Mechanical Properties of PTFE

The dynamic mechanical properties of PTFE have been measured at frequencies from 0.033 to 90 Uz. Abmpt changes in the distribution of relaxation times are associated with the crystalline transitions at 19 and 30°C (75). The activation energies are 102.5 kj/mol (24.5 kcal/mol) below 19°C, 510.4 kJ/mol (122 kcal/mol) between the transitions, and 31.4 kJ/mol (7.5 kcal/mol) above 30°C. 

Fig. 37 Comparison of mechanical properties of PTFE-EPDM composites (a) tensile strength at break (trB) and elongation at break (eB) (b) moduli Ml00 and M200. The horizontal line indicates the M100 of the composite containing nonmodified PTFE (L100XokGy-EPDM)...

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 mechanical properties of PTFE at room temperature are similar to those of medium-density polyethylene, i.e., relatively soft with high elongation, and remaining useful over a wide range of temperatures, from cryogenic (just above absolute zero) to 260°C (500°F) its recommended upper use temperature.28 Stress-strain curves are strongly affected by the temperature however, even at 260°C (500°F) the tensile strength is about 6.5 MPa (942 psi).29... 

Mechanical properties of PTFE are generally inferior to that of engineering plastics at the room temperature. Compounding with fillers has been the strategy to overcome this shortage. In the normally used temperature range, PTFE has useful mechanical properties. 

The earlier data on the mechanical properties of PTFE were collected by Chapiro [425] (Fig. 50). 

PTFE has an operating temperature range of from — 20°F to + 430°C (— 29°C to + 212°C). This temperature range is based on the physical and mechanical properties of PTFE. When handling aggressive chemicals, it may be necessary to reduce the upper temperature limit. 

PTFE has a maximum operating temperature of 500°F/260°C, and can be fusion welded. It is subject to permeation by some corrodents. Refer to Table 1.2 for the permeation of vapors in PTFE. Refer to Table 3.17 for the physical and mechanical properties of PTFE. 

---