Dynamic Mechanical Relaxations in Poly(acrylonitrile) with Different Stereoregularities

Dry-Jet Wet Spinning of Thermally Stable Lignin-Textile Grade Polyacrylonitrile Fibers Regenerated from Chloride-Based Ionic Liquids Compounds

In this paper, we report on the use of amorphous lignin, a waste by-product of the paper industry, for the production of high performance carbon fibers (CF) as precursor with improved thermal stability and thermo-mechanical properties. The precursor was prepared by blending of lignin with polyacrylonitrile (PAN), which was previously dissolved in an ionic liquid. The fibers thus produced offered very high thermal stability as compared with the fiber consisting of pure PAN. The molecular compatibility, miscibility, and thermal stability of the system were studied by means of shear rheological measurements. The achieved mechanical properties were found to be related to the temperature-dependent relaxation time (consistence parameter) of the spinning dope and the diffusion kinetics of the ionic liquids from the fibers into the coagulation bath. Furthermore, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical tests (DMA) were utilized to understand in-depth the thermal and the stabilization kinetics of the developed fibers and the impact of lignin on the stabilization process of the fibers. Low molecular weight lignin increased the thermally induced physical shrinkage, suggesting disturbing effects on the semi-crystalline domains of the PAN matrix, and suppressed the chemically induced shrinkage of the fibers. The knowledge gained throughout the present paper allows summarizing a novel avenue to develop lignin-based CF designed with adjusted thermal stability.

Impact of Alternative Stabilization Strategies for the Production of PAN-Based Carbon Fibers with High Performance

The aim of this work is to review a possible correlation of composition, thermal processing, and recent alternative stabilization technologies to the mechanical properties. The chemical microstructure of polyacrylonitrile (PAN) is discussed in detail to understand the influence in thermomechanical properties during stabilization by observing transformation from thermoplastic to ladder polymer. In addition, relevant literature data are used to understand the comonomer composition effect on mechanical properties. Technologies of direct fiber heating by irradiation have been recently involved and hold promise to enhance performance, reduce processing time and energy consumption. Carbon fiber manufacturing can provide benefits by using higher comonomer ratios, similar to textile grade or melt-spun PAN, in order to cut costs derived from an acrylonitrile precursor, without suffering in regard to mechanical properties. Energy intensive processes of stabilization and carbonization remain a challenging field of research in order to reduce both environmental impact and cost of the wide commercialization of carbon fibers (CFs) to enable their broad application.

Effects of oxygen on the structural evolution of polyacrylonitrile fibers during rapid thermal treatment

In this study, the mechanism of stabilizing polyacrylonitrile (PAN) fibers in a short period of time is investigated through probing the effects of oxygen on the structural evolution of PAN under different temperature regimes. It has been found that oxygen has a significant influence on both the chemical and physical structural evolution of PAN fibers, even in a short period of stabilization time, and the influences are dissimilar at different stabilization temperatures. At lower temperatures (below 140 °C), there is no noticeable change in the chemical and physical structures of the PAN fibers. In the mid-temperature range (140-200 °C), oxygen can slightly induce the cross-linking of PAN chains and result in a higher rate of decreasing crystallinity. When the main chemical reactions are initiated at higher temperatures (200-260 °C), oxygen is directly involved in the oxidation reaction of the PAN chains and facilitates cyclization and dehydrogenation. These reactions initiate in the amorphous regions of PAN fibers, and extend to the crystalline regions at elevated temperatures.

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.

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.

Polyacrylonitrile fibers containing graphene oxide nanoribbons

Graphene oxide nanoribbon (GONR) made by the oxidative unzipping of multiwalled carbon nanotube was dispersed in dimethylformamide and mixed with polyacrylonitrile (PAN) to fabricate continuous PAN/GONR composite fibers by gel spinning. Subsequently, PAN/GONR composite fibers were stabilized and carbonized in a batch process to fabricate composite carbon fibers. Structure, processing, and properties of the composite precursor and carbon fibers have been studied. This study shows that GONR can be used to make porous precursor and carbon fibers. In addition, GONR also shows the potential to make higher mechanical property carbon fibers than that achieved from PAN precursor only.