Poly spherulitic growth rates with

PC yields lower crystallinity and reduced crystallization rate for PCL, as would be expected from the above discussion. A similar situation exists for miscible blends of poly(butylene terephthalate) (PBT) and the polyarylate based on Bisphenol A isophthalate (PARi) [126]. PBT with a much lower Tg than PARi exhibits decreased spherulitic growth rates with PARi addition. PARi, which is very difficult to melt crystaUize (imblended), showed increasing spherulitic growth rate with PBT addition. 

In contrast to the spherulite growth rates, the overall crystallization of both components can be resolved in these blends.(33) Typical isotherms are observed for the crystallization of poly(vinylidene fluoride). They can be fitted with an Avrami = 3 for a significant portion of the transformation. There is a progressive shift of the isotherms to longer times with dilution. These results are thus consistent with the reduction in spherulite growth rates with the addition of poly(butylene... 

Spherulitic growth is a special case in crystallization. Spherulites form only within a specific temperature range for example, with it-poly(propylene) with a melting point of ITO C, they are first formed below IIS C. With spherulites, the rate of advance of the spherulite boundary is followed. This boundary encloses the crystalline portion of the spherulite. Since spherulites also contain noncrystalline material, however, the spherulite growth rate thus corresponds to the linear crystal growth rate. As the molecular weight increases, the rate of crystallization falls, since the rate of diffusion of segments and molecules decreases. 

Regime transition is presented when the data are analyzed with the Lauritzen and Hoffman kinetic theory. Di Lorenzo demonstrated that the discontinuity in the spherulite growth rate is not associated to any change in superstructural morphology. Tsuji et al. and Yuryev et al. also observed this unusual bimodal crystallization behaviour for pure PLLA, while the normal characteristic bell-shaped spherulite growth rate dependence was seen for poly(L/D-lactide) copolymers. 

In blends composed of immiscible polymers, amorphous polymer does not affect the crystallization of ciystallizable polymer, but if two polymers are miscible, amorphous polymer acts as diluent and affects crystallization of the second polymer. Poly( -caprolactone) is a ciystallizable component of the blend with poly(vi-nyl butyral), which is studied in compositions containing carbon black. Typically, blends of these two polymers form very large spherulites, and it is interesting to find out how carbon black affects crystallization and other properties of the blend as well as the distribution of carbon black in relationship to the spherulites. Figure 16.6 shows that spherulite growth rate is independent of carbon black presence (points of carbon black filled and carbon black free blend follow the same relationship). Additional data show that crystallization rate decreases with the amount of PVB increasing. Carbon black aggregates are mainly found in spherulites. 

PEO blends with poly(ether sidfone) (PES) exhibit miscibility with a lower critical solution temperature slightly above the PEO melting point [198, 199]. The addition of PES to PEO reduces the overall crystaUization rate and spherulitic growth rate as expected from the combination of miscibility and the high Tg of PES (220 °C) [200]. The phenolphthalein poly(ether ether sidfone) (PES-C) was also shown to be miscible with PEO with a lower critical solution temperature [201 ]. PEO crystaUinity was observed at PEO > 50 wt% and all films were transparent above the PEO melting point, but became turbid when heated above the lest phase boundary. 

In order to evaluate the application of modulated-temperature differential scanning calorimetry (M-TDSC) to the study of the crystallisation kinetics of semicrystalline polymers, isothermal crystallisation kinetics in poly(e-caprolactone)-SAN blends are investigated. The temperature dependence of d In G/dT (G =crystal growth rate), determined by M-TDSC agrees approximately with previous experimental data and theoretical values. These were obtained from direct measurements of spherulite growth rate by optical microscopy. Here, theoretical and M-TDSC experimental results show that the d In G/dT versus temperature plots are not sensitive to the noncrystalline component in the poly(e-caprolactone)-SAN blends. 15 refs. 

Fig. 9.71 Spherulite growth rates of isotactic poly(propylene) with different sorbitol compounds as nucleation catalysts, o pure polymer dibenzylidene sorbitol o- (p-chloro, p-methyl) dibenzylidene sorbitol, -o bis (p-ethylbenzylidene sorbitol. (Data from (249))...

The influence of block length on the spherulite growth rate can be found in a set of urethane linked poly(ethylene oxide) block copolymers.(75) The copolymers consisted of uniform block length of either 34,45 or 90 repeating units with total molecular weights that varied from several thousand to 3-6 x 10. The 34 repeating unit blocks (M = 1500) always crystallized in extended form. In contrast the 90 repeating unit blocks (M = 3900) crystallized in a folded structure at all... 

Fig. 11.1 Spherulite growth rate of poly(vinylidene fluoride) as a function of crystallization temperatures in blends with poly(methyl methacrylate) at indicated...

Fig. 11.2 Spherulite growth rate of poly(3-hydroxybutyrate) as a function temperature in blends with two different cellulose acetate butyrates. Numbers on curves cellulose ester weight percent. (From Pizzoli et al. (2))...

Fig. 11.4 Plot of spherulite growth rates of poly(pivalolactone) as a function of composition in blends with poly(vinylidene fluoride) (circles), pivalolactones and poly(3-hydroxybutyrate) in cellulose acetate butyrate (squares), at indicated crystallization temperatures. (Data from (2) and (5))...

Two typical examples of the overall crystallization rate, expressed as either fo s or peak time, are given in Fig. 11.7 for poly(ethylene oxide)-poly(vinyl phenol) (18) and for poly(aryl ether ether ketone)-poly(ether imide) (19) in Fig. 11.8. The dependence of the crystallization rates on composition are similar to one another and are closely related to the results for other binary mixtures. The overall crystallization rates follow the pattern established for spherulite growth rates. At the higher crystallization temperatures only a modest decrease in the rate is observed with the addition of the noncrystallizing component However, with a decrease in the crystallization temperature the polymeric diluent becomes more effective in reducing the rate. Because of the retardation in the rate with dilution a much wider range in isothermal crystallization temperatures can be studied. Thus, for the more dilute blends a maximum in the rates with temperature can be observed. This is... 

Fig. 11.9 Plot of spherulite growth rate of poly(ethylene oxide) in a blend with poly(methyl methacrylate) as a function of crystallization temperatures. Composition of blends 70/30 by weights. Molecular weights of the poly(methyl methacrylate) fractions are indicated. (From Alfonso (21))...

Fig. 11,9a Plot of spherulite growth rate at 30 °C of poly( -caprolactone) as a function of its molecular weight for mixtures with poly(vinyl chloride). Compositions of mixtures are indicated. (From Chen et al. (21a))...

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