Glass transition temperature pitches

A plasticizer is a substance the addition of which to another material makes that material softer and more flexible. This broad definition encompasses the use of water to plasticize clay for the production of pottery, and oils to plasticize pitch for caulking boats. A more precise definition of plasticizers is that they are materials which, when added to a polymer, cause an increase in the flexibiUty and workabiUty, brought about by a decrease in the glass-transition temperature, T, of the polymer. The most widely plasticized polymer is poly(vinyl chloride) (PVC) due to its excellent plasticizer compatibility characteristics, and the development of plasticizers closely follows the development of this commodity polymer. However, plasticizers have also been used and remain in use with other polymer types. 

Pitches were characterized by DSC andTMA by Barr and Lewis (238). The DSC curves of a typical petroleum pitch, which had a Mettler softening point of 152°C, are illustrated in Figure 7.15. An endothermic peak in the vicinity of the expected Tg point was found in the initial DSC curve. A second run of the sample, after cooling it rapidly from 240 to — 10°C, showed a well-defined Tg with an onset temperature of 83°C. The endothermic peak was no longer visible in the curve. Glass transition temperatures and softening... 

VARIATION IN GLASS TRANSITION TEMPERATURE FOR EXTRACTED CAT CRACKER BOTTOM PITCH FRACTIONS AS A FUNCTION OF THE EXTRACTION SOLVENT SOLUBILITY PARAMETER... 

There are one or two exceptions to this rule, however, such as glass and pitch. These substances remain soft for a considerable interval of temperature, becoming less and less viscous as the temperature rises, until they ultimately hquefy. This property is peculiar to so-called amorphous, i.e. non-crystalline, bodies. We shall exclude bodies of this kind from consideration, and also hquid crystals and crystalhne fiuids, substances which appear to combine the characteristic properties of the sofid and of the hquid states. They have the fixed configuration of the molecules in space peculiar to sohds, as well as the mobihty of liquids. The transition from an anisotropic crystal to a perfectly isotropic fluid always takes place at one definite temperature. The softening of crystals in the neighbourhood of the melting point is not an exception to this rule, since these softened crystals are still anisotropic. 

In the formation of carbonaceous mesophase by thermolysis (pyrolysis) of isotropic molten pitch, the development of a liquid-crystalline phase is accompanied by simultaneous aromatic polymerization reactions. The reactivity o/pitch with increasing heat treatment temperature and its thermosetting nature are responsible for the lack of a true reversible thermotropic phase transition for the bulk mesophase in most pitches. Due to its glass-like nature most of the liquid-crystalline characteristics are retained in the super-cooled solid state. 

As the temperature is decreased the chiral nematic structure transforms to a higher order phase. The phase may go through a first order phase transition and crystallize in which case the optical properties are of little interest herein. It may transform to a glass, in which case the optical properties, such as birefringence, pitch, etc., are frozen and may be used in static, or time and environment-independent devices or applications (as discussed in Sec. 2.5 of this Chapter), or it may go through a second order or second order plus a weak first order phase transition to a higher order liquid crystalline phase. Here, for simplicity, we are not considering the so-called re-entrant phases [ 14]... 

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