MECHANICAL PROPERTIES AND MOLECULAR ORIENTATION BEHAVIOR OF THE BIAXIALLY STRETCHED NYLON-6 FILMS PREPARED BY WET-PROCESS

Abstract

This paper reports on the mechanical properties and behavior of molecular orientation of the Nylon-6 films by means of the uniaxial and biaxial stretching by wet-process in a hot-water bath.Unoriented low crystalline Nylon-6 film T-die extruded with a thickness of ca. 200μ was stretched at constant rate of 400%/min in a recirculating hot water at 70°C by various methods using a filmstretcher; i. e. uniaxial stretching under free width and/or constant width, and simultaneous biaxial stretching. The molecular orientation was studied by both measurements of birefringence for a tilted specimen and x-ray diffraction. The mechanical properties of the stretched films such as tensile strength, elongation at break, Young's modulus and F5 value were measured at 20°C under 65% R. H. using an Autograph tensile tester. The dynamic viscoelasticity, i. e. the temperature dependencies of dynamic loss modulus E″ were measured at 100Hz using a Viscoelastic Junior Spectrometer.The following results were obtained;(1) The characteristics of stretched films prepared by wet-process were noted that lower Young's modulus, lower F5 value and higher degree of crystallinity as compared with that of stretched films prepared by dryprocess. These properties are due to difference of the behavior of molecular orientation and the size of crystallite in the both stretched films.(2) Irrespective of stretch ratio the anisotropy of mechanical properties for the films uniaxially stretched under free width is greater than that of the stretched under constant width at the same stretch ratio of machine direction. Particularly, the Young's modulus of latter films are nearly equal in both the machine and the transverse directions.(3) For the simultaneous-biaxially stretched films prepared by wet-process, the mechanical and dynamic viscoelastic properties are isotropic within the plane as seen for the films prepared by dry-process, during all stretch ratio. However the tensile strength and elongation of these films were found to be similar to general tendency of the change, on the contrary, the Young's modulus and F5 value is not varied with the stretching by wet-process.