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Chiu, Fang‐Chyou; Peng, Ya; Fu, Qiang

doi:10.1023/a:1021339608313

Cited by 10 publications

(8 citation statements)

References 18 publications

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“…Our microscopic observations obtained with the Ziegler–Natta copolymers (Figs. 2–4) validate the effects of branches on ethylene copolymer morphologies and are in agreement with other previous findings 29–31. Despite the effect of the cooling conditions, we observed well‐developed spherulites with a banded structure for both S539 and S244 (Figs.…”

Section: Resultssupporting

confidence: 92%

Morphology development for single‐site ethylene copolymers in rotational molding

Bellehumeur

2007

J of Applied Polymer Sci

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The morphology development of ethylene copolymers was modeled with the modified phase-field theory. The metastability of polymer crystallization was also considered in the modeling. Modeling and experimental work were simultaneously undertaken to compare the crystallization kinetics of single-site-catalyzed and Zieglercatalyzed resins and their influence on morphology development in the rotational-molding process. With a more uniform short-chain branch distribution, the single-site copolymers developed well-defined spherulitic structures.The Ziegler-Natta catalyst resins were characterized by a higher nuclei density and a faster crystallization rate and produced finer structures in the molded parts. The modeling approach proposed in our work allowed an evaluation of the processing and the material effects on the development of morphological features during melt solidification.

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Section: Resultssupporting

confidence: 92%

Morphology development for single‐site ethylene copolymers in rotational molding

Bellehumeur

2007

J of Applied Polymer Sci

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“…In the recent years, in addition to the focuses on the chain structure and processing property relationships [23, 25–27], a great deal of attentions have been paid to investigating the influence of chain structure on crystallization kinetics of polymers and their blends. Chiu et al [2, 28, 29] studied the effect of short chain branching (SCB) on crystallization kinetics and crystal morphology of metallocene polyethylenes having well‐controlled molecular weight, and found both the onset and peak cooling temperatures shifted toward lower temperatures with increasing SCB densities (SCBD) during the cooling period, which was also confirmed by Islam et al [30]. High SCBD resulted in a reduced length of crystallizable ethylene sequence.…”

Section: Introductionmentioning

confidence: 75%

Effect of long chain branching on nonisothermal crystallization behavior of polyethylenes synthesized with constrained geometry catalyst

Yang

Wang

et al. 2011

Polymer Engineering & Sci

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Nonisothermal crystallization behavior of linear and long chain branched (LCB) polyethylene (PE) samples having similar molecular weight but different long‐chain branching densities (LCBD) up to 0.44 C per 1000 carbons was investigated using differential scanning calorimetry (DSC) at various scanning rates. The LCB PE samples were prepared in our high‐temperature, high‐pressure continuous stirred‐tank reactor (CSTR) system using the constrained geometry catalyst. The existence of LCB was found to affect the PE crystallization behavior considerably. The enthalpy of crystallization and the ultimate degree of crystallinity decreased with the increase of LCBD. At the relatively low cooling rates, the small amount of LCB promoted nucleation but restrained chain movement and reduced the crystal growth rate. There was ∼ 17% of crystallinity generated from a secondary crystallization. The energy barrier became significant with the LCB structure, resulting in chain diffusion limitations and lower LCB PEs overall crystallization rates than their linear counterpart. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers

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“…where H t represents the enthalpy and t f is the time at the end of crystallization [17]. The corresponding crystallization half-times (t 1/2 ), defined as the time at which relative crystallinity reaches 50% of its ultimate value [18], are summarized in Table 2.…”

Section: Isothermal Crystallization Kineticsmentioning

confidence: 99%

Thermal properties, rheology and sintering of ultra high molecular weight polyethylene and its composites with polyethylene terephthalate

2005

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The addition of polyethylene terephthalate (PET) fibers in ultra high molecular weight polyethylene (UHMWPE) may be a promising approach to achieve improved wear properties in artificial joints. Since UHMWPE/PET composites are processed by compression molding, which involves compaction and sintering of polymeric powders, this article investigates their rheology, thermal properties, and sintering behavior to aid in the identification and selection of optimum processing conditions. Isothermal crystallization kinetics studies have revealed that crystallization of UHMWPE proceeds via heterogeneous nucleation and is governed by two-dimensional growth. The crystallization rates of the composites were lower than those of the neat material, whereas their ultimate crystallinities were higher. The UHMWPE/PET composites had higher viscosity and elasticity than the neat resin. In the presence of PET fibers the onset of sintering took place at higher temperatures but proceeded at substantially higher rates as compared with pure UHMWPE. A marked discrepancy between the Eshelby-Frenkel model and experimental sintering data suggests that viscous flow is not the prevailing mechanism for coalescence but rather that enhanced surface area, attributed to the highly developed internal morphology of UHMWPE particles, is the controlling factor. POLYM. ENG. SCI., 45:678 -686, 2005.

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Untitled

Cited by 10 publications

References 18 publications

Morphology development for single‐site ethylene copolymers in rotational molding

Morphology development for single‐site ethylene copolymers in rotational molding

Effect of long chain branching on nonisothermal crystallization behavior of polyethylenes synthesized with constrained geometry catalyst

Thermal properties, rheology and sintering of ultra high molecular weight polyethylene and its composites with polyethylene terephthalate

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