ORIENTATION OF THE LAMELLAR CRYSTALS IN POLYAMIDE-12

Three types of oriented samples of polyamide 12 have been investigated by electron microscopy, and small- and wide-angle X-ray diffraction: (a) sedimented mats of single crystals obtained by filtration from dilute solution; (b) melt crystallized samples oriented by unidirectional rolling and; (c) samples obtained by extrusion just below their melting temperature (T(m) = 170-degrees-C). The limiting faces of lamellar crystals in sedimented mats are parallel to the (001) planes. Rolled samples contain two populations of deformed lamellar crystals in a mirror relationship with respect to the rolling plane; their limiting planes are not parallel to any one of the crystallographic planes that have low Miller indices. It is only by thermal annealing in contact with formic acid, under well-defined experimental conditions, that the lamellar basal planes parallel to the (001) planes can be restored. A new crystalline phase with a triclinic unit cell is found in samples obtained by planar extrusion at 160-degrees-C, and lamellar crystals with monoclinic and triclinic unit cells coexist in these extruded samples. The two edges of the faces parallel to the rolling plane of these doubly oriented samples have an almost single texture, both at the level of the lattice and at the level of the basal planes of the lamellar crystals. Lamellar crystals with a triclinic unit cell have limiting planes parallel to the (001) planes.