Isothermal radial growth rate

For pure iPP and PB-1 homopolymers and their respective blends, the spherulite radius increases linearly with time t for all T, investigated. For all samples, the isothermal radial growth rate G was calculated at different as G = dR /dt. Generally, the G values decrease an increase in the values and with increase in the amount of noncrystallizable component in the blend. As shown in Fig. 6.1, where the relative G values of the iPP-based blends are reported for = 125°C, the depression of the G values was more pronounced for the blends prepared with HOCP as the second component. 

The spheruhte dimension, at constant T, increases with increasing concentration of noncrystallizable component. The spherulite radius R increases linearly with crystalhzation time for pure iPP and iPP/PB-l/HOCP blends for all investigated. For all samples, the isothermal radial growth rate, G = dR/dt, calculated at different Tc, is reported in Table 6.11. With the increase in the T, the G values appear to decrease for all investigated compositions. The blends prepared with the same fraction of iPP show G values that decrease with increasing of HOCP fraction at constant Tc value. 

The morphology and the isothermal radial growth rate of PEO spherulites in the blends were studied on thin films of these samples using a Reichert polarizing microscope equipped with a Mettler hot stage. The films were first melted at 85° C for 5 minutes, following which they were rapidly cooled to a fixed crystallization temperature T and the radius of the growing spherulites was measured as a function of time. 

Different morphologies can be obtained, depending on the crystallization conditions and on the crystalline forms. From the melt, SPS crystallizes according to a spherulitic morphology. Two different types of spherulites are observed sheaf-like spherulites with a fibrosity of a few micrometers, and round spheruhtes, which are 50 pm in diameter. They all show positive birefringence and have the same isothermal radial growth rate [66,67]. 

FIGURE 11 Radial growth rate of sphemlite of ( ) PHB (Cimmino et al., 1998) and (o) PHB8V (Peng et al., 2003) isothermally crystallized at different crystallization temperatures. 

From microscopic measurements of the rates of nucleation and of growth of particles of barium metal product, Wischin [201] observed that the number of nuclei present increased as the third power (—2.5—3.5) of time and that the isothermal rate of radial growth of visible nuclei was constant. During the early stages of reaction, the acceleratory region of the a—time plot obeyed the power law [eqn. (2)] with 6 temperature coefficients of these processes were used by Wischin [201]... 

The growth rate (r) has been measured as a function of temperature ( from 1173 to 1400K) and residence time (from 0.2 to 5s). The measurements were performed in situ with a microbalance. The purified graphite substrates were hung in the isothermal section by a molybdenum wire, 100pm in diameter, to the microbalance beam. No radial temperature dependence has been detected. The growth rate here is the mass gain measured by means of the microbalance per unit time and substrate area in the steady state. 

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