Thermal stabilization of polyacrylonitrile fibers

Abstract

SynopsisPolyacrylonitrile (PAN) fibers pretreated with potassium permanganate have reduced the activation energy of cyclization and the oxidation time, and also improved the properties of the resultant carbon fibers. The activation energy of cyclization is reduced to 24 5 1 kcal/mol from 30 3 kcal/mol and the tensile strength of the carbon fibers increases by about 20-40%. The method of measuring the "aromatization index" (AI) value is modified and is recommended in checking the oxidation process. All fully stabilized PAN fibers have almost the same A1 value. However, the oxidation time is decreased by 30 min when oxidation temperature is raised by looc. INTRODUCTIONPolyacrylonitrile (PAN) fiber has been used as the precursor for making high-performance carbon fibers. An important step in preparing carbon fiber from the PAN fiber is to heat the precursor from 200 to 300°C in the air. Morita et a1.l and Raskovic and Marinkovic2 stated that treating PAN fiber by sulfur dioxide gas instead of air oxidation, is a better method of stabilizing fiber structure, and results in more economical production of high-performance carbon fibers.It has been established that heat treatment of PAN fiber under a tension load improves fiber quality.3* However, recent trends in developing highperformance carbon fibers from PAN is through chemical modification of the precursor with certain additives before oxidation. Mathur et al.5 and Bahl et a1.6 have pretreated PAN fiber with CuCl to make high-performance carbon fibers. Our previous study7 presented the preliminary results of the process taking place during the pretreatment of PAN fibers with potassium permanganate. This study offers further details of our investigations, the microstructure, physical, and mechanical properties of the oxidized fibers. EXPERIMENTALA special grade acrylic fiber, Courtelle fiber (Courtaulds Limited, Coventry, UK), containing 6% methyl acrylate and 1% (itaconic) acid copolymer was used in our work. Each single tow of the fiber contains 6000 strands of 1.1 denier monofilament. A fiber-wound frame was pretreated by immersing it in a 7% potassium permanganate solution at 85°C for a few minutes, then washed with distilled water and dried to a constant weight in an oven. The color changed from clear white to brown after pretreatment. The manganese content in the prepared carbon fibers was determined by atomic emission spectrometer analysis and found to be 25 ppm for the untreated, and 1630 Oxidized PAN fibers and the pretreated precursor were heat-treated in a constant temperature zone furnace under constant load (0.1 g/denier) a t 230, 250, and 270°C from 1 to 10 h, respectively, in a purified air atmosphere. The oxidized fiber tows were carbonized to 1300°C in a ceramic reaction tube under oxygen-free Ar atmosphere. A heating rate of 250°C/h was carried out up to lOOO"C, then continued a t 6OoC/h until reaching 1300"C, then the specimens were cooled down immediately.Mechanical properties of PAN and stabilized fibers were measured by Instron 1122 tensile-tes...

Carbon Fibers: Precursors, Manufacturing, and Properties

“…An optimum of 8–10 at% of oxygen in the stabilized precursors has been reported 34. Also, SO 2 , HCl, or Br 2 and various other oxidizing agents were investigated as alternatives for oxygen,35–47 but none of these agents seem presently economically useful. Alternative stabilization methods like plasma treatment,48 electron‐beam assisted cyclization,49 or microwave assisted processing51 are under investigation to reduce stabilization times as well as energy consumption.…”

UV-Based Dual Mechanism for Crosslinking and Stabilization of PAN-Based Carbon-Fiber Precursors

“…These tensile properties of the PAN fibers are consistent with those reported in the literature: 10-25% for the breaking strain, 0.1-0.7 GPa for strength, and 1-10 GPa for tensile modulus. 15,19,30,50,[53][54][55][56][57] The tensile-testing results shown in Table 13.1 indicate that, at 95% confidence, there is a significant difference in the breaking strain between pure and 1 wt% BDP fibers; the presence of photoinitiator reduces the elongation capabilities of the fibers by B1%. These results show no significant statistical differences, at 95% confidence, between the ultimate tensile strength among different specimens.…”

Chemical structural characterization of pyrolyzed and subsequently ion-implanted poly(acrylonitrile)

“…Carbon fibers and activated carbon fibers are produced by carbonizing a raw material such as poly(acrylonitrite) (PAN) fiber [1,2]. Carbon fibers are excellent reinforced materials for composites, are now important industrially and have gained a wide range of applications in the industrial and engineering fields, from sport articles to the aerospace industry [3,4].…”