Crystalline spherulite

Surface profllometry showed that the average thickness of the CaCOj films was 1 pm. Optical microscopy, FT-IR and SEM all demonstrated that the films were amorphous with few embedded crystalline spherulites. Upon standing, the film... 

By adequately varying the catalyst content, the temperature, time and the rate of crystallization, materials with a wide range of crystallinities, spherulitic morphologies, different crystal thickness and various levels of crystal distortions have been prepared. The influence of these structural parameters on the microhardness and the detection of specific changes after controlled crystallization are of special interest. 

Dextran forms crystalline, spherulitic complexes with Ca " ", Ba, and La, but not with Mg " and Na. The optical rotation of dextran in aqueous solution is considerably increased by the addition of La and Ba, but only slightly by Ca, Mg, and Na" " acetates. Complex-formation appears to ter the conformation of the polymer chain. A 20% solution of dextran will dissolve — 5% of Fe this solution is used for the treatment of anemia. ... 

Figure 7. Secondary growth of liquid crystalline spherulites in a film of human atheroma lipoid mesophase...

Recent advances in catalysis have allowed the production of polyolefins with low crystallinity. Spherulitic structures (see next section) only occur in propylene-ethylene copolymers when the crystallinity exceeds 45% (Fig. 3.22). Sheaf-like structures occur when the crystallinity is between 30 and 45%, whereas axialites and isolated lamellae occur between 15 and 30% crystallinity. Axialites are multi-layer aggregates of lamellar crystals which splay out from a common edge. Embryonic axialites occur for crystallinity from 5 to 15%. Therefore, as the crystallinity is reduced, the microstructures become simpler. 

The properties of PLA, as indeed those of other polymers, depend on its molecular characteristics, as well as on the presence of ordered structures, such as crystalline thickness, crystallinity, spherulite size, morphology and degree of chain orientation. The physical properties of polylactide are related to the enantiomeric purity of the lactic acid stereo-copolymers. Homo-PLA is a linear macromolecule with a molecular architecture that is determined by its stereochemical composition. PLA can be produced in a totally amorphous or with up to 40 per cent crystalline. PLA resins containing more than 93 per cent of L-lactic acid are semi-crystalline, but, when it contains 50-93 per cent of it, it is entirely amorphous. Both meso- and D-lactides induce twists in the very regular PLLA architecture. Macromolecular imperfections are responsible for the decrease in both the rate and the extent of PLLA crystallization. In practise, most PLAs are made up of L-and D,L-lactide copolymers, since the reaction media often contain some meso-lactide iir turities. 

Figure 2.11 Crystalline spherulite form of polypropylene under polarizing microscope [21].

Polymers possess condensed state mainly referred to as crystalline state, and the crystalline spherulite form is shown in Figure 2.11. The condensed state can be divided into four phases, namely, no fixed shape, the transition state, liquid crystalline state, and crystalline state. Due to the complex formation process and peculiar phenomenon, transition state and liquid crystalline state have attracted much attention. The crystalline state is interesting mainly due to its multicrystalline form. 

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