Crystalline polymers morphology

In this chapter we study the characteristics that determine the crystallinity of polymers, crystalline morphology, and the factors affecting the crystallization and melting of polymers. We describe the amorphous state, focusing on the glass transition, a fundamental property for defining the mechanical behavior of polymers. The entire description refers exclusively to synthetic polymers. 

Lincoln, D.M. Vaia, R.A. Wang, Z.G. Hsiao, B.S. Krishnamoorti, R. Temperature dependence of polymer crystalline morphology in nylon 6/montmorillonite nanocomposites. Polymer 2001, 42, 9975-9985. 

PCP showed that this polymer crystalline morphology at orientational crystallisation was a mixed morphology, inclnding both crystallites with folded chains and fibrillar crystallites. An increase in the last fraction resnlts in reduction of the tension critical degree at which the transition from monomolecular nucleation to multimolecular nucleation is observed. 

The density of the polymer will clearly depend on the density of the soft phase (usually low), and the density of the hard phase (generally higher with crystallisable polar blocks) and the ratio of the soft and hard phases present. It will also clearly depend on the additives present and to some extent on the processing conditions, which may affect the crystalline morphology. 

Many polymers solidify into a semi-crystalline morphology. Their crystallization process, driven by thermodynamic forces, is hindered due to entanglements of the macromolecules, and the crystallization kinetics is restricted by the polymer s molecular diffusion. Therefore, crystalline lamellae and amorphous regions coexist in semi-crystalline polymers. The formation of crystals during the crystallization process results in a decrease of molecular mobility, since the crystalline regions act as crosslinks which connect the molecules into a sample spanning network. 

As noted in Fig. 14.1 (a), commercial fibers of semicrystallme polymers are always cold-drawn after spinning to achieve further structuring through further macromolecular orientation and crystalline morphological changes, many of which are retained because of the low temperature of the cold-drawing processes. A typical stress-strain curve for a polycrystalline polymer at a temperature Tg < T < Tm appears in Fig. 14.6. 

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