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Different Cooling Rates (different + cooling_rate)

Distribution by Scientific Domains

Polymers and Materials Science	71%

Selected Abstracts

Determination of nucleation parameters and the solid liquid interfacial energy of the KCl-ethanol-water system

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2007
Waid Omar
Abstract The kinetic parameters of homogeneous nucleation of KCl in different ethanol-water solvent mixtures were determined at 25°C from the experimental measurements of the width of the metastable zone at different cooling rates. The ethanol mass ratio in the ethanol water solvent mixture was varied from 0-0.9 and the metastable zone width for each solvent mixture was measured under the cooling rates of 10, 20 and 30 K/h. The influence of ethanol ratio on the activity coefficient was calculated. It was found that increasing the ethanol ratio in the solvent mixture leads to an increase in the mean molal activity coefficient. The experimental results obtained showed that the increase in the ethanol ratio in the solvent widens the metastable zone for the crystallization of KCl. Also it has inferred from the calculations based on the classical nucleation theory that increasing of the ethanol ratio in the solvent mixture resulted in an increase of the nucleation rate order, increase of the critical size of nuclei and increase of the solid liquid interfacial energy. It has been found that the solid liquid interfacial energy can be good correlated with inversely proportionality to the solubility. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Toughening of basalt fiber-reinforced composites with a cyclic butylene terephthalate matrix by a nonisothermal production method

ADVANCES IN POLYMER TECHNOLOGY, Issue 2 2010
J. Baets
Abstract The interest in thermoplastic composites is growing because of their advantages over thermosets, as well as their recyclability and higher toughness. The melt viscosity of thermoplastic polymers is very high, which makes fiber impregnation difficult. This difficulty can be overcome by the in situ polymerization with cyclic butylene terephthalate (CBT). However, this leads to a brittle polybutyleneterephthalate when isothermal RTM-production is applied. To solve this problem, a nonisothermal production process for composites with CBT as matrix material was developed and the influence on the toughness was investigated. In the nonisothermal production process, different cooling rates were applied to examine their influence on the toughness of the produced composites. The difference in composites properties was related to the difference in the degree of crystal perfection, which was investigated by differential scanning calorimetry. © 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:70,79, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20176 [source]

Study on the Phase Behavior of High Density Polyethylene , Ethylene Octene Copolymer Blends

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 3 2007
Daniela Mileva
Abstract The processes of melting and crystallization of blends based on HDPE and EOC were investigated. DSC thermograms showed that a separate crystallization and co-crystallization occurred in the blends studied. Avrami approach was used to analyze the kinetics of crystallization in the blends. It is shown that the Avrami exponent depends on the EOC concentration of the samples studied. The difference in the Avrami parameters for HDPE, EOC and the blends indicated that the nucleation mechanism and dimension of the spherulite growth of the blends were different from that of HDPE to some extent. The crystal growth was examined in the context of the Lauritzen-Hoffman theory. DSC traces obtained at different cooling rates were used for analyzing the non-isothermal crystallization. It was found that the Ozawa model was rather inapplicable for the materials studied. In contrast, the Avrami equation modified by Jeziorny can be used more efficiently to describe the non-isothermal crystallization behavior of HDPE-EOC blends. [source]

Nonisothermal melt crystallization kinetics of poly(ethylene terephthalate)/Barite nanocomposites

POLYMER COMPOSITES, Issue 9 2010
Chunhua Ge
Poly(ethylene terephthalate) (PET)/Barite nanocomposites were prepared by direct melt compounding. The nonisothermal melt crystallization kinetics of pure PET and PET/Barite nanocomposites, containing unmodified Barite and surface-modified Barite (SABarite), was investigated by differential scanning calorimetry (DSC) under different cooling rates. With the addition of barite nanoparticles, the crystallization peak became wider and shifted to higher temperature and the crystallization rate increased. Several analysis methods were used to describe the nonisothermal crystallization behavior of pure PET and its nanocomposites. The Jeziorny modification of the Avrami analysis was only valid for describing the early stage of crystallization but was not able to describe the later stage of PET crystallization. Also, the Ozawa method failed to describe the nonisothermal crystallization behavior of PET. A combined Avrami and Ozawa equation, developed by Liu, was used to more accurately model the nonisothermal crystallization kinetics of PET. The crystallization activation energies calculated by Kissinger, Takhor, and Augis-Bennett models were comparable. The results reveal that the different interfacial interactions between matrix and nanoparticles are responsible for the disparate effect on the crystallization ability of PET. POLYM. COMPOS., 31:1504,1514, 2010. © 2009 Society of Plastics Engineers [source]

