PTFE gaskets hold a significant position in industrial sealing due to their excellent chemical stability, corrosion resistance, and low coefficient of friction. However, their low hardness, poor wear resistance, and insufficient creep resistance limit their application under harsh working conditions. By introducing a second phase material into the PTFE matrix through filler modification technology, their overall performance can be significantly improved. The principle behind this can be analyzed from three dimensions: composite effect, interfacial bonding, and defect suppression.
The composite effect is the core mechanism by which filler modification enhances performance. PTFE molecules exhibit a helical conformation, resulting in weak intermolecular forces and relatively low mechanical properties. When rigid fillers such as glass fibers and carbon fibers are introduced, these high-modulus materials can form a three-dimensional skeletal structure, restricting the slippage of PTFE molecular chains through physical cross-linking. For example, when a glass fiber-filled PTFE gasket is subjected to stress, the load is transferred to the matrix through the fibers, increasing the composite material's flexural strength by 2-3 times and its wear resistance by hundreds of times. The addition of metal oxides such as alumina and silicon dioxide can refine grains through dispersion strengthening, hindering dislocation movement and thus improving the material's hardness and compressive strength.
Interfacial bonding strength directly affects the performance of composite materials. Pure polytetrafluoroethylene (PTFE) has poor interfacial compatibility with non-polar fillers (such as polystyrene), easily forming a weak boundary layer and leading to stress concentration. To address this issue, surface treatment techniques are often used to improve interfacial bonding. For example, treating the surface of glass fiber with rare earth elements can introduce active groups, enhancing the chemical bond with PTFE; after graphite oxidation, the resulting carboxyl and hydroxyl groups can form hydrogen bonds with PTFE, making the transfer film denser and reducing the coefficient of friction. This interfacial optimization allows stress to be evenly distributed when the composite material is under load, reducing the risk of localized failure.
Defect suppression is key to improving creep resistance through filler modification. Polytetrafluoroethylene (PTFE) is prone to cold flow under long-term loads because its molecular chains can still rearrange themselves through segmental motion at low temperatures. The addition of fillers can effectively restrict this movement: on the one hand, the pinning effect of rigid fillers (such as bronze powder) can hinder the slippage of molecular chains; on the other hand, flexible fillers (such as polyimide) can form physical cross-linking points through intermolecular entanglement, increasing the resistance to molecular chain migration. For example, PTFE composites filled with 15% polyimide show a 4.5-fold increase in creep resistance at room temperature and maintain an improvement of more than 2 times at high temperatures.
Filler modification can also optimize multiple properties through synergistic effects. For example, when graphite and glass fiber are co-filled, the lubricating effect of graphite can reduce the coefficient of friction, while the reinforcing effect of glass fiber can improve wear resistance, giving the composite material both low friction and high wear resistance. The addition of nanofillers (such as nano-alumina) can utilize the small size effect to form a uniformly dispersed nanophase in the matrix. Through dispersion strengthening and grain refinement, the hardness, wear resistance, and thermal conductivity of the composite material are simultaneously improved.
The core of filler modification technology lies in organically combining the superior properties of fillers with the inherent characteristics of PTFE through composite effects, interface optimization, and defect suppression. This modification not only significantly improves the mechanical strength, wear resistance, and creep resistance of PTFE gaskets but also expands their application range under extreme conditions such as high temperature, high pressure, and strong corrosion. With the advancement of materials science and the continuous emergence of new fillers and modification processes, the performance of PTFE gaskets will be further optimized, providing more reliable solutions for the industrial sealing field.
