Poly isothermal crystallization

Figure 11 Left Spherulites of a Ziegler-Natta isotactic poly(propylene) with Mw = 271,500 g/mol and mmmm — 0.95, isothermally crystallized at 148°C. Right Banded spherulites of a linear polyethylene with Mw = 53,600 g/mol slowly cooled from the melt.

Sodium Poly(4-styrene sulfonate). The sol—gel processing of TMOS in the presence of sodium poly-4-styrene sulfonate (NaPSS) has been used to synthesize inorganic—organic amorphous complexes (61). These sodium silicate materials were then isothermally crystallized. The processing pH, with respect to the isoelectric point of amorphous silica, was shown to influence the morphology of the initial gel structures. Using x-ray diffraction, the crystallization temperatures were monitored and were found to depend on these initial microstructures. This was explained in terms of the electrostatic interaction between the evolving silicate structures and the NaPSS prior to heat treatment at elevated temperatures. 

Answers to these questions can be obtained if one performs small angle scattering measurements during isothermal crystallization. Such measurements have been performed on different materials. The results were observed to depend strongly on the material used. So, for example, with increasing crystallization time, the long period increased with polyethylene, it decreased with polyethylene terephthalate and it stayed constant with poly-P-hydroxybutyrate. 

Figure 12,27 Variation of the complex relaxation modulus of poly(ethylene ter-ephthalate) with temperature, in the vicinity of the glass-rubber relaxation, for samples of various crystallinities obtained in isothermal crystallizations ( ) 46%, (<>) 40%, ( ), (V) 26%, ( ) 2-3%, and (O) 0%. (From Ref. 33.)...

A series of morphological images captured during isothermal crystallization of poly(p-diox-anone), PDS, at 85°C by (a) AFM, (b) HSOM, and (c) SALS. 

TAN 07] Tanaka T., Yabe T., Termachi S., et al, Mechanical properties and enzymatic degradation of poly[(R)-3-hydroxybutyrate] fibers stretched after isothermal crystallization neaxJg , Polymer Degradation and Stability, vol. 92, no. 6, 1016-1024, 2007. 

Alvarez, V. A., Kenny, J. M., and Vazquez, A., Isothermal crystallization of poly(vinyl alcohol-co-ethylene), J. Appl. Polymer Sci., 89, 1071-1077 (2003). 

Tsuji, H., Takai, H., Fukuda, N. and Taldkawa, H. (2006) Non-isothermal crystallization behavior of poly(L-lactic acid) in the presence of various additives. Macromolecular Materials and Engineering, 291,325-335. 

Kang, K.S., Lee, S.I., Lee, T.l. et al. (2008) Effect of biobased and biodegradable nucleating agent on the isothermal crystallization of poly (lactic acid). Korean Journal of Chemical Engineering, 25, 599-608. 

Cao, D. and Wu, L. (2009) Poly(L-lactic acidj/sUicon dioxide nanocomposite prepared via the in situ melt polycondensation of L-lactic acid in the presence of acidic silica sol Isothermal crystallization and melting behaviors. Journal of Applied Polymer Science, 111, 1045-1050. 

As an example of P(3HB) copolymers, high-strength commercial-P(3HB-co-3HV) and poly[(/ )-3-hydroxybutyrate-co-(/ )-3-hydroxyhexanoate] [P(3HB-co-3HH)] fibers were produced by same method of stretching after isothermal crystallization (Tanaka et al. 2006, 2007a). The maximum draw ratio of P(3HB-co-3HV) fibers with isothermal crystallization time of 24 h was about ten times in the initial length of the sample. The mechanical properties of one-step-drawn P(3HB-co-3HV) fibers without and after isothermal crystallization are summarized in Table 4. The... 

Kg. 6 Scanning electron micrograph and WAXD pattern of commerdal-poly[(/J)-3-hydroxybutyrate-co-(f )-3-hydroxyvalerate], P(3HB-co-3HV), fibers after isothermal crystallization a, a non-drawn b, b ten times one-step-drawn. (Reprinted with permission from Tanaka et al. 2006. Copyright 2006, American Chemical Society)... 

Yang HS, Yoon JS, Kim MN (2005) Dependence of biodegradability of plastics in compost on the shape of specimens. Polym Degrad Stab 87 131-135 Yasuniwa M, Tsubakihara S, Satou T, lura K (2005) Multiple melting behavior of poly(butylene succinate).II. Thermal analysis of isothermal crystallization and melting process. J Polym Sci B Polym Phys 43 2039-2047... 

In this section experimental results are discussed, concerned with analyses of melting and crystallization kinetics, as well as reversibility of the phase transition. The frame of the discussion is set by Fig. 3.76, which will be supported by experimental data on poly(oxyethylene). The thermal analysis tools involved are TMDSC, optical and atomic-force microscopy, DSC, adiabatic calorimetry, and dilatometry. Most of these techniques are described in more detail in Chap. 4. Results from isothermal crystallization, and reorganization are attempted to be fitted to the Avrami equation. This is followed by a short remark on crystallization regimes and finally some data are presented on the polymerization and crystallization of trioxane crystals. 

Hu WB (2005) Molecular segregation in polymer melt crystallization simulation evidence and unified-scheme interpretation. Macromolecules 38 8712-8718 Hu WB, Cai T (2008) Regime transitions of polymer crystal growth rates molecular simulations and interpretation beyond Lauritzen-Hoffman model. Macromolecules 41 2049-2061 Jeziomy A (1971) Parameters characterizing the kinetics of the non-isothermal crystallization of poly(ethylene terephthalate) determined by DSC. Polymer 12 150-158 Johnson WA, Mehl RT (1939) Reaction kinetics in processes of nucleation and growth. Trans Am Inst Min Pet Eng 135 416-441... 

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