The core of modified PTFE is the introduction of a second phase material into the matrix PTFE through filler or blending, thereby improving its mechanical, thermal, or functional properties. Common modified materials can be divided into the following categories:
1. Filler-Type Modification: Enhanced Mechanical and Wear Resistance
Filler-type modification directly addresses PTFE's physical shortcomings by adding inorganic or organic fillers. Common fillers and their functions are as follows:
Glass Fiber (GF): Typically comprises 5% to 40%. Glass fiber significantly improves PTFE's compressive strength (up to 2-3 times), creep resistance, and dimensional stability, while also reducing cold flow. However, its coefficient of friction may slightly increase, requiring optimization with other fillers.
Carbon Fiber (CF): Typically comprises 5% to 15%. Carbon fibers not only enhance mechanical strength but also impart higher thermal conductivity (the thermal conductivity coefficient increases from 0.25 W/(m·K) for pure PTFE to approximately 5 W/(m·K)), making them suitable for high-load dynamic sealing applications. Furthermore, the surface activity of carbon fibers improves the adhesion of PTFE to other materials.
Bronze powder (CuSn alloy): The addition level is typically 10% to 30%. Bronze powder significantly improves PTFE's wear resistance (reducing the wear rate by over 80%) and enhances thermal conductivity (raising the thermal conductivity coefficient to approximately 2-3 W/(m·K)). It is commonly used in parts requiring sliding friction, such as bearings and guide rails.
Molybdenum disulfide (MoS₂): 1% to 5%. As a solid lubricant, MoS₂ further reduces the coefficient of friction (to 0.03-0.05) and enhances wear resistance, making it particularly suitable for lubrication needs in vacuum or high-temperature environments.
Graphite: 5% to 20%. Graphite, similar to MoS₂, has a layered structure that provides self-lubrication while also improving thermal and electrical conductivity (if electromagnetic shielding is required).
Combined filling (e.g., glass fiber + carbon fiber + MoS₂) can simultaneously achieve the multi-objective optimization of high strength, low friction, and wear resistance. For example, a modified PTFE formulation used in an industrial seal consists of: PTFE matrix + 20% glass fiber + 5% carbon fiber + 3% MoS₂. Its wear rate is only 1/10 that of pure PTFE and it can operate stably at high temperatures of 200°C for a long time.
2. Blending Modification: Expanding Functional Boundaries
Blending modification is the process of blending PTFE with other polymers or functional materials to impart specialized properties:
Polyphenylene ester (PPE): Blending with PTFE enhances heat resistance (extending long-term operating temperatures to over 300°C) and improves melt processing flowability, making it suitable for injection molding of complex-shaped parts. Polyetheretherketone (PEEK): The addition of a small amount of PEEK (5%-10%) can enhance the rigidity of PTFE while maintaining a certain degree of flexibility, making it suitable for applications requiring impact resistance.
Conductive fillers (such as carbon nanotubes and metal micropowders): By adding conductive fillers, modified PTFE can achieve electromagnetic shielding properties (reducing surface resistivity to below 10³Ω/sq), making it suitable for electronic equipment seals or anti-static components.
3. Surface Treatment Modification: Targeted Optimization of Interfacial Properties
In addition to filling and blending, surface chemical treatments (such as plasma etching and sodium-naphthalene treatment) can alter the polarity of PTFE's surface, enhancing its adhesion to other materials (such as metals and rubbers). This makes it suitable for parts requiring composite structures (such as PTFE and stainless steel laminated gaskets).
