Miscible blends crystalhzation

PEI forms miscible blends with polyesters such as polybutylene tereph-thalate (PBT), polyethylene terephthalate (PET), and polyethylene naph-thanoate (PEN) [30-32]. These blends have a single Tg between that of the PEI and that of polyester. In blends with slower crystallizing polyesters such as PET and PEN, crystalhzation is reduced and one-phase, transparent compositions can be molded. Such blends have reduced thermal performance versus the base PEI polymer, but improved melt flow, reduced yellowness, and slightly better solvent resistance. 

Another area in which self-generated field studies has been useful is in the crystalhzation from miscible blends in... 

A simultaneous (or concurrent) crystallization can only occur when the crystallization temperature ranges overlap and if the crystallizability of both blend components is similar. Cocrystallization is only possible when the components are isomorphic or miscible in the amorphous as well as in the crystalline phase. In both cases mixed crystals can result, but in the case of concurrent crystallization no changes in crystal strucmre may be induced. Cocrystallization requires chemical compatibihty, close matching of the chain conformations, lattice symmetry and comparable lattice dimensions [Olabisi et al., 1979]. Some examples of miscible polymer blends with two crystalline components are given in Table 3.3 together with the type of crystalhzation. 

Blending PEO with m-PLLA indicates, based on Avrami exponent, kinetic constant and crystalhzation half-time, that the blend has 3-dimerrsiorral growth. The crystallization growth rate increases more than 4 times as compared with PEO. Also, size of spherulites was decreased and their ntrmber increased. m-PLLAs not orrly functioned as nucleating agents but also errhanced the miscibility of the blerrds. ... 

The former discussion deals with liquid-liquid phase behavior however, one or both components of the blend can sometimes crystallize. For a polymer pair that is miscible in the melt, cooling well below the melting point of pure ciystallizable component leads to a pure crystalline phase of that component. Far below the melting point, the free energy of crystallization is considerably larger than that of mixing- Because polymers never become 100% crystalline, the pin-e crystals coexist with a mixed amorphous phase consisting of the material that did not crystalhze (6,7). 

Liu TY, et al. Miscibility, thermal characterization and crystalhzation of poly (l-lactide) and poly (tetramethylene adipate-co-terephthalate) blend membranes. Polymer 2005 46 12586-94. 

Chapter 1 covers experimental techniques widely used in studies of polymer crystalhzation. Chapter 2, Chapter 3, Chapter 4, and Chapter 5 are devoted to the structure of crystalline polymers and also to the kinetics of nucleation and growth of the crystaUine phase. Chapter 6 is focused on molecular modeling of polymer crystallization, whereas Chapter 7 describes overah crystalhzation kinetics, with special reference to the theories widely used in practice. Chapter 8 covers the subject of epitaxy. Chapter 9 is dedicated to melting of polymer crystals. Chapter 10, Chapter 11, and Chapter 13 describe the crystahization in copolymers, miscible and immiscible polymer blends, and also polymer composites. Chapter 12 is focused on phenomena related to the confinement of polymer chains. Chapter 14 describes the effect of flow on crystahization, and finally Chapter 15 covers the crystalhzation in processing conditions. 

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