Structural changes in thermal-induced polyacrylonitrile gel under uniaxial drawing

The influences of uniaxial drawing on the different structural scales in thermal-induced polyacrylonitrile (PAN) gel were studied. The results of atomic force microscopy (AFM) and swelling tests indicated that the drawn PAN gels had more compact structure with less solvent contained. Besides, some microphase separations occurred in the highly drawn gel and caused the gel to become more porous, as verified by the results from differential scanning calorimetry (DSC). The wide-angle X-ray diffraction (WAXD) results confirmed that drawing induces chain orientation and partial crystallization in the thermal-induced PAN gels, and higher draw ratio generated greater structural changes in the gels. It was also found from the tensile stress relaxation of the gels that the crosslinks in the gel increased with the draw ratio. In Fourier transform infrared (FTIR) spectra, the blue shift in wave numbers of two absorption peaks (3200-3700 cm⁻¹ and around 2244 cm⁻¹), and a gradually disappearing peak at 1036 cm⁻¹ all indicated the weakening hydrogen bonding between the PAN molecular chains and dimethyl sulfoxide (DMSO) molecules during the drawing process.