Factors Influencing the Overall Crystallization Kinetics

Both the experimental results and theories show that the overall crystallization kinetics is governed by the 

The number of nucleation sites can be increased by use of nucleation agents that not only shortens the crystallization time but also causes the elevation of the effective temperature of nonisothermal crystallization during cooling, especially in polyolefins. Addition of 0.2-0.5 wt% of bis(3,4-dimethylbenzylidene) sorbitol to iPP increased its crystallization peak temperature by approximately 18°C [40]. Polymer molecular weight, polymorphism, and application of pressure are other factors that affect nucleation and growth and, hence, the overall crystallization kinetics. 

It must be also mentioned that spatial limits and the additional nucleation process on outer surfaces influence the solidification, although the overall effect depends strongly on the relation between the sample size, for instance, thickness, and the spherulite size. 

Polymers are poor heat conductors hence, temperature gradients develop during cooling inside thick-walled products, and they can be further enhanced by the release of heat of crystallization [31,41 ]. Flow affects both the structure and the overall crystallization kinetics, as it enforces orientation of polymer chains. The 

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In this chapter, we will briefly describe experimental measurements and computer modeling of the overall crystallization kinetics. Furthermore, we will review the overall crystallization theories including the recent developments. Factors influencing the overall crystallization kinetic and reasons for discrepancies between the theories and experimental results will be also addressed. 

Nucleation and Growth (Round 1). Phase transformations, such as the solidification of a solid from a liquid phase, or the transformation of one solid crystal form to another (remember allotropy ), are important for many industrial processes. We have investigated the thermodynamics that lead to phase stability and the establishment of equilibrium between phases in Chapter 2, but we now turn our attention toward determining what factors influence the rate at which transformations occur. In this section, we will simply look at the phase transformation kinetics from an overall rate standpoint. In Section 3.2.1, we will look at the fundamental principles involved in creating ordered, solid particles from a disordered, solid phase, termed crystallization or devitrification. 

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