Polyethylene spherulite growth rates

Armistead JP, Hoffman JD (2002) Direct evidence of regimes I, II, and III in linear polyethylene fractions as revealed by spherulite growth rates. Macromolecules 35(10) 3895-3913 Armstrong SR, Offord GT, Paul DR, Freeman BD, Hiltner A, Baer E (2014) Co-extruded polymeric films for gas separation membranes. J Appl Polym Sci 131(2) 39765 Azzurri F, Alfonso GC (2008) Insights into formation and relaxation of shear-induced nucleation precursors in isotactic polystyrene. Macromolecules 41(4) 1377-1383 Baekeland LH (1909) Method of making insoluble products of phenol and formaldehyde. US Patent 942,699... 

The spherulite growth rates of linear polyethylene fractions have been studied in detail.(167,171) The data obtained have been used extensively in arguments and discussions as to whether or not Regimes I and II exist, and, if they do, whether the transition from one to the other is sharp or diffuse.(178a-e,188) Detailed analysis... 

Fig. 9.49 Fit of experimental spherulite growth rate data ( ) to theoretical plot of a linear polyethylene fraction M = 133000. (Data from Labaig (171))...

Fig. 9.97 Log-log plot of spherulite growth rate, G, against weight average molecular weight, Mw, for linear polyethylene fractions at indicated crystallization temperatures. Data from Labaig (171) o, A data from Hoffman et al. (167,337).

Spherulite growth rates of blends of linear polyethylene, M = 66000/M = 2500, plotted as a function of the crystallization temperature for different... 

In another example, the spherulite growth rates of a similar type ethylene-butene copolymer and of a low molecular weight fraction of linear polyethylene (M = 2500) are very close to one another over a range of crystallization temperatures.(53)... 

Fig. 11.35 (a) Spherulite growth rate of isotactic poly(propylene) in blends with low density polyethylene as a function of composition at indicated crystallization temperature. (From Galeski et al (84)) (b) Spherulite growth rate of poly(ethylene oxide) in blends with poly( vinyl chloride) as a function of composition at indicated crystallization temperatures. (From Martenette and Brown (85))... 

Besides the changes in crystallinity, the crosslinks change also the morphology of low density polyethylene [169], The diameter of spherulites and the sheaf-shaped superstructure decreases with an increasing network. This result can be referred to as a decreased crystal growth rate related to an increase in the mdt viscosity owing to an increasing network density. 

The crystallisation from strained melt as for instance in a blown film or in the jet during fibre spinning produces a row nucleated structure. " Linear nuclei are formed parallel to the strain direction. They contain more or less extended polymer chains. Secondary epitaxial nucleation on the surface of such linear row nuclei produces folded chain lamellae which are oriented perpendicular to the strain (Fig. 6). In such a case the sample exhibits a high uniaxial orientation of chain axes in the strain direction with random orientation of the a- and b-axes perpendicular to it. If the growing lamellae exhibit a helical twist the chain orientation in the strain direction is very soon replaced by the orientation of the axis of maximum growth rate (b-axis in the case of polyethylene) perpendicular to the strain direction and a more random orientation of the remaining two axes (a- and c-axes in the case of polyethylene) with a maximum in the strain direction. Such a row nucleated structure has parallel cylindrical spherulites (cylindrites) as its basic supercrystalline element. 

Galeski A. Pracella M. Martuscelh E. Polypropylene spherulite morphology and growth rate changes in blends with low density polyethylene. Journal of Polymer Science. PartB. Polymer Physics. 1984, 22, 739-747. 

Figure 43 is a typical example of a dilatometrically determined crystallization rate for polyethylene, from which all the principle features of the primary crystallization process (spherulitic growth to its termination) can be deduced (246). 

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