Flame-Retardant-Functionalized Pineapple Leaf Fibers for Sustainable Acoustic Absorption

Pineapple leaf fibers (PF), a byproduct of pineapple cultivation, inherit high cellulosic content and porosity that offer a sustainable and cost-effective alternative for manufacturing nonwoven materials with excellent acoustic absorption properties. However, one major drawback of natural-based acoustic materials is their high flammability due to their high cellulosic content. This presents a challenge in complying with fire safety standards required in the building industries. In this work, extractions of PF via an enzymatic and a combined enzyme-chemical treatments were performed before finishing the extracted PF with phosphorus-based flame-retardant agents (FR) and an antistatic oil (oil) additive-based finishing agents using the simple padding process. The finished fibers are physically and chemically characterized by mechanical testing, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy, and thermogravimetric analysis. The flame-retardant properties were evaluated by the modified method aligned with vertical UL 94 standard testing, while the acoustic absorption performance was measured using ASTM E1050-95 standard. The results showed that PF treated with oil prior to FR in both staple fibers and nonwoven samples demonstrated superior flame-retardant performance, which was attributed to the increased surface energy examined by contact angle measurements after oil treatment, leading to improved dispersion and physical attachment of the FR. In addition, noise reduction coefficient values of the flame-retarded PF samples were found to be in the range from 0.55 to 0.60, which indicated that the functional finishing did not deteriorate the acoustic performance. Furthermore, the PF needle-punched nonwoven exhibited superior performance in terms of flame retardancy, acoustic absorption, and compression resilience properties. Based on overall functionality, morphological stability, and cost considerations, the flame-retarded PF samples show strong potential as a sustainable flame-retarded sound absorbing materials.