Speaking of carbon fiber T300, the industry will first think of Japan Toray, yes, the carbon fiber T300 is Japan Toray invented in the 1970s, after three series of carbon fibers are gradually known, respectively, high-strength T series, high-modulus M series, both high-strength and high-modulus MJ series of carbon fibers, in recent years, the T700 replaced the T300 to become a new generation of general-purpose grade carbon fiber.

When it comes to the difference between the various types of carbon fiber, many people can also off the top of their heads their strength, modulus, density, etc., but from the process point of view, what is the difference between them. In this article, we will talk about T300 and T700 carbon fibers. Why these two series of fibers for comparison, this is because these two series of carbon fiber filament technology has a fundamental change, this is the wet spinning and dry spray wet spinning transformation.

We all know that polyacrylonitrile can be dissolved in dimethyl sulfoxide but not in water, while dimethyl sulfoxide can be infinitely miscible with water. Using this principle, we take the aqueous solution of Dimethyl Sulfoxide as the solidifying liquid. When the polyacrylonitrile solution is sprayed into the solidifying liquid by the nozzle, the difference in solvent concentration is generated due to the contact of the two substances, and the difference in concentration leads to diffusion. This diffusion is a two-way change between the diffusion of water into the interior of the polyacrylonitrile solution and the diffusion of dimethyl sulfoxide into the coagulant. Polyacrylonitrile solidifies when it meets water, and the surface of the sprayed tow produces a surface layer with a certain degree of hardness, which prevents water from diffusing into the interior of the fibers and also prevents the dimethyl sulfoxide solution from diffusing to the exterior.

Next, we give you an analysis of the differences between T300 and T700:

First, from the performance

T300 and T700 have the same tensile modulus of 230Gpa and ping poly diameter 7μm, but in the tensile strength, the two are very different, T300 for 3.53Gpa, while T700 reached 4.90Gpa, 38.8% higher than the former, and the elongation at break of T700 increased by 40%, the bulk density increased by 2.27%.

Second, from the elemental composition

After scientific tests have confirmed that the chemical composition of T300 and T700 is mainly carbon, the former mass fraction of 92.5%, the latter 95.58%; followed by nitrogen, the former 6.96%, the latter 4.24%, compared to T700 carbon content is significantly higher than the T300, the carbonization temperature is higher than the T300, which makes its carbon content and low nitrogen content.

Third, from the appearance of morphology

Due to the different spinning process, the surfaces of T300 and T700 show significantly different characteristics, in which the surface of T300 is bark-like, and there are obvious grooves of varying depths, which is a characteristic of the wet spinning process. T700, on the other hand, presents a smooth surface, which is characteristic of the dry spray wet spinning process.

Fourth, from the morphology of the cross section

Both T300 and T700 carbon fibers show granular characteristics internally, the original fiber bundle structure is clearly visible, there are axial micropores between each other, and the densification of the fibers is relatively uniform. Moreover, the surface morphology of SEM images can also be judged that the process used for T300 is wet-spinning of protofilaments, while the process used for T700 is dry-spinning of protofilaments with dry-spray wet-spinning.

Although wet spinning and dry spraying wet spinning are just a short section of the air layer, they do have a great influence on the performance of carbon fiber. So there are many small differences in the whole production process that will affect the final performance of carbon fiber.