Manager Hao (pre oxygenation thread): 13831164999
Manager Shi (pre oxygenation wire): 17332928150
Manager Gu (Pre oxygenation Silk): 13833138900
Manager Zhao (woven fabric, pre impregnated fabric, prefabricated body): 15028196018
Manager Zhang (woven fabric, axial fabric): 13703314888
Manager Zhao (Composite Products): 13944687090
Address: 226 Shifu East Road, Gaocheng District, Shijiazhuang City, Hebei Province
The conversion rate of pre-oxidized fiber to carbon fiber (essentially the carbon yield rate of the final carbon fiber, i.e., the percentage of the carbon fiber mass relative to the pre-oxidized fiber mass after carbonization and graphitization) is a core technical indicator that directly affects the production efficiency, cost, and performance of carbon fiber. Its key influencing factors cover pre-oxidized fiber quality, carbonization process parameters, equipment precision, and auxiliary conditions, which are detailed below for industrial B2B application scenarios:
The structural and chemical stability of pre-oxidized fiber is the foundation for high conversion rate—only qualified pre-oxidized fiber can ensure a high carbon yield and low defect rate during subsequent high-temperature processing.
Degree of pre-oxidation
Moderate oxidation: Pre-oxidized fiber with a density of 1.3–1.4 g/cm³ and oxygen content of 10–15% has a complete three-dimensional cross-linked structure. During carbonization, it only removes small-molecule impurities (water, ammonia), and the carbon yield can reach 50–60% (PAN-based).
Under-oxidation: Insufficient cyclization and cross-linking reactions make the fiber retain thermoplasticity. During high-temperature carbonization, it will melt, stick, or decompose in large quantities, reducing the carbon yield to below 40% and producing porous, low-strength carbon fiber.
Over-oxidation: Excessive oxidation causes the fiber surface to form brittle oxygen-containing groups, and the internal structure is damaged. During carbonization, microcracks expand, leading to fiber breakage and a carbon yield reduction of 10–15%.
Uniformity of pre-oxidized fiber structureUneven temperature or tension during pre-oxidation will cause differences in the degree of oxidation between different parts of the fiber bundle. The non-uniform structure will lead to localized over-decomposition during carbonization, reducing the overall conversion rate and causing performance inconsistency of the final carbon fiber.
Precursor type of pre-oxidized fiberDifferent precursor-based pre-oxidized fibers have inherent differences in carbon yield:
PAN-based: Carbon yield 50–60% (highest among mainstream types, suitable for high-performance carbon fiber).
Pitch-based: Carbon yield 70–85% (mesophase pitch has a high carbon content, but the conversion rate is affected by the orientation of the liquid crystalline structure).
Rayon-based: Carbon yield only 20–30% (large amount of non-carbon elements such as oxygen and hydrogen need to be removed, gradually eliminated in industrial applications).
Carbonization is the core step of converting pre-oxidized fiber to carbon fiber. The control of temperature, heating rate, atmosphere, and tension directly determines the retention rate of carbon elements.
Carbonization temperature and heating rateCarbonization is usually divided into two stages: low-temperature carbonization (400–800°C) and high-temperature carbonization (800–1500°C).
Low-temperature stage: It is mainly for removing non-carbon elements (dehydration, deamination). The heating rate should be slow (1–3°C/min). Too fast heating will cause rapid escape of small molecules, forming bubbles inside the fiber and reducing the carbon yield; too slow heating will reduce production efficiency.
High-temperature stage: It is for graphitization of the carbon structure (formation of oriented graphite microcrystals). The temperature should be stable (1200–1500°C for PAN-based). Too low temperature will lead to incomplete carbonization; too high temperature will cause sublimation of partial carbon elements and reduce the conversion rate.
Carbonization atmosphereCarbonization must be carried out in a strict inert atmosphere (nitrogen or argon) to prevent oxidation of the pre-oxidized fiber at high temperatures (oxidation will consume carbon elements and form CO₂, drastically reducing the conversion rate).
The oxygen content in the furnace must be controlled below 50 ppm; if the atmosphere is not pure, the carbon yield may decrease by 20–30%.
Tension control during carbonizationApplying appropriate tension (0.5–1.0 cN/dtex) during carbonization can align the carbon microcrystals along the fiber axis, reduce structural shrinkage, and avoid fiber breakage. Excessive tension will cause fiber fracture, while insufficient tension will lead to loose structure and increased small-molecule escape, both of which reduce the conversion rate.
Carbonization furnace equipment performanceThe temperature uniformity of the carbonization furnace directly affects the consistency of the conversion rate:
The temperature difference in the furnace should be controlled within ±5°C; if the temperature is uneven, some fibers will be over-carbonized while others are under-carbonized, resulting in a low overall conversion rate.
The sealing performance of the furnace body ensures the purity of the inert atmosphere; poor sealing will lead to air leakage and oxidation of the fiber.
Cleanliness of the process environmentDust, oil stains, or other impurities in the production environment will adhere to the surface of the pre-oxidized fiber. During carbonization, these impurities will react with the fiber, causing surface defects and reducing the effective conversion rate of the carbon fiber.
Graphitization is a high-temperature treatment process (2000–3000°C) after carbonization, which is mainly used to improve the modulus of carbon fiber. It has a slight impact on the conversion rate:
Appropriate graphitization temperature can optimize the graphite crystal structure without significant carbon loss; excessive temperature (>3000°C) will cause carbon sublimation, reducing the conversion rate by 3–5%.
To improve the conversion rate of pre-oxidized fiber to carbon fiber, the core is to produce moderately oxidized, structurally uniform pre-oxidized fiber, and then match it with precise carbonization process parameters (stable temperature, slow heating rate, pure inert atmosphere, and appropriate tension). This can not only ensure a high carbon yield but also guarantee the mechanical properties of the final carbon fiber.
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Ltd. All rights reserved.
Manager Hao (Pre-oxidized Fiber): 13831164999,hjh@hbtangu.com
Manager Shi (Pre-oxidized Fiber): 17332928150,sj@hbtangu.com
Manager Gu (Pre-oxidized Fiber): 13833138900
Manager Zhao (Woven Cloth, Prepreg Cloth, Preform): 15028196018,zb@hbtangu.com
Manager Zhang (Woven Cloth, Axial Cloth): 13703314888
Manager Zhao (Composite Products): 13944687090, zqy@hbtangu.com
Email: hbtg@hbtangu.com
Address: No. 226, East Shifu Road, Gaocheng District, Shijiazhuang City, Hebei Province
