Immiscible polymer blends morphology

Rusu D (1997) In-situ study of immiscible polymer blends morphology under simple shear PhD thesis Ecole des Mines de Paris, Sophia Antipolis... 

Shokoohi S, Arefazar A. A review on ternary immiscible polymer blends Morphology and effective parameters. Polym Adv Technol 2009 20(5) 433 47. 

The effect of viscosity ratio on the morphology of immiscible polymer blends has been studied by several researchers. Studies with blends of LCPs and thermoplastics have shown indications that for good fibrillation to be achieved the viscosity of the dispersed LCP phase should be lower than that of the matrix [22,38-44]. 

Since the processing conditions and mixing equipment have a crucial effect on the morphology of immiscible polymer blends [45], experiments were carried out in four different types of extruders to find optimal conditions for blend preparation and fibrillation. Nevertheless, the morphologies of PP-LCP blends produced by... 

Sundaraj, U., Dori, Y., and Macosko, C. W., Sheet formation in immiscible polymer blends model experiments on an initial blend morphology. Polymer 36,1957-1968 (1995). Swanson, P. D., and Ottino, J. M., A comparative computational and experimental study of chaotic mixing of viscous fluids, J. Fluid Mech. 213, 227-249 (1990). 

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 compatible polymer blend. 

Polymer or copolymer that, when added to an immiscible polymer blend, modifies its interfacial character and stabilizes its morphology. 

The properties of immiscible polymers blends are strongly dependent on the morphology of the blend, with optimal mechanical properties only being obtained at a critical particle size for the dispersed phase. As the size of the dispersed phase is directly proportional to the interfacial tension between the components of the blend, there is much interest in interfacial tension modification. Copolymers, either preformed or formed in situ, can localize at the interface and effectively modify the interfacial tension of polymer blends. The incorporation of PDMS phases is desirable as a method to improve properties such as impact resistance, toughness, tensile strength, elongation at break, thermal stability and lubrication. 

Several factors can be identified as being crucial for the foaming of immiscible polymer blends the blend morphology, the phase size of the blend constituents, the interfacial properties between the blend partners, and, last but not least, the properties of the respective blend phases such as the melt-rheological behavior, the glass transition temperature, the gas solubility, as well as the gas diffusion coefficient. Most of these factors also individually influence the melt-rheological behavior of two-phase blends. 

B. D. Favis, Factors Influencing the Morphology of Immiscible Polymer Blends in melt Processing, in Polymer Blends, Vol. I, D. R. Paul and C. B. Bucknall, Eds., Wiley-Interscience, New York, 1999. 

The question might be addressed now to know whether phase morphology and properties of Immiscible polymer blends can be modified by a way different from the previously described emulsification. 

This chapter, related to the crystallization, morphological structure and melting of polymer blends has been divided into two main parts. The first part (section 3.1) deals with the crystallization kinetics, semicrystalline morphology and melting behavior of miscible polymer blends. The crystallization, morphological strucmre and melting properties of immiscible polymer blends are described in the second part of this chapter (section 3.4). 

In the following part, a discussion on the crystallization behavior in immiscible polymer blends is given, including the nucleation behavior, spheiuhte growth, overall crystallization kinetics, and final semicrystalline morphology. Each topic is illustrated with several examples from the literature, to allow the reader to find enough references on the discussed subject for further information. 

The discussion on the crystallization behavior of neat polymers would be expected to be applicable to immiscible polymer blends, where the crystallization takes place within domains of nearly neat component, largely unaffected by the presence of other polymers. However, although both phases are physically separated, they can exert a profound influence on each other. The presence of the second component can disturb the normal crystallization process, thus influencing crystallization kinetics, spherulite growth rate, semicrystalline morphology, etc. 

The majority of polymer blends containing elastomeric, thermoplastic, and/or liquid crystalline polymers are processed by melt extrusion at some point in their history. After melt extrusion with intensive mixing, the morphology of an immiscible polymer blend on a microscopic scale will often consist of a dispersed phase of the more viscous polymer in a continuous matrix of the less viscous polymer (depending upon the relative amounts and viscosities of the two polymers in the blend). A good analogy from every-day experience is a dispersed mixture of viscous oil in an immiscible water matrix. 

