Crystallization Behaviour

Molecular weight is an important parameter to determine the mechanical properties of polymeric materials and is given by the following empirical equation  

Notes 300 nm, 23 °C water vapour transmission rate at 25 °C P(HB-HV) (94/6) tensile strength oriented fibre nonoriented film Young s modulus elongation at break. 

Porous PLA-based materials can be used as scaffolds for the regeneration of organs. These materials are prepared by the formation of a phase-separated structure of PLA-based materials 

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The europium shift NMR spectra of both parents have also been studied (710MR(3)575), as has the nematic liquid crystal behaviour of pyrido[2,3-f ]pyrazine (760MR(8)155). 

Typical materials that exhibit liquid crystalline behaviour are made up of long, thin molecules. Hence in principle polymers ought to show the basic requirement for liquid crystal behaviour. Conventional polymers, however, are too flexible and tend to adopt random coil configurations in the melt. They are thus not sufficiently anisotropic to exhibit a mesophase. 

Unlike low molar mass liquid crystals, these materials do not undergo a nematic-isotropic transition. Instead, they adopt liquid crystal behaviour throughout the region of the phase diagram for which they are in the melt. Above a particular temperature, rather than adopting an isotropic liquid structure, they decompose. 

Certain polymers will exhibit liquid crystal behaviour in solution. This phenomenon was first noted for natural polypeptides, but was found to be obtainable in synthetic systems initially for poly(7-benzyl L-glutamate)... 

The prime requirement for the formation of a thermotropic liquid crystal is an anisotropy in the molecular shape. It is to be expected, therefore, that disc-like molecules as well as rod-like molecules should exhibit liquid crystal behaviour. Indeed this possibility was appreciated many years ago by Vorlander [56] although it was not until relatively recently that the first examples of discotic liquid crystals were reported by Chandrasekhar et al. [57]. It is now recognised that discotic molecules can form a variety of columnar mesophases as well as nematic and chiral nematic phases [58]. 

Jabarin, S. A., Crystallization kinetics of polyethylene terephthalate. III. Effect of moisture content on the crystallization behaviour of PET from the glassy state, J. Appl. Polym. Sci., 34, 103-108 (1987). 

To override any effect that particulate impurities or polyolefin contamination would have in modifying the crystallization behaviour of recycled PET. 

This polymer suffered thermal degradation only above 400 C, before melting. For molecular weights higher than about 20,000, it showed a lyotropic liquid-crystal behaviour in N-metnypyrrolidone containing LiCl. This is the first reported example of a furanic polymer with mesogenic properties. 

As already mentioned above, the functional properties of whippable emulsions depend largely on the properties of the fat globules they contain. The fat globules form the skeleton of the foam. The crystallization behaviour inside the fat globules of whippable emulsions is decisive for the stabilization of the foam structure after aeration. It is a well-known fact in the food industry that whippable emulsions made with liquid fats are totally devoid of functionality. 

More recently the treatment was extended to piezoelectric devices in contact with viscoelastic media (i.e., liquids and polymers). It was then realised that if the deposited mass was not rigidly coupled to the oscillating quartz crystal, separation of inertial mass and energy losses was not possible with the measurement of the resonant frequency alone. Quartz crystal impedance in the acoustic frequencies was introduced in order to study mass and viscoelastic changes and a full electrical characterization of the crystal behaviour near resonance was employed. 

Foley, J., Brady, J.P. 1984. Temperature-induced effects on crystallization behaviour, solid fat content and the firmness values of milk fat. J. Dairy Res. 51, 579-589. 

Simon, K., Siiverkriip, R. 1995. Comparison of recent techniques to characterize the crystallization behaviour of fatty suppository bases. Thermochim. Acta 248, 271-287. 

Though numerous groups have fabricated CNT-polymer composites, mechanical behaviour has not been the main focus of such studies. The bulk of the work has focused on studying the effect of the addition of CNT on the crystallization behaviour and on the electrical conductivity and improving dispersion by employing different techniques, as described earlier. 

Stearic acid is often considered a prototype for the long chain acids used in many processes and applications. Sato and Boistelle (1984) studied the occurrence and crystallization behaviour of three of the polymorphic modifications (A, B, and C) by varying conditions such as temperature, supersaturation, and solvent from which they determined occurrence domains for the existence of the three forms. Polymorph A is thermodynamically unstable at all temperatures studied below 30 °C form B is most stable, while form C is more stable above 30 °C. Forms A and C nucleate... 

The crystallization behaviour has been described by Oyumi et al. (1987a). An amorphous phase, unstable at room temperature, can be prepared under kinetic conditions by rapid removal of solvent (acetone or acetonitrile) or rapid cooling of the melt. It initially appears as a transparent waxy material that transforms into a crystalline material over about an hour. It can also be prepared on a DTA instrument by cooling from the melting point of the crystalline material (406 K) to the temperature range 333-290 K. On the other hand, crystals suitable for single crystal structure determination (carried out by the same authors) can be grown by slow evaporation from the same solvents. 

Herrera, M.L. Crystallization Behaviour of Hydrogenated Sunflowerseed Oil Kinetics and Polymorphism, Ibid. 71 1255-1260 (1994). 

Mulder, H., and P. Walstra, Crystallization Behaviour in Milk Fat, in The Milk Fat Globule, Commonwealth Agricultural Bureaux, Centre for Agricultural Publishing and Documentation, Wageningen, The Netherlands, 1974, pp. 33-53. 

Forsyth S A, Fraser K J, Howlett P C, et al. N-methyl-N-alkylpyrroli-dinium nonafluoro-l-butanesulfonate salts Ionic hquid properties and plastic crystal behaviour. Green Chem. 2006. 8, 256-261. 

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