Chopped carbon Fiber: Characteristics, Preparation, Applications and Industry Key Points!

Short-cut Carbon Fiber (Chopped carbon Fiber, abbreviated as CCF) is the fiber form of continuous carbon fiber precursor cut into a fixed length (usually a few millimeters to tens of millimeters) through a specific process. It retains the core advantages of carbon fiber, which is "lightweight and high strength", and also has the processing flexibility of easy dispersion and easy combination with the matrix material. It is one of the important reinforcing substrates in the field of composite materials.

I. Core Features: Inheriting the advantages of carbon fiber, it is suitable for multi-scenario processing

The performance of chopped carbon fiber stems from its raw material - carbon fiber. Meanwhile, due to its "chopped" form, it has developed unique processing adaptability. The core characteristics can be summarized as the following five points:

The ultimate "lightweight and high-strength" ratio

Its density is only 1.7 to 1.8g/cm³ (about 1/4 of steel and 2/3 of aluminum), but its tensile strength can reach 3000 to 7000MPa (5 to 10 times that of steel), and its elastic modulus is 200 to 400GPa. It can significantly reduce weight while doing so. It provides excellent mechanical reinforcement effects for composite materials (such as tensile resistance, impact resistance, and bending resistance).

Excellent environmental stability

It has strong chemical inertness, is resistant to acid and alkali corrosion (except for strong oxidants), and can withstand high and low temperatures (long-term service temperature -180 ℃ to 250℃, and can withstand even higher temperatures for a short time). It does not absorb moisture or age, and can maintain stable performance under humid and harsh working conditions, far exceeding traditional reinforcing materials (such as glass fiber).

Good electrical and thermal conductivity

Carbon fiber itself has the characteristics of electrical conductivity (volume resistivity approximately 10⁻³ to 10⁰Ω · cm) and thermal conductivity (thermal conductivity approximately 100 to 180W/(m · K)). Even after being chopped short, it can still form a "fiber network", which can endow composite materials with the functions of electrical conductivity (anti-static, electromagnetic shielding) and thermal conductivity (heat dissipation components), which cannot be achieved by insulating materials such as glass fiber.

Easy to disperse and compound compatible

The short-cut form enables it to be evenly dispersed in various matrices such as plastics (like PP, PA, PPS), resins (epoxy resin, phenolic resin), rubber, cement, etc., and it can be formed through conventional processes such as injection molding, extrusion, compression molding, and spraying without the need for complex continuous fiber layering equipment, thus lowering the production threshold of composite materials.

Controllable length and surface modification

The short cutting length can be customized according to requirements (common 3mm, 6mm, 12mm, 25mm) : short lengths (3 to 6mm) are suitable for thin-walled injection molded parts, while long lengths (12 to 25mm) are suitable for structural parts that require high mechanical properties. At the same time, the bonding force with the substrate can be enhanced by "surface coating of coupling agents" (such as silane coupling agents, epoxy coupling agents), to prevent the performance decline caused by fiber "debonding".

Ii. Preparation Process: The key steps from continuous raw filaments to short-cut finished products

The preparation of short-cut carbon fibers requires strict control over "cutting accuracy" and "fiber integrity" (to avoid the generation of fuzz and broken fibers during cutting). The core process is divided into three major links:

1. Raw material pretreatment: Select suitable carbon fiber precursor

First, the type of carbon fiber precursor should be selected based on the application scenario. The core distinction lies in "precursor material" and "performance grade" :

Raw silk material: The mainstream is PAN-based (polyacrylonitrile-based) carbon fiber (accounting for over 90% of global production, with moderate cost and balanced performance), and a small amount is asphalt-based (high modulus, high thermal conductivity, used in special fields such as aerospace heat dissipation parts).

Performance grades: They are classified by tensile strength into "Standard type" (T300, T700, used in industrial fields) and "High Strength Type" (T800, T1100, used in aerospace and high-end equipment), and by elastic modulus into "Standard modulus" (SM), "Medium Modulus" (IM), and "High Modulus" (HM).

Pretreatment step: Unwind the continuous carbon fiber precursor to remove the residual sizing agent on the surface (if the sizing agent of the precursor is incompatible with the subsequent matrix), or retain the suitable sizing agent (such as epoxy-based sizing agent compatible with the resin matrix).

2. Precise cutting: Core equipment determines product quality

Cutting is a crucial step. It is necessary to ensure "uniform length" (deviation ≤±0.5mm) and "flat fiber ends" (no splitting or fuzz). There are two mainstream types of equipment:

Rotary blade cutting machine: Suitable for medium and short lengths (3 to 12mm), continuous raw silk is uniformly conveyed to the high-speed rotating blade through the "roller" (the blade spacing can be adjusted), with high cutting efficiency (up to over 1000kg per hour), and is suitable for industrial mass production.

Ultrasonic cutting machine: It is suitable for long-length (12 to 50mm) or high-modulus carbon fibers that are prone to splitting. It uses ultrasonic vibration to make the blade "micro-vibration cut", reducing fiber damage. However, its efficiency is relatively low and it is mostly used for high-end customized products.

3. Post-treatment: Ensure dispersion and stability

The chopped carbon fiber after cutting needs to go through two post-processing steps:

Screening and impurity removal: "super-long filaments", "short broken filaments" and impurities are removed through vibrating screens to ensure consistent length.

Surface modification (optional) : If it is necessary to enhance the adhesion to the substrate, "coupling agent coating" (such as diluting silane coupling agent and spraying it) or "plasma treatment" (activating the fiber surface and increasing active groups) will be carried out, and finally packaged into "bagged" or "canned" finished products (to prevent agglomeration).