Polyethylene crystallization half-time

The above observations are similar to those obtained for peroxide-crosslinked polyethylene. An addition of filler, such as silica, results in an increased crystallization rate and a decrease in the crystallization half-time, ti/2. ... 

Fig. 11.23 (a) Plot of crystallization half-time, ti/2, against percent M = 9000 for binary blends of linear polyethylene molecular weight fractions. Pure components M = 9000and370000.Crystallizationtemperature 130°C Ol29°C Dl27°C. (b) Plot of crystallization half-time, ti/2, against percent M = 26000 for binary blends of linear polyethylene. Pure components M = 26000 and 3.8 x 10 . Crystallization temperature 130°C o 128 °C. (From Ohno (37))... 

Fig. 11.41 Plot of crystallization half-time for crystallization of poly(phenylene sulfide) in blends with linear polyethylene and with poly(ethylene terephthalate) as a function of crystallization temperature. Pure poly(phenylene sulfide) . Composition poly(phenylene sulflde)-linear polyethylene blends 50/50 A 75/25 o 90/10. Composition poly(phenylene sulfide)-poly(ethylene terephthalate) blends 50/50 T 75/25 A 90/10. (From Jog et al. (81))...

The overall crystallization kinetics of an unfractionated linear polyethylene, cross-linked by a peroxide reaction has also been studied. (95,96) A special feature of this work was the study of the separated sol and gel portions at different levels of cross-linking. The overall crystallization rates, in terms of the reciprocal of the half-time, l/ti/2, are plotted against the crystallization temperamre in Figs. 10.41 and 10.42 for a set of sol and gel fractions respectively. The gel fractions are characterized by the molecular weight between cross-links. Me, assuming ideal network formation. The sol portions are defined by their number average molecular... 

Fig. 10.41 Plot of reciprocal half-time as a function of crystallization temperature for sol fraction of cross-linked linear polyethylene. Number average molecular weight, Afni o original non-cross-linked polymer 7106 7077 6422 A 4561 A 5634 o 4150. (From Phillips and Lambert (95))...

Fig. 10.42 Plot of reciprocal of half-time against crystallization temperature for the crystallization of the gel portion of cross-linked linear polyethylene. Molecular weight between cross-links. Me x 10 o original polymer 12.7 9.4 A 5.7 A 4.5 O 3.6 3.1 i2.2 11.9 6 1.3 0.96 V 0.56. (From Lambert etal (96))...

Figure 11.20 Variation of the inverse of the half-ciystalhzation time (l/f5o%) as a funetion of the crystallization temperature for the polyethylene component within the studied blends and for the neat polyethylene copolymers as a function of the crystallization temperature (T ) see Table 11.7. Adapted from Cordova et al. [69].

Here r denotes some characteristic time of the crystallization process, for example, that at which half of the final crystallinity is reached. The exponential change of r with temperature tells that, as in the nucleation step, crystal growth is associated with an activation barrier. For polyethylene, where t changes by a decade within 4 K, this barrier is lower and more temperature sensitive than in s-polypropylene, where a shift in the crystallization temperature of 15 K is necessary for a comparable change. There are different views in the literature about the nature of this barrier one possible explanation is given later in Sect. 5.3.1. 

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