Linear polymers epitaxial crystallization

Epitaxial crystallization of polymers has been investigated for a wide variety of substrates minerals (alkali halides, talc, mica, and so on), low molecular weight organic materials (condensed and linear aromatics, benzoic acid and many of its substituted variants and their salts or hemiacids, other organic molecules of different types), and other crystalline polymers. 

R. Su, K. Wang, Q. Zhang, F. Chen, Q. Fu, N. Hu, E, Chen, Epitaxial crystallization and oriented structure of linear low-density polyethylene/isotactic polypropylene blends obtained via dynamic packing injection molding. Polym. Adv. Technol. 22, 225-231 (2011)... 

Other aspects are that linear polymers without crosslinking possess thermoplastic properties, which means they can be plastically deformed on heating and can retain the deformed situation on cooling. In the rubbing process, the plastic polymer is sheared and retains the extended state. These processes change the chain orientation and can cause partial crystallization, which can induce epitaxial growth of smectic liquid crystalline alignment. 

Epitaxial crystallization of PE may be considered as a rather academic concern. It is indeed so for most linear PEs produced for example by Ziegler-Natta catalysis, which crystallize fast, as they have high nucleation and growth rates. However, modem PEs, such as the linear low density ones (LLDPE), have much reduced growth rates. It is therefore of technological interest to develop nucleating agents that are efficient for this class of polymers. 

Among many more linear polymers, poly(ethylene terephthalate) (PET) is of particular relevance since its maximum crystal growth rate is slow. The enhanced crystallization of PET has been, and still is, a topic of technological relevance. Following extended work by Legras, Mercier, and Nield [21], the impact of chemical nucleation (as opposed to epitaxial, i.e., physical interactions) has been widely publicized and is indeed... 

Thierry, A. Epitaxial crystallization (of linear polymers). In Polymeric Materials Encyclopedia, Vol. 3, Salamone, J.C., ed. CRC Press, Boca Raton, FL, 1996, pp. 2167-2179. 

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