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Cold Crystallization (cold + crystallization)

Distribution by Scientific Domains

Polymers and Materials Science	85%

Selected Abstracts

Glass transition and cold crystallization in carbon dioxide treated poly(ethylene terephthalate)

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2009
Yeong-Tarng Shieh
Abstract An amorphous poly(ethylene terephthalate) (aPET) and a semicrystalline poly(ethylene terephthalate) obtained through the annealing of aPET at 110°C for 40 min (aPET-110-40) were treated in carbon dioxide (CO2) at 1500 psi and 35°C for 1 h followed by treatment in a vacuum for various times to make samples containing various amount of CO2 residues in these two CO2 -treated samples. Glass transition and cold crystallization as a function of the amount of CO2 residues in these two CO2 -treated samples were investigated by temperature-modulated differential scanning calorimetry (TMDSC) and dynamic mechanical analysis (DMA). The CO2 residues were found to not only depress the glass-transition temperature (Tg) but also facilitate cold crystallization in both samples. The depressed Tg in both CO2 -treated poly(ethylene terephthalate) samples was roughly inversely proportional to amount of CO2 residues and was independent of the crystallinity of the poly(ethylene terephthalate) sample. The nonreversing curves of TMDSC data clearly indicated that both samples exhibited a big overshoot peak around the glass transition. This overshoot peak occurred at lower temperatures and was smaller in magnitude for samples containing more CO2 residues. The TMDSC nonreversing curves also indicated that aPET exhibited a clear cold-crystallization exotherm at 120.0°C, but aPET-110-40 exhibited two cold-crystallization exotherms at 109.2 and 127.4°C. The two cold crystallizations in the CO2 -treated aPET-110-40 became one after vacuum treatment. The DMA data exhibited multiple tan , peaks in both CO2 -treated poly(ethylene terephthalate) samples. These multiple tan , peaks, attributed to multiple amorphous phases, tended to shift to higher temperatures for longer vacuum times. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source]

Dielectric study of equimolar acetaminophen,aspirin, acetaminophen,quinidine, and benzoic acid,progesterone molecular alloys in the glass and ultraviscous states and their relevance to solubility and stability

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2010
G.P. Johari
Abstract Equimolar mixtures of acetaminophen,aspirin, acetaminophen,quinidine, and benzoic acid,progesterone have been vitrified and dielectric properties of their glassy and ultraviscous alloys have been studied. For 20,K/min heating rate, their Tgs are 266, 330, and 263,K, respectively. The relaxation has an asymmetric distribution of times, and the distribution parameter increases with increase in temperature. The dielectric relaxation time varies with T according to the Vogel,Fulcher,Tammann equation, log10(,0),=,AVFT,+,[BVFT/(T,,,T0)], where AVFT, BVFT, and T0 are empirical constants. The equilibrium permittivity is highest for the aspirin,acetaminophen and lowest for the benzoic acid-progesterone alloy, indicating a substantial interpharmaceutical hydrogen bonding that makes the alloy more stable against crystallization than the pure components. The benzoic acid,progesterone alloy is thermodynamically the most nonideal. It showed cold crystallization on heating, which is attributed to its relatively greater magnitude of the JG relaxation in relation to its ,-relaxation. It is argued that the difference between the free energy of an alloy and the pure components would have an effect on the solubility. Studies of solution thermodynamics of a glassy molecular alloy may be useful for optimizing choice of components and composition to form molecular alloys and to impact drug delivery. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 1358,1374, 2010 [source]

Ultra-Small-Angle X-Ray Scattering Study of PET/PC Nanolayers and Comparison to AFM Results

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 13 2008
Fernando Ania
Abstract The forced assembly of two immiscible polymers, produced by layer-multiplying co-extrusion, is analyzed by means of USAXS. Comparison of scattering and AFM results sheds light on many details of the nanolayered structure in PET/PC films. The role played by the volume concentration and cold crystallization of PET on the experimental scattering is discussed. The appearance of at least two scattering maxima in all cases, corresponding to higher orders of the same repeating distance, accounts for the high regularity of the developed nanostructure. It is finally shown that long spacing values, derived from a localized area in AFM, are in a good agreement with the USAXS values averaged over much larger areas. [source]

Crystallization and biodegradation of polylactide/carbon nanotube composites

POLYMER ENGINEERING & SCIENCE, Issue 9 2010
Defeng Wu
The crystallization behavior of polylactide/carbon nanotube composites was studied using differential scanning calorimeter and polarized optical microscope. The nucleation mechanisms and the crystallization kinetics were explored. The results show that the presence of nanotubes has nucleating effect on both the melt crystallization and the cold crystallization of PLA. However, the nanotubes also play the role of physical barrier, impeding the crystal growth dynamically. In the experimental range of temperatures, the presence of nanotubes accelerates the melt crystallization, while retards the overall kinetics of the cold crystallization. The biodegradability of the samples with various crystallization histories was then further examined. The results show that the presence of nanotubes reduces the biodegradation rate of PLA, and the amorphous sample shows the highest degradation levels. Moreover, a lower degradation level is observed both on the surface and inside the sample with melt crystallization history in contrast to the one with cold crystallization history. POLYM. ENG. SCI., 50:1721,1733, 2010. © 2010 Society of Plastics Engineers [source]

Synthesis and characterisation of branched and partially crosslinked poly(ethylene terephthalate)

POLYMER INTERNATIONAL, Issue 7 2003
DN Bikiaris
Abstract In the present study, a series of branched and partially crosslinked poly(ethylene terephthalate) (PET) samples were prepared by the two-stage melt polycondensation method, using different amounts of trimethyl trimellitate (TMT) as polyfunctional monomer. The samples were characterised with respect to intrinsic viscosity, density and gel content as well as thermal and mechanical properties. The intrinsic viscosity of the polymers ranged between 0.7 and 1.6 dl g,1 depending on the concentration of the TMT comonomer. When TMT was used at a concentration 0.625 wt% or higher, gel formation was observed. For the sample containing 1.25 wt% TMT, almost half of the polymer was insoluble in phenol,tetrachloroethane mixture, due to extensive crosslinking. The increase of TMT content resulted in a small decrease of crystallinity attributed to branching and crosslinking, both of which restrict the organisation of the polymer chains in the crystal structure. This was reflected directly in the thermal properties of the polymers prepared. Increasing the TMT content decreased the melting point and the heat of fusion. In contrast, cold crystallization and glass transition temperatures were shifted to higher temperatures. Mechanical properties like tensile strength and elongation at break increased with increasing the content in branching agent. However, crosslinking had a negative effect on elongation at break. Copyright © 2003 Society of Chemical Industry [source]