Applied crystallization kinetics

Applied Crystallization Kinetics. III. Comparison of Polyepichlorohydrins of Different Stereoregularity... 

Hostomsky, J. and Jones, A.G., 1991. Calcium carbonate crystallization kinetics, agglomeration and fomi during continuous precipitation from solution. Journal of Physics D Applied Physics, 24, 165-170. 

In addition to the general steric requirements reported in the introductory section for macromolecular isomorphism, if chains differ in chemical structure, they must also show some degree of compatibility to intimate mixing and not too much different crystallization kinetics. The first condition is strictly similar to the one that applies to liquid mixtures. As a well known example, liquids without reciprocal affinity in general cannot form a unique phase. Attempts to obtain mixed crystals from polyethylene and polyvinyl or polyvinylidene fluoride has been unsuccessful hitherto, in spite of the similarity in shape and size of their chains. In view of the above somewhat strict requirements, it is not surprising that relatively few examples of this type of isomorphism have been reported. 

The a-time curves were then fitted to the following classical Avrami-Erofe ev (AE) rate equation, which has been widely applied to the analysis of nucleation and crystallization kinetics... 

Ramanan, V. R. V. Fish, G. E. (1982). Crystallization kinetics in Fe-B-Si metallic glasses. Journal of Applied Physics, 53, 2273-5. 

Pan, R, Zhu, B., Kai, W. et al. (2008) Effect of crystallization temperature on crystal modifications and crystallization kinetics of poly(L-lactide). Journal of Applied Polymer Science, 107, 54-62. 

Liao, R., Yang, B., Yu, W. and Zhou, C. (2007) Isothermal cold crystallization kinetics of polylac-tide/nucleating agents. Journal of Applied Polymer Science, 104,310-317. 

Ke, T. and Sun, X. (2003) Melting behavior and crystallization kinetics of starch tmd poly(lactic add) composites. Journal of Applied Polymer Science, 89, 1203-1210. 

Other than PEO/PMMA system, the miscibility of blends of PEO/PiBMA and PEO/PtBMA (Katime and Cadenato, 1995) is verified by the suppression of with ascending amorphous component content and negative values of -0.106 and -0.034, respectively. The reduction in TJ is due to the formation of imperfect PEO crystallites as a result of dismpted crystallization caused by the presence of the amorphous component. Meanwhile, the isothermal crystallization kinetics of the PEO/PiBMA and PEO/PtBMA blends follow the Avrami equation (Avrami, 1939) implying that the rate of crystallization of PEO in the blends decreases progressively with ascending amorphous PiBMA and PtBMA content. The Avrami equation applied under isothermal crystallization conditions is presented as Equation (9) ... 

Ma, X., Liang, G., Liu, H., Fei, J., and Huang, Y. 2005. Novel intercalated nanocomposites of polypropylene/organic-rectorite/polyethylene-octene elastomer Rheology, crystallization kinetics, and thermal properties. Journal of Applied Polymer Science 97 1915-1921. 

Finally, the Avrami equation modified by Jeziorny (II.I) was applied for studying the non-isothermal crystallization kinetics (Xu et al. 2005) ... 

On the basis on the carried out structural investigations of amorphous PET fibers simultaneous heat - mechanically modified at isothermal conditions and constant strain stress values it can be make the following conclusions The mechanical strain force applied simultaneously with the linear heating of the studied PET yarns affects significantly the deformation behaviour and samples crystallization kinetics. Moreover in contrast to the results obtained in the first experiment, all of the so treated specimens are partially crystaUine. The role of the tensile stress in the adjustment of the interacting processes of the fluid like deformation and stress-induced crystallization clearly reveals in the ultimate samples deformation. At stress values from 1.56 MPa to 2.16 MPa predominates the fluid like fibers extension, while the further stress increasing leads to the earlier crystallization start and thereby to decrease of the final fibers length. 

Processing operations such as injection and compression moulding, extrusion, fibre spuming, etc. are likely involved for the preparation and commercialization of polymer/clay nanocomposites. The flow applied during processing play a decisive role in crystallization kinetics and in the morphology obtained. For neat polymers, it has been demonstrated that the flow accelerates crystallization kinetics when compared with the quiescent melts (Keller and Kolnaar 1997 Kumaraswamy et al. 1999) and some crystallization mechanism has been proposed (Somani et al. 2000 Seki et al. 2002), whereas for polymer/clay nanocomposites, studies are still lacking and most of results have been reported for iPP and nylon 6/clay nanocomposites. 

Usually, the Avrami equation is applied in Isothermal crystallization kinetics ... 

Ziabicki proposed to analyze nonisothermal processes as a sequence of isothermal steps [170-172]. The proposed equation is a series expansion of the Avrami equation. In quasi-static conditions, provided that nucleation and growth of the crystals are governed by thermal mechanisms only, that their time dependence comes from a change in external conditions, and that the Avrami exponent is constant throughout the whole process, the nonisothermal crystallization kinetics can be expressed in terms of an observable half-time of crystallization, T]/2, a function of time, and of the external conditions applied. The following equation was derived for the dependence of the total volume of the growing crystal, E(t), with time ... 

Dynamic mechanical analysis is quite useful to observe the result of chemical reactions of polymer chains (e.g., transesterification) as evidenced by Figs. 3.12 and 3.13 [26]. The DMA method can be applied isothermally to determine crystallization kinetics (modulus versus time measurements) [13, 27] and reaction rate of thermosetting materials (e.g., epoxy) [28]. For reaction rate determination of liquid systems, the torsional braid analyzer is most appropriate as the braid can be saturated with the prepolymer liquid. A cellulose blotter could be used for the torsion pendulum, and a section of nylon hosiery could be used for forced vibration studies (both supports saturated with liquid prepolymer). 

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