Compatibilization Compatibilizer forced

Miscibility or compatibility provided by the compatibilizer or TLCP itself can affect the dimensional stability of in situ composites. The feature of ultra-high modulus and low viscosity melt of a nematic liquid crystalline polymer is suitable to induce greater dimensional stability in the composites. For drawn amorphous polymers, if the formed articles are exposed to sufficiently high temperatures, the extended chains are retracted by the entropic driving force of the stretched backbone, similar to the contraction of the stretched rubber network [61,62]. The presence of filler in the extruded articles significantly reduces the total extent of recoil. This can be attributed to the orientation of the fibers in the direction of drawing, which may act as a constraint for a certain amount of polymeric material surrounding them. 

Note Although dispersing agents achieve results similar to compatibilizers, they function differently in that they reduce the attractive forces between fine particles, which allows them to be more easily separated and dispersed. 

Given the morphological complexity of AB diblock and ABA triblock copolymers, it might be expected that the phase behaviour of ABC triblocks would be even more rich, and indeed this has been confirmed by recent experiments from a number of groups. From a practical viewpoint, ABC triblocks can also act as compatibilizers in blends of A and C homopolymers (Auschra and Stadler 1993). In addition to the composition of the copolymer, an important driving force for structure formation in these polymers is the relative strength of incompatibilities between the components, and this has been explored by synthesis of chemically distinct materials. 

Also noteworthy is the appreciable coalescence caused by the shear flows in the single screws, of the rheology section of the TSMEE following the mixing element section. Flow of dispersed immiscible blends involves continuous breakdown and coalescence of the dispersed domains (122). Shear flows, where droplet-to-droplet collisions are frequent—in contrast to extensional flows—favor coalescence over dispersion. The presence of compatibilizers shifts the balance toward reduced coalescence rate. Macosko et al. (123) attribute this to the entropic repulsion of the compatibilizer molecules located at the interface as they balance the van der Waals forces and reduce coalescence, as shown on Fig. 11.36. 

In the majority of the methods discussed above, CNTs are directly mixed with PMMA using ultrasonication or shear forces. Another approach which has been studied to improve quality of dispersion of CNTs in PMMA is third component assisted dispersion of CNTs (65-67). In this method, a third component such as a surfactant or a compatibilizer is added to assist the dispersion of CNTs in a solvent before mixing with the polymer solution (40). This is an effective non-covalent functionalization technique. 

Demonstier-Champagne et al. used atomic force microscopy (AFM) to observe microphase separation within cast films of PS-PMPS-PS/ PS-PMPS block copolymer mixtnre [43] that were nsed to compatibilize a blend of PMPS and PS. The fractnre snrface of blend films with the block copolymer incorporated show a far finer dispersion of particle sizes than those without. Matyjaszewski et al. studied PMPS-PS thin films by SFM (scanning force microscopy) and TEM (transmission electron microscopy) and Fig. 8 shows a TEM picture of a thin section of a film which was prepared by slow evaporation from THE, which is slightly selective for the polystyrene block [73]. 

The first two ways are operating with physical, secondary bonding forces, the last two methods of compatibilization are reactive ways. Radiation processing is capable to form chemical bonds between the components, promising higher efficiency. 

A compatibilizing agent is also formed in situ when incompatible polymers are subjected to shearing forces which rupture polymer chains to generate radicals which undergo coupling. 

For the strategies of compatibilization, Helfand s theory provides three important conclusions (1) the chain-ends of both polymers concentrate at the interface, (2) any low molecular weight third component is forced by the thermodynamic forces to the interface, and (3) the interfacial tension coefficient increases with molecular weight up to an asymptotic value. 

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. 

When assessing the rheological behavior of PA/PO blends, a strong effect of shear forces upon should be considered. The reason is a qualitative difference between the flow curves for PO and PA. Aliphatic PAs show an extended Newtonian plateau typical of polymers with a narrow MWD (71). PA6, for instance, can retain the Newtonian pattern of flow (72) up to a shear rate of 10 s . The curve describing the relationship of rj versus y for PO is typical of polymers with a wide MWD the anomaly in viscosity ( j decreases with increase in the shear rate) was observed at a much lower shear rate of < 10 s . That is why the effects of viscosity s growth—in the case of PA6/PO compatibilized blends—manifest themselves to the utmost at relatively low shear rates, upto 10 s . Such shear rates are typical of extrusion of polymer materials (72). 

The incorporation of rubber particles within the matrix of brittle plastics may enormously improve their impact resistance. When a force is applied to a blend, several deformation mechanisms of the major phase and of cracks that are formed in the blend are important. Their relative importance may depend on the polymer and on the nature of the loading. The best-known effect from compatibilization is the reduction of the interfacial tension in the melt. This causes an emulsifying effect and leads to an extremely fine dispersion of one phase into the other. A second effect is the increase of the adhesion at phase boundaries giving... 

In the case of compatibilized systems it may be the low-viscosity compatibilizer that is forced to migrate toward the wall. In such a case, the CPNC viscosity at low Y are larger than that of neat polymer, but smaller at high y. Numerous examples of this behavior have been reported [Wang et al., 2003 Gu et al., 2004], Manifestly, the magnitude of the effect depends on the relative (to the matrix) viscosity of the compatibilizer and its concentration [Lee et al., 2006],... 

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