Rate of polymer crystallization

In the broadest terms, the rate of polymer crystallization is increased by factors that increase the free energy difference between the amorphous and crystalline states and factors that favor the re-organization of amorphous chain segments. The factors that influence the crystallization rate fall into two categories molecular characteristics and external conditions. Molecular... 

In 1926, Volmer and Weber found that the nucleation rate shows a negative exponential dependence on critical free energy barrier (Volmer and Weber 1926). Becker and Doting further proposed that the activation energy for the short-distance diffusion of molecules molecules to enter the crystalline phase should be considered as well (Becker and Doring 1935). Turnbull and Fisher derived the prefactor for the rate equation of crystal nucleation (Turnbull and Fisher 1949). The rate of polymer crystal nucleation i with the change of critical free energy barrier can be expressed as... 

The growth rate of polymer spherulites crystallized isothermally from the melt, G, can be measured by a polarizing optical microscope with a hot-stage. The crystallization temperature, T., was controlled by the hot-stage. The following procedure is recommended for the measurement of the spherulitic growth rate of polymers crystallized from the melt ... 

Kovacs and others have observed that the spherulite growth rates correspond exactly with the growth rates of polymer crystals whenever the two are measured under the same conditions, i.e. in the melt, since growth rates are concentration dependent. 

For systems in which the polymer and filler have an affinity for each other [strong adsorption], increases in the surface area/ volume ratio of the filler can result in large changes in the volume fraction of polymer that is henceforth considered to be "bound" to the filler interface. Many changes in physical phenomena related to the polymer chain dynamics, e.g., the glass transition temperature [Tg] and degrees and rates of polymer crystallization, could be drastically altered due to this bound layer. This has been referred to as the "nano-effect." ° In cases where Tg shifts are observed, the effect is somewhat similar to that reported for thin polymer films. The most important result of an increased bound-polymer layer is the consequent changes in mechanical properties of the final composite.i ... 

Section 4.6 described the essential role of epitaxy in heterogeneous nucleation by formulating and confirming a relationship, / /q oe Cna/ na, where I is the nucleation rate of polymer crystals, lo is a prefactor of I, Cna is the concentration of NA in the mixture of NA and... 

The Lauritzen-Hoffman growth rate of polymer crystals is defined by ... 

In 2005, Manchado and co-workers prepared SWNT/ polypropylene (PP) composite by introduction of small amounts of SWNTs into isotactic PP via shear mixing. Hiese results indicated that low amounts of SWNTs added (less than 1 wt.%) led to an inaease in the rate of polymer crystallization with no substantial changes in the crystalline stracture. A modulus inaease from 0.85 to 1.19 GPa with addition of 0.75 wt.% SWNTs and a strength inaease from 31 to 36 MPa with addition of 0.5 wt.% SWNTs were also observed. ... 

Some other generalizations can be made in light of what has been said so far. The rate of polymer crystallization increases as the tanperature is lowered from T. However, no crystallization takes place effectively below T. Consequently, the maximum rate of crystallization occurs at a tanperature between and (Figure 3.22). The maximum rate occurs about halfway between and T for natural rubber, but it... 

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