## 3 Results and Discussion  
### The Effect of Filter Material Properties on Filtration Efficiency  
#### 3.1.1 Comparison of the Filtration Efficiency of Different Materials of Filter Media  
Under the standard test conditions in Table 2, the filter materials of PPS, PI, and PTFE (sample No. 1-3) were tested for comparisons of filtration efficiency. The experimental results were shown in Table 3. The surface microstructures of the filter materials of PPS, PI, and PTFE were shown in Figure 3.  
It can be concluded from Table 3 that in the 30 cycles before aging, the PTFE filter material had the highest filtration efficiency, followed by the PPS filter material, and the PI fiber filter material had the lowest efficiency. After aging, the performance of the PPS filter material and PI filter material were significantly improved. Theoretically, the PI single fiber has a trilobal cross-section with a larger filtration surface area [29; 30], and its filtration performance should be better than PPS and PTFE, but the results of this experiment were the opposite. In order to verify the filtration performance of the PI filter material, under standard test conditions, five PI filter cloths provided by different manufacturers were tested for the filtration performance. The test results show that the filtration efficiency of the PI sample cloth before aging was 99.9505-99.9575%, and the filtration efficiency after aging was 99.9874-99.9965%. The filtration efficiency of the filter cloth produced by different manufacturers was different, but the overall was still not as good as PPS. This might be because the filtration performance of the PI filter media was greatly affected by the manufacturing process. Although the PI fiber has a larger specific surface area, as the irregular fiber cross-section means that the fibers naturally curl, resulting in a strong holding force between the fibers and entanglement, the filtration performance itself is not necessarily better than PPS and PTFE filter media [31; 32]. In addition, during the aging process of the PTFE filter material, due to the large amount of dust penetrating the filter material, the test system was blocked and the experiment was terminated, which shows that the PTFE filter media has a better filtration performance in the short term, but its filtration performance will be significantly reduced after long-term use. From the comparison of the experimental results of the three material filter materials, it is concluded that the PPS filter material has a high and stable filtration performance.  
3.1.2. Comparison of the Filtration Efficiency of Filter Media with Different Grams  
Under standard test conditions, the filtration efficiency of two kinds of PPS filter media (sample 4 and sample 5) with gram weights of 536 g\(\cdot\)m\({}^{-2}\) and 589 g\(\cdot\)m\({}^{-2}\) was experimentally compared. The experimental results were shown in Table 4.  
It can be concluded from Table 4 that the filtration efficiency of the PPS filter material with a gram weight of 589 g\(\cdot\)m\({}^{-2}\) was significantly better than that of the PPS filter material with a gram weight of 536 g\(\cdot\)m\({}^{-2}\) in the 30 cycles before aging. However, after 30 cycles of aging, the filtration efficiency of the two was basically the same. It shows that a filter with a larger weight had a better filtration advantage in the short term, but after a period of use, there was no obvious advantage in the filtration efficiency [28; 33; 34]. For the same material and the same area of filter media, the grammage of the filter media was greater in density and surface area, which increased the chance of trapping dust particles. Therefore, for 30 cycles before aging, the filtering advantage of the filter media with high grammage was obvious, while for 30 cycles after aging, the filter media filtration mainly relied on the dust layer, so the filtration effect was not significantly affected by grammage.