Dynamic Self-Stiffening and Structural Evolutions of Polyacrylonitrile/Carbon Nanotube Nanocomposites

The self-stiffening under external dynamic strain has been observed for some artificial materials, especially for nanocomposites. However, few systematic studies have been carried out on their structural evolutions, and the effect of the types of nanofillers was unclear. In this study, we used a semicrystalline polymer, polyacrylonitrile (PAN), and various types of carbon nanomaterials including C₆₀, carbon nanotube (CNT), and graphene oxide (GO). An external uniaxial dynamic strain at small amplitude of 0.2% was applied on the prepared nanocomposite films. It was observed that PAN/CNT exhibited significant self-stiffening behavior, whereas PAN/GO showed no response. Systematic characterizations were performed to determine the structural evolutions of PAN/CNT film during dynamic strain testing, and it was found that the external dynamic strain not only induced the crystallization of PAN chains but also aligned CNT along the strain direction

Lignin/Polyacrylonitrile Composite Hollow Fibers Prepared by Wet-Spinning Method

Lignin is the second most abundant and inexpensive natural biopolymers on earth. In this work, lignin/polyacrylonitrile composite fibers were prepared by wet-spinning method. A transition from solid fiber to hollow fiber was observed when the volume fraction of water in a mixed dimethyl sulfoxide/water coagulation bath was increased. The rheological measurements results showed that the spinning solution had no chemical reactions and was stable at the spinning conditions. Lots of interconnected macro- and medium pores (50–90 nm) were formed inside the wall section of these hollow fibers. The change of coagulation solvent had little influence on the outer diameters of the fibers. The formations of the hollow structure and the pores are ascribed to a diffusion controlled procedure. The reaction between formaldehyde and hydroxyl groups (−OH) in lignin molecule was found to improve slightly fiber modulus and thermal stability. This study provides a facial way to prepare lignin-based hollow fibers for many applications