filled polyolefin compounds, as well as
improving filler dispersion and providing metal release for both molding and extrusion
operations. TPW 113, which is a blend of complex modified fatty acid esters, can provide
superior filler wetting and dispersion characteristics in a wide range of polymer systems.
Technology Outlook
The development of polymer blends, composites and laminates is of great economic
importance for the plastics industry and for other industries where the use of such products is
becoming increasingly common. Advanced polymer modification techniques have grown in
importance during the last two decades as the "point of diminishing returns" has been
approached in improving the performance/price balance by altering just the chemical
structures of polymers.
The most important polymer modification techniques are blending dissimilar polymers,
preparing composites where a matrix polymer is modified by fillers, and creating multilayer
(laminate) structures. The objective is to seek synergies between the components so that one
can attain better performance without increasing cost or maintain acceptable performance at
lower cost.
Polymeric compatibilizers are polymers that can be used (normally in small percentages) as
additives to help assemble dissimilar components into polymer blends, composites and
laminates with improved properties. These more attractive properties generally result from
phase separation on a finer scale (microscale or even better nanoscale, instead of
macroscale) along with stronger interconnections between phase domains. Impact
modification (toughening) is one major benefit that can often be attained by using polymeric
compatibilizers. It can be inferred from the anticipated continued growth of markets for
polymer-based heterophasic products that polymeric compatibilization technologies will also
contine to grow in importance.
The five key factors that every compatibilization additive developer must consider in order to
improve the likelihood of achieving technical and commercial success simultaneously are (1)
performance versus price, (2) thermodynamic equilibrium phase diagram, (3) metastable
morphologies often induced by processing conditions, (4) practical implications of kinetic
barriers to equilibration and (5) morphology-property-connections. Progress in the
development of predictive methods based on theory and simulation was summarized.
Methods for the prediction of the thermodynamic behavior of nonreactive systems are quite
well-established. Significant further progress is needed for the development of more robust
models for the thermodynanmic equilibrium state of reactive systems, for the dynamic
Page 44
behavior of both nonreactive and reactive systems, and for the relationships between
morphology and mechanical properties under large deformation. While major progress can be
anticipated in all of these "frontier" areas of materials science over the next decade, a semi-
empirical approach will be most useful in the practical development of new technologies for
the foreseeable future.
The largest number of polymeric compatibilizers, by far, consist of modified polyolefins, most
of which contain polar groups and some of which also contain reactive groups. Styrenic block
copolymers, which are thermoplastic elastomers, constitute the second largest class of
polymeric compatibilizers. Other commercial polymeric compatibilizers include methacrylate-
based polymers, polycaprolactone polyesters, polycaprolactone polyester /
poly(tetramethylene glycol) block polyols, methacrylate-terminated reactive polystyrene, and
mixtures of aliphatic resins of low or medium molecular weight.
Significant progress can be anticipated over the next decade in the development of more
refined grades (tailored for specific applications) of both modified polyolefin and styrenic
block copolymer (and perhaps also selected non-styrenic block copolymer) technologies. A
major guiding principle for such work will be the desire to attain control over the resulting
morphology at an increasingly finer scale. The development of compatibilizers for
biodegradable polymer-based systems (a relatively minor area at this time) may also grow if
the environmental and regulatory driving forces towards biodegradable polymer technology
development gain strength.
Many companies are in the polymeric compatibilizer market with products falling into the
same two major classes (modified polyolefins, styrenic block copolymers) competing for
similar types of applications so that competition is fierce. On the other hand, these are
currently also the two most versatile polymeric compatibilizer families. The markets for other
types of polymeric compatibilizers (where the competitive landscape is less crowded) are
more limited.
Customized additive compunding services are provided by many companies. Organizations
that provide such services range from the technical service depar™ents of giant multinational
corporations to small specialty compounding shops. Customized compounders can provide
complete technology solutions and hence great value to their customers. It is anticipated that
such specialized services (the detailed discussion of which fell outside of the scope of this
review of polymeric compatibilizer products) will also continue to grow over the next decade.
Automotive and electrical/electronic applications provide the broadest range of opportunities
for new polymeric compatibilizers; as blend compatibilizers, coupling agents, adhesion
promoters and/or impact modifiers. Significant opportunities also exist in the packaging, major
appliance, sports/recreation equipment and medical device industries. The continued
development of plastics recycling technologies may also stimulate the growth of
compatibilization technologies if it becomes driven by stronger environmental and regulatory
Page 45
forces in the future.
