ADVANCES IN PRECURSORS FOR CARBON/GRAPHITE FIBERS

Recent Advances in Precursors for Carbon/Graphite Fibers

Recent Advances in Precursors for Carbon/Graphite Fibers

Introduction

Carbon fibers can be produced from a variety of precursors, such as polyacrylonitrile (PAN), mesophase pitch, rayon, etc., among which PAN-based carbon fibers are the preferred reinforcement for structural composites with the result of their excellent specific strength and stiffness combined with their light weight as well as lower cost. In order to meet expanded use in some high-tech sectors, many novel approaches, such as dry-wet spinning, steam drawing, increasing the molecular weight of precursors polymer, modifying the precursors prior to stabilization, etc., have been performed to increase the tensile strength of PAN-based carbon fibers. Now it has been popularly accepted that the quality of the high performance carbon fibers depends mainly on the composition and quality of the precursor fibers. However, the physical and chemical structural transformations that take place during heat treatments are extremely complicated. However, it is difficult to predict how to effectively improve the performances of the resultant carbon fibers, and it is not fully clear which one comonomer is the optimum selection and which one precursor index has the most influence on their structure and properties because of commercial secrets or other reasons. One way to address these issues is to take different PAN precursors and comparatively study their different evolution of structure features and properties of PAN precursor fibers during the thermal stabilization and carbonization process. In this study, some factors limiting the mechanical properties of carbon fibers are investigated, with the aim of generating guidelines to improve the quality of the resultant carbon fibers.

Recent Advances in Precursors for Carbon/Graphite Fibers

Different PAN precursors (named as P0, P1, P2 and P3, respectively) were selected in this study. For wet spinning precursor P1 fibers, a 20 wt.% solution was prepared in dimethylsulfoxide (DMSO) by using a copolymer of acrylonitrile/itaconic acid (AN/IA 97.5/2.5 w/w) with average molecular weight of 150 000 g mol-1. For precursor P2 fibers, which were wet-spun from a 22 wt.% solution in DMSO of a copolymer of acrylonitrile/acrylamide (AN/AM 97.5/2.5 w/w) with average molecular weight of 110 000 g mol-1. In comparison, a PAN precursor, designated as P0, was also wet-spun from a 22 wt.% solution in DMSO using a homopolymer of acrylonitrile with average molecular weight of ca. 120 000 g mol-1. The precursor P3 fibers, however, were supplied by Mitsubishi Rayon (Japan).

A self-designed pilot carbon fibers production line, which is composed of two oxidizing furnaces and two horizontal furnaces, respectively, is used for the preoxidation and closely linked carbonization of PAN precursors. Each furnace has some separated temperature zones. The whole temperature zones were programmed as the follows: 125-192-203-214-231-243-253-268-283-428-603-803-1003-1350 °C. The first oxidation oven has four different temperature zones, and the second oxidation oven has five different temperature zones. In the first two hot-air circulation preoxidation furnaces, a precursor fiber was thermal stabilized in a purified air atmosphere at 125-283 °C under a 10% stretching ratio, the total preoxidation time was about 50 min ...