The induction times for the crystallization, under isothermal conditions, of refined, bleached, and deodorized palm oil from the melt were studied by viscometry. At temperatures below 295 K, the crystallization of palm oil was observed to occur in a two-stage process. This two-stage process was caused by the fractionation of palm oil, most probably into the stearin and olein fractions. At temperatures higher than 295 K, only a single-stage crystallization process was observed. As seen under polarized light microscopy, spherical crystals were initially formed from the first fraction at temperatures from 287 to 293 K. The diameters of these spherical crystals decreased as the temperature increased. After that, needle-shaped crystals were formed from the second fraction and continued to grow from the surface of these spherical crystals until the spherical crystals were fully enclosed, i.e., the cocrystallization of two polymorphs was observed. At temperatures higher than 293 K, the needleshaped crystals formed from a mixture of the two fractions were found to be the only polymorphs developed with the onset of crystallization. X-ray diffraction results showed that for temperatures below 295 K, the spherical crystals formed from the first fraction were in α form, whereas the needle-like crystals that nucleated later from the second fraction were in β′ form. β′ crystals were the only polymorphs formed for temperatures above 295 K. The results obtained were in good agreement with the discontinuity observed in the induction time vs. temperature curve. Activation free energies for nucleation were calculated according to the Fisher-Turnbull equation for the various polymorphic forms. Viscometry was observed to be a sensitive method for characterizing the overall crystallization process. This technique is suitable for induction time studies of palm oil crystallization, especially at lower temperatures and with viscous oil.

The isothermal crystallization behavior of nano‐alumina particle‐filled poly(ether ether ketone) (PEEK) composites has been investigated using differential scanning calorimeter. The results show that all the neat PEEK and nano‐alumina‐filled PEEK composites exhibit the double‐melting behavior under isothermal crystallization. The peak crystallization times (τp) for all the neat PEEK and PEEK/aluminum oxide (Al2O3) composites increase with increasing crystallization temperature. Moreover, the crystallinity of the PEEK/Al2O3 composite with 7.5 wt % nano‐filler content reached the maximum value of 44.8% at 290°C, higher than that of the neat PEEK polymer. From the lower value in τp and higher value in Xc for the PEEK/Al2O3 composites, the inclusion of the nano‐alumina into the PEEK matrix favored the occurrence of heterogeneous nucleation. The Avrami exponents n of all the neat PEEK and PEEK/Al2O3 composites ranged from 2 to 3, and the n values for PEEK/Al2O3 composites were slightly higher than that of the neat PEEK polymer, indicating that the inclusion of the nano‐filler made the crystallization mechanism more complex. However, the growth rate of crystallization was lowered as the nano‐ filler was introduced, and the decrease in growth rate reduced the grain size of the PEEK spherulites because of the lowering of molecule mobility during isothermal crystallization. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012