Polymeric Sealing Materials in Pneumatic Actuators: From Degradation Mechanisms to Failure Diagnostics and Service-Life Prediction

Polymeric sealing materials play a critical role in the reliability, efficiency, and dynamic performance of pneumatic actuators. Their long-term behavior is governed by the interaction between polymer structure, operating conditions, degradation mechanisms, tribological damage, and loss of sealing functionality. This review compares the principal sealing materials used or considered for pneumatic systems, including polyurethane (PU), thermoplastic polyurethane (TPU), nitrile butadiene rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR), fluoroelastomers (FKM), ethylene–propylene–diene rubber (EPDM), silicone elastomers, and PTFE-based materials. Particular attention is given to thermo-oxidative aging, hydrolysis, crosslinking, chain scission, swelling, compression set, fatigue, and wear. Their selection involves trade-offs between friction, wear resistance, chemical and thermal stability, elastic recovery, compression set, and leakage performance. Material-characterization and condition-assessment methods, including scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS), Fourier-transform infrared spectroscopy (FTIR), electron paramagnetic resonance (EPR), thermal analysis, mechanical testing, and tribological measurements, are evaluated with respect to their ability to detect material deterioration. Accelerated-aging and service-life prediction approaches are also discussed. The literature shows that no single material is optimal under all pneumatic operating conditions and that material degradation does not necessarily coincide with functional failure. Future research should therefore integrate physicochemical diagnostics with friction, leakage, and actuator-performance measurements to develop reliable degradation-state and remaining-life models for pneumatic sealing systems. This review compares the principal sealing materials used in pneumatic systems, including PU/TPU, NBR, HNBR, FKM, EPDM, silicone elastomers, and PTFE-based materials.