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 ...

The possibility of modifying viscose fibre with hybrid systems containing flame retardants was demonstrated. The effect of the flame retardants on the physicomechanical properties of the fibres was determined. Bath compositions and modification parameters that ensure the sorption-diffusion reaction of the flame retardant and fibre and production of material with a high oxygen index (greater than 70%) were developed.A great deal of work has been done to create fibres with reduced combustibility. Different flame retardants (FR) are used to give fibres fireproof properties. Multicomponent systems that simultaneously contain several kinds of flame retardants (FR) have recently been used. These so-called hybrid compositions have a synergistic effect due to the combustion inhibitors they contain -phosphorus and nitrogen.We previously selected the FR and determined the temperature and duration of modification of viscose fibres [1] with hybrid systems. The FR Pyrofax (PF), diamidomethylphosphate (T-2), and methazine (MTZ) were incorporated in the hybrid systems and the following sequence of manufacturing operations was established; impregnation, heat treatment, washing, drying. We investigated the effect of the composition of the modifying systems on the properties of the viscose fibres.The viscose fibres were modified from water baths containing 20 and 30 wt. % mixtures of FR consisting of T-2, PF, MTZ, and phosphoric acid (PA). In addition, all components of the modifying bath containing phosphorus and nitrogen affected thermooxidative degradation and combustion of the fibre; methazine held the FR in the fibre, and PA played the role of a catalyst that accelerates the reaction of the reactive groups in FR and the fibre. Based on previous studies on sorption of FR, the duration of impregnation with a solution of FR of 20% concentration was 60 sec, and it was 30 sec for the 30% concentration.The amount of sorbed flame retardants increased both with an increase in their content in the bath from 20 to 30 wt. % and with a change in the ratio of methazine and phosphoric acid in it (Fig. 1). The weight losses in heat treatment and washing were lower in the fibres modified in a bath with a high content of MTZ and PA.The efficiency of the reaction (E r , %) of FR with viscose fibre [2] was determined with the equationwhere ω la , ω im are the amount of FR retained by the fibre after laundering and impregnation, respectively.Simultaneously increasing the content of both MTZ and PA in the modifying bath increased the effectiveness of the reaction and the content of FR in the fibre (Table 1). Simultaneously increasing the content of both MTZ and PA in the bath gave the fibre higher resistance to wet treatments and increased E r by 6-16%.Since the fibres were modified from water baths and viscose fibre is hydrophilic, the effect of the modification conditions on the deformation-strength properties of the fibre is natural.The studies established a correlation between the ratio of the components in the bath and the properties of the ...

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