References
1.W. J. Work, K. Horie, M. Hess and R. F. T. Stepto, "Definitions of Terms Related to Polymer Blends, Composites,
and Multiphase Polymeric Materials", Pure Appl. Chem., 76, 1985-2007 (2004).
2.L. A. Utracki and T. V. Khanh, "Filled Polymers", Chapter 7 in Multicomponent Polymer Systems, edited by I. S.
Miles and S. Rostami, Longman Scientific & Technical, Essex, England (1992), 207-268.
3.J. Bicerano, Prediction of Polymer Properties, revised and expanded third edition, Marcel Dekker, New York
(2002).
4.A.-V. Ruzette and L. Leibler, "Block Copolymers in Tomorrow's Plastics", Nature Materials, 4, 19-31 (2005).
5.L. Leibler, "Emulsifying Effects of Block Copolymers in Incompatible Polymer Blends", Makromol. Chem.,
Macromol. Symp., 16, 1-17 [1988].
6.R. Israels, D. Jasnow, A. C. Balazs, L. Guo, G. Krausch, J. Sokolov and M. Rafailovich, "Compatibilizing A/B
Blends With AB Diblock Copolymers: Effect of Copolymer Molecular Weight", J. Chem. Phys., 102, 8149-8157
[1995].
7.Y. Lyatskaya, D. Gersappe, N. A. Gross and A. C. Balazs, "Designing Compatibilizers to Reduce Interfacial
Tension in Polymer Blends", J. Phys. Chem., 100, 1449-1458 [1996].
8.G. H. Fredrickson and S. T. Milner, "Time-Dependent Reactive Coupling at Polymer-Polymer Interfaces",
Macromolecules, 29, 7386-7390 [1996].
9.G. H. Fredrickson, "Diffusion-Controlled Reactions at Polymer-Polymer Interfaces", Phys. Rev. Lett., 76, 3440-3443
[1996].
10.B. O'Shaughnessy and U. Sawhney, "Polymer Reaction Kinetics at Interfaces", Phys. Rev. Lett., 76, 3444-3447
[1996].
11.B. O'Shaughnessy and D. Vavylonis, "Interfacial Reactions: Mixed Order Kinetics and Segregation Effects", Phys.
Rev. Lett., 84, 3193-3196 [2000].
12.S.-P. Lyu, J. J. Cernohous, F. S. Bates and C. W. Macosko, "Interfacial Reaction Induced Roughening in Polymer
Blends", Macromolecules, 32, 106-110 [1999].
13.M. Y. Gelfer, H. H. Song, L. Liu, B. S. Hsiao, B. Chu, M. Rafailovich, M. Si and V. Zaitsev, "Effects of Organoclays
on Morphology and Thermal and Rheological Properties of Polystyrene and Poly(methyl methacrylate) Blends", J.
Polym. Sci., Polym. Phys. Ed., 41, 44-54 [2003].
14.Y. S. Lipatov, "Polymer Blends and Interpenetrating Polymer Networks at the Interface With Solids", Progress in
Polymer Science, 27, 1721-1801 [2002].
15.Y. S. Lipatov, A. E. Nesterov, T. D. Ignatova and D. A. Nesterov, "Effect of Polymer-Filler Surface Interactions on
the Phase Separation in Polymer Blends", Polymer, 43, 875-880 [2002].
16.Y. S. Lipatov, L. V. Kosyanchuk, A. E. Nesterov and O. Antonenko, "Filler Effect on Polymerization Kinetics and
Phase Separation in Polymer Blends Formed In Situ", Polymer International, 52, 664-669 [2003].
17.J. Bicerano, S. Balijepalli, A. Doufas, V. Ginzburg, J. Moore, M. Somasi, S. Somasi, J. Storer and T. Verbrugge,
"Polymer Modeling at The Dow Chemical Company", J. Macromol. Sci. - Polymer Reviews, 44, 53-85, 2004.
18.P. M. Subramanian, "Permeability Barriers by Controlled Morphology of Polymer Blends", Polym. Eng. Sci., 25,
483-487 (1985).
Page 46
19.L. Chen, S.-C. Wong, T. Liu, X. Lu and C. He, "Deformation Mechanisms of Nanoclay-Reinforced Maleic
Anhydride-Modified Polypropylene", J. Polym. Sci., Polym. Phys. Ed., 42, 2759-2768 (2004).