Characterization of PPS Piston and Packing Ring Materials for High-Pressure Hydrogen Applications

Abstract

The widespread adoption of renewable energy hinges on the efficient transportation of hydrogen. Reciprocating piston compressor technology in non-lubricated operation will play a key role, ensuring high flow rates and compression ratios. These systems rely on advanced high-strength sealing solutions for piston and rod packing rings utilizing advanced fiber-reinforced polymers. Polyphenylene sulfide (PPS) polymer matrix composites have seen use in tribological applications and promise high mechanical strength and wear resistance. The presented work describes carbon and glass fiber-reinforced PPS matrix polymers in comparison, which are characterized by complementary methods to investigate their properties and potential for application in reciprocating compressor under non-lubricated operation. Thermo-mechanical and tribological testing was supported by microstructure analysis utilizing advanced X-ray and electron imaging techniques. New insights in micromechanical deformation behavior in regard to fiber materials, interface strength and orientation in fiber-reinforced polymers are given. Conclusions on the suitability of different PPS matrix composites for high-pressure hydrogen compression applications were obtained.

Keywords: X-ray imaging; fiber-reinforced polymers; friction and wear; hydrogen technology; thermo-mechanical properties; transmission electron microscopy; visco-elastic deformation.

Figure 1

Test setup, CT region of interest and specimen location (a) image adapted from [26]. (b) Shape the of the injection-molded sample plates with the orientation of extracted tensile test specimen and ROI for microsection analyses. (a) Tensile test sample and region of interest for imaging. (b) Tensile test sample and region of interest for LOM (not to scale).

Figure 2

Test setup, tribology test setup schematic (a), image adapted from [26]. (b) The shear testing setup according to ISO 6721-5 [29]. (a) Tribology test setup. (b) Shear testing setup.

Figure 3

LOM, microstructure of PPS test specimen. Glass fibers (dark) are embedded in the PPS matrix (bright) in (a) with dark PTFE particles in (c). Carbon fibers (bright) embedded in the PPS matrix (dark gray) in (b) with dark PTFE inclusions in (d). (a) PPS/GF30f. (b) PPS/CF30f. (c) PPSPTFE/GF30f. (d) PPSPTFE/CF30f.

Figure 4

Tomography, fiber orientation tensor components in PPS/GF30f (a) and PPSPTFE/GF30f (b). Orientation of the coordinate system can be seen in Figure 1b.

Figure 5

LOM, microstructure of PPS/GF30f (a) and PPS/CF30f (b) in comparison. Highly oriented fiber distribution in skin and core layers of the work piece.

Figure 6

Standard testing, tensile test results at an inspection speed of 5 $\mathrm{m}$$\mathrm{m}$/$\mathrm{s}$ and sample temperature 23 °C until fracture (left). Shear testing results for tests according to ASTM D 732 with $1.25$$\mathrm{m}$$\mathrm{m}$/$\min$ crosshead speed (right). (a) Tensile test results. (b) Shear test results.

Figure 7

Thermal property testing, (a) illustrating the thermal expansion of in a temperature range of −50 to 300 °C and heating rate of 2 $\mathrm{K}$/$\min$. Dynamic mechanical analysis in a temperature range of −100 to 300 °C at a heating rate of 3 $\mathrm{K}$/$\min$ in (b). (a) Dynamic mechanical analysis results. (b) Thermal expansion test results.

Figure 8

XCT, fracture surface images of PPS/GF30f (a) and PPSPTFE/GF30f (b) at a voxel edge length of ( 1 μm³). Bright glass fibers embedded in gray PPS polymer matrix.

Figure 9

XCT, fracture surface images of PPS/CF30f (a) and PPSPTFE/CF30f (b). Darker carbon fibers embedded in gray PPS polymer matrix. ROI indicated in (b) shown in (c). Adjusted contrast settings increasing visibility of PTFE (bright) in (b,c). All images were acquired with a voxel edge length of ($0.5$$\mathsf{\mu }\mathrm{m}$³). (a) PPS/CF30f. (b) PPSPTFE/CF30f. (c) ROI PPSPTFE/CF30f.

Figure 10

LOM, microstructure of PPS shear test fracture surfaces. Glass fibers (dark gray) are embedded in the PPS matrix (bright) in (a,c) with dark PTFE particles in (c). Carbon fibers (bright) embedded in the PPS matrix (dark gray) in (b,d) with dark PTFE inclusions in (d). (a) PPS/GF30f. (b) PPS/CF30f. (c) PPSPTFE/GF30f. (d) PPSPTFE/CF30f.

Figure 11

Tribology testing, coefficient of friction (CoF) and cumulative pin wear on a solution heat-treated W720 ($R_a=0.16 \mathsf{\mu }\mathrm{m}$) counter-surface with $24.8$$\mathrm{M}$$\mathrm{Pa}$ contact pressure and $0.1$$\mathrm{m}$/$\mathrm{s}$ sliding speed for each tested material. The black line depicts the arithmetic mean of the test data represented with colored lines. Standard deviation of CoF and cumulative wear is illustrated by the colored surfaces. (a) PPS/GF30f. (b) PPS/CF30f. (c) PPSPTFE/GF30f. (d) PPSPTFE/CF30f.

Figure 12

SEM, surface image of wear track on W720 tested against PPS/CF30f (a) and PPSPTFE/CF30f (b). Sliding direction is vertical with respect to image orientation. (a) Steel counter-surface tested against PPS/CF30f. (b) Steel counter-surface tested against PPSPTFE/CF30f.

Figure 13

FIB, depth profile of W720 wear track tested with the PPS composites in transmission. (a) The W720 grain structure, covered preparation wise by protective Pt (black) and graphite (white) layers. (b) Polymer depositions (bright) on the metal covered by a Pt layer. Region of interest for line scan data presented in Figure 14 is shown in (b). (a) Steel counter-surface tested against PPS/CF30f. (b) Steel counter-surface tested against PPSPTFE/CF30f.

Figure 14

EELS, concentration of fluorine (orange, solid line) and sulfur (purple, dashed line) atoms in polymer layer from tribo-testing PPSPTFE/CF30f against W720 steel along line scan region indicated in Figure 13b.