The Preparation, Structure And Properties Of Flame-retarded Lyocell Fiber

Lyocell fiber is a kind of regenerated cellulose fiber which becomes popular among people because of its good moisture absorption and air permeability, hand feeling and wearing comfort. And it’s made from cellulose which exists widely on the earth. However, Lyocell fiber is extremely flammable so that it brings risks to burn. Fire disasters resulted from cellulose fiber fabric have serious impacts on people’s lives and property. In order to protect people’s lives and property from fire disasters, it has meaningful significance to develop flame-retarded Lyocell fiber （FR Lyocell fiber）.In this thesis, three flame retardants: cyclic thiopyrophosphate （DXL1212）,2-carboxyl ethyl（phenyl） phosphinic acid （CEPPA） and melamine （MA） were selected to add into cellulose/N-methylmoprholine-N-oxide monohydrate（NMMO·H₂O） with blending method. FR Lyocell fibers were prepared by dry-wet spinning.Nano particle size and zeta potential analyzer, Ultrasonic cell crusher and the centrifuge were used to characterize the particle size and dispersity of flame retardants （FRs）. The results showed that DXL1212were dispersed in NMMO aqueous solution uniformly and stably, and both CEPPA and MA were able to dissolve in NMMO aqueous solution. The results of TGA showed the initial decomposition temperature of DXL1212, CEPPA and MA were315℃,349℃and346℃, respectively, and they have good thermo stability.The rheological and spinning properties of FR/cellulose/NMMO·H2O were studied by HAKEE rheometer. The results showed that cellulose/NMMO·H2O spinning dopes filled with FR belong to the typical shear thinning fluid. The apparent viscosity of spinning dopes decreased with the increase of the adding amount of FRs.The results of SEM showed that DXL1212particles adhered to the fibers, and the surface of the fibers was not smooth. However, CEPPA and MA had less effect on the surface of the fibers. The results of FTIR and Elemental analysis showed that the content of DXL1212in Lyocell fibers was much lower than that in theory because DXL1212was lost during spinning process but CEPPA and MA combined with cellulose. The results of Lyocell fibrillation after ultrasonic treatment observed by the optical microscope showed that DXL1212seldom improved the Lyocell fibrillation, but CEPPA and MA obviously improved the Lyocell fibrillation. The mechanical properties of the FR fibers were measured by the fiber tensile strength tester. The results showed that the mechanical properties of the FR fibers enhanced with the increase of spinning velocity. With the increase of the adding amount of these three FRs, the breaking strength and initial modulus of Lyocell fibers firstly increased and then decreased, but their elongation decreased gradually. When the adding amount of CEPPA was20%, the breaking strength and initial modulus of Lyocell fibers reached optimal performance with10.3%and40%enhancement, respectively.The thermo stability of FR Lyocell fibers was investigated by TG. The results showed that the residual carbon amount of Lyocell fibers with15%DXL1212was10%, which was more than that of pure Lyocell fibers. And CEPPA and MA have improved the initial decomposition temperature. The flammability of FR Lyocell fibers was investigated by Limit Oxygen Index （LOI）. The results showed that the LOI of FR Lyocell fibers has reached26%when the adding amount of DXL1212, MA was30%, but when the adding amount of CEPPA was20%, the FR Lyocell fibers has satisfied the requirements of flame-retardant performance and achieved the best mechanical properties, so CEPPA was the best choice. Finally, the flame-retardant mechanism of these three FRs was studied by SEM and TG. The results showed that DXL1212belongs to condensed phase flame-retardant mechanism and CEPPA and MA belong to gas phase flame-retardant mechanism.