Structural changes during the thermal stabilization of modified and original polyacrylonitrile precursors

Abstract

A polyacrylonitrile (PAN) precursor fiber of a special grade for preparing carbon fibers was modified by the impregnation of an aqueous KMnO 4 solution. The effects of the modification on the lateral and morphology structure, related to the crystalline properties of both the precursors and preoxidized fibers, such as the orientation index, crystal size, and crystallinity index, were measured by wide-angle X-ray diffraction. For both modified and original PAN fibers, a comparative study of the changes of the elemental content during the process of preoxidation, the relations between the thermal stress and heat-treatment temperature, and the effect of the modification on the skin/core structure of a preoxidized fiber were also introduced by the use of elemental analysis, optical microscopy, and so on. The modification of KMnO 4 was demonstrated to increase the density, increase the crystallinity index, increase the preferred orientation index, and decrease the crystal size for a modified precursor fiber and for a preoxidized fiber developed from a modified precursor fiber after a different heat-treatment temperature. KMnO 4 also showed a catalytic action, accelerating the rate of preoxidation and reducing the time of thermal stabilization; this improved the homogenization of the cross-section structure and led to an improvement in the tensile strength of 15-20% and an improvement in the elongation of 20 -30% in the resulting carbon fibers.

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.…”

“…As mentioned before, skin-core structure is undesired during the stabilization of PAN-based fibers because it leads to poor quality (mechanical properties of the) stabilized and carbonized fibers. 11,12,46,54 13.3.5 Mechanical Properties Figure 13.17 displays representative tensile responses of various carbonized fibers. Figure 13.17(a) corresponds to conventionally thermal stabilized non-UV-treated pure and UV-treated pure as well as fast-thermal stabilized pure PAN fibers.…”

Effects of cross-linking methods for polyethylene-based carbon fibers: review

“…To establish CFs in the mass market, the price of CF precursors has to be significantly reduced [10,20,[23][24][25][30][31][32][33][34][35][36][37][38][39][40]. The lowest priced CF precursors primarily consist of polyethylene (PE) [41], lignin [33], and cellulose [42].…”

Chemical Characterization of Stabilized and Carbonized Polyacrylonitrile (PAN) Fibers Treated with Oleic Acid.

“…Polyacrylonitrile (PAN) polymer was spun to form polyacrylonitrile (PAN) fiber and treated with solution known as post spinning treatment. Post spinning were divided into three categories, such as modification through coating, impregnation with chemicals (catalytic modification) and drawing/stretching with plasticizer [4,5,6 ]. Previous study shows fatty acid derivatives react as coating agent to reduce the entangling, fluffy, fusion and fiber to fiber adhesion of the PAN precursor fibers during thermal stabilization process [7].…”