The long-term impact of sterilization processes on the filtration performance of disposable breathing filters (BFIs) is primarily reflected in core aspects such as material stability, structural integrity, and microbial retention efficiency. Different sterilization methods physically or chemically alter the internal structure of BFIs, thereby affecting their long-term performance.
Ethylene oxide sterilization is one of the most commonly used processes for BFIs. It works by destroying microbial protein and DNA structures through an alkylation reaction. However, residual ethylene oxide may chemically modify the polypropylene (PP) or polytetrafluoroethylene (PTFE) membranes used in BFIs. After long-term storage or use, residual ethylene oxide may gradually release, altering the surface charge distribution of the membrane and reducing its ability to retain charged microorganisms, such as viruses. Furthermore, chemical residues may cause material embrittlement, making the membrane more susceptible to cracking due to mechanical vibration or airflow, thereby impairing its microbial retention efficiency.
Radiation sterilization (such as gamma radiation or electron beams) destroys microbial genetic material through high-energy radiation, but it poses challenges to the stability of polymer materials. Long-term radiation exposure can cause molecular chain breakage or crosslinking in filter membranes, altering their porosity and pore size distribution. For example, after irradiation, the charge decay of PP electrostatic cotton filter layers can reduce their adsorption capacity for submicron particles, while changes in the crystallinity of PTFE hydrophobic membranes can lead to fluctuations in air permeability. Although modern processes can mitigate material degradation by optimizing radiation dose rates, cumulative dose effects still cause filtration efficiency to gradually decrease with increasing sterilization cycles. This is the core reason why re-sterilization of disposable products is generally not recommended.
Autoclave sterilization achieves sterilization through high temperature and pressure, but it places stringent requirements on the thermal stability of disposable breathing filters. Under damp heat conditions, filter membranes can absorb water and expand, reducing their porosity. Inorganic filter materials such as glass fiber are particularly susceptible to fiber breakage or delamination during repeated damp heat cycles. For composite disposable breathing filters, the difference in thermal expansion coefficients between the wetted paper and the filter membrane can cause interfacial stress, leading to delamination after long-term use and directly impacting the gas flow path. Furthermore, if liquid water produced by steam condensation is not promptly removed, it may remain within the filter layer, creating a microbial breeding environment and weakening the sterilization effect.
The long-term impact of the sterilization process on filtration performance is also reflected in the dynamic changes in microbial retention efficiency. Ethylene oxide sterilization may leave chemical residues on the filter membrane surface, which may inhibit microbial activity. However, after long-term use, the reduced amount of residual substances may lead to a decrease in retention efficiency. Radiation sterilization may cause uneven charge distribution on the filter membrane surface, reducing the adsorption capacity for charged microorganisms. High-pressure steam sterilization may alter the porosity due to thermal deformation of the material, affecting the retention of microorganisms of different particle sizes. The interaction of these mechanisms results in a nonlinear decay in the bacterial filtration efficiency (BFE) and viral filtration efficiency (VFE) of disposable breathing filters after sterilization.
From an engineering perspective, the impact of sterilization processes on disposable breathing filter performance requires verification through accelerated aging testing. For example, sterilized disposable breathing filters are placed in a high-temperature, high-humidity environment to simulate long-term use, with parameters such as filtration efficiency and resistance pressure drop regularly tested. These tests have shown that performance degradation of products sterilized with ethylene oxide is primarily related to the release of chemical residues, while performance fluctuations of products sterilized with radiation are concentrated within the first few sterilization cycles. These findings provide data support for optimizing sterilization process parameters (such as radiation dose rate and steam temperature slope), helping to balance sterilization effectiveness and material stability.
