Flame-retardant treatment of Lyocell fibers and effects on various fiber properties

Hexamethylolmelamine was used as a cross-linking agent to graft 3-(dimethylphosphono)-N-methylolpropionamide (MDPA) onto Lyocell fibers in a posttreatment process to reduce flammability. The effects of processing conditions on the mechanical properties and P content of the fibers were examined. The results show that increasing the MDPA concentration, microwave treatment time, baking temperature, and baking time increases the P concentration in the fibers, although the mechanical properties of the fibers are reduced to varying degrees. The optimal processing conditions comprise a 40% MDPA concentration, a 320 W microwave treatment for 3 minutes, and baking at 160 degrees C for 5 minutes. Under these conditions, flame-retardant Lyocell fibers with a breaking strength of 2.47 cN center dot dtex(-1) and a limiting oxygen index of 34.6% were obtained, which meet the performance requirements for textile fibers. Thermogravimetric data indicate that the residual fiber mass after heating increased from 4.7% before treatment to 21.5% after treatment. There was only a minimal change in the hygroscopicity of the treated Lyocell fibers. In addition, after 30 washes, the limiting oxygen index was decreased to 26.5% while maintaining a good flame-retardant effect.