Lamellae stacks

A study of the lamella stack in two dimensions was made by one of the authors and Lock51). In this model rectangular elements of two different materials are stacked along the axis of loading and the overall modulus calculated. For completeness the otter moduli should be calculated but this was not done. 

Sample PTEOX-83P, on the other hand, shows a ring-like WAXS pattern (Figure 6C). The reason for the absence of discrete scattering may possibly be attributed to the Isotropic structure of lamella stacking. The amorphous halos in all of the PTEOX samples may be due to the amorphous regions between the lamellae of folded chain crystals. 

The amorphous component of the crystalline polymer solid contains beyond the amorphous component of single crystals, i.e. crystal defects (linear vacancies, kinks, and interstitials), chain folds and free chain ends, as new elements the rejected non-crystallisable impurities and tie molecules. The former concentrate on the outer boundaries of lamella stacks and spherulites, the latter in the amorphous layers separating the lamellae of the same stack. With the exception of impurities all other components of the amorphous phase are intimately connected with the crystals and cannot be physically separated from them or moved independently of them. 

Crystals Grown from the Melt and Lamellae Stacks... 

When a PP is extruded and taken-up at a high draw ratio and crystallized under a high stress and annealed, a lamella-stacked structure is formed. In this structure, the lamellae are oriented perpendicular to the extrusion direction and connected by the tie molecules. When such an extrudate is stretched in the extrusion direction, the lamellae open elastically with the tie molecules working as fixing points. Therefore, after stress removal, the initial shape and structure are restored. Since such a part shows a high elastic recovery after a deformation and the elastic modulus is nearly the same as that of the usually processed article, it is called a Tiard-elastic item. When the hard-elastic film or fiber is drawn beyond the yielding point, plastic deformation occurs, leading to void formation, and a microporous film or fiber can be obtained. 

On the macrocrystalline level in linear polyethylene, typical, closely arranged, sphere-shaped crystalline areas, the so-called spherulites, can be observed in the crystalline phase with a size of about up to 10 pm (Fig. 2.4). The lamellae are arranged into longish lamella stacks, which are directed outwards from the centre of the spherulite. The b-axis along the greater longitudinal dimension of the lamellae points in the direction of the spherulite radius, while the a-axis of the lamellae in the stacks, being perpendicular to the radius, rotates. Thus the stacks create outward directed spirals (fibrils) (Fig. 2.4). 

The lamella stacks, which grow during spherulite formation, may break and branch out, new lamella stacks may emerge or grow together with others. The ball-shaped spherulite is filled with such crystalline fragments. 

CRYSTALS GROWN FROM THE MELT AND THE CRYSTAL LAMELLA STACK... 

Small-angle X-ray diffraction provides information about the period of the lamella stacking in semicrystalline polymers and about the layer thickness of smectic liquid-crystalline polymers. The azimuthal angle dependence of the small-angle pattern provides information about the orientation of these superstructures (Fig. 9.12). 

There are three, currently recognized, principal modes of deformation of the amorphous material in semicrystalline polymers interlamellar slip, interlamellm-separation and lamellae stack rotation [84,85]. Interlamellar slip involves shem-of the lamellae parallel to each other with the amorphous phase undergoing shear. It is a relatively easy mechanism of deformation for the material above Tg. The elastic part of the deformation can be almost entirely attributed to the reversible interlamellar slip. 

Figures.16 shows the variation of the nanoscopic strain during load-cycling. By its definition e measures the deformation of well-correlated lamellae stacks. The difference between s and indicates a heterogeneous strain distribution in the sample. Adding MMT to the polypropylene matrix (PP+MMT) enhances strain-heterogeneity (lower values of ). The nanocomposite samples show higher ...

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