電暈駐極與水駐極濾材過濾特性之研究

Abstract

近年來空氣品質議題與呼吸道傳染疾病流行，使空氣過濾產品需求快速增加，導致一次性濾材大量消耗並衍生環境永續議題。靜電濾材可透過靜電吸引機制在維持高過濾效率的同時降低空氣阻抗，然而其電荷會隨使用條件與微粒負載而衰減。水駐極技術具備重新賦電潛力，為靜電濾材重複使用提供可行方向。本研究以相同基材條件之電暈駐極、水駐極與純聚丙烯(PP)濾材，以及市售N95濾材為研究對象，採用溶液浸泡方式探討濾材帶電行為。濾材之纖維直徑、濾材厚度、填充密度與電荷密度，結合實驗量測與單一纖維過濾理論模型進行推估。溶液浸泡測試系統性比較溶液種類、純水比例、浸泡時間、浸泡次數和駐極體之影響，並評估液態(DEHS)與固態(NaCl)微粒負載後之過濾特性與再帶電可行性。 結果顯示，純水浸泡若未能穿透濾材結構，未帶電濾材之穿透率仍約為75%；經抽氣使純水穿透後，水駐極未帶電濾材之穿透率可由75%降至15%。透過添加異丙醇或乙醇降低溶液表面張力至約32 dyne/cm以下，使溶液可穿透濾材結構，未帶電濾材之穿透率隨純水比例由10%、25%至50%分別降至75%、35%與20%。在相同純水比例下，異丙醇水與乙醇水溶液呈現近似之穿透率變化趨勢；即使相對介電常數不同，例如25%純水-異丙醇與乙醇溶液之相對介電常數分別為28.5與33.7，其穿透率仍同為35%。反之，在相對介電常數相近條件下(28.5與28.4)，穿透率卻分別為35%與75%，顯示相對介電常數並非唯一影響因素，濾材帶電效果同時受純水比例與表面張力控制之潤濕與穿透行為所主導。 於純水比例75%條件下，電暈駐極與水駐極未帶電濾材之穿透率分別可降至 19%與7%，其帶電量分別為1.1×10-4與2.1×10-4 C/m2。浸泡時間(0.2-5分鐘)與浸泡次數(1-5次)對帶電效果影響不顯著。以市售75%酒精浸泡可使未帶電濾材之穿透率降至20-40%，再接續高純水比例浸泡後，水駐極未帶電濾材之穿透率可進一步降至10%，其帶電量高於市售N95濾材。微粒負載結果顯示，負載後再帶電能力以水駐極濾材最佳，其次為電暈駐極，純PP濾材最為受限；即使微粒清除率達 95%，再帶電效果仍難以完全恢復。此外，依據臺灣2024年PM10年平均濃度估算，日常環境微粒負載對浸泡再帶電影響有限。 綜上所述，本研究透過控制溶液中純水比例與表面張力，使高介電常數純水得以進入濾材結構，是實現溶液浸泡帶電的關鍵機制。此外，在75%酒精與75%純水連續浸泡提供濾材同時消毒和帶電的效果，且優於N95本身的帶電量，並提供未來濾材重複使用上的參考依據。

In recent years, increasing concerns over air quality and respiratory infectious diseases have led to a rapid growth in the demand for air filtration products, resulting in extensive consumption of disposable filters and associated sustainability issues. Electrostatic filter can maintain high filtration efficiency with low pressure drop through electrostatic attraction; however, charges of filter gradually decay under usage conditions and particle loading. Water electret technology offers the potential for recharging electrostatic filters and provides a feasible pathway for filter reuse. In this study, corona electret, water electret, and pure polypropylene(PP) filter fabricated under identical base material, together with a commercial N95 filter, were investigated to evaluate charge generation via solution immersion. Fiber diameter, filter thickness, packing density, and charge density were estimated using experimental measurements combined with single fiber filtration theory. Solution immersion tests systematically examined the effects of solution type, pure water ratio, immersion time, immersion cycles, and electret masterbatch, and rechargeability was further evaluated after liquid (DEHS) and solid (NaCl) particle loading. The results indicate that when pure water failed to penetrate the filter structure, the penetration of uncharged filter remained 75%; after suction-assisted penetration, the penetration of water electret uncharged filter decreased to 15%. By adding isopropanol or ethanol to reduce solution surface tension to below 32 dyne/cm, the solution was able to penetrate the filter structure, and the penetration of uncharged filter decreased with increasing pure water ratio, reaching 75%, 35%, and 20% at pure water ratios of 10%, 25%, and 50%, respectively. Under identical pure water ratios, isopropanol-water and ethanol-water solutions exhibited nearly identical penetration trends; despite different relative dielectric constant (28.5 and 33.7 for 25% pure water with isopropanol and ethanol solutions, respectively), the penetration remained 35%. In contrast, under similar relative dielectric constant (28.5 and 28.4), the penetration differed substantially (35% and 75%), indicating that relative dielectric constant alone does not govern the charging behavior, which is jointly controlled by pure water ratio and surface tension regulated wetting and penetration. At a pure water ratio of 75%, the penetration of corona electret and water electret uncharged filter decreased to 19% and 7%, respectively, corresponding to charge densities of 1.1×10-4 and 2.1×10-4 C/m2. Immersion time (0.2-5 min) and immersion cycles (1-5 times) had no significant influence on charging performance. Immersion in commercial 75% ethanol reduced the penetration of uncharged filter to 20-40%, and subsequent immersion in high pure water ratio further reduced the penetration of water electret uncharged filter to 10%, with a charge density exceeding that of the commercial N95 filter. Rechargeability after particle loading was highest for water electret filter, followed by corona electret, while pure PP filter showed the most limited recovery; even at a particle removal efficiency of 95%, the charging performance could not be fully restored. Based on the annual average PM10 concentration in Taiwan in 2024, the impact of daily environmental particle loading on solution immersion recharging was limited. Overall, this study demonstrates that controlling the pure water ratio and solution surface tension to enable effective penetration of high relative dielectric constant water into the filter structure is the key mechanism for charging via solution immersion. Consecutive immersion in 75% ethanol and 75% pure water provides both disinfection and recharging effects, outperforming the intrinsic charge level of commercial N95 filters and offering a practical reference for extending the life of electrostatic filter.