Compatibility in Polymer Blends

A compatibilized blend exhibits no gross symptoms of phase separation and has a desirable set of final properties. This implies at least some mixing of polymer segments on a microscopic scale and a certain thermodynamic 

The desired compatibilization can be obtained by different methods such as the addition of a third component (copolymer or functional polymer) or by inducing in situ chemical reactions (reactive blending) among blend components, leading to the modification of the polymer interfaces and tailoring the blend phase structure and the final properties. The final properties of a blend will be determined not only by the components properties but also by the phase morphology and the interface adhesion, both of which determine the stress transfer within the blend and its end-use applications. 

The blend morphology is determined by the processing history to which the blend has been subjected. The processing history depends on several factors, such as type of mixer, rate of mixing, temperature, rheology of the blend components, and interfacial tension between phases. 

Compatibilizers reduce the interfacial tension in the melt between blend components and retard the coalescence process via steric stabilization, leading to an extremely fine dispersion of one phase into the other one. Compatibilizers also improve stress transfer by increasing the adhesion between phases and stabilize the disperse phase against growth during further annealing. 

One of the most studied approaches to compatibilize a blend is the addition of a third component, such as a block or graft copolymer. Copolymers that contain segments chemically identical to the blend components are frequently used because they enhance the miscibility between the copolymer segments and the corresponding blend component (Fig. 27.5). 

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The technological compatibility in polymer blends can result from any of the following mechanisms ... 

S. Krause, Polymer-Polymer compatibility, in Polymer Blends, D.R. Paul and S. Newman... 

The model has,also,been applied to mixture of three random copolymers. Conditions for the enhancement of compatibility in polymer blends by the use of a third copolymer are examined as well as the influence of temperature in the phase behavior of ternary mixtures whose constituent binaries may show either UCST or LCST. These findings are, as yet, only theoretical and for space limitation they are not reproduced here. They will be, however, the subject of a forthcoming publication. 

The previous notes on compatibility in polymer blends are important for the better understanding of one of the main advantages of MFCs prepared from condensation polymers. Dealing with such p>ol5rmers, in addition to isotropization dirring short (several hours) thermal treatment, chemical reactions additional condensation and transreacUons) between condensation p>olymers in the melt [78] as well as in the sohd state [79] can take place at the interfaces, as schematically shown below [67] ... 

A plausible interpretation of these fracture surface images is that pectin/PVOH mixtures form compatible composites at all ratios. Thus at high pectin PVOH ratios they should behave as a pectin matrix with islands of PVOH, while the reverse would be expected at low pectin PVOH ratios. These films for the most part appear transparent to the naked eye which is a necessary, but not sufficient condition for compatibility in polymer blends (27). The SEM images appear to dictate against the possibility of these films being true blends. 

Krause, S., Polymer-polymer compatibility, in Polymer Blends (D. R. Paul and S. Newman, eds.), Academic Press, New York (1978), Vol. 1, Chap. 2, pp. 15-113. 

It is always desirable to achieve some level of compatibility in polymer blends for effective stress transfer and particle size control. The miscibility of the novel OBCs with other olefin homopolymers and copolymers would be of interest to both, the industrial and scientific community. It becomes important to understand the effect... 

Interfacial adhesion and, thereby, compatibility can be enhanced by the selective crosslinking reaction in polymer blends. Inoue and Suzuki [26] reported the properties of blends dynamically crosslinked PP-EPDM blends. The crosslinking agent was yV,N -/w-phenylene-bismaleimide - poly(2,2,4 - trimethyl - 1,2-dihydroquino -line) system. Increase in interfacial adhesion leads to... 

In a fundamental sense, the miscibility, adhesion, interfacial energies, and morphology developed are all thermodynamically interrelated in a complex way to the interaction forces between the polymers. Miscibility of a polymer blend containing two polymers depends on the mutual solubility of the polymeric components. The blend is termed compatible when the solubility parameter of the two components are close to each other and show a single-phase transition temperature. However, most polymer pairs tend to be immiscible due to differences in their viscoelastic properties, surface-tensions, and intermolecular interactions. According to the terminology, the polymer pairs are incompatible and show separate glass transitions. For many purposes, miscibility in polymer blends is neither required nor de-... 

One practical example of demixing that might be attributed to a difference in crystallizability is the incompatibility in blends of polymers with different stereochemical compositions. The stereochemical isomers contain both chemical and geometrical similarities, but differ in the tendency of close packing. In this case, both the mixing energy B and the additional mixing entropy due to structural asymmetry between two kinds of monomers are small. However, the stereochemical differences between two polymers will result in a difference in the value of Ep. Under this consideration, most experimental observations on the compatibility of polymer blends with different stereochemical compositions [89-99] are tractable. For more details, we refer the reader to Ref. [86]. 

