MOLECULAR ORIENTATION OF THE BIAXIALLY STRETCHED NYLON-6 FILMS PREPARED BY DRY-PROCESS

Abstract

Molecular orientation and crystallization of Nylon-6 films by means of the biaxial stretching in a hot dry-air bath are reported in this paper. The unoriented low crystalline Nylon-6 film T-die extruded with a thickness of ca. 200 μ were stretched at constant rate of 400%/min in a recirculating hot air at 120°C by various methods using a filmstretcher; i. e. uniaxial stretching under free width and/or constant width, and simultaneous biaxial stretching. The stretched films were then set at 160°C for 5min. The molecular orientation was studied by both measurements of birefringence for a tilted specimen and x-ray diffraction.
The obtained results are summerized as follows;
(1) The Nylon-6 films uniaxially stretched with free width give a uniaxial orientation with cylindrical symmetry distribution similar to Nylon-6 fiber where the molecular chain coincides with the b-axis.
(2) In the films uniaxially stretched with constant width, the molecular chain shows double orientation along MD direction and a considerable amount of TD direction together with a uniplanar orientation parallel to the film surface. This crystal orientation was proved to be a selective uniplanar-axial orientation where (200) plane lies parallel to stretching direction and perpendicular to film surface and (002) plane orients almost parallel to film surface; this is similar to the hot-rolled film.
(3) In the simultaneous-biaxially stretched films, the molecular chain shows a random orientation within the film along with a uniplanar orientation parallel to the film surface. This is interpreted as a uniplanar orientation where b-axis lies random and a-axis parallel to the film surface and c-axis tilts about 60-70° from it. Therefore, the hydrogen bonded planes characteristic to Nylon-6 seem to orient roughly parallel to the film surface.