Materials Science and Engineering A 485 (2008) 251–257 The effect of processing conditions on a polyacrylonitrile fiber produced using a solvent-free free coagulation process A.F. Ismail a,∗ , M.A. Rahman a , A. Mustafa a , T. Matsuura b a Membrane Research Unit, Faculty of Chemical and Natural Resources Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia b Department of Chemical Engineering, Industrial Membrane Research Institute, University of Ottawa, Ottawa, Ont., Canada KIN 6N5 Received 3 April 2007; received in revised form 25 July 2007; accepted 20 August 2007 Abstract PAN fibers were fabricated using a solvent-free coagulation process and characterized using SEM and tensile testing. Eighteen weight percent of polymer solution was found to be the most suitable composition for fabrication process and consequently produced fibers with the best mechanical properties. The PAN fibers fabricated using a coagulation bath temperature of 13 ◦ C exhibited the highest Young’s modulus of 2.93GPa and the highest tensile strength. The number of nano-pores was significantly reduced due to low inward diffusion of non-solvent. © 2007 Elsevier B.V. All rights reserved. Keywords: Polyacrylonitrile fiber; Carbon fiber; Solvent-free coagulation process; Nano-pores; Young’s modulus 1. Introduction PAN fiber is considered as a crucial precursor for the pro- duction of carbon fiber. PAN is transformed into fiber form by melt spinning, wet spinning and dry spinning [1]. In addition to these techniques, PAN precursor fibers are also fabricated using dry–wet spinning to improve the mechanical properties [2]. In this method, the dope travels through an air gap of less than 1 cm before emerged into coagulation bath. PAN homopolymer is rarely used as a carbon fiber precursor since it initiates a retrograde core during the stabilization process due to partial melting caused by exothermic nature of oxidation process [3]. It is also generally not favorable for spinning pur- poses compared to its copolymers which are more soluble in solvents and easier to handle for preparation and storage [2]. The solubility of PAN and thermal properties of PAN fibers can be enhanced by the incorporation of either acidic, neutral or hydrophilic moieties as comonomers during polymerization or as spinning dope additives before the fabrication process [4]. Numerous studies have shown that the PAN fibers should possess the following characteristics; small diameter, maximum crystallinity, low comonomer contents and high modulus for the ∗ Corresponding author. Fax: +60 7 5581463. E-mail address: afauzi@utm.my (A.F. Ismail). preparation of good quality carbon fibers [5–7]. The Young’s modulus of PAN precursor fiber is being the best parameter rep- resenting the carbon fiber performance since there is a direct correlation between the Young’s modulus of primary precursor and the resulting carbon fiber [8]. Therefore, the conditions of PAN fiber fabrication process play an important role in the pro- duction of high performance carbon fibers since the properties of PAN precursor fibers depend much on it. Normally, the spinning solution with polymer concentration ranging from 10 wt.% to 30 wt.% was used for the fabrication of PAN fibers by the wet spinning process [1,9]. By increasing the polymer concentration in the spinning dope, the spinnability can be improved, the tenacity increases and the porosity decreases [4,10]. The polymer concentration in the spinning solution also influences the fiber morphology and density. According to Knud- sen [10], an increase in the dope solid in the range of 15–25% improved the homogeneity of the fiber structure by reducing the generation of large voids. Besides, an increase in the dope solid slightly increased the density of PAN fibers [9]. As compared lower polymer concentration with less viscosity, a higher con- centration of polymer solution contributes to a higher packing of the polymer molecules per unit volume inside the fiber. Besides polymer composition, dope viscosity plays an impor- tant role in PAN fiber fabrication process. For example, Bajaj et al. kept the spinning dope viscosity between 5700 cps and 6250 cps in order to eliminate the die-swelling effect and to 0921-5093/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2007.08.060