We also looked at polymers under compression in sCO2 at 100☌ and 20 MPa pressure to imitate actual sealing performance required of these materials in sCO2 systems. ![]() Fast diffusion, supported by higher pressures and long exposure times (1000 hours) at the test temperature, caused increased damage in sCO2 environments to even the most robust polymers. It was clear that the same selectivity was observed in these experiments wherein certain polymeric functionalities showed more propensity to failure over others. In FY 2020, the focus was to understand the effect of sCO2 on polymers at low (10 MPa) and high pressures (40 MPa) under isothermal conditions (100☌). Findings showed that elevated temperatures accelerated degradation of polymers in sCO2, and that certain polymer microstructures are more susceptible to degradation more » over others. In FY 2019, we conducted experiments at high temperatures (100☌ and 120☌) under isobaric conditions (20 MPa). O-rings and gaskets made from these polymers face stringent performance conditions such as elevated temperatures, high pressures, pollutants, and corrosive humid environments. Polymers such as PTFE (polytetrafluorethylene or Teflon), EPDM (ethylene propylene diene monomer) rubber, FKM fluoroelastomer (Viton), Nylon 11, Nitrile butadiene (NBR) rubber, hydrogenated nitrile rubber (HNBR) and perfluoroelastomers (FF_202) are commonly employed in super critical CO 2 (sCO2) energy conversion systems. Attempts were also made to qualitatively link sCO2 effects such as lowering or increase in glass transition temperatures, storage modulus changes, mass and compression set changes, chemical changes seen in FTIR analyses and blister and void formation seen post-exposure to polymer microstructure-related mechanisms such as plasticization of the polymer matrix, escape of volatiles from the polymer during depressurization, and filler and plasticizer effects on microstructure with rapid depressurization rates. For each polymer, the dominance of one type of effect over the other was evaluated. Super-critical CO 2 effects have been identified as either physical or chemical effects. Microcomputer tomography (micro CI) data was generated on select specimens. Density and mass changes immediately after removal from test and 48 more » hours later, and optical microscopy techniques were also used. The polymer samples were examined for physical and chemical changes by Dynamic Mechanical and Thermal Analysis (DMTA), Fourier Transform Infrared (FTIR) spectroscopy, and compression set. Samples were extracted for ex-situ characterization at t = 200 hours and then at the completion of the test at t=1000 hours. ![]() In a second study, elastomers perfluoroelastomer (FF202) and EPDM were exposed to 25 MPa sCO hours at 150☌. The polymers (PEEK, Nylon, PTFE, EPDM, Nitrile rubber, EPR, Neoprene, perfluoroelastomer FF 202 and Viton) were exposed for 1000 hours at 100☌ to 25 MPa sCO2 pressure in an autoclave. To understand these effects, we have studied nine commonly used polymers subjected to elevated temperatures under isobaric conditions of sCO2 pressure. Critical knowledge gaps about polymer degradation from sCO2 exposure need to be addressed. O-rings and gaskets made from these polymers face stringent performance conditions such as elevated temperatures, high pressures, pollutants and corrosive humid environments. Polymers such as PTFE (polytetrafluorethylene or Teflon), PEEK (polyetheretherketone), EPDM (ethylene propylene cliene monomer) rubber, Viton, EPR (ethylene propylene rubber), Nylon, Nitrile rubber, and perfluoroelastomers are commonly employed in super critical CO 2 (sCO2) energy conversion systems.
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