Lamellae radially growing

Spherulites consist of crystal lamellae of about 10-20 nm in thickness and a lateral range of some micrometers. In PP, the spherulites show a cross-hatched lamellae structure [4] with radial lamellae as well as tangential lamellae, which grow up on the radial lamellae ( homo-epitacticity ). 

In Fig. 2.9b, the specimen was crystallized at 120 °C, so that there is a preponderance of cross-hatching lamellae located roughly perpendicular to the dominant radially growing ones. This reverses the birefringence, giving positive spherulites... 

Figure 3.64 Schematic of a radially growing lamella that experiences instabilities of the growth faces at width W = The new lamellae grow with a splay of AO that can be in either direction. The instability and splitting recur when the new lamellae grow to W = Am again. From Kajioka et al. [97] with permission of Elsevier.

The volume inside the semicrystalline polymers can be divided between the crystallized and amorphous parts of the polymer. The crystalline part usually forms a complicated network in the matrix of the amorphous polymer. A visualization of a single-polymer crystallite done [111] by the Atomic Force Microscopy (AFM) is shown in Fig. 9. The most common morphology observable in the semicrystalline polymer is that of a spherulitic microstructure [112], where the crystalline lamellae grows more or less radially from the central nucleus in all directions. The different crystal lamellae can nucleate separately... 

The granule grows radially from the hilum in alternating amorphous and semi-crystalline rings, forming a lamellar structure [10, 19, 20]. The idealized model describes the crystalline and the amorphous amylopectin lamellae in terms of effectively spherical blocklets, whose diameter ranges from 20 to 500 nm [21]. 

Spherulite radial growth continues at a constant rate, even after other portions of the spherulite have impinged with its neighbors — indicating that lamellae within a given spherulite grow independently... 

If G is constant, then the rate of volume increase is proportional to the surface area of the growing sphere, a reasonable conclusion since growth occurs at this developing surface. This assumption requires that the radial lamellae branch at a rate sufficient to maintain density and that the degree of crystallinity is constant throughout the spherulite. This infers... 

The role chitin as a material of highly ordered crystalline structure has been reported in the study [96]. X-ray diffraction analysis was carried out in order to find the changes of the crystalline structure upon the substitution reaction with NCO terminated prepolymer. The X-ray diffraction studies showed that crystallinity mainly depends on the concentration of chitin in the polyurethane backbone, crystallinity increased as the concentration of chitin into the final PU increased (Fig. 3.22). The crystallinity of some polymers was clearly observed by optical microscopic studies [114]. The results of X-ray diffraction experiments correlate with optical microscopy findings. A crystalline polymer is distinguished from an amorphous polymer by the presence of sharp X-ray Unes superimposed on an amorphous halo. Under an optical microscope, the presence of polycrystalline aggregates appear as spherulites [114]. The spheruhtes are made of small crystallites and grow Irom a nucleus at their centre. They consist of narrow chain folded lamellae growing radially. Since the fibrous crystals are radial, the chains folded with the lamellae are circumferentially oriented. From the evaluation of the X-ray and optical microscopic studies, it has been observed that the involvement of chitin in the PU formulation and have improved crystallinity of the final polyurethane. 

Electron microscopy on thin films [2-5] led to Peterlin s sphemlite model [6] consisting of a sheaf-shaped nucleus growing under radial-symmetric formation of lamellar stmctures. Within the lamellae Kanig [7] found inclination of chain-segments using a special contrasting procedure. 

Figure 37 Polarized light image of a banded spherulite of PIT. The inset shows schematics of twisted crystalline lamellae growing radially from the spherulite center. " The inset adapted with permission from Barham PJ, Keller A. J Mater Sci 1977,12,2141. Copyright Kluwer Academic/Plenum Publishers.

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