Improving CFRP material performance is the key topic in this article. We mainly discuss the theories and methods to improve CFRP material performance.
Theories for Enhancing CFRP Material Performance
The interface phase is a key research focus in CFRP materials. Interface treatment enhances the adhesion between fibers and polymers, achieving a smooth modulus transition within the composite material. This allows for uniform stress transfer between fibers and the polymer matrix, preventing stress concentration, enhancing the integrity of fiber composites.
The bonding methods between carbon fibers and polymers can be divided into physical bonding (primarily mechanical interlocking, adsorption, van der Waals forces, and hydrogen bonds) and chemical bonding (mainly covalent bonds). The main interface enhancement theories include:
| Mechanical interlocking theory: studying fiber roughness and surface structure;
| Chemical bond theory: researching the grafting of reactive functional groups and covalent bonds on fiber surfaces;
| Wettability theory: studying the wettability between fiber surfaces and the matrix.
Optimizing Carbon Fibers to Enhance CFRP Material Performance
Oxidation Method
| Definition of Oxidation Method:
The oxidation method is a chemical bonding approach, which can be divided into gas-phase, liquid-phase, and electrochemical oxidation.
Gas-phase oxidation generally uses gaseous oxidizing agents to generate active groups on the carbon fiber surface. Liquid-phase oxidation refers to oxidizing carbon fibers in liquid media such as concentrated nitric acid, mixed acids, or strong oxidizers. Electrochemical oxidation uses carbon fibers as the anode and substances like sodium bicarbonate as the electrolyte to activate the carbon fiber surface.
| Characteristics of Oxidation Method:
Gas-phase oxidation reaction conditions are difficult to control and can easily damage the inherent strength of fibers;
Liquid-phase oxidation is milder than gas-phase oxidation but requires longer processing times and poses risks due to dangerous liquids like strong acids, which can pollute the environment.
Anodic oxidation can optimize carbon fibers under mild oxidation conditions and obtain modified carbon fibers with different surface activities by changing the electrolyte. It has already entered industrial application, achieving continuous industrial production.
Chemical Grafting Method
| Definition of Grafting Method
Chemical grafting involves grafting treatment on the carbon fiber surface to activate it. Surface grafting substances can be classified into three categories:
Small molecules: such as diazo compounds, nitro-terminated, and amino-terminated diazo molecules.
Polymers: such as epoxy and hyperbranched polyimides.
Nanomaterials: such as carbon nanotubes (CNTs) and silica nanoparticles.
| Characteristics of the Grafting Method
Highly designable, easy to operate, and effective, but requires testing of grafting effects and stability. Stability is an issue that needs to be resolved for industrial applications.
Coating Method
| Definition of Coating Method
Coating involves applying molecules or polymers with high viscosity and activity to the fiber surface. Sizing treatment, vapor deposition, and coupling agent treatment are commonly used methods.
| Characteristics of the Coating Method
High design flexibility, low cost, good implementation effects, and suitability for industrial production. Sizing coating has already been commercialized, but the use of certain sizing agents can cause environmental pollution.
Optimizing Polymer Compatibility to Enhance CFRP Material Performance
Compatibility between fibers and polymers is a key issue in composite material research. Polymer modulus, fluidity, curing conditions, and post-curing mechanical properties affect fiber-polymer compatibility and CFRP material performance.
Different composite forming processes require different polymer curing properties, and polymer selection needs to be determined based on the forming method requirements. Different types of polymers also require different interface treatment methods.
Thermosetting Resins
Carbon fiber surfaces are inert and have poor wettability, so epoxy resin is generally chosen as the matrix for CFRP. This is because epoxy resin contains many polar hydroxyl, ether, and ester groups, which have strong adhesion and are relatively easy to bond with carbon fiber.
Advantages of thermosetting resins include heat resistance, pressure resistance, fire resistance, and good dimensional stability of products. The disadvantage is high brittleness. Carbon fibers have a high modulus, which enhances the modulus of the matrix resin, improves the modulus matching between fibers and resin, and can increase the overall interface strength of the composite material without damaging the fibers, thereby enhancing the rigidity of the composite material and CFRP material performance.
In addition, the epoxy resin curing agent is also crucial. It is generally divided into room-temperature curing and heat curing. Room temperature curing agents include aliphatic polyamines, polyamides, and alicyclic polyamines, while heat curing agents often include acid anhydrides and polyamines.
Thermoplastic Resins
In recent years, research on carbon fiber-reinforced thermoplastic resins, such as polyamide (PA), has also increased.
Although thermoplastic resins are more difficult to bond with carbon fibers compared to thermosetting resins, effective carbon fiber surface modification and resin modification methods, as well as the development of specialized thermoplastic sizing agents, can promote the development of high-performance carbon fiber-reinforced thermoplastic composites. Moreover, the reprocessability of thermoplastic resins is beneficial for recyclability, meeting the demand for recyclable CFRP.
Applications of High-Performance CFRP
With improved CFRP material performance, it offers the advantages of lightweight, high specific strength, and high specific modulus, with broad application prospects in aerospace, wind turbine blades, new energy vehicles, and other fields.
|Aircraft: The application of CFRP in aircraft started with ailerons, winglets, and rudders. With the progress in mechanical property development of CFRP materials, CFRP can now be applied to main structures such as fuselages, vertical stabilizers, and wings, gradually replacing lightweight metal alloys. The Airbus A350 also mainly uses CFRP, accounting for 53% of its weight. Private aircraft and helicopters use CFRP, reaching 70%-80%.
|Vehicles: The weight issue of new energy vehicles is a key factor affecting vehicle range. For every 10% reduction in vehicle weight, the range increases by approximately 5.5%. Using lightweight and high-strength CFRP as load-bearing components in new energy vehicles significantly reduces vehicle weight and enhances vehicle strength, vibration-damping characteristics, and fatigue resistance, achieving the goals of reducing energy consumption and increasing range.
Image Source: Researchgate & Tieusplastics & Vem-tooling
