Chopped carbon fiber is carbon fiber that is cut short. Here the carbon fiber is only a morphological change, from carbon fiber filament into a short filament, but the performance of the short-cut carbon fiber itself has not changed. So why do you want to cut a good filament short?
First of all, we have to start from the molding process of the composite material. Usually carbon fiber filament to be woven into carbon fiber cloth or made into carbon fiber prepreg, and then through the molding process, RTM, vacuum bagging, hot press cans and other processes into a variety of carbon fiber composite products. Of course, there are also some molding processes that do not require intermediate materials, directly through the carbon fiber filament for molding, such as pultrusion molding, winding molding and so on.
Carbon fiber woven into carbon fiber cloth or made into prepreg, go to make products, there is a natural disadvantage, is not good to stick the mold. The existence of the mold is to give shape to the composite material, the mold has what kind of shape, the final composite material also has what kind of shape. However, if the carbon fiber cloth or prepreg does not fit the mold well, the shape of the composite material does not match the shape of the mold. In addition, in some corners, the carbon fiber cloth is easy to bridge, forming a local cavity, which ultimately causes a decline in the performance of carbon fiber composite products.
The carbon fiber filament inside the carbon fiber cloth or prepreg is bound and not easy to move. Especially in the case of pressure, the resin and carbon fiber filament mobility is very poor, which will eventually cause molding difficulties or performance degradation.
The shorter the length, the better the fluidity of the chopped carbon fiber. It should be known that injection molding is the most widely used and mature technology in plastic molding process. If applied to the production of composite materials, it will be a radical change.
However, the length of the short-cut carbon fiber can not be reduced, because the shorter the length of the short-cut carbon fiber, the resin and carbon fiber bonding will become weaker. Because the bond between resin and carbon fiber is directly proportional to the contact area between them, if the length is shortened, then the contact area is definitely reduced.
Then there is a contradiction here, that is, the contradiction between the performance of the short-cut fiber and the mobility. The longer the fiber length, the less likely to be dispersed, fiber and fiber are easy to knot, but the stronger the fiber and resin combination, out of the composite material performance will be higher. The shorter the fiber length, the easier it is to disperse, with good flowability, but the fiber and resin bond is a little weak. How to balance this contradiction, need to be studied, usually, to do short-cut carbon fiber reinforced plastic pellets, the length of 1-9mm range.
There is also a way to enhance the bonding strength between carbon fiber and resin, which is sizing agent. Usually, there is a sizing agent on the surface of the carbon fiber factory, which is used to protect the carbon fiber from linting in the process of packing, transferring and operating, and on the other hand, it is used to combine the carbon fiber and the resin, and play the role of enhancing the bonding strength.
However, this sizing agent is basically for thermosetting resin. Most of the resins used to make pellets are thermoplastic resins, so the sizing agent must be readjusted. One is to burn the original sizing agent and make a new layer of sizing agent. One is to burn the original sizing agent and make a new layer of sizing agent; the other is to sizing agent again on the basis of the original sizing agent, which is called secondary sizing.
In addition to making granules for injection molding, chopped carbon fiber has other uses, such as made of carbon fiber mat, or made of carbon fiber paper. The required length of chopped carbon fiber will be longer than the length of chopped fiber for granules.
In addition, in addition to the haphazardly chopped carbon fibers, there are also bundled chopped carbon fibers. This short-cut fiber is in the short cut before the carbon fiber tow for a certain predetermined type, then cut out of the short-cut fiber has the characteristics of a bundle, containing the amount of resin will be much more than other short-cut fiber.
Post time: Oct-08-2024
