EPDM vs PTFE

EPDM rubber belongs to the thermoset elastomers (rubber) classification, while PTFE belongs to the thermoplastics. Please note that the two materials have significantly dissimilar densities. 

EPDM rubber is a thermoset elastomer or rubber material. It has a fairly low density and the highest heat capacity relative to other rubber materials. 

PTFE is a fluoroplastic (fluorine-based thermoplastic). It can have a fairly high density among thermoplastics. In addition, it can have a moderately high ductility and a fairly low tensile strength.

EPDM is softer and makes a better sealing material (conforms better to rough surface finishes).  Teflon is stiffer and slicker, which might hold up better in a dynamic or abrasive application.  Both could care less about sea water from a chemical attack/corrosion standpoint.

The decomposition temperature of PTFE is >490°C (>910°F) and the main decomposition products are hydrogen flouride gas (extremely corrosive) and carbon dioxide. It is unsuitable for use where it will come into contact with acetone or hot alkaline applications.

If you want the parts to seal use EPDM or Natural rubber, the PTFE material will not seal well at all. It is harder, yet more durable & certainly more costly but it most likely will not seal as well as an elastomer.

Source:https://www.sukoptfe.com/epdm-vs-ptfe

Physical & Chemical properties of rubber

Physical properties:In relaxed state, rubber is in the form of long, coiled-up chains. By stretching of rubber the all chains will come very close as result, kinetic energy exerted in the form of heat. In chain elongation process entropy and temperatures required during this process are increases. When chain in relaxed state both entropy and temperatures decreases.

 

Relaxation of a stretched rubber band is thus driven by a decrease in entropy and temperature, and the force experienced is a result of the cooling of the material being converted to potential energy. The material undergoes adiabatic cooling during contraction.

 

Vulcanization of rubber creates disulfide bonds between chains. The result is that the chains tighten more quickly for a given strain, thereby increasing the elastic force constant and making rubber harder and less extensible.

 

Chemical properties:Like plastic, rubber is also a type of polymer, made of subunits called monomers. In rubber, the monomer is isoprene. As the latex dries, the isoprene molecules mass together and one isoprene molecule attacks a carbon-carbon double bond of a neighboring molecule. One of the double bonds breaks and the electrons repositioned to form a bond between the two isoprene molecules.

 

The process continues until long strands of many isoprene molecules linked like a chain. This long chain of strands is called as polyisoprene polymer. As the drying continues, the polyisoprene strands stick together by forming electrostatic bonds. The attraction between these strands holds the rubber fibers together and allows them to stretch and to recover.