Correlation between foaming and controlling nucleation-induced dimensional stability of injected polyetheretherketone samples under gas-counter-pressure and supercritical-fluid influence

Abstract Polyetheretherketone (PEEK) is a high-performance polymer valued for its biocompatibility, radiolucency, and resistance to sterilization, making it suitable for long-term implants. However, its high-density limits applications in weight-sensitive orthopedic devices. This study applies MuCell ® microcellular foaming to reduce density by introducing uniformly distributed microscale cells. Nitrogen (N 2 ) serves as the supercritical fluid (SCF) foaming agent, injected into molten PEEK to form the cellular structure. Material dosage and SCF concentration vary, with and without gas counter-pressure (GCP) assistance. Key parameters – melt pressure, molding time, cell stability, dimensional accuracy, cycle time, and power consumption – are analyzed. Higher SCF concentration increases cell density near the gate but also enlarges cell size due to sharp pressure drops. GCP suppresses bubble overgrowth and coalescence, yielding uniform morphology and improved dimensional precision. At higher melt-to-resin ratios, cells become more stable and homogeneous, reducing wall rupture risk. PEEK’s viscosity, combined with optimized SCF and GCP, enables controlled shrinkage and mitigates localized deformation. MuCell ® shortens cycles by eliminating the holding stage and reducing cooling time, while SCF enhances flowability and shortens filling. GCP stabilizes foam and geometry, balancing energy use. Collectively, SCF, melt-to-resin ratio, and GCP synergistically achieve lightweight, dimensionally stable, and energy-efficient medical-grade PEEK components.