X-ray and Trichroic Infrared Orientation Analyses of Uniaxially Stretched PA6 and MXD6 Nanoclay Composite Films

Cast films of aliphatic (PA6) and aromatic (MXD6) nylons and their in situ polymerized nanocomposites with 4 wt % clay were prepared by an extrusion process and rapid cooling using an air knife. The precursor films were then uniaxially stretched at 110 degrees C with draw ratios varying from 1.5 to 5. The changes in orientation of clay and crystal axes of all the crystalline phases and amorphous region were examined using X-ray diffraction and Trichroic Infrared analyses. The clay alignment was measured with three different techniques: FTIR peak deconvolution, FTIR interactive spectral subtraction and X-ray diffraction. It was found that the clay platelets are mainly oriented in the machine direction (MD) and their orientation improved upon uniaxial stretching. X-ray analysis showed that gamma crystals (designated as gamma(1)) of both nylons were mainly formed during rapid cooling of cast films. However, only the PA6/clay films showed an extra gamma crystal population (designated as gamma(2)). WAXD and FTIR analyses revealed that the c-axis of gamma(1) crystal population was oriented in the normal and transverse directions (ND and TD), while the c-axis of gamma(2) was aligned in the normal direction (ND), indicating that this later crystal population formed perpendicular to the (001) plane of the clay platelets. The orientation of gamma(1) and gamma(2) crystal populations increased after uniaxial deformation. The MXD6 showed very little crystallinity due to its higher stiffness and low relaxation rate of the aromatic chains. The amorphous region had a lower orientation in the nanocomposite films due to the spatial hindrance caused by the presence of clay platelets.