Immiscible blends, polymer

Crystallizable immiscible blends may consist of both crystallizable polymer components (crystalUne/crystaUine blends), or of one crystalline component (crystalline/ amorphous blends), which can be present as matrix phase or as dispersed phase. The crystallization behavior and the structure-properties relationships of immiscible blends of various polymer classes have been investigated by numerous authors a comprehensive overview of the crystallization phenomena and morphological characteristics of these systems has been reported in References [19,72], 

Immiscibility of polymers in the melt is a common phenomenon, typically leading to a two-phase random morphology. If the phase separation occurs by a spinodal decomposition process, it is possible to control the kinetics in a manner that leads to multiphase polymeric materials with a variety of co-continuous structures. Common morphologies of polymer blends include droplet, fiber, lamellar (layered) and co-continuous microstructures. The distinguishing feature of co-continuous morphologies is the mutual interpenetration of the two phases and an image analysis technique using TEM has been described for co-continuous evaluation.25 

The behavior of chemical phase-separated blends in the bulk after thermal quenching into the unstable region of the phase diagram is variable. In the bulk, the concentration fluctuations that govern the phase-separation process are random. As a result, the final morphology consists of mutually interconnected domain structures rich in a given blend component that coarsen slowly with time. 

Average diameters of DAP particles (24 h after sample preperation) 

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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... 

Leibler [17] and Noolandi et al. [18,19] developed thermodynamic theories concerning the emulsification of copolymers (A-b-B) in immiscible polymer blends (A-B). 

Immiscible Polymer Blends A subclass of polymer blends referring to those blends that exhibit two or more phases at all compositions and temperatures,... 

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). 

Another important class of copolymers synthesized by chain polymerisation are block (or sequenced) copolymers diblock and triblock copolymers being the most important ones. They are very useful as compatibilisers (emulsifiers) in immiscible polymer blends. Another major use is as thermoplastic elastomers. Both uses are best explained through the example of butadiene-styrene block copolymers. 

Immiscible liquids, static mixing of, 16 715 Immiscible polymer blends, 20 318-319 barrier polymers, 3 396-398 heterogeneous, 20 357-358 Immiscible polymers, compatibilization of, 20 324-325... 

The preparation of immiscible polymer blends is another way to disperse a bulk polymer into fine droplets. It has been reported for several polymers that when they are dispersed in immiscible matrices into droplets with average sizes of around 1 pm, they usually exhibit multiple crystallization exotherms in a differential scanning calorimetry (DSC) cooling scan from the melt (at a specific rate, e.g., 10 Cmin ). Frensch et al. [67] coined the term fractionated crystallization to indicate the difference exhibited by the bulk polymer, which crystallizes into a single exotherm, in comparison with one dispersed in a large number of droplets, whose crystallization is fractionated temperature-wise during cooling from the melt. 

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.

Capability of the individual component substances in either an immiscible polymer blend or a polymer composite to exhibit interfacial adhesion. 

Note 2 Compatibility is often established by the observation of mechanical integrity under the intended conditions of use of a composite or an immiscible polymer blend. 

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. 

Measure of the strength of the interfacial bonding between the component substances of a composite or immiscible polymer blend. 

Immiscible polymer blend that exhibits macroscopically uniform physical properties. 

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

Region between phase domains in an immiscible polymer blend in which a gradient in composition exists [3]. 

This exponential dependence leads to the dramatic compatibilization effect of block copolymers in immiscible polymer blends. Leibler (1988) noted that for strongly incompatible systems, the exponential increase of Ay with h only occurs for small c. At larger copolymer content, the reduction in interfacial area per block causes a slower increase in Ay (i.e. reduction in y). 

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. 

Ruckdaschel H, Rausch J, Sandler JKW, Altstadt V, Schmalz H, Muller AHE (2007) Foaming of miscible and immiscible polymer blends. Mater Res Soc Symp Proc 977... 

Potschke P, Paul DR (2003) Formation of co-continuous structures in melt-mixed immiscible polymer blends. J Macromol Sci Polym Rev C43 87-141... 

Chain functionalized polymers or graft copolymers are of great technological importance. They are used as compatibilizing agents for immiscible polymer blends (8) and adhesive layers between polymer-polymer co-extruded surfaces (8). Currently, of all polymers sold, about 30% are in the form of compatibilized immiscible blends (9-12). Next we discuss a few examples of chain functionalization. 

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. 

L. A. Utracki, On the Viscosity-concentration Dependence of Immiscible Polymer Blends, J. Rheol., 35, 1615-1637 (1991). 

Utracki LA (1991) On the viscosity-concentration dependence of immiscible polymer blends. J Rheol 35(8) 1615-1637... 

Anastasiadis SH, Gancarzl, Koberstein JT (1988) Interfacial tension of immiscible polymer blends temperature and molecular weight dependence. Macromolecules 21(10) 2980-2987... 

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