Abstract:

Objective At present, the problem of air pollution is becoming increasingly serious. Melt-blown nonwovens have the characteristics of fine fibers, high porosity, and small pore size, which can effectively filter out dust and ensure the health of the wearer. Most of the commercially available melt-blown nonwovens are made from polypropylene (PP) due to their excellent filtration performance, but their non-renewable and non-degradable nature of the materials themselves may lead to resource crises and environmental pollution issues. Therefore, the development of green and renewable melt-blown nonwovens is of great significance.

Method Different types of electrets and polylactic acid(PLA) were selected to prepare PLA/electret composites by melt blending and hot pressing, in order to obtain the best electret SiO₂ for PLA. Next, the SiO₂ was modified by silane coupling agent KH570 to reduce its agglomeration. As the last step, PLA/SiO₂ melt-blown nonwovens were prepared by melt-blown spinning and high pressure in-situ electret technology, and charge storage capacity and air filtration performance of the samples were systematically investigated.

Result The PLA/electret composite membrane material was successfully prepared using the melt blending method. The PLA/SiO₂ membrane material showed an increase in peak intensity at 1 109 cm^-1, which is the symmetric stretching vibration peak of Si—O of SiO₂, proving the successful composite(Fig.2). The starting thermal decomposition temperature of the PLA/polytetrafluoroethylene(PTFE) membrane material is reduced to around 240 ℃ and the starting thermal decomposition temperature of the PLA/ SiO₂ membrane material is set at around 302 ℃, demonstrating that the addition of the electret SiO₂ has little effect on the thermal stability of PLA(Fig.3). The electret significantly improves the charge storage capacity of the PLA membrane material, where the surface electrostatic charge is 8.154 kV for the pure PLA membrane material and 17.44 kV for the PLA/ SiO₂ membrane material, an increment of up to 113.88%(Fig.3). The residual electrostatic charge on the surface of the PLA membrane material was 3.23 kV after 48 h, while the residual electrostatic charge on the surface of the PLA/ SiO₂ membrane material was still as high as 6.34 kV. This demonstrates that the addition of a 1% mass fraction of SiO₂ nanoparticles resulted in a better electret effect on the PLA membrane materials. In order to reduce the agglomeration of SiO₂, the silane coupling agent KH570 was used to modify the SiO₂. The modified SiO₂-570 sample shows a C—H vibration peak at a wavelength of 2 930 cm^-1 and a weak C=O stretching vibration peak at 1 720 cm^-1, both of which are characteristic peaks of KH570 Both of them are characteristic peaks of KH570, which proves that KH570 was successfully grafted onto the SiO₂ surface(Fig.5). The modified SiO₂-570 nanoparticles are more uniformly dispersed in the PLA matrix, effectively reducing the agglomeration of SiO₂(Fig.6). The air filtration efficiency of the PLA melt-blown nonwovens was only 37.5% at a gas flow rate of 32 L/min (Fig.8). The filtration performance of the PLA/SiO₂-570 melt-blown nonwovens was superior, with a signifi-cant increase in filtration efficiency to 88.4% and a filtration resistance of only 6.2 Pa, making it more valuable for practical applications.

Conclusions Firstly, PLA/PTFE, PLA/tourmaline and PLA/SiO₂ composite membrane materials were prepared by melt blending method. Among them, the electret SiO₂ has less influence on the thermal stability of PLA, and the prepared composite membrane materials have a high surface charge and relatively slow charge decay. Secondly, in order to reduce the agglomeration of SiO₂, the silane coupling agent KH570 was successfully grafted onto the SiO₂ surface, and the SiO₂-570 nanoparticles were more uniformly dispersed in the PLA matrix, significantly reducing the agglomeration of SiO₂. Finally, the PLA/SiO₂-570 melt-blown nonwovens prepared by melt-blown spinning processing and in situ electret technology has excellent filtration performance, with a significant increase in filtration efficiency to 88.4% and a filtration resistance of only 6.2 Pa. It has great potential for applications in personal protection and air filtration.

Key words: poly lactic acid, nano SiO₂, electret, melt-blown nonwoven, air filtration