Polyamides epitaxial crystallization

A typical shish-kebab crystalline structure has been foimd by Maiti and Okamoto (2003) and Kim et al. (2001) in polyamide/organoclay nanocomposite and by Choi and Kim (2004) in PP/EPR/talc nanocomposite where a preferential orientation of polymer lamellae perpendicular to the surface of organoclay layers was inspected by TEM measurements. The unique observation of lamellar orientation (Ml the clay layers was ascribed to nucleation and epitaxial crystallization at the interface between layered silicate and polymer matrix especially the surfaces of clay platelets acted as heterogeneous nucleation sites. Orientation of iPP crystals was also enhanced in rPP/PP-MA/o-MMT injection-moulded parts, especially manufactured by dynamic packing injection moulding (Wang et al. 2005). MMT... 

Wittmann JC, Hodge AM, Lotz B. Epitaxial crystallization of polymers onto benzoic acid, polyethylene and paraffins, aUphatic polyesters, and polyamides. J Polym Sci B 1983 21 2495-2509. 

Similar investigations performed with polyamides are comparatively less telling. Indeed, the hydrogen-bonded sheets are a strong structural feature that does not leave much leeway for diverse epitaxial crystallizations. So far, the only contact plane observed in epitaxial crystallization of polyamides is indeed the hydrogen-bonded sheet [16]. This in turn implies that substrates with a periodicity close to 0.48 to 0.5 nm are most appropriate (provided of course that their compatibility with polyamides is sufficient). In this respect also, investigation of epitaxial crystallization of polyamides teaches us less than that of PE. However, further research is needed to investigate if some less standard crystal modifications of polyamides, such as the 7 form of polyamide 6, can be produced by epitaxial crystallization. 

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