The differences between carbon fiber T300 and T700.
2021-11-01
When it comes to carbon fiber T300, industry insiders will first think of Toray from Japan. Indeed, carbon fiber T300 was invented by Toray in the 1970s, and subsequently, three major series of carbon fibers gradually became known: the high-strength T series, the high-modulus M series, and the MJ series, which combines high strength and high modulus. In recent years, T700 has replaced T300 as the new generation of general-purpose carbon fiber.
When discussing the differences between various models of carbon fiber, many people can easily mention their strength, modulus, density, etc. However, from a process perspective, what are the differences between them? This article will elaborate on T300 and T700 carbon fibers. The reason for comparing these two series of fibers is that there has been a fundamental change in the raw silk technology of these two series of carbon fibers, which is the transition from wet spinning to dry-jet wet spinning.
We all know that polyacrylonitrile can dissolve in dimethyl sulfoxide but is insoluble in water, while dimethyl sulfoxide can be infinitely miscible with water. Using this principle, we treat the aqueous solution of dimethyl sulfoxide as the coagulation liquid. When the polyacrylonitrile solution is sprayed into the coagulation liquid from the spinneret, a solvent concentration difference is generated due to the contact of the two substances. With a concentration difference, diffusion will occur. This diffusion is a bidirectional change where water diffuses into the polyacrylonitrile solution and dimethyl sulfoxide diffuses into the coagulation liquid. Polyacrylonitrile solidifies upon contact with water, creating a surface layer with a certain hardness on the sprayed filament bundle, which hinders the diffusion of water into the fiber and also hinders the diffusion of the dimethyl sulfoxide solution outward.
Next, let's analyze the differences between T300 and T700:
1. From a performance perspective
Both T300 and T700 have the same tensile modulus of 230 GPa and a fiber diameter of 7 μm, but there is a significant difference in tensile strength. T300 has a tensile strength of 3.53 GPa, while T700 reaches 4.90 GPa, which is 38.8% higher than the former. Additionally, T700's elongation at break has increased by 40%, and its bulk density has increased by 2.27%.
2. From the perspective of elemental composition
Scientific experiments have confirmed that the chemical composition of T300 and T700 is primarily carbon, with the former having a mass fraction of 92.5% and the latter 95.58%. The second element is nitrogen, with T300 at 6.96% and T700 at 4.24%. In comparison, T700 has a significantly higher carbon content than T300, and its carbonization temperature is higher than that of T300, resulting in a higher carbon content and lower nitrogen content.
3. From the perspective of surface morphology
Due to the differences in spinning processes, T300 and T700 exhibit distinctly different characteristics on their surfaces. T300 has a bark-like surface with grooves of varying depths, which is characteristic of the wet spinning process. In contrast, T700 has a smooth surface, which is characteristic of the dry-jet wet spinning process.
4. From the perspective of cross-sectional morphology
Both T300 and T700 carbon fibers exhibit a granular structure internally, with a clear original fiber bundle structure and axial micropores between them, resulting in relatively uniform fiber density. Moreover, SEM images of the surface morphology can also indicate that T300 uses the wet spinning process, while T700 employs the dry-jet wet spinning process.
Although the wet spinning and dry-jet wet spinning processes are separated by just a thin layer of air, their impact on the performance of carbon fibers is indeed significant. Therefore, in the entire production process, many small differences can affect the final performance of carbon fibers.
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