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Poly(acrylonitrile-co-methacrylic acid) (PAN-co-MAA)/N,N-dimethylformamide (DMF) solutions were prepared and dynamic shear rheology of these solutions were investigated. With increasing stirring time up to 72 h at 70°C, the polymer solution became less elastic (more liquid-like) with a ~60% reduction in the zero-shear viscosity. Relaxation spectra of the PAN-co-MAA/DMF solutions yield a decrease in relaxation time (disentanglement time, [τ.sub.d]), corresponding to an about 8% decrease in viscosity average molecular weight. The log-log plot of G' (storage modulus) versus G' (loss modulus) exhibited an increase in slope as a function of stirring time, suggesting that the molecular level solution homogeneity increased. In order to study the effect of solution homogeneity on the resulting carbon fiber tensile strength, multiple PAN-co-MAA/ DMF solutions were prepared, and the precursor fibers were processed using gel-spinning, followed by continuous stabilization and carbonization. The rheological properties of each solution were also measured and correlated with the tensile strength values of the carbon fibers. It was observed that with increasing the slope of the G' versus G' log-log plot from 1.471 to 1.552, and reducing interfilament fiber friction during precursor fiber drawing through the addition of a fiber washing step prior to fiber drawing, the carbon fiber strength was improved (from 3.7 to 5.8 GPa). This suggests that along with precursor fiber manufacturing and carbonization, the solution homogeneity is also very important to obtain high strength carbon fiber., INTRODUCTION High-performance (high tensile strength and high tensile modulus) fibers such as Spectra™, Dyneema™, Kevlar™, Zylon™, and carbon fibers, etc., are now available in the consumer market. The key parameters [...]

Polyacrylonitrile (PAN) and PAN/carbon nanotube (PAN/ CNT) fibers were manufactured through dry-jet wet spinning and gel spinning. Fiber coagulation occurred in a solvent-free or solvent/nonsolvent coagulation bath mixture with temperatures ranging from -50 to 25°C. The effect of fiber processing conditions was studied to understand their effect on the as-spun fiber cross-sectional shape, as well as the as-spun fiber morphology. Increased coagulation bath temperature and a higher concentration of solvent in the coagulation bath medium resulted in more circular fibers and smoother fiber surface. as-spun fibers were then drawn to investigate the relationship between as-spun fiber processing conditions and the drawn precursor fiber structure and mechanical properties. PAN precursor fiber tows were then stabilized and carbonized in a continuous process for the manufacture of PAN based carbon fibers. Carbon fibers with tensile strengths as high as 5.8 GPa and tensile modulus as high as 375 GPa were produced. The highest strength PAN based carbon fibers were manufactured from as-spun fibers with an irregular cross-sectional shape produced using a -50 C methanol coagulation bath, and exhibited a 61% increase in carbon fiber tensile strength as compared to the carbon fibers manufactured with a circular cross-section. POLYM. ENG. SCI., 55:2603-2614, 2015., INTRODUCTION Gel spinning has been used for the production of polyethylene [1], poly(vinyl alcohol) [2], and PAN [3] fibers, as well as their nanocomposite counterparts [4-8]. Advantages associated with gel [...]

Various bioengineering and industrial applications demand hard, tough, and mechanically strong polymeric blends. A novel combination of polyvinyl alcohol (PVA) and polyacrylonitrile was used to synthesize semi-IPNs using redox polymerization method in order to achieve desired property combinations in terms of toughness, generally not found in a single polymeric material. The synthesized end products in the form of polymer matrix were characterized by FTIR spectral analysis in order to confirm the incorporation of PAN into PVA, while the morphological aspects studied by AFM analysis showed fair compatibility between the component polymers exhibiting quite smooth surface and nanosize domains. Microhardness investigations were undertaken using the Vicker's indentation technique and the results were analyzed in terms of strain hardening phenomenon. Increase in surface hardness was observed as a result of variation of PVA content within the gel matrix whereas the presence of acrylonitrile as the second network was found to impart toughness as observed by the tensile strength measurements., INTRODUCTION In this era of polymers, when the polymeric materials are replacing most of the conventional materials, there is an increasing demand for new and novel materials with much improved [...]

The viscoelastic behavior of concentrated polyacrylonitrile (PAN) /1-butyl-3-methylimidazolium chloride ([BMIM]CI) solutions at different concentrations and temperatures has been investigated by rheology. For concentrated polymer solutions at low temperature (4°C), the shear viscosity was found to show a raid decrease from the ending of Newtonian plateau. At relatively high shear rate or frequency for the concentrated PAN/[BMIM]CI solutions, the deviation from the empirical Cox-Merz rule was quite evident, which suggested the formation of heterogeneous structures within these solutions. However, the dependence of G' and G' on angular frequency presented approximate linearity with similar slope at some temperatures between 100°C and 20°C. All the results lead us to the fact that the gelation has occurred within the concentrated solutions during cooling and the process was found to be thermoreversible. The gelation temperatures of the solutions have exhibited strong concentration dependence. It may be suggested that the microphase separation may be the major reason for the gelation of the concentrated PAN/[BMIM]CI solutions during cooling process. POLYM. ENG. SCI., 54:598606, 2014. ©2013 Society of Plastics Engineers, INTRODUCTION Polyacrylonitrile, as one of the important polymeric material for fiber and membrane is capable of gelation by adopting different mechanisms. The commonly accepted classification of polymer gets related to [...]