Crystal growth molecular fractionation

Studies on PEO fractions in the molecular weight range between 1500 and 12 000 have shown [18] that the slope of the increasing crystal growth rate with supercooling dG/d(AT) does indeed increase abruptly at a series of spe-... 

Fig. 29 Linear growth rates from melt of extended-chain crystals of PEO fractions 3000, 4000 and 6000 molecular weight as a function of crystallization temperature (re-plotted from [18]). Dashed lines are maximum slope tangents (after [25])...

This chapter presents first some fundamental aspects of nucleation, and second the general Avrami equation, which is frequently used to describe overall crystallization. The growth theories of Lauritzen and Hoffman and Sadler and Gilmer are discussed in sections 8.4.2 and 8.4.3. Molecular fractionation and orientation-induced crystallization are dealt with in sections 8.5 and 8.6. 

Growth rate studies of linear polyethylene from other solvents have also been re-ported.(51,53) The results obtained with decalin, a relatively good solvent, are very similar, at all concentrations, to those obtained with p-xylene.(51) In contrast, in a poorer solvent, n -octane, a maximum in the growth rate is observed at all concentrations studied, 0.001 % to 0.1 wt%.(48) However, the rate of decrease is much steeper in this case. Growth rates of linear polyethylene crystallizing from tetradeconol (0.05%), over the molecular weightrangeM = 1.4x 10" to 1.2x 10, are essentially constant at the lower crystallization temperatures. (5 3) However, as the temperature is raised the crystallization rate of the lowest molecular fractions decreases. 

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