Isotherms, crystallization

Fig. 1 Annealing time dependences of the crystallization isotherm 0 (below) and the macroscopic density (above) of PET annealed at 115 °C [6]... 

Table 5.2 Half -times and induction times (in min) for different PET samples when crystallized isothermally from the melt [26]. From Wick, G., Characterization of PET polymer for bottle manufacturing, presentation given at the Society of Plastics Engineers Benelux Seminar, 20-21 May, 1980, Amsterdam, and reproduced with permission of KoSa GmbH Co. KG...

Our broad-line XH NMR analysis showed that this type of sample generally consists of the phase structure of lamellar crystallites and noncrystalline overlayer with a negligible amount of the noncrystalline amorphous phase [16,62]. In broad-line H NMR spectra of solution-grown linear polyethylene samples, a narrow component that suggests the existence of a liquid-like amorphous phase is hardly recognized. In Table 2, the three-component analysis of the broad-line XH NMR spectra of linear polyethylene samples with different molecular weights that were crystallized isothermally from 0.08% toluene solution at 85 °C for 24 hours under a nitrogen atmosphere is summarized. 

Fig. 22 Crystallization isotherm 0(f) as a function of annealing temperature for PEN (a), PET (b), sPS (c), and iPS (d), crystallized from the glassy state [15]...

Isothermal crystallization Injection molded sPS/PPE blends having different composition [19], melted at Tmax = 300 °C for tmax = 5 min and then crystallized isothermally for 60 min at various Tc (from 232 to 244 °C), were investigated by means of DSC and WAXD and compared with pure sPS. DSC measurements do not show a melting peak for sPS < 40 wt%, suggesting the absence of crystallinity. In contrast, at higher contents (80 wt%) three separate melting endotherms (labeled I, II and III) between 260 and 271 °C are clearly found, as in pure sPS (Figure 20.2a). 

Similar studies [23,24] performed with WAXD on sPS/aPS and sPS/PPE blends of various compositions, melted at Tmax = 320°C and then crystallized isothermally at various Tcl (242-250 °C for 4 h), show instead that only the 3 form is present. Correspondingly, DSC exhibits only melting peaks I and III, and peak II, assigned to a, is practically absent. A comparison between the two kinds of blends suggests that the formation of the a form is entropically inhibited by the random distribution of sPS chains in the other component, rather than by a strong sPS-PPE interaction, as suggested by Guerra et al. [16]. 

NMR spectra of linear polyethylene samples with different molecular weights that were crystallized isothermally from 0.08% toluene solution at 85 °C for 24 hours under a nitrogen atmosphere is summarized. 

Fig. 3.17 TM-AFM height image of PET quenched from the melt to liquid nitrogen temperature (left) and sample crystallized isothermally at 190°C for 10 min (z range 14 nm) [42]...

Fig. 3.29 Cross-sectional analyses of [3-iPP lamellae (crystallized isothermally in a thick film at 140°C for 1 h and subsequently exposed to KMn04 etching) viewed in (a) flat-on projection (top) and (b) in edge-on projection (bottom) together with corresponding section analyses and histograms of lamellar thicknesses. With kind permission from Springer Science+Business Media from [65]. Copyright (1998).. Springer-Verlag...

Fig. 3.31 TM-AFM images of unfractionated ePP bulk film crystallized isothermally at 120°C (left height image, z scale from dark to bright 3.5 pm right, phase image). Reproduced from [51] with permission. Copyright 2002. American Chemical Society...

Fig. 11,7. C CP/MAS spectra of i-PP at various temperature. This sample is crystallized isothermally at 140°C. The stick spectrum indicates the chemical shifts in solution NMR spectrum.

Equation 6.30 reproduces the familiar S-shaped crystallization isotherms that are often observed. The constant K contains a superposition of nucleation and growth parameters. It is related to the time for half conversion during crystallization (ti/2) by Equation 6.31, which can be obtained from Equation 6.30 by setting oc(ti/2)=0.5 and solving for K as a function of ti/2-... 

Figure 6.28. Examples of crystallization isotherms satisfying Avrami s equation (Equation 6.30, with K obtained from Equation 6.31). Curve labels denote ti/2 and n. Changing ti/2 from 100 to 200 seconds at a constant n (3 in this example) results in the simple scaling of the crystallization isotherm along the time axis without any other change in its shape. Decreasing n at a constant ti/2 (100 seconds in this example) broadens the crystallization isotherm so that the induction time (the time lapsed before the onset of appreciable crystallization) becomes shorter but it takes a much longer time for crystallization to approach completion.

In Figure 3.12 typical crystallization isotherms were obtained by plotting a versus the crystallization time for the PEG/PEMA 80/20 blend at different crystallization temperatures. Erom such curves, the half time of crystallization, can be deduced. 

Figure 3.12. Crystallization isotherms for the PEG/PEMA 80/20 blend crystaUized at different T [Cimmino et al., 1989].

Figure 3.14. Comparison between a typical experimental crystallization isotherm (solid line) and the Avrami equation (Eq 3.17, broken line). The three regions 1, II and III correspond to primary, primary and secondary, and secondary crystallization, respectively. [Perez-Cardenas et al., 1991].

The DSC crystallization isotherms of pure iPP, pure PB-1, and blends compared at the same demonstrate that the overall crystallization rate constant progressively decreases with increase in the amount of the diluent component in the sample. 

Figure 7.3 AFM images showing the dependence of supercooling on the morphologies of sPP crystals in blends of sPP/POE (10/90) (a) at 125°C and (b) crystallized isothermally at 120°C for 3 h and taken at 110°C after reheating. AFM images in (a), (c), and (d) were carried out at room temperature after the samples were isothermally crystallized at a present temperature and subsequently cooled to room temperatures.

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