Crystallinity lamellae

Pig. 1. Interpenetrating network morphology of thermoplastic elastomer where A = the crystalline domain, B = the junction of crystalline lamellae, and... 

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... 

Another type of fibril substructure in PET fibers, besides the microfibrillar type already discussed, is the lamellar substructure, also referred to as the lateral substructure. The basic structural unit of this kind of substructure is the crystalline lamella. Formation of crystalline lamellae is a result of lateral adjustment of crystalline blocks occurring in neighboring microfibrils on the same level. Particular lamellae are placed laterally in relation to the axis of the fibrils, which explains the name—lateral substructure. The principle of the lamellar substructure is shown in Fig. 2. 

Figure 2 The lamellar substructure of a fibril. (a) Reciprocal positions of crystalline lamellae as a result of fiber annealing. (b) The situation after relaxation of stress affecting TTM. ai.2 - average angle of orientation of TTM CL - crystalline lamellae CB - crystalline blocks (crystallites) mF -border of microfibrils and F - fibril. In order to simplify it was assumed that (1) there are the taut tie molecules (TTM) only in the separating layers, (2) the axis of the fibril is parallel to the fiber axis.

Structurally, plastomers straddle the property range between elastomers and plastics. Plastomers inherently contain some level of crystallinity due to the predominant monomer in a crystalline sequence within the polymer chains. The most common type of this residual crystallinity is ethylene (for ethylene-predominant plastomers or E-plastomers) or isotactic propylene in meso (or m) sequences (for propylene-predominant plastomers or P-plastomers). Uninterrupted sequences of these monomers crystallize into periodic strucmres, which form crystalline lamellae. Plastomers contain in addition at least one monomer, which interrupts this sequencing of crystalline mers. This may be a monomer too large to fit into the crystal lattice. An example is the incorporation of 1-octene into a polyethylene chain. The residual hexyl side chain provides a site for the dislocation of the periodic structure required for crystals to be formed. Another example would be the incorporation of a stereo error in the insertion of propylene. Thus, a propylene insertion with an r dyad leads similarly to a dislocation in the periodic structure required for the formation of an iPP crystal. In uniformly back-mixed polymerization processes, with a single discrete polymerization catalyst, the incorporation of these intermptions is statistical and controlled by the kinetics of the polymerization process. These statistics are known as reactivity ratios. 

Many polymers solidify into a semi-crystalline morphology. Their crystallization process, driven by thermodynamic forces, is hindered due to entanglements of the macromolecules, and the crystallization kinetics is restricted by the polymer s molecular diffusion. Therefore, crystalline lamellae and amorphous regions coexist in semi-crystalline polymers. The formation of crystals during the crystallization process results in a decrease of molecular mobility, since the crystalline regions act as crosslinks which connect the molecules into a sample spanning network. 

Figure 1 Semi-crystalline lamellae. Crystalline, interfacial and liquid-like (amorphous) regions are indicated.

For instance, crystalline lamellae in an amorphous matrix (semicrystalline polymer materials), hard domains in a soft matrix (thermoplastic elastomers)... 

Frequently at least one of the phases forms particles (e.g., crystalline lamellae). The shape and position of the ith particle from the irradiated volume is described by a shape function Yi (r). It is obvious that the scattering intensity of an ideal multiphase system can be expressed in terms of autocorrelations Y 2 (r) and cross-correlations of the shape functions and the average electron densities of each phase (cf. Sect. 2.5). 

The development of order in each layer is actually the growth of crystalline lamellae. We show in Fig. 22 a typical snapshot of the system of 640 chains of Cioo (64 000 atoms) at 12.8 ns after quenching from 600 K down to 350 K. It is clearly noticed that the stacked lamellae grow from both side substrates. For further analysis of the data we need to extract crystalline regions. In order to... 

Fig. 27 Shape of crystalline domains at 330 K after 6.4 ns (grey spheres). The crystalline lamellae are found to have rather flat 100 surfaces. Also shown are newly added stems (black spheres) during the next 0.128 ns of simulation. The addition of the stems starts preferentially at kink sites... 

Some of the chains, when in contact with the shish, will stretch almost completely. However, these highly stretched chains are not dominant compared to the highly folded bundles that form crystalline kebabs around the shish. Also, none of the highly stretched chains formed a structure with part of it stretched and attached to the shish and part of it in folded crystalline lamella. The formation of kebabs in these simulations is clearly growth of lamellae, nucleated on the shish. 

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... 

Homogeneous melt, Todt < Tc > Tg. In diblock copolymers exhibiting homogeneous melts, microphase separation is driven by crystallization if Tg of the amorphous block is lower than Tc of the crystallizable block. This generally results in a lamellar morphology where crystalline lamellae are sandwiched by the amorphous block layers and spherulite formation can be observed depending on the composition [6-10]. 

Maltese cross (Blanshard, 1979). The crystallinity of starch is caused essentially by amylopectin pol)Tner interactions (Banks and Greenwood, 1975 Biliaderis, 1998 Donald, 2004 Hizukuri, 1996). An illustration of currently accepted starch granule structure is given in Fig. 5.5. It is believed that the outer branches of amylopectin molecules interact to arrange themselves into "crystallites" forming crystalline lamellae within the granule (Fig. 5.5 Tester et al., 2004). A small number of amylose polymers may also interact with amylopectin crystallites. This hypothetical structure has been derived based on the cluster model of amylopectin (Hizukuri, 1986 Robin et ah, 1974 Fig. 5.1). 

Most polymers consist of a combination of crystalline and amorphous regions. Even within polymer crystals such as spherulites (Figures 2.15 through 2.17), the regions between the ordered folded crystalline lamellae are less ordered, approximating amorphous regions. 

Figure 4.3 The building block structure of potato amylopectin clusters. Branched building blocks (encircled) are mainly found inside amorphous lamellae (A) of semi-crystalline rings in starch granules. Double helices (symbolized as cylinders) extend from the building blocks into the crystalline lamellae (C). Enlargements of a double helix segment, in which the single strands are parallel and left-handed, and a building block are shown to the right.

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