Modified PTFE

Modified PTFE surfaces show a high degree of biocompatibility with good cell adhesion and proliferation [7-11], However, the UV-treatment results also in a loss of mechanical stability due to the scission of polymer chains, especially for light-sources with wavelengths below 193 nm [6], Similarly to the ion implantation or plasma modification, also the UV light-irradiation is performed on both sides of a polymer foils in order to avoid the material torsion. 

Fig. 6 Radical coupling mechanism of modified PTFE radicals and the unsaturated diene EPDM...

Fig. 33 Friction coefficient (/ ) as a function of (a) tan delta at 25°C, (b) hardness, and (c) mean agglomerate size. Squares indicate PTFE-EPDM composites containing nonmodified PTFE and circles modified PTFE...

This indicates that the PTFE particles are being pulled out of the matrix on application of stress. The microstructures of the corresponding CR composites measured by are shown in Fig. 45. The enhanced interfacial compatibility of modified PTFE particles in PTFE500kGy-CR is clearly visible in the corresponding micrographs. The modified agglomerate particles are embedded and partially enwrapped by the CR matrix. No clear and sharp interphase is... 

Although the vulcanization mechanisms are well established for other elastomers, vulcanization of CR is a complicated process and has not been, until now, well understood. To our knowledge, there are only a few studies that discuss the vulcanization chemistry of CR [87]. The vulcanization mechanism for CR proposed in these pioneering studies was considered to be a planar three-component reaction mechanism in which the structural and special peculiarities were fully taken into consideration. Here, we propose an explanation of the chemical coupling mechanism between the CR matrix and electron-modified PTFE powder based on the similar vulcanization mechanism of CR. Such a mechanism can also be applied to vulcanization of CR in the presence of a ethylenethiourea compound. 

Fig. 51 Possible reaction mechanism of modified PTFE powder and chloroprene rubber...

The use of irradiated PTFE powder in EPDM gives enhanced mechanical properties as compared to composites containing nonirradiated PTFE. The existence of compatibility between modified PTFE powder and EPDM is indirectly revealed by , DSC, and SEM. shows that modified PTFE powder (500 kGy-irradiated) is obviously but partially enwrapped by EPDM as compared to nonirradiated PTFE powder. This leads to a characteristic compatible interphase around the modified PTFE. The resultant chemically coupled PTFE-filled EPDM demonstrates exceptionally enhanced mechanical properties. Crystallization studies by DSC also reveal the existence of a compatible interphase in the modified-PTFE-coupled EPDM. The synergistic effect of enhanced compatibility by chemical coupling and microdispersion of PTFE agglomerates results in improvement of mechanical properties of PTFE-coupled EPDM compounds. In summary, an effective procedure both for the modification of PTFE powder as well as for the crosslinking of PTFE-filled EPDM by electron treatment has been developed for the preparation of PTFE-coupled EPDM compounds with desired properties. 

The recently developed modified PTFE (e.g., Teflon NXT), because of its improved processing, lower creep, improved permeation, less porosity and better insulation than standard PTFE, finds use in pipe and vessel linings, gaskets and seals, fluid-handling components, wafer processing, and electric and electronic industries. An example of a molded part from modified PTFE is shown in Figure 4.15. 

FIGURE 4.14 Molded part from modified PTFE. (Courtesy of DeWAL Industries.)... 

Major research efforts resulted in the development of a modified PTFE, which contains a small amount (0.01 to 0.1 mol%) of a comonomer. The most suitable comonomer was found to be perhuoro propylvinyl ether (PPVE).94 The comonomer reduces the degree of crystallinity and the size of lamellae.95 The polymerization process is similar to that for standard PTFE except additives to control the molecular weight are used.96... 

Modifed PTFE can be used in practically all applications, where the conventional polymer is used. In addition to that, new applications are possible because of its improved flow and overall performance. In the chemical process industry, it is used for equipment linings, seals, gaskets, and other parts, where its improved resistance to creep is an asset. In semiconductor manufacturing, modified PTFE is used in fluid handling components and in wafer processing components. Typical applications in electrical and electronic industries are connectors and capacitor films. Other applications are in unlubricated bearings, laboratory equipment, seal rings for hydraulic systems, and antistick components.103... 

TEFLON NXT 70 Fluoropolymer Resin, Modified PTFE Granular Molding Resin, Publication 2474696 C (4/98), DuPont Fluoroproducts, Wilmington, DE. 

Modified PTFE — Copolymer of TFE and a small amount (less than 1%) of other perfluorinated monomer (e.g., perfluoroalkoxy monomer) exhibiting considerably improved physical properties, moldability, and much lower microporosity. 

ETFE, FEP, PFA, PTFE, amorphous PTFE, modified PTFE, PTFE micropowders, PVF, ionomers... 

Modified PTFE represents a relatively new technology that is designed to overcome the limitations of conventional PTFE, namely, poor creep resistance (i.e., tendency to cold flow), difficult welding, and high level of microvoids [35], These changes of properties are accomplished by addition of small amount comonomer in amounts less than 0.1%. Such modifier is most frequently perfluoropropylvinyl ether (PPVE). The copolymerization is carried out in aqueous suspension under practically the same conditions as the homopolymerization of tetrafluoroethylene, that is, at TEE pressures in the range 5 to 20 bar (72 to 290 psi) and temperature range 35°C to 90°C (95°E to 194°E) [36]. There is more on modified PTFE in Section 7.7. 

Property ASTM Test Method Modified PTFE Conventional PTFE... 

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