Activation Energy Of Non-isothermal Crystallization Research Articles

Crystallization behavior of poly(butylene succinate)/corn starch biodegradable composite

AbstractThe effects of corn starch (CS) filler and lysine diisocyanate (LDI) as a coupling agent on the crystallization behavior of a poly(butylene succinate) (PBS)/CS ecocomposite were investigated using differential scanning calorimetry. In isothermal crystallization, n values for pure PBS were from 2.33 to 2.82. On the other hand, both composites showed values of 3 < n < 4. In nonisothermal crystallization, the Avrami exponent varied from 2.12 to 2.55 for pure PBS, from 1.58 to 1.96 for the composite without LDI, and from 1.79 to 1.91 for the composite with LDI, depending on the cooling rate. There was not a large difference of the crystallization rate constant (k) as adjusted by the Jeziornay suggestion. The activation energy for nonisothermal crystallization was also calculated on the basis of three different equations (Augis–Bennett, Kissinger, and Takhor equations). However, the values of the activation energy were in contradiction with the results of the kinetics. The addition of the filler (CS) and coupling agent (LDI) affected the morphological structure of PBS spherulites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1107–1114, 2005

Crystallization kinetics of magnetron-sputtered amorphous CoNbZr thin films

For non-isothermal and isothermal annealing, the crystallization kinetics of magnetron sputtered Co 85.5Nb 8.9Zr 5.6 amorphous alloy thin films have been investigated by differential scanning calorimetry measurements. As a result, in the case of non-isothermal crystallization, one distinct exothermic peak is observed at 470 °C, which is due to the crystallization of hcp α-Co. With the Kissinger method, the apparent activation energy was obtained to be 99.82 kJ/mol. By using the Deloy–Ozawa method, the local activation energy of non-isothermal crystallization was calculated. For isothermal crystallization, the Avrami exponents were determined by means of the Johson–Mehl–Avrami equation, which is in the range of 1.19–1.37. Based on an Arrhenius relationship, the local activation energy was analyzed, which yields an average value E c =88.51 kJ/mol. Finally, the local Avrami exponent was used for discussing the details of the nucleation and growth behaviour during the isothermal crystallization.

Crystallization kinetics of CoNbZr amorphous alloys thin films

In modes of non-isothermal and isothermal annealing, the crystallization kinetics of magnetron sputtering Co 85.5Nb 8.9Zr 5.6 amorphous alloys thin films have been investigated by differential scanning calorimetry measurements. As a result, in the case of non-isothermal crystallization, one distinct exothermic peak is observed due to the crystallization of hcp α-Co. With Kissinger method, the apparent activation energy was obtained to be 99.82 kJ mol −1. By using Deloy–Ozawa method, the local activation energy of non-isothermal crystallization was calculated. For isothermal crystallization, the Avrami exponents were determined by means of the Johnson–Mehl–Avrami equation, which are in the range of 1.19–1.37. Based on Arrhenian relationship, the local activation energy was analyzed, which yields average value E c = 88.51 kJ mol −1. Finally, the local Avrami exponent was used for discussing the details of the nucleation and growth behaviors during the isothermal crystallization.

Nonisothermal melt crystallization kinetics of poly(ethylene terephthalate)/clay nanocomposites

AbstractVarious kinetic models, namely, the Avrami analysis modified by Jeziorny, the Ozawa model, and a method developed by Mo, were applied to describe the nonisothermal melt crystallization process of poly(ethylene terephthalate) (PET) and two PET/clay nanocomposites of different viscosities. The Avrami analysis modified by Jeziorny could gratifyingly describe the primary nonisothermal crystallization stage of PET and two PET/clay nanocomposites. The difference in the values of the Avrami exponent between PET and PET/clay nanocomposites suggested that the nonisothermal crystallization of PET/clay nanocomposites corresponds to a tridimensional growth with heterogeneous nucleation. The values of half‐time showed that the crystallization rate of PET/clay nanocomposites is faster than that of PET at a given cooling rate. The Ozawa analysis failed to provide an adequate description of the nonisothermal crystallization of PET/clay nanocomposites. The method developed by Mo was successful in describing the nonisothermal crystallization of pristine PET and PET/clay nanocomposites. The activation energy for nonisothermal crystallization of pristine PET and two PET/clay nanocomposites of different viscosities, based on the Augis–Bennett method, the Kissinger method, and the Takhor method, respectively, were evaluated, and it was concluded that the absolute value of activation energy for PET is lower than that of PET/clay nanocomposites, and this showed that introduction of clay into PET matrix weakens the dependence of the nonisothermal crystallization exotherms peak temperatures on the cooling rates used. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 308–314, 2004

