Polytetrafluoroethylene (PTFE), commonly known as the “Plastic King”, is a thermoplastic industrialized by DuPont in 1950. In PTFE, the hydrogen atoms in polyethylene are replaced by fluorine atoms. Since the radius of the fluorine atom (0.064 nm) is larger than that of the hydrogen atom (0.028 nm), the C—C chain is twisted by the planar, fully extended tortuous conformation of polyethylene. is the helical conformation of PTFE.
The composition and structural characteristics of PTFE determine its high and low temperature resistance, corrosion resistance, weather resistance, high lubrication, non-adhesion and other characteristics, but also have low hardness, large coefficient of linear expansion, poor thermal conductivity, poor mechanical properties, resistance to The disadvantages of poor wear, poor creep resistance, easy cold flow, and difficulty in secondary processing limit its wide application to a certain extent. Therefore, its modification research has always been a hot spot.
What are the modification methods?
The modification methods of PTFE mainly include surface modification, blending modification, filling modification, chemical modification, etc. Among them, filling and blending modified PTFE is a simple and effective method.
01Inorganic filler filling modification
Commonly used inorganic fillers include nanoparticle fillers, metal and oxide fillers, whisker fillers, and graphite, carbon fiber (CF), glass fiber (GF), and the like.
Filled with nanoparticle fillers
Nanoparticles have the characteristics of small size, large specific surface area, and large interfacial area and interaction with polymers, so the combination of the two can obtain ideal interfacial adhesion. In addition, nanoparticles can also eliminate the mismatch of thermal expansion coefficients of the two components and bind the interchain motion of PTFE macromolecules, which are beneficial to improve the tribological and mechanical properties of the polymer. At present, the nanomaterials used to fill PTFE mainly include nanometer Al2O3, SiO2 and TiO2.
Filled with metal and oxide fillers
Metal fillers have good thermal and electrical conductivity, as well as many excellent properties such as wear resistance. Adding metal fillers to PTFE can not only significantly improve the thermal conductivity of PTFE, but also greatly improve its wear resistance. For example: Cu particles, Al2O3 fibers, etc.
Whisker Filler Fill
Whiskers are single crystal fibers with few defects, usually only a few microns in diameter. Its mechanical strength is high, and its tensile strength is close to the theoretical strength of pure crystals. It can be widely used to enhance the properties of composite materials and is a promising new material.
The whisker materials include four needle-shaped zinc oxide whiskers, calcium sulfate whiskers, and the like.
Other fillers are graphite, CF, GF, etc. CF, GF and graphite can be filled individually or synergistically filled with PTFE modified PE composites. The study found that synergistically reinforced PTFE composites exhibit plastic fracture when stretched, and are high-performance lubricating and sealing materials with better comprehensive mechanical properties.
02 Polymer blending modification
The PTFE composite material formed by inorganic filling usually has a large friction coefficient, which causes great damage to the worn parts, and the mechanical properties of the product are not high enough; while the polymer blended modified PTFE significantly improves the above shortcomings. The organic polymers used to fill PTFE mainly include polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polyimide (PI), and polyphenylene ester (POB).
For example, PEEK/PTFE composites are prepared by a hot molding process and used as composite bearing materials. The results show that with the increase of PTFE content, the friction coefficient of the composite material decreases significantly, and the life of the bearing material is prolonged.
Some scholars have prepared 5 kinds of composite materials, including PPS/PTFE, PI/PTFE, PEEK/PTFE, POB/PTFE, and aramid/PTFE. The study found that the PTFE composite filled with 15% polyphenylester (POB) had the best anti-friction effect, and the PTFE composite filled with 15% PI had the best wear resistance. In contrast, the PTFE composite filled with 15% aramid has the best friction and wear properties and mechanical properties, and its wear resistance is nearly 400 times higher than that of pure PTFE, while the friction coefficient is only 84% of that of pure PTFE.
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