Prepartion of low-cost blended lyocell fibres with phosphorus, nitrogen, halogen and inorganic flame retardants and study on their synergistic fame retardancy mechanism

Cellulose is a kind of green and renewable materials, but its flammability limits its wide application. In order to enhance the flame retardancy of cellulose materials, herein, melamine cyanurate, decabromodiphenyl ethane, 1,2-Bis(2-oxo-5,5-dimethyl-1,3,2-dioxyphosphacyclohexyl-2-imino)ethane(BODIE) and montmorillonite were used as four typical flame retardants. These flame retardants were used alone or in combination to prepare several flame retardant lyocell fibres by physical blending method. Furthermore, the flame retardancy mechanism of phosphorus, nitrogen, halogen and inorganic flame retardant was studied through TG-IR and Raman test, and the synergistic flame retardant between four flame retardants were studied for the first time. The results showed that the nitrogen and halogen-containing flame retardants played the gas-phase flame retardant action by inert gas dilution and chemical quenching of active radicals, respectively. The inorganic flame retardant exerted condensed-phase flame retardant mechanism. The phosphorus flame retardant played both gas and condensed-phase flame retardant effect by chemical quenching of active radicals and cellulose carbonization. Furthermore, the synergism index of phosphorus‑nitrogen and phosphorus-halogen in cellulose materials were 2.1 and 1.7, respectively. There was no obvious synergistic effect between inorganic flame retardant with other flame retardants. In addition, the use of any flame retardant alone tailored the fibre's Limiting Oxygen Index (LOI) lower than 28 %. In contrast, the fibres achieved a LOI of 31 % and a tensile strength of 3.0 cN/dtex when the content of phosphorous flame retardant, nitrogen flame retardant and halogen flame retardant were 45–75 %, 12–55 %, 0–25 %, respectively. This study prepared a method for preparing flame retardant cellulose materials with extremely low-cost and large-scale application potential, and provided a theoretical basis that the selection of flame retardants helped to improve the flame retardant performance of cellulose materials.