The increasing interest in polymer blends has acted as a stimulus not only to the aspects just outlined but also to a study of interactions between polymer A and polymer B in solution as a route to quantifying their thermodynamic compatibility. Hyde167 has reviewed the relevant theory whilst Kratochvfl and co-workers168,169 have been responsible for much of the latest experimental studies. 

Figures 20.13 and 20.14 describe the effect of dibutyltin dilaurate (DBTDL) on the tensile strength and tensile modulus for the 25/75 LCP/PEN blend fibers at draw ratios of 10 and 20 [13]. As expected, the addition of DBTDL slightly enhances the mechanical properties of the blends up to ca. 500 ppm of DBTDL. The optimum quantity of DBTDL seems to be about 500 ppm at a draw ratio of 20. However, the mechanical properties deteriorate when the concentration of catalyst exceeds this optimum level. From the previous relationships between the rheological properties and the mechanical properties, it can be discerned that the interfacial adhesion and the compatibility between the two phases, PEN and LCP, were enhanced. Hence, DBTDL can be used as a catalyst to achieve reactive compatibility in this blend system. This suggests the possibility of improving the interfacial adhesion between the immiscible polymer blends containing the LCP by reactive extrusion processing with a very short residence time.

Coleman et al. 2471 reported the spectra of different proportions of poly(vinylidene fluoride) PVDF and atactic poly(methyl methacrylate) PMMA. At a level of 75/25 PVDF/PMMA the blend is incompatible and the spectra of the blend can be synthesized by addition of the spectra of the pure components in the appropriate amounts. On the other hand, a blend composition of 39 61 had an infrared spectrum which could not be approximated by absorbance addition of the two pure spectra. A carbonyl band at 1718cm-1 was observed and indicates a distinct interaction involving the carbonyl groups. The spectra of the PVDF shows that a conformational change has been induced in the compatible blend but only a fraction of the PVDF is involved in the conformational change. Allara M9 250 251) cautioned that some of these spectroscopic effects in polymer blends may arise from dispersion effects in the difference spectra rather than chemical effects. Refractive index differences between the pure component and the blend can alter the band shapes and lead to frequency shifts to lower frequencies and in general the frequency shifts are to lower frequencies. 

The use of borane-containing monomers clearly presents an effective and general approach in the functionalisation of polyolefins, which has the following advantages stability of the borane moiety to coordination catalysts, solubility of borane compounds in hydrocarbon solvents (such as hexane and toluene) used as the polymerisation medium, and versatility of borane groups, which can be transformed to a remarkable variety of functionalities as well as to free radicals for graft-form polymerisations. The functionalised polymers are very effective interfacial modifiers in improving the adhesion between polyolefin and substrates and the compatibility in polyolefin blends and composites [518],... 

There are now available a number of theoretical treatments (1-11) dealing with the problem of polymer compatibility and the polymer-polymer interfaces either in polymer blends or in block copolymers. 

Klotz, S. Schuster, R. H. Cantow, H. -J., "Compatibility of Polymers in Polymer Blends Investigated by Gas Chromatography," Makromol. Chem. 187, 1491 (1986). 

The compatibility of polymer blends has been a snbject of mnch interest. Polymer blends are systems with two (or more) polymers, most of which are incompatible (immiscible). Finding compatible polymer pairs is an important task in the design of snch advanced materials. Moreover, several new polymeric materials with interesting properties involve novel structures, which go beyond the well-known ones (linear, branched, cross-linked, and network). Such novel strnctnres, e.g., starlike polymer and dendrimers may require new concepts for selecting proper solvents and generally for nnderstanding their solnbility behavior. "... 

Such cubic equations of state as van der Waals correlate very satisfactorily the UCST-type behavior for polymers solutions, as shown by Harismiadis et al. ° A generalized correlation of the interaction parameter of the van der Waals equation of state for polymer blends based exclnsively on polystyrene blends has been presented. By nsing this equation, the van der Waals eqnation of state can be used as a predictive tool for investigating the compatibility of polymer blends. Predictive GC thermodynamic methods such as Entropic-FV, GC-Flory, UNIFAC, and UNIFAC-FV perform rather poorly, at least from a quantitative point of view. Entropic-FV performs best among these models, on a qualitative basis. For semiquantitative predictions in polymer blends, the approach proposed by Coleman et al. is recommended. 

While miscible blends have attracted considerable interest due to the thermodynamic implications and commercial relevance, phase separated blends have had a prominent role in polymer blend technology. While mechanical compatibility is assured in miscible blends, phase separated blends can often achieve property advantages not capable with single phase blends. (Mechanical... 

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