Fast crystallization

Neoprene AC (1947). This polychloroprene was developed to provide better viscosity stability and resistance to discolouration, but it cures much more slowly at room temperature. It is a fast crystallizing grade and contains about 90% trans-, 4 structure. 

Solution and peel properties of polychloroprenes with fast crystallizing characteristics but different molecular weight... 

Neoprene 400. It contains a fast-crystallizing polymer with the highest chlorine content and the highest uncured cohesive strength among all anionic latexes. However, this latex has a relatively short open time and requires high lamination pressures to achieve coalescence. 

Fig. 5 shows the details of bonding of the two substrates by a waterborne PUD adhesive. The figure shown assumes a PUD adhesive with a fast crystallizing backbone [59]. 

The crystallization kinetics defines the open time of the bond. For automated industrial processes, a fast crystallizing backbone, such as hexamethylene adipate, is often highly desirable. Once the bond line cools, crystallization can occur in less than 2 min. Thus, minimal time is needed to hold or clamp the substrates until fixturing strength is achieved. For specialty or non-automated processes, the PUD backbone might be based on a polyester polyol with slow crystallization kinetics. This gives the adhesive end user additional open time, after the adhesive has been activated, in which to make the bond. The crystallization kinetics for various waterborne dispersions were determined by Dormish and Witowski by following the Shore hardness. Open times of up to 40 min were measured [60]. 

The thermoplastic polyurethane (TPU) adhesives must, of necessity, contain low gel content because they must be processable in an extruder. Most adhesives are relatively linear, with a functionality of 2.0, although small amounts of branching may be introduced, usually at the expense of a lower melt flow. Good physical properties of TPU s are obtained when the thermoplastic urethanes have molecular weights of 100,000 or higher (see p. 56 in [63]). Most TPU adhesives are based on symmetrical polyesters with a fast crystallizing backbone or a backbone slightly modified to increase the open time. 

Although not in wide use, a fast crystallizing TPU adhesive can be used in the shoe industry as an alternative to solvent-borne urethane adhesives. The TPU adhesives have good holding strength soon after crystallization, which can be a distinct advantage over curing hot-melt adhesives. TPU adhesives normally have... 

In the world of molecular simulation, it would be more conventional to consider that the present model is a coarse grained model of real polymers, where the real time-scale is much longer than that of the present MD simulation time-scale. However, we did not intend to make a coarse grained model. The crystallization of polymers was shown to be rather universal. Various kinds of polymers, either fast crystallizing or slow crystallizing, were known to follow the same scheme with respect to the molecular mechanism of crystallization. So we studied this simple model expecting that the present model would also follow the same crystallization scheme and show the general molecular mechanisms of polymer crystallization. 

In the context of crystallinity as a crucial factor with respect to haze, it has to be pointed out that PET and PBT as the most industrially used polyesters are both crystallizable depending on the conditions of subsequent processing. The amorphous state can be obtained by a rapid quenching of the melt below the Tg. Heating above the 7 g induces fast crystallization. PBT exhibits a significantly increased crystallization rate when compared with PET. 

PBT is used for textile applications due to its stretchability, increased crystallinity and improved dyeability. It is introduced in the production of carpets and stretchable fabrics, where a certain degree of elasticity is desired. PBT is used preferably for the production of engineering plastics due to its combination of dimensional stability, tensile strength, increased flexibility and fast crystallization rate. 

Economic Aspects. The first company to introduce nucleated PET molding resins was Akzo Plastics BV with their Amite range. This business has been taken over by DSM NV as part of a portfolio exchange between die two companies. Du Pont introduced their Rynite fast crystallizing materials in 1978, and other manufacturers followed. 

PURELY SILICEOUS HFI-tvoe ZEOLITES. Among the templating cations which were uaed, P R proved to be the moat efficient for easy and fast crystallization. In Table IT are given the crystallographic oharacteriatica of the obtained siliceous HFI-type zeolites (16) aa a function of the template. 

In our case since we have a very fast crystallizing polymer (PBT), we wanted to see if there was any difference in the crystallization of the blends depending on how the study was performed. Two sets of studies were done, in which the samples were crystallized at 110°C in one of them from the glass and in the other from the melt. The crystallization half-times and ultimate crystallinities obtained for each component were plotted in Figures 24, 25, 26, and 27. 

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