Kinetic isothermal crystallization

KNUDSEN J c, ANTANUSE H s, RisBO j and SKIBSTED L H (2002) Induction time and kinetics of crystallization of amorphous lactose, infant formula and whole milk powder as studied by isothermal differential scanning calorimetry, Milchwissenschaft, 57, 543-546. 

The overall isothermal crystallization kinetics of polymers can be described by the Avrami equation [88-90] ... 

In order to study the overall crystallization kinetics of the PCL block within PPDX-fo-PCL diblock copolymers, Muller et al. [ 103] first crystallized the PPDX block until saturation by performing a special thermal procedure (it consisted of first cooling from the melt as in Fig. 6 to allow both blocks to crystallize, then the sample was heated to 62 °C and annealed at that temperature for 70 min, a temperature at which the PCL is molten, before quenching to a Tc where the PCL block isothermal crystallization was followed by DSC). With the use of such a procedure the overall isothermal crystallization of only the PCL block was determined in the diblock copolymers where the PPDX block was already crystallized. 

Recently, the isothermal crystallization kinetics of the PE block within SEC triblock copolymers was investigated [94]. When the PE content in the... 

Jabarin, S. A., Crystallization kinetics of polyethylene terephthalate. I. Isothermal crystallization from the melt,. /. Appl. Polym. Sci., 34, 85-96 (1987). 

Verhoyen, 0., Dupret, F. and Legras, R., Isothermal and non-isothermal crystallization kinetics of polyethylene terephthalate mathematical modeling and experimental measurement, Polym. Eng. Sci., 38, 1592-1610 (1998). 

Chuah [54, 55] compared the isothermal crystallization kinetics of PET, PTT and PBT using DSC, and found PTT to have a crystallization rate in between those... 

Figure 20.26 Polarized optical micrographs of isothermal crystallized (4h) melt blends (x400) (a) 210°C (b) 230°C (c) 210°C (d) 230°C [44], From Park, J. K Park, Y. H., Kim, D. J. and Kim, S. H., Crystallization kinetics of TLCP with polyester blends, J. Korean Fiber Soc., 37, 69-76 (2000). Reproduced with permission of The Korean Fiber Society...

The isothermal crystallization of PEO in a PEO-PMMA diblock was monitored by observation of the increase in radius of spherulites or the enthalpy of fusion as a function of time by Richardson etal. (1995). Comparative experiments were also made on blends of the two homopolymers. The block copolymer was observed to have a lower melting point and lower spherulitic growth rate compared to the blend with the same composition. The growth rates extracted from optical microscopy were interpreted in terms of the kinetic nucleation theory of Hoffman and co-workers (Hoffman and Miller 1989 Lauritzen and Hoffman 1960) (Section 5.3.3). The fold surface free energy obtained using this model (ere 2.5-3 kJ mol"1) was close to that obtained for PEO/PPO copolymers by Booth and co-workers (Ashman and Booth 1975 Ashman et al. 1975) using the Flory-Vrij theory. 

To applying Eq. (2.47) to non-isothermal problems, it is necessary to generalize it by introducing temperature-dependent constants. The basic approach was proposed by Ziabicki94,95 who developed a quasi-static model of non-isothermal crystallization in the form of a kinetic rate equation ... 

The temperature dependencies of K, a and Bo in Eq. (2.50) can be found from experimental data for the kinetics of isothermal crystallization. As a general rule, the temperature dependence of K can be represented by a double exponential function. 

There have been many related works by other research groups that are concerned with the phase behavior, isothermal crystallization kinetics, and tensile properties of cellulose propionate (DS = 2.75)/PHB blends [129], the miscibility and crystallization behavior of CAB/PHB blends [ 130], or the melt... 

D. W. Henderson, Thermal Analysis of Non-Isothermal Crystallization Kinetics in Glass Forming Liquids , Journal of Non-Crystalline Solids, 30 301-315 (1979). 

The stereosequence length also has a marked effect on the isothermal crystallization kinetics of the propylene oxide polymers. These studies and analysis of results on crystallization kinetics will be described in detail in another communication. Here we summarize briefly the main conclusions of the effect of stereosequence length on the isothermal crystallization rates. 

Foubert, I., Vanrolleghem, P.A. and Dewettinck, K. (2003). A differential seanning calorimetry method to determine the isothermal crystallization kinetics of cocoa butter. Thermochemica Acta, 400 131-142. 

Duff et al. [27] reported a study made by means of DSC and WAXD on SPS/ PPE blends of various compositions, precipitated from ethylbenzene solutions, compression molded at 330 °C for 2 min and then slowly cooled to room temperature. In particular, the WAXD patterns show that in sPS-rich blends (>50 50 wt%) sPS is in a 0 or (3 form, while small amounts of a are present in the 50 50 wt% blend. The kinetics of crystallization and the mechanism of nucleation of sPS were investigated under isothermal and nonisothermal conditions as a function of blend composition and molecular weights of the components. The experimental curves show that the half-time to crystallization, t j2, increases with increasing content and molecular weight of PPE, but is not influenced by the molecular weight of sPS. The crystallization kinetics were... 

From this analysis it is clear that the trade-off between kinetics and thermodynamics is not at all obvious. Consider a monotropic, dimorphic system (for simplicity) whose solubility diagram is shown schematically in Fig. 2.10. It is quite clear that for the occurrence domain given by solution compositions and temperatures that lie between the form II and I solubility curves only polymorph I can crystallize. However, the outcome of an isothermal crystallization that follows the crystallization pathway indicated by the vector in Fig. 2.10 is not so obvious since the initial solution is now supersaturated with respect to both polymorphic structures, with thermodynamics favouring form I and kinetics (i.e. supersaturation) form II. 

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