Fabrication of multifunctional air filter paper with flame retardant, antibacterial and hydrophobic properties

With the rapid development of the automotive industry, people have put forward higher requirements for automotive air filter paper, hoping that it can meet the more complex air environment. Therefore, there is an urgent need to develop "green" multifunctional air filters with excellent filtration efficiency, flame retardancy, hydrophobicity, antibacterial properties and low cost. In this work, a multifunctional cellulose-based air filter paper with flame retardant, antibacterial and hydrophobic properties was prepared from mercerized pulp and softwood pulp via chemical treatment with pre-synthesized N, N-biguanide-diethyl phosphonic acid (AGDEPA) and octadecyl trichlorosilane (OTS). Due to the high nitrogen and phosphorus content of AGDEPA, the air filter paper shows remarkable self-extinguishing behavior and have no afterglow with an intact textile structure. The limiting oxygen index (LOI) value of air filter paper reached 38.8%, meeting the industry standard for flame retardant materials. Antimicrobial tests confirm that the killing efficiency against E. coli and S. aureus reached 93.9% and 99.99%. Furthermore, OTS containing hydrophobic long chains successfully constructed a multi-layer micro/nanostructure on the paper surface, and its contact angle to water was up to 153.6°. The addition of mercerized fibers also effectively improves the air permeability of the filter paper, which can reach 619 L/m2·s, and subsequent impregnation avoided the impact on the pore size of the material.