Crystallization promoters

To facilitate and accelerate folding and crystallization of polymer chains, internal plasticizers are often added to PET to serve as crystallation promoters. Such additives are usually based on poly(ether ester)s. These plasticizers are liquids that are typically added at levels of 2-4 wt%. They reduce cycle time in injection moulding operations by increasing the rate of crystalline formation. They also plasticize the resin and act as processing aids by virtue of their lubricating action in the melt. On a molecular level, these plasticizers reduce the intermolecular... 

Figure 14.16 Mechanism by which poly(ether ester)s function as crystallization promoters. Such materials internally lubricate and plasticize the PET molecular chains, thus allowing reptation (i.e. chain folding) to occur more quickly...

If it is assumed that being in the same orientation as the molecules of a crystal promotes incorporation into the lattice, then the value of AS can be accounted for more accurately by subtracting from it the probability that a liquid molecule will be found in such a position, i.e. ... 

Slow crystallization promotes disentangling since the process of reeling-in of chains from the entangled melt onto the crystal surface is promoted and this in turn enhances the maximum drawability, despite the fact that this increases the crystallinity. However, there is a critical lower limit for the number of entanglements between crystals in order to achieve high drawability and in the extreme limit of very slow isothermal crystallization, linear standard polyethylenes (not the UHMW-PE grades) can lose their drawability completely and become brittle materials. 

Cancrinite crystallization, promoted by the joint presence in the reaction system of lithium and a large cation, has been thoroughly investigated, pointing out the specificity of the cationic couple for the synthesized phase. The products obtained have been characterized by means of X-ray diffraction, chemical, microscopy and thermal analyses. A hypothesis on the mechanism of cancrinite formation has been worked out, also on the basis of the preliminary results of structural analysis. 

The reaction of this solid [48] was the first [133] example of Smith-Topley behaviour recognized and studies of this rate process have continued. Flanagan and Kim [133] showed that irradiation decreased the induction period to dehydration and the rate of water evolution rapidly reached a maximum value which was maintained between 0 < nr < 0.4. Water evolution was more rapid than that found for unirradiated salt and the value of , was decreased. Irradiation damage to the crystal promoted nucleation and there was rapid initial establishment of a constant area of reaction interface (the contracting volume equation approximates to zero-order kinetics at low values of nr). There was also evidence [134] that preirradation aided recrystallization during vacuum dehydration. 

Uses Emollient in cosmetics textile lubricant pharmaceutical intermediate, diluent, crystallization promoter, m.p. modifier, bodying agent, lubricant, moisturizer emulsifier mold release agent buffing compd. filler in capsules, tablets, and suppositories in food-pkg. adhesives defoamer in food-contact paper/paperboard in food-contact textiles Regulatory FDA21CFR 175.105,176.180,176.210,177.2800,182.70, 182.170 BP, EP compliance... 

Low-dimensional crystals such as epitaxial needles and solution-grown platelets of TPCOs act as a microscale gain medium. The self-cavity and self-waveguiding effects of these crystals result in ASE in the wavelength region of the fluorescence band where the self-absorption loss is minimized. Furthermore, the uniaxial orientation of the TPCO molecules in these low-dimensional crystals promotes the stimulated emission process and enhances the polarized ASE. 

The intermolecular interaction between the surfactant and the liquid crystal promotes the... 

Figure 9.2. Schematic presentation of the distribution of small crystallization promoting particulate impurities (dark dots) in the bulk phase (left) and dispersed state (right).

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