Interlamellar ties

The formation of the microstructure involves the folding of linear segments of polymer chains in an orderly manner to form a crystalline lamellae, which tends to organize into a spherulite structure. The SCB hinder the formation of spherulite. However, the volume of spherulite/axialites increases if the branched segments participate in their formation [59]. Heterogeneity due to MW and SCB leads to segregation of PE molecules on solidification [59-65], The low MW species are accumulated in the peripheral parts of the spherulite/axialites [63]. The low-MW segregated material is brittle due to a low concentration of interlamellar tie chains [65] and... 

These results demonstrate that the embrittlement of the PE implants accompanies a microhardening of a surface layer and an increase in crystallinity. The two pieces of evidence are complementary and imply a reduction in the crack-blunting ability of the material, i.e. a diminution of the number of interlamellar tie molecules which connect adjacent lamellar stacks. In consequence the elastic properties of the material diminish and cause the material to microharden during wear. The increase in microhardness at the wear surface is partly because the amorphous component decreases in quantity and partly because its chemical nature changes as it undergoes simultaneous microhardening and loss of elasticity. 

Fig. 4. Molecular model of a stack of parallel lamellae of the spherulitic structure A, interlamellar tie molecule B, boundary layer between two mosaic blocks C, chain end in the amorphous surface layer (c ilium) D, thickness of the crystalline core of the lamella E, linear vacancy caused by the chain end in the crystal lattice L. long period I, thickness of the amorphous layer (Peterlir ).

The concentration of interlamellar tie chains in a given sample depends on molar mass, which determines the spatial distribution of the chains, and long period, i.e. the sum of crystal and amorphous layer thicknesses. Figure 7.33 shows two very... 

The number of interlamellar tie chains must be sufficiently high to prevent early brittle fracture. 

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