Kinetics of polymer crystallization from the melt (calorimetric approach)

Abstract

Crystallization kinetics for 12 polymers including polyolefins, polyesters, polyurethanes, polysiloxanes was measured by the evolution of heat in a modified Calvet‐type calorimeter over wide temperature ranges. The results are analyzed in terms of the Avrami equation and a comparison between calorimetric and dilatometric results is carried out. It is concluded that, although in the majority of cases experimental results do not obey the Avrami equation, for some polymers the agreement is rather good. The Avrami parameter obtained, however, depends on the experimental technique. Possible reasons for this disagreement are discussed. Analysis of the calorimetric crystallization rate in the vicinity of the melting point by using the kinetic theory of crystallization shows that the growth is controlled by surface (two‐dimentional) nucleation. Energy parameters for the crystallites were determined and it is shown that the surface energy of the crystallites depends on the molecular structure of the polymer. Temperature dependence of the calorimetric crystallization rate of the polymers for which crystallization rates could be determined above and below the maximum rate are analyzed using a kinetic equation with common approximations for the transport term. The influence of melting conditions on the crystallization rate was studied. The results indicate heterogeneous nucleation in the polymer melt. It is concluded that this may be due both to impurities and to high regularity of macromolecules in the polymer melt.

Cristalização e taxa crítica de resfriamento para vitrificação do poli(sebacato de decametileno)

“…Os valores de n apresentaram-se fracionários e em torno de 3, como também proposto por Godovsky et al 24 . Segundo a teoria, o valor de n = 3 implica em crescimento tridimensional (por meio de microscopia ótica com luz polarizada, o P10MS mostrou cristais na forma elipsoidal) e nucleação atérmica.…”

Crystallization kinetics of compatibilized blends of a liquid crystalline polymer with polypropylene

“…Characterization However, less information is available on the effect of MA on the crystallization behavior of the Fourier transform infrared spectroscopy (FTIR) was used to characterize the changes in the chem-PP and PP/LCP blends. The isothermal [15][16][17][18] and nonisothermal [19][20][21][22] crystallization kinetics of pure ical structure of the PP matrix after maleation. Thin-film specimens with a thickness of about 40 PP were reported in the literature.…”

Determination of non-isothermal crystallization rate constant for pseudo-experimental calorimetric data

“…However, this parameter is necessary to generate the pseudo-experimental data for applying the Master Curve Approach. This non-isothermal induction time was therefore estimated using the Godovsky and Slonimsky equation 20 :…”