Cold-crystallization

Melting a polymer sample and cooling it quickly to a temperature lower than the glass transition point (Eg) produces an amorphous glass sample. The next section describes this cold crystallization process. 

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The Phillips process is a two-stage crystallisation process that uses a pulsed column in the second stage to purify the crystals (79,80). In the pulsed column, countercurrent contact of the high purity PX Hquid with cold crystals results in displacement of impurities. In the first stage, a rotary filter is used. In both stages, scraped surface chillers are used. This process was commercialized in 1957, but no plants in operation as of 1996 use this technology. 

Direct evidence of nucleation during the induction period will also solve a recent argument within the field of polymer science as to whether the mechanism of the induction of polymers is related to the nucleation process or to the phase separation process (including spinodal decomposition). The latter was proposed by Imai et al. based on SAXS observation of so-called cold crystallization from the quenched glass (amorphous state) of polyethylene terephthalate) (PET) [19]. They supposed that the latter mechanism could be expanded to the usual melt crystallization, but there is no experimental support for the supposition. Our results will confirm that the nucleation mechanism is correct, in the case of melt crystallization. 

A quenched low-crystalline PTT often cold-crystallizes when it is heated to above its Tt (see Figure 5, curve (b)). Bulkin et al. [57, 58] found that PTT cold-crystallizes at a much faster rate than PET by following the increase in the PTT crystalline band at 1220 cm-1 using rapid-scanning Raman spectroscopy. 

Stellar matter exhausts itself to maintain its sparkle, diamond dust in a cold crystal. The galaxies are glitter, sprinkled across the heavy, transparent darkness of the cosmos. 

Low-form Dewar flask Cold crystal wand Cold cryotongs Face shield Lint-free tissue... 

Crystallization can occur far below the melting point. Such crystallization has been called cold crystallization , Dole (1959), Dole and Wunderlich (1959) and is defined as the crystallization that occurs between randomly situated nearest neighbor segments without any molecular rearrangements taking place. Wunderlich (1958) has derived equations giving the statistical probability of such crystallization (see below). 

Wunderlich (1958) has calculated the expected fraction of cold crystallization assuming (1) that A -units crystallize only with nearest neighbor A -units having a random distribution, as in a melt, (2) that for an, 4-unit to be a member of a crystal it must have 4 lateral, 4-unit nearest neighbors and must be a member of a crystal at least 3 /4-units long. His equation is... 

Wunderlich s theory also predicts that the maximum melting point of the cold-crystallized crystals in the 90/10 copolymer would be equal to the correct thermodynamic melting point. It would be interesting to test this prediction. 

Fig. 12. Equilibrium extent of crystal lization, curve 2( and extent of cold crystallization, curve I. Calculated for equalmolecularweightsofri and B units...

Wunderlich, B. Theory of cold crystallization of high polymers. J. Chem. Phys. 29, 1395—1404 (1958). 

Tg of either polymer components. In addition to the two distinguishable Tg signals, the melting endotherm and cold-crystallization exotherm of CA are both detectable for every blend at almost the same temperature positions as those for the CA (DS = 2.95) alone, with a proportional reduction of the respective peak areas. In contrast to the result, the thermograms compiled in Fig. 9a for the pair of CA (DS = 2.70) and P(VP-co-VAc) (VP/VAc = 0.51/0.49) (combination A) indicate a definitely single Tg that shifts to the higher temperature side with increasing CA content. As summarized in Fig. 8, CA/PVAc blends are immiscible irrespective of the DS of the CA component, while PVP forms a miscible monophase with CAs unless the acetyl DS exceeds a value of... 

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