The majority of commercially important, immiscible polymer blends rely for compatibilization on the presence of a copolymer of the blended polymers. Nowadays, such a copolymer is almost never synthesized in a separate step and then added as a distinct entity to the blend of immiscible polymers. Instead, a compatibUizing copolymer is most economically formed simultaneously with generation of interphase morphology during extrusion processing, a process referred to as Reactive Compatibilization. The Reactive Compatibilization process is logically a sub-category of the broader class of Interchain Copolymer Formation reactions performed by Reactive Extrusion [Brown, 1992],... 

As defined in Appendix 5 compatibilization means A process of modification of interfacial properties of an immiscible polymer blend, leading to creation of polymer alloy . A polymer alloy in turn is defined as An immiscible polymer blend having a modified interface and/or morphology , whereas a polymer blend is simply A mixture of at least two polymers or copolymers . In other words, all polymer alloys are blends, but not all polymer blends are alloys. A somewhat more elaborate definition of a polymer alloy would describe a blend of at least two immiscible polymers stabilized either by covalent bond or ionic bond formation between phases, or by attractive intermolecular interaction, e.g., dipole-dipole, ion-dipole, charge-transfer, H-bonding, van der Waals forces, etc. 

Before discussing the rheological performance of polymer blends, it is important to recall the basic features of morphology in immiscible polymer blends. 

With the knowledge of the flow behavior of simpler systems, viz. suspensions, emulsions, block copolymers, as well as that of the mumal interactions between the rheology and thermodynamics near the phase separation, one may consider the flow of more complex systems where all these elements may play a role. Evidently, any constitutive equation that may attempt to describe flow of immiscible polymer blends should combine three elements the stress-induced effects on the concentration gradient an orientation function and the stress-strain description of the systems, including the flow-generated morphology. Such a comprehensive description stiU remains to be formulated. 

It should be noted that the Doi and Ohta theory predicts oifly an enhancement of viscosity, the so called emulsion-hke behavior that results in positive deviation from the log-additivity rule, PDB. However, the theory does not have a mechanism that may generate an opposite behavior that may result in a negative deviation from the log-additivity rule, NDB. The latter deviation has been reported for the viscosity vs. concentration dependencies of PET/PA-66 blends [Utracki et ah, 1982]. The NDB deviation was introduced into the viscosity-concentration dependence of immiscible polymer blends in the form of interlayer slip caused by steady-state shearing at large strains that modify the morphology [Utracki, 1991]. 

Meijer et al. [1988] and Elemans et al. [1988] investigated the potential of electron irradiation to stabilize the morphology of immiscible polymer blends. Their concept was that selective crosslinking of a dispersed phase in a matrix that remains unaffected, or degrades, should help fix the morphology of the blend. 

Figures 16.8 and 16.9 illustrate the extend to which the judicious stabilization is able to protect polyolefin resins and their blends from the thermo- (Figure 16.8) or photo-degradation (Figure 16.9). As the data indicate, the recyclates even after five extrusions show performance within 10% approximating that of a virgin material. Similar behavior is expected for strongly immiscible polymer blends, under the condition that the recyclates will be re-compatibilized to recover the original morphology.

Because of the high interfacial tension, the morphology of the blends is not stable. Coalescence readily occurs in the molten state. As suggested by Macosko et al. (121), in melt mixing of immiscible polymer blends, the disperse phase is first stretched into threads and then breaks into droplets, which can coalesce together into larger droplets. The balance of these processes determines the final dispersed particle sizes. With increase of disperse phase fraction (usually more than 5 wt%), the coalescence speed increases and the dispersed phase sizes increase (121-123). 

In Reference 154, PMMA was selected as it is immiscible with PET. The description of the electroconductive properties of this immiscible polymer blend filled with CB was carried out. To properly analyze the results obtained, models that predicted the selective location of CB in the blend were considered. The presence of CB extensively modified the rheological and conductive properties of the blend. Resistivity decreased similarly in both PET and PMMA with CB concentration. However, the immiscible polymer blend extensively modified this behavior because resistivity became a function of morphology and location of CB in the polymers. Viscosity was observed to be a strong function of PET content at high CB concentrations. Indeed, resistivity decreases continuously (a drop of seven decades) for 20% CB (PET basis) from 0% to 60% PET content. The same behavior (similar slope) was observed for 5% CB, but the conductivity curve was shifted to higher PET contents. It was shown that the preferential CB location in... 

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