Morphology Formation During Crystallization

It is very important to study the solidification process in the miscible blends considering that the miscibility in the molten state dominantly affects the final morphology. In the actual processing, the solidification process, such as cooling condition and flow field, affects the structure in the solid state and thus the mechanical properties to a great extent. 

The ethylene-a-olefin copolymer chains that are miscible in the molten state also are excluded out from the crystalline region of iPP as described in Section 9.2. Therefore, the applied crystallization condition affects not only the characteristics of crystalline region such as spherulite texture, degree of crystallinity, and the defects in crystals but also the molecular aggregation state of iPP and the copolymers, which will play a central role in controlling the mechanical properties. 

In this part, the effect of crystallization temperature on the morphology is discussed by means of the dynamic mechanical properties (24,64) that are important informations on the characterization of injection-molded products as described in Section 9.4.2 (65). 

The a-relaxation process in the iPP/EHR51 samples is located at higher temperatures than that for the iPP/EHR33, suggesting that blending of EHR51 affects the crystalline structure of iPP, despite the fact that no EHR51 molecules are incorporated into the crystal lattice. Details of a- and jS-relaxation processes are discussed below. 

It is well known (66) that the a-relaxation process of crystalline polymers consists of at least two processes, referred to as ai and U2 in the order of lower temperature, respectively. The ai-process (67-77) is pronounced in melt crystallized samples and is associated with the relaxation of grain boundaries, such as dislocation of lamellae with a frictional resistance related to disordered interface layers. The magnitude of the ai-process increases with the increase in the crystal defects. The o 2-process (71,73,78-83) is pronounced in single crystal mats and is ascribed to incoherent oscillations of the chains about their equilibrium positions in the crystal lattice in which intermolecular potential suffers smearing out. The magnitude of the Q 2-process increases with the increase in the lamellar thickness and/or the degree of crystallization (39). 

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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. 

Mineral Habit. The shape or morphology that single crystals or crystal aggregates take during crystal formation (Veblen and Wylie 1993). Mineral habit is influenced by the environment during crystal formation. Habits of single crystals include prismatic, acicular, platy, and fiber. Habits of crystal aggregates include asbestiform, fibrous, lamellar, and columnar. 

The complex salts usually crystallize as platelets of a size up to 1 X 2 X 0.5 mm. They exhibit a layered structure and a characteristic twinning. Microscopic studies indicate that the morphology of the crystals essentially remains unchanged during polymerization (21). However, occasionally crystals can be found that exhibit a splitting or crack formation subsequent to y-irradiation. The good quality of the crystals of 2 allowed to determine their structure by single crystal x-ray diffraction. The crystal data are listed in Table II. 

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