Designing index of void structure and tensile properties in wet‐spun polyacrylonitrile (PAN) fiber. I. Effect of dope polymer or nonsolvent concentration

Abstract

An index Xh21 with numerator calculated solely from solubility parameters and denominator measured by on-line viscosity of the fiber precursor in coagulation medium was defined as an indicator of the fiber structure and tensile properties. The Xh 21 values of wet-spun and wound polyacrylonitrile fibers from their dimethylformamide solutions with different polymer concentrations (series A) or nonsolvent concentrations in 10 vol % polymer solutions (series B) into water with draw ratio of one were determined and compared with the corresponding fiber structure and tensile properties. The Xh 21 value of about 0.8 3 10 6 s 21 led to finger-like structure with overall fiber porosity of 82 vol %. By reducing Xh 21 through dope polymer concentration enhancement to 20 vol %, overall fiber porosity decreased to 62 vol % via substitution of some micrometer voids with dense polymer ligament. Accordingly, strong fiber modulus and elongation at break enhancement were observed due to structural defect reduction and cohesive energy density increment. On the other hand, dope nonsolvent concentration increment from 0 to 5 vol % at 10 vol % polymer concentration showed minute overall fiber porosity decrement via Xh 21 increment through micrometer void substitution with nanometer ones (nuclei). Therefore, mild fiber modulus and elongation at break improvements were detected due to defect size reduction which magnifies mechanical properties improvements. Curve fitting of the Wang's second order modulus-porosity correlation to the as-spun fibers modulusporosity data verified the solid-liquid phase separation through nuclei growth-resistance as the main governing morphological evolution mechanism.

Simultaneously electrochemical exfoliation and functionalization of graphene nanosheets: Multifunctional reinforcements in thermal, flame‐retardant, and mechanical properties of polyacrylonitrile composite fibers

“…Pure PAN fiber presented a lot of finger-like channels which extended from exterior to center, ascribed to the exchange of solvent and water in the coagulation bath. [57] As observed in Figure 13B2, the incorporation of FGNS led to a more roughly fractured appearance in PAN/FGNS-3.0 fiber. This phenomenon indicated that the FGNS formed a strong interfacial interaction with PAN matrix.…”

“…To assess the interfacial interaction between FGNS and PAN matrix, the fracture morphologies of pure PAN and its composite fibers were observed through SEM (Figure ). Pure PAN fiber presented a lot of finger‐like channels which extended from exterior to center, ascribed to the exchange of solvent and water in the coagulation bath . As observed in Figure B2, the incorporation of FGNS led to a more roughly fractured appearance in PAN/FGNS‐3.0 fiber.…”

Application of response surface methodology to evaluate the effect of dry‐spinning parameters on poly (ε‐caprolactone) fiber properties

“…In both methods polymer is dissolved into a suitable solvent and the polymer solution pumped through the spinneret. In dry‐spinning, fiber is obtained through solvent evaporation, while in wet‐spinning, fiber is obtained through a phase inversion mechanism in which the polymer solution gets in contact with a fluid that is miscible with the spinning solvent but is not a solvent for the polymer . Some studies have used solution spinning to produce PCL fibers for different biomedical applications.…”

Ranking the key parameters of immersion precipitation process and modeling the resultant membrane structural evolution

“…Then, its cross-section was coated with a thin layer of gold and examined with a scanning electron microscope (SEM; model E382, Herisau Schweiz). 23 RESULTS AND DISCUSSION Figure 1 shows membrane thickness and porosity versus the FA ratio in the CA casting solutions. The increase in FA ratio enhanced membrane thickness monotonically, whereas a short plateau was observed in porosity increase.…”