Static small‐angle x‐ray scattering study of polymer deformation

Abstract The small‐angle x‐ray scattering (SAXS) approach has been employed in an effort to understand the deformation mechanism of semicrystalline polymers in terms of submicroscopic structure of lamellae. Isotropic melt‐pressed polyethylenes of low, medium, and high densities (LDPE, MDPE, and HDPE, respectively) having spherulitic texture were investigated by SAXS for various Static elongations between 10% and 40%. The SAXS isointensity contours of the deformed polymers are anisotropic (elliptical) with the long axis perpendicular to the stretching direction. Slice averages at various azimuthal angles between 0° and 90° reveal distinct SAXS peaks with respect to scattering angle. The peak position of SAXS profile characterizes the long period or lamellar spacing, while integrated intensity distribution is relevant to lamellar orientation. At low elongations, there is an increase in intensity at both azimuthal angles of 0° and 90°, suggesting that excess scattering arises during deformation, probably associated with lamellar untwisting process. Lamellar orientation distribution and second‐order orientation are defined to account for the lamellar orientation process. Experimental results are compared with Kratky's floating rod model coupled with Stein's lamellar untwisting model. The lamellar orientation closely follows the affine deformation scheme, while the lamellar spacing deviates appreciably from it, particularly at large elongations.