Uniaxial Drawing of Isotactic Poly(acrylonitrile): Development of Oriented Structure and Tensile Properties

In situ wide-angle X-ray scattering study on the change of microcrystalline structure in Jincheng anthracite during high-temperature carbonization

Carbonization is an effective way to achieve the comprehensive utilization of coal. However, the in situ variation of graphite-like microcrystals, the basic structure of coal macromolecules, with heating and cooling during carbonization has not been fully characterized so far. Anthracite is a type of humic coal with the highest degree of coalification, and its structure change can be monitored well by X-ray scattering or diffraction techniques. In this contribution, an in situ synchrotron radiation wide-angle X-ray scattering (WAXS) study on high-temperature (1200°C) carbonization of a high-quality anthracite mined in Jincheng, China, is presented. The results show that, during the continuous process of heating and cooling, the size and height of the aromatic lamellae first decrease and then increase with minima at 900 and 1000°C, respectively, while the interlayer spacing first increases and then decreases with a maximum at 1000°C. The roadmap of graphite-like microcrystalline structure change during the whole continuous process of heating and cooling is revealed and described.

Rheological Behavior of Amino-Functionalized Multi-Walled Carbon Nanotube/Polyacrylonitrile Concentrated Solutions and Crystal Structure of Composite Fibers

The rheological behavior of amino-functionalized multi-walled carbon nanotubes (amino-CNTs)/polyacrylonitrile (PAN) concentrated solutions in the dimethyl sulphoxide solvent and the effects of the amino-CNTs on the PAN precursor fibers by wet-spinning method were investigated. The amino-CNT/PAN concentrated solutions prepared by in situ solution polymerization with homogeneous dispersion of amino-CNTs have higher complex viscosity, storage modulus and loss modulus as compared to the control PAN concentrated solutions containing 22% PAN polymer by mass. The composite fibers with amino-CNTs of 1 wt % have lower degree of crystallization, crystal size and crystal region orientation compared to the control PAN precursor fibers. However, the amino-CNT/PAN composite fibers with diameter of about 10.5 μm exhibit higher mechanical properties than the control PAN precursor fibers with diameter of about 8.0 μm. Differential scanning calorimetry analysis demonstrated that the cyclization reaction in composite fibers have broad exothermic temperature range and low exothermic rate. These results indicate that the addition of amino-CNTs into PAN precursor fibers is beneficial to controlling the process of thermal stabilization and obtaining the higher performance of composite fibers.

Drawing dependent structures, mechanical properties and cyclization behaviors of polyacrylonitrile and polyacrylonitrile/carbon nanotube composite fibers prepared by plasticized spinning

Drawing to change the structural properties and cyclization behaviors of the polyacrylonitrile (PAN) chains in crystalline and amorphous regions is carried out on PAN and PAN/carbon nanotube (CNT) composite fibers. Various characterization methods including Fourier transform infrared spectroscopy, differential scanning calorimetry, X-ray diffraction and thermal gravimetric analysis are used to monitor the structural evolution and cyclization behaviors of the fibers. With an increase of the draw ratio during the plasticized spinning process, the structural parameters of the fibers, i.e. crystallinity and planar zigzag conformation, are decreased at first, and then increased, which are associated with the heat exchange rate and the oriented-crystallization rate. A possible mechanism for plasticized spinning is proposed to explain the changing trends of crystallinity and planar zigzag conformation. PAN and PAN/CNT fibers exhibit various cyclization behaviors induced by drawing, e.g., the initiation temperature for the cyclization (Ti) of PAN fibers is increased with increasing draw ratio, while Ti of PAN/CNT fibers is decreased. Drawing also facilitates cyclization and lowers the percentage of β-amino nitrile for PAN/CNT fibers during the stabilization.

Gel Spinning of Polyacrylonitrile/Cellulose Nanocrystal Composite Fibers

Polyacrylonitrile (PAN)/cellulose nanocrytal (CNC) fibers containing 0, 1, 5, and 10 wt % CNCs have been successfully produced by gel spinning. The rheological properties of solutions were investigated and the results showed that the complex viscosity and storage modulus of solutions were significantly affected by the presence of CNCs in the solution. Structure, morphology, mechanical properties and dynamic mechanical properties of these fibers have been investigated. Tensile modulus and strength increased from 14.5 to 19.6 GPa and from 624 to 709 MPa, respectively, as CNC loading increased from 0 to 10 wt %. Wide-angle X-ray diffraction results showed better PAN chain alignment and higher PAN crystallinity with the incorporation of CNCs.

The plasticized spinning and cyclization behaviors of functionalized carbon nanotube/polyacrylonitrile fibers

The plasticized spinning and cyclization behaviors of polyacrylonitrile (PAN) and polyacrylonitrile/functionalized carbon nanotube (PAN/CNT-COOH) composite fibers were studied.

Electrical activation of artificial muscles containing polyacrylonitrile gel fibers

Gel fibers made from polyacrylonitrile (PAN) are known to elongate and contract when immersed in caustic and acidic solutions, respectively. The amount of contraction for these pH-activated fibers is 50% or greater, and the strength of these fibers is shown to be comparable to that of human muscle. Despite these attributes, the need of strong acids and bases for actuation has limited the use of PAN gel fibers as linear actuators or artificial muscles. Increasing the conductivity by depositing platinum on the fibers or combining the fibers with graphite fibers has allowed for electrical activation of artificial muscles containing gel fibers when placed in an electrochemical cell. The electrolysis of water in such a cell produces hydrogen ions at an artificial muscle anode, thus locally decreasing the pH and causing the muscle to contract. Reversing the electric field allows the PAN muscle to elongate. A greater than 40% contraction in artificial muscle length in less than 10 min is observed when it is placed as an electrode in a 10 mM NaCl electrolyte solution and connected to a 10 V power supply. These results indicate potential in developing electrically activated PAN muscles and linear actuators, which would be much more applicable than chemically activated muscles.