Functional modification of softwood fiber and its application in natural fiber-based sound-absorbing composite

Natural fiber-based sound-absorbing materials have received more and more attention due to the increasingly severe noise pollution. However, the current natural fibers’ sound-absorbing materials often have poor flame-retardant performance and degradability, which limits their further application. In this study, flame-retardant cellulose fiber (FRCF) was prepared by modifying softwood fiber, and a kind of fiber-based sound-absorbing material, natural fiber-based sound-absorbing composite (NFSC), was prepared by replacing glass fiber with FRCF. The results show that the synthesis of FRCF is successful, and the functional groups containing phosphorus and nitrogen introduced into the cellulose side chain can significantly improve the thermal stability of softwood fiber. FRCF is able to bestow initial flame-retardant capability on the NFSC, allowing NFSC to get the V-1 level in vertical burning test with fewer flame retardants, and the limiting oxygen index (LOI) of NFSC can reach 28.5 %. The NFSC with FRCF instead of glass fiber also has better sound absorption performance; its maximum sound absorption coefficient reaches 0.90, and its noise reduction coefficient (NRC) reaches 0.45. This work is expected to provide inspiration for the design and preparation of environmentally friendly natural fiber-based sound-absorbing materials.