关键词: 聚乳酸, 掺杂银二氧化硅气凝胶, 生物可降解, 复合熔喷材料, 空气过滤

Abstract: The rapid development of the modern industry brings economic benefits, but also causes air pollution, which seriously endangers human physical and mental health. The use of air filter materials is an effective way to improve air quality. Melt-blown nonwovens are the main industrial air filter materials due to the large specific surface area, adjustable air permeability, moderate hardness and high production efficiency. However, at present, most of the raw materials used in the production of melt-blown nonwoven materials for air filtration are non-renewable petroleum-based polymer material polypropylene, which is non-degradable and will cause a serious burden on the living environment after being used. 
Polylactic acid (PLA) is a biodegradable thermoplastic aliphatic polyester with good processability and mechanical properties. Nowadays, PLA melt-blown nonwoven materials have achieved industrial processing. However, the melt-blown nonwoven material prepared only from PLA has a single function and poor air filtration performance. Blending modification is a simple and effective method that allows PLA melt-blown nonwoven materials to have multiple functions. Silica (SiO2) aerogels have been widely used in adsorption, filtration and catalyst support in view of the high porosity and large specific surface area. At present, the modification of SiO2 aerogels mainly includes improving the mechanical properties or high temperature resistance by introducing metal elements such as aluminum and pickaxe into the precursor. In this paper, ethyl orthosilicate (TEOS) and AgNO3 were used as the silicon source and Ag particle source, respectively. Methyl triethoxysilane (MTES) was selected as the hydrophobic modifier. SiO2-Ag aerogel was prepared by in-situ doping by the sol-gel method. Then SiO2-Ag with different mass ratios was blended with the PLA melt blending method. Subsequently, SiO2-Ag/PLA blended materials were processed into the corresponding composite melt-blown nonwoven materials. The structure and properties of SiO2-Ag aerogel, pure PLA and SiO2-Ag/PLA composite melt-blown nonwoven materials with different mass ratios were characterized and analyzed. The results show that: (i) the synthesized SiO2-Ag presents a three-dimensional porous network structure, the diffraction peak of Ag with face-centered cubic structure appears in the XRD spectrum. The FT-IR spectrum confirms that the synthesized SiO2-Ag has a Si−O−Si frame structure, and the hydrophobic modification has a certain effect. (ii) SiO2-Ag can be evenly distributed in the PLA matrix, and has good interfacial compatibility with the matrix. With the increase of SiO2-Ag content, the fiber surface of the SiO2-Ag/PLA composite melt-blown material is gradually roughened, and the average diameter and average pore size of the fiber continue to increase. (iii) With the increase of SiO2-Ag content, the filtration efficiency and tensile strength of SiO2-Ag/PLA composite melt-blown materials first increase and then decrease, while the filtration resistance decreases, and the air permeability and quality factors increase. When the SiO2-Ag quality score is 3%, the filtration efficiency and tensile strength of the composite melt-blown material reach the maximum, and increases by 37.99% and 37.50%, respectively, compared with pure PLA melt-blown materials. 
It is hoped that the research in this paper can provide some new ideas for the modification of PLA-based melt-blown filter materials

Key words: polylactic acid, SiO2-Ag aerogel, biodegradable, composite melt-blown material, air filtration