Uniaxial deformation of nylon-6 and nylon-11: changes in orientation and crystal phase

The effect of uniaxial drawing on orientation of the crystalline fraction o f two polymers forming hydrogen bonds, nylon-6 and nylon-11, has been inves tigated using X-ray diffraction. These two polymers have similar crystal ph ases, although their hydrogen bond density differs. For both polymers, the deformation occurs in two steps, the first being a plastic deformation of t he a-phase spherulites. This leads to two populations of crystals, one with the chain axis oriented parallel to the draw direction, the second with th e a axis (hydrogen bond direction) aligned along the draw direction. In the second step, the a-axis aligned population gradually tilts, leading to a u niaxial orientation of the samples with chain axis aligned along the draw d irection. For nylon-ii, the onset of this step corresponds to the emergence of crystals of the gamma phase, which rapidly becomes the major phase. It reaches a higher orientation than the a phase, and stems from crystallizati on upon tension of the polymer. For nylon-6, although the gamma phase also appears during drawing, at the maximum draw ratio only a small fraction is present. This difference is attributed to the relative stability of the two phases, which is different for nylon-6 than for nylon-ii.