Lamellae polyethylene films

We analyzed the ICB-deposited polyethylene films using JEM-200CX transmission electron microscope. The results show that these thin films were uniform and a mixture of crystalline and noncrystalline phases. The crystalline phase area appears rhombic. Ihe size of the crystalline lamellae is 2-20 mm. The electron diffraction pattern of the crystalline phase appears as an ordered array of spots (Fig. 5a shows a TEM micrograph and Fig. 5b an electron diffraction pattern). The chemical elements of these samples are analyzed with LEED-AES (Parkin-Elmer... 

Fig. 5.22 Direct imaging of lamellae is shown in this enlarged SEM micrograph of a blown polyethylene film surface. The arrow shows a single lamella. (From Tagawa and Ogura [128] reproduced with permission.)...

Seguela, R. (2007). On the natural draw ratio of semi-crystalline polymers Review of the mechanical, physical and molecular aspects. Macromol. Mater. Eng. 292, 235-244 Tagawa, T. Ogura, K. (1980), Piled-lamellae structure in polyethylene film and its deformation. J. Polym. Sci. Polym. Phys., 18,5,971-979 Ward, I.M., Sweeney, J. (2004) An Introduction to The Mechanical Properties of Solid Polymers. Wiley, IBSN 047-149626X, New York. 

D. Xu, Y. Song, X. Shi, P. Tang, M. Matsuo, Y. Bin, Temperature dependence of lamellae orientation of a branched low molecular weight polyethylene/ultrahigh molecular weight polyethylene blend film under a controlled temperature gradient Polymer 54, 4037-4044 (2013)... 

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. 

Fig. 11.14 TEM micrograph of polyethylene thin film with a particle of CaCOa (seen as a continuous black region in the left-hand side). Crystalline lamellae seen as black ribbons when oriented edge on against interface (From Chacko et al. (1982) reproduced with permission of Wiley)...

Early experiments on solution-grown lamellae revealed not only the earlier melting of the 100 sectors in polyethylene lamellae (25) [which Atomic Force Microscopy (AFM) has confirmed (33) to be thinner than 110 sectors in collapsed, and presumably as-grown, crystals] but also the presence of holes (43) in lamellae that had been heated in contact with a carbon film (Fig. 2). While providing clear evidence of lamellar thickening, the presence of holes is a response to the carbon film, which restrains lateral contraction holes do not appear on thickened upper layers of the same sample that are not so restrained. 

The random arrangement of adjacent crystals in the fringed-micelle model (see Fig. 2.4), does not accord with evidence obtained from microscopy. The electron microscope shows the crystals in polyethylene to be very thin twisted lamellae laid one upon another (Fig. 1.7). The lamellae are too small to be observed with the light microscope. Light microscopic examination of thin films or sections between crossed polarizers reveals complex polyhedral objects known as spherulites (see Fig. 2.5). They are in fact a complex ordered aggregation of the sub-microscopic crystals. In polyethylene the crystal lamellae are about 10 nm thick. They are separated one from another by thin lamellae of amorphous polymer of about the same thickness. The lateral... 

The optical observations cannot resolve the crystalline-amorphous structure. Observation of single crystallites requires methods which provide an analysis in the 10-nm range. Electron microscopy is particularly suited for this purpose. Figure 4.4 shows as an example the surface of a partially crystalline polyethylene, as it becomes reproduced in the electron microscope when using a carbon film replica technique. The picture of the surface resembles a landscape with many terrasses. These obviously result from cuts through stacks of laterally extended, slighty curved lamellae whiqh have thicknesses in the order of 10 nm. 

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