Lamellar texture

We understand now why fluorescence contains the term fluor, but what is the origin of fluorspar or fluorspath and why are these materials fluorescent Spar (in English) and spath (in German) were the names given in the eighteenth century8 to stones that are more or less transparent and crystallized with a lamellar texture. Because these materials can be easily melted, and some of them can help to melt... 

Texture and structure are not explicitly defined terms. Structure is usually applied to macroscopic heterogeneity due to macroscopic movement such as flow structure or foliated structure, whereas texture usually refers to microscopic heterogeneity, such as holocrystalline texture, porphyritic texture, and lamellar texture due to exsolution. 

Fig. 5.31 Schematic illustration of the morphology formed by blends and copolymers of two crystallizable polymers (Nojima et al. 19926) (a) a PEG/PCL blend, (b) a PCL-PEG-PCL triblock. In the blend, PEG and PCL are phase-separated into domains in which each homopolymer crystallizes in a lamellar texture. In the copolymer, PEG and PCL blocks cyrstallize in the same domain due to chain connectivity.

Morphological explanations for the improved ductility of the fl nucleated materials have focussed on the lamellar texture. That crazes in a iPP are more localised and better defined than in /3 iPP may reflect both the influence of the cross-hatched structure on lamellar slip described in the previous section, and the strong correlation between deformation in ft iPP and the local orientation of the lamellae with respect to the tensile axis. Indeed, the trend towards more localised deformation in a spherulites may simply reflect the relatively homogeneous lamellar textures of these latter [24]. 

Fig. 1 The differing optical textures, between crossed polars, of linear polyethylene after crystallization from the melt at pressures close to the triple point, 0.3 GPa (a) the conventional spherulitic texture of the orthorhombic phase (b) the coarse lamellar texture formed as the hexagonal phase then transformed to orthorhombic during return to ambient temperature and pressure from [ 14]...

Fig. 14.—Polymer Single Crystal from Esparto-grass Xylan. (Screw dislocations and lamellar texture are typical of these crystals, which contain folded polymer-chains. The insert shows the schematic diagram of the electron diffractogram that corresponds to the dry crystal form (see Section V,l, p. 460), and confirms that the molecular axis is normal to the lamellar plane).

Polymers can exhibit a hierarchical organization of structure at four successive levels, the molecular, nano-, micro-, and macrolevel [33, 34], On the scale of tens of microns, semicrystalline polymers contain spherulites, the spherulites have a lamellar texture, and the molecules within the lamellae are organized in crystals and amorphous domains. Amorphous polymers are structured on the molecular and macroscopic scale only [34]. Thermoplastic SMPs are usually phase-segregated materials, i.e., they consist of at least two different domains, which are related to different thermal transition temperatures (Tinms)- Therein hard domains have a TJrans (glass transition temperature Tg or melting temperature 7]n) usually much higher than room temperature and determine the permanent shape, while switching domains show a lower thermal transition (Tg or 7]n). SMP networks contain chemical crosslinks instead of hard domains to fix the permanent shape. 

Spherulitic superstructures were formed at low shear strains and an oriented, row-nucleated stacked lamellar texture developed with increasing shear strain. At higher recoverable shear strain values, a fine surface roughness developed due to high melt elastic instabilities. 

The morphologies of both ABA and ANA homopolymers and 73/27 ABA/ANA copol5nner prepared by thin-film polymerization show that crystallization occurs in the homopolymerization systems and the liquid crystal state remains stable in the copolymerization system (39-44), clearly indicating that the random copolymerization is an effective way to retard the crystallization. Transmission electron microscopy revealed that the microstructures of homopol5nners of ABA and ANA had more obvious lamellar texture (41-44). 

Permanganic etching, on the other hand, is able to reveal lamellar textures well in all polyolefines plus a munber of other polymers including aromatic... 

Fig. 6. Lamellar texture of a developing spherulite of linear low density polyethylene grown at 124°C. From Ref 82.

Fig. 7. (a) Banded spherulites of poly(trimethylene glutarate) viewed between crossed polars in a polarizing microscope. From Ref 118.. (b) lamellar texture in a banded spherulite of butyl-branched linear low density polyethylene crystallized at 124°C. From Ref. 119. 

It was realized by Takayanagi [17] that oriented highly erystalline polymers with a clear lamellar texture might be modelled in terms of a two-eomponent composite... 

Fig. 1.5 Schematic of cold drawing process with transformation of the lamellar texture into a microfibrillar structure. (From Peterlin [24] used with permission.)...

Staining permits TEM observation of the dispersed phases in multiphase blends. Osmium tetroxide is the most commonly used stain for this application, while other stains have more limited application. Detailed fine structure of polymers is also made visible by staining. For example, chlorosulfonic acid staining enhances the lamellar texture of PE [105]. There are cases where a stain has been associated with a specific functional group of polymers. A specific stain for nylon, developed by Reimschuessel and Prevor-sek [106], showed the sizes of the macrofibrils and microfibrils of nylon. Fibers were immersed in 10% aqueous solution of SnCl2 for 10 min at 100°C, rinsed, placed in NH4OH solution to convert the tin chloride to insoluble SnO and then embedded for ultrathin sectioning. 

Chlorosulfonic acid was used to show the lamellar structure in both linear and branched PE and to study the effects of drawing and annealing [122, 136, 137]. Dlugosz et al [138] examined cryosections of drawn, rolled and annealed, bulk oriented PE which clearly showed a lamellar texture. Lamellae were shown to have two preferred orientations and to be arranged in... 

The stained lamellar texture is shown (Fig. 4.15) to result from the chlorosulfonation of linear PE crystallized isothermally from the melt [105]. Although large parts of the section show no detail, some regions do contain the parallel dark lines shown in this figure. These lines are a few hundred Angstroms apart, and they appear and... 

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