A Practical Guide to Polymeric Compatibilizers for Polymer ...
A Practical Guide to Polymeric Compatibilizers for Polymer Blends, Composites and Laminates.
|[pic]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. |
| |
|Adhesion |
|Holding together of two bodies by interfacial forces or mechanical interlocking on a scale of micrometers or less. |
| |
|Adhesion promoter |
|See Coupling agent. |
| |
|Chemical adhesion |
|Adhesion 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 blend, modifies its interfacial character and stabilizes its|
|morphology. |
| |
|Compatible polymer blend |
|Immiscible 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 compatibility |
|Measure 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 bonding |
|Bonding 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. |
| |
|Laminate |
|Material 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. |
| |
|Miscibility |
|Capability of a mixture to form a single phase over certain ranges of temperature, pressure and composition. |
| |
|Miscible polymer blend |
|Polymer blend that exhibits miscibility. |
| |
|Morphology |
|Shape, 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. |
| |
|Nanocomposite |
|Composite in which at least one of the phases has at least one dimension of the order of nanometers. |
| |
|Phase domain |
|Region 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 blend |
|Macroscopically 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 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 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: |
|[pic] |
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|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. |
|[pic] |
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|Figure 1: Schematic illustration of the "commodity trap"; namely, the empirical rule2 that, if a 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 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. |
|[pic] |
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|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 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 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 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 AB0), 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. |
|[pic] |
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|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 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. |
|[pic] |
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|[pic] |
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|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 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 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: |
|[pic] |
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|Figure 4: Use of a block copolymer for compatibilization. The block copolymer will prefer to migrate to the interface to |
|reduce the interfacial tension. Red blocks are compatible with Polymer A (matrix). 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). |
|[pic] |
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|Figure 5: Use of an nonreactive polymer containing polar groups for compatibilization by the creation of nonbonded |
|interactions [in order of increasing strength, 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 |
|compatibilization 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. |
| |
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|Nonreactive polymers containing polar groups (Figure 5). |
|[pic] |
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|Figure 6: Use of a reactive functional polymer for compatibilization. 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. |
|[pic] |
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|Figure 7: Compatibilization by MAH-grafted reactive functional polymers. Maleated polymers can be prepared directly by |
|polymerization 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 groups of |
|Polyamide 6,6 (Nylon 6,6) compatibilizes a polyamide/polyolefin blend. |
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|[pic] |
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|Figure 8: Compatibilization by GMA-grafted (epoxidized) reactive functional polymers. They react with amine, anhydride, |
|acid and alcohol groups, making them effective in compatibilizing polar polymers with nonpolar polymers according to the |
|mechanism shown above. |
| |
|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. |
|[pic] |
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|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 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 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. |
|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 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 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 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 |
|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 |
| |
|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 |
|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 |
|[pic] |
| |
| |
|Figure 10: Characteristics 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 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 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 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 |
| |
|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. |
| |
| |
|[pic] |
| |
| |
|Figure 11: Example showing the finer dispersion and more regular and stable morphologies that can result from |
|compatibilization. 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% 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. |
|[pic] |
| |
| |
|Figure 12: Effects of using a small amount of Elvaloy as an impact modifier in polymers. (a) PC(50)/PBT(50)/Additive(10) |
|blend compared with PC(50)/PBT(50). Effect the choice of impact modifier on notched Izod 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. |
|[pic] |
| |
| |
|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) 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 |
|[pic] |
| |
| |
|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-b-styrene) [polystyrene-b-poly(ethylene/butylene)-b-polystyrene (SEBS)]. (Bottom right) |
|Hydrogenated poly(styrene-b-isoprene/butadiene-b-styrene) [polystyrene-b-poly(ethylene-ethylene/propylene)-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. |
|[pic] |
| |
| |
|Figure 15: Main 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. |
|[pic] |
| |
| |
|Figure 16: Scanning Electron Micrographs (×1000), illustrating compatibilization 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 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. |
|[pic] |
| |
| |
|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 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) ................
................
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