Poly blends spherulite growth rates

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. 

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 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. 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. 11.15 Plot of spherulite growth rates of poly(vinylidene fluoride) in blend with poly( 1,4-butylene adipate) as a function of temperature at indicated composition. (From Pennings and Manley (33))...

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... 

Fig. 11.17 Plot of spherulite growth rate of poly(butylene succinate) in blends with poly(vinylidene fluoride) as a function of crystallization temperature. Composition poly(butylene succinate)/poly(vinylidene fluoride) 100/0 80/20 a 60/40. (From Lee et al. (35))...

The spherulite growth rates of poly(ethylene oxide) blends, M = 5000/M = 270 000, display a qualitatively similar behavior. (39) In this case, both components co-crystallize in a common lattice at large undercoolings. At the low undercoolings separate phases result. There is no indication of this fractionation in the growth rate-temperature plots. Morphological studies demonstrate the fractionation. 

A typical example of the spherulite growth rates of these blends is given in Fig. 11.28 for the isotactic-atactic poly(styrene) pair as a function of temperature for different compositions.(54) The molecular weights in this mixture are 5.5 x 10 and 4.8 x 10 for the isotactic and atactic polymers, respectively. The usual rate maximum for the pure polymer is found at about 180 °C and is maintained for all the blends, even the most dilute one. There is a systematic, continuous decrease in growth rate as the atactic component is added. Similar results are found with... 

Fig. 11.28 Spherulite growth rates of isotactic poly(styrene) in blend with atactic poly(styrene) at indicated composition. (From Yeh and Lambert (54))...

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