Pitch glass transition

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... 

Table 7,11. Softening Points and Glass Transitions (DSC) for Isotropic Pitches (238)...

Pitch Metller Softening Point (Wo Glass Transition (7 ) by DSC (°C) Onset Span ... 

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

Figure 5.44 Elastic deformations of CDLC helices, (a) Low-pitch helix free from external force attached to glass rod at one end, (b) same helix attached at both ends and slightly extended, and (c) helix extended beyond 16.5° and allowed to come to equilibrium with respect to the straightening transition (helix ends are off screen). Reprinted from Ref. 163 with permission of the author. Copyright 2001 by the American Physical Society.

Figure 4 shows the experimentally determined friction factor as a function of the Reynolds number for a laboratory PPR module with six 4-mm-thick catalyst slabs of 68-mm width and 500-mm height, spaced apart with a pitch of 11 mm, and made up from 2.2-mm-diameter glass spheres enclosed in 0.5-mm gauze mesh [6]. It can be seen that the transition of laminar to turbulent flow occurs already at a low Reynolds number (approximately 1(XX)), which is attributable to the roughness of the channel walls caused by the wire gauze. 

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. 

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