A Comparative Study of the Structure and Mechanical Properties of Uniaxially and Biaxially Stretched PA6-66/Montmorillonite Films

The polyamide 6-66 (PA6-66) and PA6-66/montmorillonite films were prepared via extrusion film casting, followed by uniaxial and biaxial stretching on a biaxial stretcher. The structure and mechanical properties of the uniaxially and biaxially stretched films were comparatively studied. According to the results of small-angle X-ray scattering (SAXS), the biaxial orientation gave rise to a higher long period with respect to the uniaxial orientation, and the unstretched films presented a lowest long period. The wide-angle X-ray scattering (WAXS) patterns depicted that all the films mainly present α form crystal population, which could be due to the thermal annealing procedure after stretching. The orientations of α crystal and MMT were investigated in detail with WAXS and trichroic FTIR. It was found that the uniaxial stretching could result in a high alignment of b-axis along the machine direction (MD), and in contrast, the biaxial stretching facilitated the orientation of c-axis along the normal direction (ND) effectively. The MMT layers initially aligned along ND in unstretched PA6-66/MMT films attributed to the extrusion film casting process, and preferred to orient parallel to the film surface after stretching, with biaxial stretching presenting a more efficient influence. With the increase in the stretch ratio, the uniaxially stretched films showed increased tensile strength along MD while decreased tensile strength along transverse direction (TD). In contrast, the biaxially stretched ones presented balanced mechanical properties.