The Investigation Of Preparation Technics And Properties Of Needle-punching Felt Made Of PAN-based Carbon Fiber

Carbon fiber and its reinforcement composites are widely used for many application because of their outstanding properties of high specific strength, high specific modulus, low density, good resistance to corrosion and high temperature, et al. PAN-based carbon fiber, with good integrated properties and simple manufacturing technics, has occupied more the90%of the whole output of the world. The form of preform, to some extent, decides properties of the composites. Integrated needle-punching is a method in which one needle-punches the embryonic felt into a3D structure with a Needle-punching machine, this method has an advantage over resin bonding method because of it high interlayer shear strength, well-distributed density and properties, also it has a simpler technics and shorter period compared to3D weaving method. The outlook of this method to manufacture preform is inspiring.Author of this article prepares the PAN-based pre-oxidized fiber felt with needle-punching method. Physical and chemical reaction, thermal behavior of the felt during carbonization, as well as the influence different technical parameters have on the properties of the felt are studied using element analysis, tension test, FTIR analysis, mass-density analysis, and reaction theory analysis. Some effort is done to optimize the technics for both laboratory experiment and industrial application. The result is shown below.During low-temperature carbonization, the uncyclized linear molecules in the pre-oxidized fiber will cyclize and crosslink. During high-temperature carbonization, polymer with trapezoidal frame will crosslink and turn aromatized, cyclized unit forms conjugated face consist of hexatomic ring, the carbon-based face grows as temperature rises and finally turns to a graphite-like structure.The main motor frequency and velocity of the conveyor belt will influence the density of the felt during needle-punching process, change these two parameters and we could get felt with different density. Mechanical properties of Z direction are enhanced on the premise that mechanical properties of X-Y direction decrease.Shrinkage and curl of fiber will lead to tensile strength decrease of the felt during carbonization, reduce of fiber diameter functions similarly. Volume shrinkage is weaker than mass shrinkage, but the change of density is similar to that of mass. When the carbonization temperature is above1000℃, carbon content of the fiber exceeds90%, what means that the fiber is eligible on ingredient. The choosing of carbonization temperature should depend on practical demand, balancing element content, mass yield and mechanical properties. Under lower heating rate, the degree of carbonization will be higher, which means higher carbon content, less mass yield, but the influence of heating rate on the mass yield is weaker compared with that of carbonization temperature. The influence heating rate has on the X-Y direction tensile strength is too small to be count in, we should balance element content and mass yield to choose proper heating rate. Under our experimental condition, soaking time is not an important parameter. But for industry, soaking time should be considered to make sure that the felt will get a well-distributed ingredient and structure. PAN-based carbon fiber shows good resistance of destruction and pseudoplasticity.