Thermally- and solvent-induced crystallization kinetics of syndiotactic polystyrene viewed from time-resolved measurements of infrared spectra at the various temperatures (1) estimation of glass transition temperature shifted by solvent absorption

Polymer ◽  
2003 ◽  
Vol 44 (21) ◽  
pp. 6681-6688 ◽  
Author(s):  
Akiko Yoshioka ◽  
Kohji Tashiro
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Crystallization Kinetics ◽  
Infrared Spectra ◽  
Syndiotactic Polystyrene ◽  
Time Resolved ◽  
Solvent Absorption ◽  
Kinetics Of ◽  
Induced Crystallization

Elastomer Structures and ‘Cold Crystallization’

1979 ◽  
Vol 52 (1) ◽  
pp. 207-212 ◽  
Author(s):  
M. Bruzzone ◽  
E. Sorta
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Melting Point ◽  
Natural Rubber ◽  
Crystallization Rate ◽  
Cold Crystallization ◽  
Structural Defects ◽  
Strain Induced Crystallization ◽  
Induced Crystallization

Abstract In a great number of applications an ideal elastomer should satisfy, to a certain extent, both of the following requirements: (1) nearly instantaneous crystallization upon application of strain (strain induced crystallization) and (2) slow or no crystallization when cooled at the temperature of maximum crystallization rate (cold induced crystallization). A noteworthy case of (2) is elastomer crystallization in a strained state. The connection between the points (1) and (2) has not been clearly understood up to now, but it is known that some crystallizable elastomers fulfil the requirements of both (1) and (2) better than others. From an experimental point of view, cold induced crystallization kinetics are substantially easier to measure than those of very fast strain induced crystallization. The phenomenon of cold induced crystallization in natural rubber, NR, has been known since the very beginning of elastomer technology and the tendency of natural rubber to crystallize by cooling has been overcome by crosslinking it with sulphur (vulcanization) without impairing its ability to crystallize by stretching (Goodyear, 1836). The synthesis of cis-polyisoprenes (IR) and cis-polybutadiene (BR) of different microstructural purity (different cis content) gave the possibility of changing the crystallization rate. It has also been reported that the very fast cold crystallization of trans-polypentenamer (TPA) could be reduced by lowering the trans content. The same fact had been observed earlier for trans-polychloroprene. There is a general agreement in postulating that the reduction of the crystallization rate, obtained either by cross-linking or by chain regularity reduction, can be linked with the lowering of the melting point. In both cases the low level of structural defects introduced in the chains does not affect the glass transition temperature in such a way as to vary the crystallization rate. The aim of this paper is to emphasize the importance of the variations of the glass transition temperature and melting point on the elastomeric cold crystallization rate and the way these may be used in planning new elastomer structures.

Reentanglement Kinetics of Freeze-Dried Polymers above the Glass Transition Temperature

2012 ◽  
Vol 45 (16) ◽  
pp. 6648-6651 ◽  
Author(s):  
Chao Teng ◽  
Yun Gao ◽  
Xiaoliang Wang ◽  
Wei Jiang ◽  
Chen Zhang ◽  
...  
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Freeze Dried ◽  
Kinetics Of

Cure Kinetics of Nanocomposites Prepared From Aqueous Dispersion of Nanoclay

2006 ◽  
Author(s):  
Levent Aktas ◽  
M. Cengiz Altan
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Storage Modulus ◽  
Glass Fibers ◽  
Aqueous Dispersion ◽  
Cure Kinetics ◽  
Temperature Cycle ◽  
Waterborne Epoxy ◽  
Kinetics Of

The effect of nanoclay on the cure kinetics of glass/waterborne epoxy nanocomposites is investigated. First step in sample preparation involves dispersing Cloisite® Na+, a natural montmorillonite, in distilled water at 70°C with the aid of a sonicator. Then, desired amounts of dicyandiamide and 2-methyl imidazole, serving as cross-linkers, are mixed to the aqueous nanoclay solution. As the mixing continues, Epi-Rez 3522-W-60 waterborne epoxy resin is introduced to the solution and the compound is mixed for an additional 30 minutes. The nanoclay content of this batch is adjusted to be at 2wt%. An identical second batch, which does not comprise nanoclay, is also prepared to serve as the baseline data. Glass/waterborne epoxy prepregs containing 30% glass fibers are prepared from these batches and used to characterize the effects of nanoclay. The evolution of viscoelastic properties during curing are characterized by the APA2000 rheometer. Using the storage and loss moduli profiles during curing, gel time and maximum storage modulus are characterized. Effect of nanoclay on the glass transition temperature is determined by applying an additional temperature cycle following the cure cycle. In addition, mechanical performances of the samples are characterized by three point bending tests. Nanoclay is observed to yield 2-fold higher storage modulus during curing. Rate of curing is measured to be substantially slower for the samples comprising nanoclay. In addition, glass transition temperature improved by 5% to 99°C with the addition of nanoclay compared to 94.5°C for the samples without nanoclay. Flexural stiffness of the samples containing nanoclay is measured to be 20% higher than the samples without nanoclay while the strength remained virtually unaffected.

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