Construction Of Flame Retardant Lyocell Fiber Based On "Homogenization" Bio-based Flame Retardant Molecular Structure Design

Lyocell fiber is an artificial"green"regenerated cellulose fiber with excellent mechanical strength,drapability,and biodegradability.The flammability of lyocell fibers poses significant safety hazards,limiting their widespread application.Blending,as a simple,economical and efficient modification method,has significant advantages in achieving industrial production of flame-retardant lyocell fibers without changing the production process and equipment.At present,few studies on the flame retardant lyocell fibers via blending and no eco-friendly flame retardant are applied in practice.Based on the unique structure of lyocell fibers,the principle of"homogenization"flame retardant modification is proposed aiming to develop eco-friendly cellulose-based flame retardants for constructing flame retardant lyocell fibers.The principle of"homogenization"flame retardant modification is to modify the material with similar structures to the matrix according to the principle of similar compatibility for solving poor compatibility and dispersion of flame retardant in spinning dope.A solvent-free reaction system was elaborately designed.A cellulose-based flame retardant CBFF-PN containing phosphorus and nitrogen was successfully synthesized via phosphoric acid,phosphorus pentoxide,cellulose powder and urea as raw materials.CBFF-PN exhibited good dispersibility in lyocell fiber spinning dope and subsequently CBFF-PN/LF fibers were prepared on a small-scale wet spinning line.Specifically,when the addition of CBFF-PN was 20 wt%,the peak heat release rate（PHRR）and total heat release rate（THR）of CBFF-PN/LF decreased by 82.4%and87.6%,respectively.At 700℃,the residual char content is as high as 35.4%,which is a significant improvement compared to that of pure lyocell fibers（16.2%）.CBFF-PN disrupted the crystalline properties of lyocell fibers,therefore the mechanical properties of CBFF-PN/LF decreased by 37%compared to commercial pure lyocell fibers.To balance the mechanical properties and flame retardancy of lyocell fibers,a green-solvent system was designed by employing phosphorus containing ionic liquids as solvent and modifier.Phosphorus containing cellulose-based flame retardant CBFF-P was successfully achieved and exhibited good dispersibility in lyocell fiber spinning solution.CBFF-P/LF fibers were spun adopting a simple wet spinning device made in the laboratory.The flame retardancy of CBFF-P/LF fibers with 10wt%dosage was specifically reflected in the decrease of PHRR and THR by 50.9%and42.6%,respectively.At 700℃,the residual char content of CBFF-P/LF fibers is23.2%,which is slightly higher than that of pure lyocell fibers（16.2%）.CBFF-P formed chemical cross-linking and hydrogen bonding with cellulose molecules making the arrangement between fibers closer.The breaking strength of CBFF-P/LF fibers increased by 6%compared to pure lyocell fibers.CBFF-P/LF fibers displayed significant improvement compared to the breaking strength of flame retardant regenerated cellulose fibers prepared by blending method in literature.Aiming at exploring the path to solve massive solid waste generated by"fast consumption"economy and further expanding the application of the"homogenization"flame retardant modification principle,ionic liquid was utilized to convert waste fabric and waste paper into phosphorus containing cellulose-based flame retardants CBFF-P@WF and CBFF-P@WP.Two composite fibers,CBFF-P@WF/LF and CBFF-P@WP/LF,were successfully prepared by a simple wet spinning device made in the laboratory.The composite fibers exhibited different colors compared to pure lyocell fibers,resulting from dye molecules attached to surface or inside of waste fabric or paper transfer into the interior of lyocell fibers during the spinning process.The flame retardancy of CBFF-P@WF/LF and CBFF-P@WP/LF composite fibers with 10wt%filler was reflected in the PHRR decreased by 37.6%and 50.9%,respectively and the THR decreased by 53.7%and 36.1%,respectively.The residual char content at 700℃is 29.2%and 26.0%,respectively,which is significantly higher than that of pure lyocell fibers.The above results confirmed the feasibility of the"homogenization"flame retardant modification principle proposed in the previous chapter.To develop the diversified function of lyocell and explore the recycling solution of waste textiles,colored cellulose-based ionogel fibers CIFs were designed and synthesized by using phosphorus containing ionic liquids and waste textiles.Three different color cellulose-based ionogel fibers（CIF-White,CIF-Black and CIF-Blue）were prepared by a simple wet spinning device made in the laboratory.The THR of CIFs decreased by 43.7%,68.5%and 40.0%respectively.The residual char content under 700℃in air atmosphere is 8.6%,7.8%,and 12.3%,respectively,which have a certain improvement compared to pure lyocell fibers.The conductivity of CIF-Blue is approximately 1.7×10^-2S/m,equivalent to the conductivity of cellulose fibers filled with less than 10%carbon material.In CIFs fibers,anions containing phosphate groups acted as the fixed sites that did not move,while imidazole ring cations severed as movable ions that generated relative motion under an external electric field forming ion conduction.This work provided an effective and simple recycling strategy to solve the negative impact of waste textiles on the environment and developed a new color conductive cellulose-based ionogel fibers.