Effect Of Technology Conditions On The Supramolecular Structure Of Polyacrylonitrile

Different solvents (DMF, NaSCN aqueous solution, ionic liquid) for polyacrylonitrile (PAN), with different molding methods (gel casting, wet spinning and dry-jet-wet spinning), and other technology conditions were studied to illustrate the effect of processing conditions on polyacrylonitrile supramolecular structure. Consequentially, the influence of supramolecular structure's changes on the properties polyacrylonitrile was investigated.Firstly, the polyacrylonirile gel films and fibres prepared from conventional solvent of DMF and NaSCN aqueous solution was investigated respectively. The results indicated that the crystal structure of polyacrylonitrile gel film prepared from solvent of DMF fits hexagonal system. With the increasing concentration of PAN solution from the gel film being prepared, the draw ratio increased with the maximum draw ratio above 10 and the maximum orientation degree of 92%. The crystal structure of Polyacrylonitrile fiber prepared from solvent of NaSCN aqueous solution fits hexagonal system too, with absence of three-dimensional ordered chain structure. During processing of PAN fiber with the solvent of NaSCN aqueous solution,, the maximum draw ratio was 16.5. The influence of draw temperature, draw load and draw ratio on the structure and tensile properties of acrylic fiber was discussed in detail. PAN fibers showed different tensile properties at different draw temperature. An optimum draw temperature of 170℃was selected to investigate the structure changes of the second-stage drawn fibers. The tensile modulus and tensile strength achieved a maximum value when the strain is about 160%.Furthermore, the polyacrylonirile fiber prepared from ionic liquid was invstigated. It was found that high concentration of spinning solution corresponding to high draw ratio the fiber. With the draw ratio increased, the crystal structure of the fiber gradually improved. While the concentration of PAN was above 13wt%, the diffraction of (002) crystal face was observed in the WAXD pattern of fiber, which means three-dimensional ordered crystal structure began to take shape with the draw ratio above 6 times. Meanwhile the streak at around 2θ= 39.7°corresponding 3/1 helical conformation of PAN in the fiber. Small angle X-ray scattering studies have shown that, with the draw ratio increases, the microvoids in fiber elongated gradually, with length above 0.5μm, and the misorientation under 35% during the voids oriented along the fiber axis. When PAN powder was dissolved in ionic liquids by kneading in an evacuated chamber and then formed fiber through dry-jet-wet spinning, the ductility of PAN fiber improved significantly comparing to the fiber prepared from the solution of PAN & ionic liquid with no kneading at the same concentration. After high ratio drawing, the fiber appeared obvious three-dimensional ordered structure, the meridian scanning of WAXD pattern was shown that the chain of the 3/1 helical conformation have higher amounts than that obtained in the PAN & ionic liquid solution by no kneading. Although the expectations of chain of planar zigzag sequences, which probably corresponding to high mechanical property do not appear, the consequential fibers can obtain the draw ratio of 107 after the solution was kneading, corresponding to the tensile strength of 0.52GPa.