Flow effects, polymer crystal nucleation

Abstract. Kinetic theory of crystal nucleation is proposed for flexible chain polymers subjected to flow deformation with transient molecular deformation and orientation. Significant transient effects in the kinetics of oriented nucleation are expected in melt processing involving high deformation rates, like in high-speed melt spinning. 

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. 

Finally, shear viscosity is strongly affected by the clay in the blends, especially at high PEN contents. A lubricating effect rather than a filler effect reveals the possibility that the clay is not well dispersed in the polymer blend, and migration of particles in the flow to the wall region can explain the observed reduction in shear viscosity. When MMT clay is mixed with crystallizable polymers such as polyesters, some processing problems arise because the crystallization process is modifled by nucleation effects induced by the nanoparticles. Moreover, these particles also influence the kinetics of transesteriflcation between PET and PEN, besides other factors such as the reaction time and extruder processing temperature. In Reference 72, a quaternary alkyl ammonium compound (Cl8) and MAH were used to modify the surface properties of the clay... 

The degree of exfoliation also depends on the melt flow rate of the polymer used. It was found that PP with high melt flow rate of 25 g/10 min results in the formation of well-exfoliated nanocomposites than with polymers possessing low melt flow rate [27]. The presence of PP-g-MA in CPN has the potential to create the heterogeneous nucleation effect, which alters the crystallization temperature [25,29]. 

While crystallization of polymers in the absence of deformation is conceptually simpler, most polymers in industrial practice are solidified under the influence of deformational flow fields. The consequences of such fields are far from trivial, giving rise to strikingly different crystal sizes, orientations, and semicrystalline morphology these effects are dealt with in greater detail in Chapter 14 and Chapter 15. The shish-kebab morphology observed during crystallization of PE in uniaxial flow is one such well-known distinction. Another is the amplification of nucleation density, by as much as five orders of magnitude for a modest input of work of... 

The overall crystallization kinetics of polymers is governed by nucleation and growth of crystalline aggregates, and is influenced by the thermomechanical crystallization conditions and history, including temperature field, pressure, and effects of flow. Also, dimensionality of the process plays an important role. Usually, crystallization in thin films is slower than in polymer bulk, although the nucleation on film surfaces might markedly accelerate the crystallization. In addition, internal interfaces, for instance, in fiber-reinforced composites or in polymer blends, also influence the overall crystallization kinetics. 

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