Interlamellar links

Figure 5-22. Interlamellar links between poly(ethylene) lamellae. Crystallization of mixtures of poly(ethylene) and paraffin wax (after H. D. Keith, F. J. Padden, and R. G. Vadimsky).

When crystallization is carried out from concentrated solution or from the melt, there is a high probability that parts of the same polymer molecule will crystallize into more than one lamella. Such interlamellar links (see Figure 5-18) were first shown to occur by jointly crystallizing poly(ethylene) with paraffin mixtures and subsequently dissolving the paraffins away (Figure 5-22). The number of interlamellar links increases with increasing molecular weight because the probability that parts of... 

Hase and Geil [219, 220] utilizing swelling techniques showed the presence of interlamellar fibrils between separated lamellae. The shape and density of interlamellar links were also revealed by electron microscopy of these preswollen samples. The density and thickness of the links were independent of crystallization temperature. These authors also indicated that swelling occurred heterogeneously in the interlamellar regions with only a small number of interlamellar links. 

Interlamellar connections are cmcial to the mechanical properties of polyethylene because they transmit forces between crystallites. Tie chains determine or influence a variety of mechanical properties, such as ductility, toughness, and modulus. Without the benefit of interlamellar links, polyethylene would be a brittle material with little physical strength. 

Mechanical properties, such as elastic modulus and yield point, that depend on crystallinity per se are not seriously affected by low to moderate doses of ionizing radiation. On the other hand, those mechanical properties that are sensitive to interlamellar activity are most dramatically affected by the low to moderate radiation doses. This is seen in the ultimate tensile strength and elongation at failure of the polyolefins. It is also reflected in the large change in melt index between 0 and 18 Mrad, which indicates formation of cross-links that increase with increasing... 

The hydration water in the interlamellar space is acidic and, therefore, able to work as an acid catalyst. The nature of the acid sites is discussed with respect to the origin of the lattice charge (tetrahedral or octahedral). The mechanism of cross-linking smectites with oligomeric inorganic cations shed light on the reactivity of the basal planes as well. 

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