Oxygen permeability of biaxially oriented polypropylene films

POLYMER ENGINEERING & SCIENCE, Issue 4 2008
Y.J. Lin
The effect of thermal history on the oxygen permeability of biaxially oriented polypropylene (BOPP) films was investigated. Compression-molded sheets prepared with different cooling rates were biaxially oriented at several temperatures in the range between the onset of melting and the peak melting temperature and at a strain rate similar to that encountered in a commercial film process. The stress response during stretching was found to depend on the residual crystallinity in the same way regardless of the thermal history of the compression-molded sheet. Biaxial orientation reduced the oxygen permeability measured at 23°C; however, the reduction did not correlate with the amount of orientation as measured by birefringence or with the fraction of amorphous phase as determined by density. Rather, the decrease in permeability was attributed to reduced mobility of amorphous tie molecules. A single one-to-one correlation between the oxygen permeability and the intensity of the dynamic mechanical ,-relaxation was demonstrated for all the films used in the study. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source]

Molecular, rheological, and crystalline properties of low-density polyethylene in blown film extrusion

POLYMER ENGINEERING & SCIENCE, Issue 12 2007
Khokan Kanti Majumder
The molecular weight and its distribution, degree of long chain branching and cooling rate strongly influence crystallinity during processing, which in turn determines the processability and the ultimate properties of the blown film. Generally a decrease in the number of branches and molecular weight of the polymer and the cooling rate results in an increase of the crystallinity. Length of the main chain and extent of branching in low-density polyethylene (LDPE) are also factors that affect melt rheology and film crystallinity. Long chain branched polyethylene is suitable in the blown film process due to its better melt strength for bubble stability. The objective of this article is to describe the effect of molecular properties (e.g. molecular weight and its distribution, degree of long chain branching etc) of LDPE on film crystallinity at different cooling rates of blown film extrusion. Two different grades of LDPE were selected to investigate molecular characteristics, crystallinity, and rheology. The resins were processed in a blown film extrusion pilot plant using four different cooling rates. Molecular, rheological, and crystalline properties of the resins were key parameters considered in this study. POLYM. ENG. SCI., 47:1983,1991, 2007. © 2007 Society of Plastics Engineers [source]

Nonisothermal crystallization behavior of a luminescent conjugated polymer, poly(9,9-dihexylfluorene- alt -2,5-didodecyloxybenzene)

POLYMER INTERNATIONAL, Issue 2 2007
Gui-Zhong Yang
Abstract The nonisothermal crystallization kinetics of poly(9,9-dihexylfluorene- alt -2,5-didodecyloxybenzene) (PF6OC12) from the melt were investigated using differential scanning calorimetry under different cooling rates. Several analysis methods were used to describe the nonisothermal crystallization behavior of PF6OC12. It was found that the modified Avrami method by Jeziorny was only valid for describing the early stage of crystallization but was not able to describe the later stage of PF6OC12 crystallization. Also, the Ozawa method failed to describe the nonisothermal crystallization behavior of PF6OC12. However, the method developed by combining the Avrami and Ozawa equations could successfully describe the nonisothermal crystallization kinetics of PF6OC12. According to the Kissinger method, the activation energy was determined to be 114.9 kJ mol,1 for the nonisothermal melt crystallization of PF6OC12. Copyright © 2006 Society of Chemical Industry [source]