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Spherulitic Morphology (spherulitic + morphology)

Distribution by Scientific Domains

Polymers and Materials Science	80%

Selected Abstracts

Polymer Morphology: A Guide to Macromolecular Self-Organization

MACROMOLECULAR SYMPOSIA, Issue 1 2004
D.C. Bassett
Abstract The study of polymer morphology continues to be the principal means of acquiring knowledge and understanding of macromolecular self-organization. Longstanding problems of the nature of melt-crystallized lamellae and spherulitic growth have been resolved, bringing understanding of how characteristic properties such as a broad melting range and spatially-varying mechanical response are inherent in spherulitic morphologies. This reflects the distinctive features of the crystallization of long molecules, i.e. that they impede each other and, for faster growth, form rough basal surfaces. Knowledge of morphology is an essential accompaniment to the informed development of advanced polymeric materials and a full understanding of their structure/property relations. [source]

Rotationally molded polyethylene: Structural characterization by x-ray and microhardness measurements

ADVANCES IN POLYMER TECHNOLOGY, Issue 2 2001
Maria Clara Cramez
Rotationally molded polyethylene (PE) blended in two ways (turbo blending and extrusion) with nucleating and nonnucleating pigments is structurally characterized by wide- and small-angle x-ray scattering (WAXS and SAXS, respectively), DSC and microhardness measurements. Morphological observations are performed by polarized light microscopy. The melting temperature and the degree of crystallinity (from both DSC and WAXS) remain essentially constant regardless of sample preparation and type of pigment. The same holds for the crystal sizes from WAXS and the lamella thickness from SAXS. Only the values of microhardness depend on the type of pigment, increasing about 10% when a nucleating type is used. The almost constant values of these properties, contrasting to the spherulitic morphology, are explained by the fact that the processing conditions in rotational molding are very favorable for crystallization. As a consequence, optimal crystalline structure is achieved, which masks significantly the effect of pigments and blending conditions on the crystallization behavior of polyethylene. © 2001 John Wiley & Sons, Inc. Adv Polym Techn 20: 116,124, 2001 [source]

Crystalline morphology and dynamical crystallization of antibacterial ,-polypropylene composite

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008
Xin Chen
Abstract The crystalline morphology and dynamical crystallization of antibacterial polypropylene composite and pure polypropylene were investigated via differential scanning calorimeter (DSC), wide angle X-ray diffraction (WAXD), and real-time hot-stage optical microscopy (OM). The results reveal that the crystalline morphology of antibacterial PP composites changes with variations of the crystallization conditions and compositions. The crystalline phase consists of both ,-PP and ,-PP crystals. The content of ,-PP decreases with the increase in antibacterial agent content and cooling rate. With the addition of ,-nucleating agent, the morphologies of all dynamically crystallized antibacterial PP composites show no obvious spherulitic morphology, and the decrease of crystal perfection and the increase of nucleation density of antibacterial PP composite system could be observed. With the increase of antibacterial agent content, the overall crystallization rates of the antibacterial PP composite increase dramatically, while the content of ,-PP in all antibacterial PP composite decrease distinctly under given cooling conditions. These results can be explained by the interruptive effect of antibacterial agent on interactions of ,-nucleating agent components and the obstructing effect of antibacterial agent on the mobility of PP chains in melts. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Synthesis, crystallization, and morphology of star-shaped poly(,-caprolactone)

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2005
Jing-Liang Wang
Abstract Six-arm star-shaped poly(,-caprolactone) (sPCL) was successfully synthesized via the ring-opening polymerization of ,-caprolactone with a commercial dipentaerythritol as the initiator and stannous octoate (SnOct2) as the catalyst in bulk at 120 °C. The effects of the molar ratios of both the monomer to the initiator and the monomer to the catalyst on the molecular weight of the polymer were investigated in detail. The molecular weight of the polymer linearly increased with the molar ratio of the monomer to the initiator, and the molecular weight distribution was very low (weight-average molecular weight/number-average molecular weight = 1.05,1.24). However, the molar ratio of the monomer to the catalyst had no apparent influence on the molecular weight of the polymer. Differential scanning calorimetry analysis indicated that the maximal melting point, cold crystallization temperature, and degree of crystallinity of the sPCL polymers increased with increasing molecular weight, and crystallinities of different sizes and imperfect crystallization possibly did not exist in the sPCL polymers. Furthermore, polarized optical microscopy analysis indicated that the crystallization rate of the polymers was in the order of linear poly(,-caprolactone) (LPCL) > sPCL5 > sPCL1 (sPCL5 had a higher molecular weight than both sPCL1 and LPCL, which had similar molecular weights). Both LPCL and sPCL5 exhibited a good spherulitic morphology with apparent Maltese cross patterns, whereas sPCL1 showed a poor spherulitic morphology. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5449,5457, 2005 [source]

Effects of SBS on phase morphology of iPP/aPS blends

POLYMER ENGINEERING & SCIENCE, Issue 10 2000

The supermolecular structure of binary isotactic polypropylene/poly(styrene- b -butadiene- h -styrene) (iPP/SBS) and isotactic polypropylene/atactic polystyrene (iPP/aPS) compression molded blends and that of ternary iPP/aPS/SBS blends were studied by optical microscopy, scanning and transmission electron microscopy, wide-angle X-ray diffraction and differential scanning calorimetry. Nucleation, crystal growth, solidification and blend phase morphology are affected by the addition of amorphous components (SBS and aPS). As a compatiblizer in immiscible iPP/aPS blends, SBS formed interfacial layer between dispersed honeycomb-like aPS/SBS particles and the iPP matrix, thus influencing the crystallization process in iPP. The amount of SBS and aPS, and compatibilizing efficiency of SBS, determine the size of dispersed aPS, SBS, and aPS/SBS particles and, consequently, the final blend phase morphologies: well-developed spherulitic morphology, cross-hatched structure with blocks of sandwich lamellae and co-continuous morphology. The analysis of the relationship between the size of spherulites and dispersed particles gave the criterion relation, which showed that, in the case of a well-developed spherulitization, the spherulites should be about fourteen times larger than the incorporated dispersed particles; i.e. to be large enough to engulf dispersed inclusions without considerable disturbing of the spherulitic structure. [source]