基于超临界二氧化碳的高效低阻聚丙烯熔喷纤维制备及其性能

为降低聚丙烯(PP)熔喷纤维的直径，解决其在空气过滤过程中过滤效率和过滤阻力之间的矛盾，借助静电场和超临界二氧化碳协同静电场制备PP熔喷纤维，并对PP纤维的形貌、过滤性能、力学性能进行表征与分析。结果表明：在制备过程中添加静电场后，PP纤维的平均直径从3.22μm降低至2.44μm,在此基础上经超临界二氧化碳处理后PP纤维的平均直径进一步降低至1.73μm,最小纤维直径达780 nm;随着纤维直径的降低，PP纤维直径分布变窄，纤维间黏结点减少，孔隙率和比表面积增加，微纳米纤维的过滤效率和过滤阻力均得到明显改善，其对0.3μm的颗粒物过滤效率高达99.25%,32 L/min气流量下过滤阻力仅为23 Pa。

Preparation and performance of high efficiency and low resistance polypropylene melt-blown fiber based on supercritical carbon dioxide

Objective This work was carried out to reduce the diameter of melt-blown polypropylene (PP) fabric and to solve the contradiction between filtration efficiency and filtration resistance of the melt-blown fabric during air filtration.Method Two types of novel PP superfine melt-blown fiber were prepared. One was prepared by melt-blowing assisted by electrostatic field, and the other was prepared by firstly treating PP with supercritical carbon dioxide and then melt-blowing assisted by electrostatic field.Results PP melt-blown fiber was prepared by melt-blowing assisted by electrostatic field. The fiber was thinned, the average diameter of the fiber was decreased from 3.22 μm to 2.44 μm by about 24.2%, and the filtration efficiency was increased from 98.78% to 99.01%. After supercritical CO₂ treatment, the viscosity of PP melt decreased, and the average diameter of the fiber was further decreased to 1.73 μm with the minimum diameter of 780 nm under the synergistic effect between electrostatic field and airflow field. With the decrease of the fiber diameter, the fiber diameter distribution became narrower, the bond point between fibers was decreased, the porosity and specific surface area were increased, and the fiber was more likely to capture the charge generated by corona discharge in the electret process, significantly improving the barrier capability and air permeability of micro-nano fiber. In other words, the contradiction between filtration efficiency and filtration resistance was effectively overcome. The filtration efficiency of the prepared melt-blown fiber was 99.25% for 0.3 μm particles, the filtration resistance was only 23 Pa, with a satisfactory quality factor of 0.213 Pa^-1. Compared with ordinary PP melt-blowing fiber, the breaking strength of melt-blown fiber prepared assisted by only electrostatic field or the combination of supercritical CO₂ treatment and electrostatic field decreased from 2.12 MPa of conventional melt-blown fiber to 1.17 and 1.26 MPa, representing decrease rates of about 44.8% and 40.0%, respectively. The elongation at break was significantly improved, and the decrease of the breaking strength was mainly attributed to the decrease of fiber diameter. In addition, the effective bonding points between fibers became fewer, leading to further reduction in fiber strength.Conclusion Two types of novel PP superfine melt-blown fiber were prepared, by melt-blowing assisted by electrostatic field and by melt-blowing assisted by electrostatic field following the fiber treatment by supercritical carbon dioxide. Thanks to the synergistic effect of supercritical carbon dioxide pre-treatment and the assistance of electrostatic field, the prepared melt-blowing fiber shows good barrier capability as well as good air permeability. The contradiction between filtration efficiency and filtration resistance of melt-blown fiber in the process of air filtration is effectively solved.