Maximum crystal growth rate

The overall rate of crystallization is determined by both the rate of nuclei formation and by the crystal growth rate. The maximum crystal growth rate lies at temperatures of between 170 and 190 °C [71, 72], as does the overall crystallization rate [51, 61, 75], The former is measured using hot stage optical microscopy while the latter is quantified by the half-time of crystallization. Both are influenced by the rate of nucleation on the crystal surface and the rate of diffusion of polymer chains to this surface. It has been shown that the spherulite growth rate decreases with increasing molecular weight due to the decrease in the rate of diffusion of molecules to this surface [46, 50, 55, 71, 74],... 

In general, nucleation and crystal growth rates reach a respective maximum with increasing temperature. In many systems, the temperature of the maximum nuclei formation rate is lower than that of the maximum crystal growth rate. Therefore, an intermediate precipitation temperature may be chosen for obtaining fine particles. 

Gmax is presented by only one rate at a given molecular weight and can be formulated by equating to zero the derivative of Eq. (19.2), either Arrhenius or WLF expression of molecular transport term [75]. The crystal growth rate (G) can be formulated as a function of the maximum crystal growth rate and the reduced super-cooling (Z) based on Eq. (19.2) with the Arrhenius expressions in the molecular transport term, as follows ... 

It is crucial to the whole of the manufacturing process that the melt remains sufficiently free of crystals so that it stays in a glassy state during machining and subsequent annealing. Later conversion into its partially crystalline condition is possible because of the difference between the temperature for maximum nucleation rate and the temperature for maximum crystal growth rate. 

Among many more linear polymers, poly(ethylene terephthalate) (PET) is of particular relevance since its maximum crystal growth rate is slow. The enhanced crystallization of PET has been, and still is, a topic of technological relevance. Following extended work by Legras, Mercier, and Nield [21], the impact of chemical nucleation (as opposed to epitaxial, i.e., physical interactions) has been widely publicized and is indeed... 

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