Oxidation process of polyacrylonitrile fibers

Abstract

The effect of the content of active co-monomer, itaconic acid (IA), in PAN fiber on the thermal chemical transformations of the fiber during oxidation was studied. It was shown that the temperature for the start of the exotherm decreased as the IA content increased to 1. 8-1.9% and remained constant at 182°C as the content was increased further. A study of the effect of the degree of oxidation on the change of thermochemical characteristics of PAN fiber found that two successive exothermic processes occurred. The difference in their mechanisms was explained by the effect of autocatalysis that was due to catalytically active centers of the macromolecules that arose during the oxidation and contained polyconjugated bonds.The process for producing carbon fibers from fibers based on acrylonitrile copolymers includes two basic steps that differ in their reaction conditions. In the initial step (oxidation), polyacrylonitrile (PAN) fiber is subjected to relatively lengthy (60-100 min) gradient heating in air. The oxidized PAN fiber is subjected to further heat treatment (carbonization) that is carried out in a non-oxidizing gas, Ar or high-purity N 2 .Two principal processes, structuring of PAN fiber and destruction of the polymer, occur during the course of the oxidation. The term structuring means the rearrangement of linear PAN macromolecules into molecules with a staircase structure that contain polyconjugated systems [1]. This process can be viewed as the initial step in the transformation of the polymer structure into a graphitic one. Two principal reactions, oxidative dehydrogenation of the PAN macromolecule hydrocarbon chain and polymerization of nitrile groups to form naphthyridine heterocycles, occur during the structuring. Conditions such as heating, which favor preferential occurrence of structuring and minimize destructive processes, make it possible to convert PAN fiber into carbon fiber.One of the most important features of the oxidation of PAN fiber, which is characteristic of the oxidation of any organic compound, is its exothermicity. If the process heating regime is not followed, the heat released as a result of the reaction can increase uncontrollably and lead to destruction as a result of the predominance of destructive processes. Therefore, one of the main methods for investigating the oxidation of PAN fiber is to study the heat releases accompanying this process.The kinetics of thermal oxidation of PAN fiber are rather complicated and depend on the heating conditions. Published results of numerous investigations of this process were based on a study of fiber samples that were oxidized under laboratory conditions and did not correspond with heating regimes under industrial conditions. These conditions can be considered only to approximate those of the actual industrial process for producing conditioned carbon fiber. However, it is impossible to measure directly heat releases during continuous heat treatment of PAN fiber under conditions close to the industrial ones.Herein thermal effects observed ...

Surface-mediated twin polymerisation of 2,2′-spirobi[4H-1,3,2-benzodioxasiline] on multi-walled carbon nanotubes, polyacrylonitrile particles and copper particles

“…The cyano functionalities react to the complex structure of carbonyl groups and aromatic rings due to oxidative pretreatment (Scheme S1, ESI †). 59,[79][80][81][82][83][84][85][86][87][88][89][90] Compared to pristine PAN, quantitative elemental analysis (Table S2, ESI †) shows decreased contents of carbon, hydrogen and nitrogen in combination with an increased content of other elements, like oxygen.…”

The formation of conjugated structure and its transformation to pseudo-graphite structure during thermal treatment of polyacrylonitrile

“…It was reported that the initial temperature (T i ) of the exothermic process decreased with increase in IA content to 1.8-1.9%, which also decreased the cyclization degree and increased the oxidation degree. 10,11 Moreover, the distribution of comonomer in the polymer chain can affect the stabilization reactions. The PAN-co-IA chains with regular and block architecture show more prominent cyclization and oxygen-uptake capabilities compared with randomly structured chains.…”

Studies on cytocompatibility of human dermal fibroblasts on carbon nanofiber nanoparticle-containing bioprinted constructs

“…GelMA contains polar molecules such as NH 2 , COOH, and OH groups and acts as a charge carrier [26]. CNF NPs produced from PAN, due to thermal oxidation and carbonization processes, exhibit a polyconjugated system with mobile π-electrons [30]. Hence, when CNF NPs are blended with GelMA, the net polarized moieties present in the constructs increase, which is inferred from the steepness of the Nyquist admittance curves.…”