ESTIMATING THE ACTIVATION ENERGY FOR NON-ISOTHERMAL CRYSTALLIZATION OF POLYMER MELTS

The advanced isoconversional method can be used to determine the effective activation energy of non-isothermal crystallization of the polymer melts. The method has been applied to DSC data on crystallization of poly(ethylene terephthalate) (PET). The resulting activation energy increases with the extent of crystallization from -270 to 20 kJ mol-1. The variation is interpreted in terms of the Turnbull and Fisher crystallization theory.

Isoconversional Analysis of Calorimetric Data on Nonisothermal Crystallization of a Polymer Melt

The activation energy, E, of nonisothermal crystallization of polymer melts has been frequently evaluated by the Kissinger equation with positive rates of temperature variation, β. It is demonstrated that reversing the sign for β is a mathematically invalid procedure that generally invalidates the Kissinger method. As an alternative we propose the advanced isoconversional method that can be used for evaluating the effective activation energy of nonisothermal crystallization of the polymer melts. The application of this method to calorimetric data on crystallization of poly(ethylene terephthalate) (PET) yields an activation energy that increases with the extent of crystallization from −270 to +20 kJ mol-1. It is demonstrated that this variation is consistent with data on isothermal crystallization of the PET melts and can be interpreted in terms of the accepted crystallization models.

Isoconversional Analysis of the Nonisothermal Crystallization of a Polymer Melt

extended the Avramiequation to nonisothermal conditions. While offering asimple way of estimating the Avrami exponent, Ozawa’sanalysis does not suggest a method of determining theactivation energy. However, estimating the activationenergy for nonisothermal crystallization of melts is not asstraightforward as it may seem. The value of k in Equa-tion (3) has the overall nature because the macroscopiccrystallization rate is generally determined by the rates oftwo processes, nucleation and nuclei growth. Since thesetwo processes are likely to have different activation ener-gies, the temperature dependence of the overall rate con-stant can rarely be fit by a single Arrhenius equationk ¼ A exp ERTð4ÞCommunication: The advanced isoconversional methodcan be used to determine effective activation energies ofthe nonisothermal crystallization of polymer melts. Theapplication of this method to differential scanning calori-metric data on the crystallization of poly(ethylene ter-ephthalate) yields an activation energy that increases withthe extent of crystallization from –270 to 20 kJ N mol

Crystallization and melting behavior of regioregular poly(3-dodecylthiophene)

Non-isothermal and isothermal crystallization and melting behavior of regioregular poly(3-dodecylthiophene) (P3DT) was investigated by differential scanning calorimetry (DSC) with an emphasis on the main chain crystallization. P3DT showed a sharp exothermic peak at 114°C which was attributed to the main chain crystallization and a broad one peaked at 59°C which was due to the side chain crystallization during cooling at 2.5°C/min from the isotropic melt. During heating, the side chains melting took place from 27 to 80°C, while the main chains melting consisted up to three overlapped melting peaks. Avrami analysis for the non-isothermal crystallization revealed two linear regions with a sharp transition in the log(− ln (1−θ)) vs. log t plots at the relative crystallinity of 63% for all cooling rates studied. The average Avrami exponent, n, was around 4.9 when the relative crystallinity was lower than 63%, while the n was around 1.5 when the relative crystallinity was higher than 63%. The Ozawa method failed to describe the non-isothermal crystallization process. The non-isothermal crystallization activation energy was estimated to be 222 kJ/mol by the Kissinger method, which was in good agreement with that of isothermal crystallization. Isothermal crystallization and subsequent melting were also investigated at different temperatures. The formations of ordered structures were highly dependent on the crystallization temperatures and time. At lower crystallization temperatures, three melting peaks could be discerned. However, only one melting peak could be observed when the crystallization temperature was high.