Study On The Structure And Dissolution And Dyeing Properties Of Different Cross-Linked Types Of Lyocell Fibers

Lyocell fiber is a type of regenerated cellulose fiber that has gained widespread attention due to its environmentally friendly production process,and it is hailed as one of the most representative green fibers of the 21 st century.Lyocell fiber combines the natural comfort of cotton fibers,the drape and flow of viscose fibers,the high strength of polyester fibers,and the soft touch and elegant luster of silk fibers.It is also easily biodegradable.Depending on the degree of crosslinking,Lyocell fiber can be divided into three types: regular type(G100),semicrosslinked type(LF),and fully crosslinked type(A100).The addition of crosslinking agents during the spinning stage and subsequent crosslinking cause certain changes in the structure and properties of Lyocell fibers.Crosslinking agents also interconnect the cellulose macromolecular chains,resulting in an increase in the molecular weight of cellulose chains and making the fibers difficult to dissolve in typical cellulose solvent systems.Therefore,it is challenging to prove the influence of dyeing and finishing processes on the internal crosslinking bonds of crosslinked Lyocell fibers by examining changes in fiber molecular weight.Furthermore,the crosslinking bonds formed between cellulose macromolecular chains by different crosslinking agents may have different alkaline resistance levels,leading to varying degrees of changes in the fibers after sodium hydroxide treatment.Therefore,based on the structural and performance differences of Lyocell fibers with different crosslinking types,this study investigates the structure,dissolution system,the influence of alkaline treatment on its structure,and the differences in dyeing performance of different crosslinked Lyocell fibers..Firstly,a comparative analysis of the structural differences among Lyocell fibers with different types of crosslinking was conducted using instrumental analysis methods.By comparing the surface morphology and supramolecular structure of Lyocell fibers with different types of crosslinking,it was found that all three types of fibers exhibited a core-shell structure,with variations in the dyeing performance between the shell and core layers.The internal giant fibrils in G100 fibers appeared in a loose state,while those in A100 and LF fibers exhibited interconnections.By testing the crystallinity,orientation,and specific surface area of the three different types of Lyocell fibers,it was observed that the order of crystallinity was A100 > G100 > LF,the order of orientation was G100 > LF > A100,the order of specific surface area was A100 > G100 > LF,the order of pore size was G100 > LF > A100,and the order of wet swelling ratio was A100 > G100 > LF.Through comparative analysis of the elemental composition of the three different types of crosslinked Lyocell fibers,it was found that they exhibited variations in the types of elements present.The non-crosslinked G100 fibers only contained carbon(C),hydrogen(H),and oxygen(O),while the semi-crosslinked LF fibers and fully crosslinked A100 fibers contained carbon(C),hydrogen(H),oxygen(O),nitrogen(N),sulfur(S),and carbon(C),hydrogen(H),oxygen(O),nitrogen(N)elements,respectively.Secondly,by exploring the dissolution behavior of Lyocell fibers with different types of crosslinking in various solvent systems such as copper ethylenediamine,lithium chloride/N,Ndimethylacetamide(Li Cl/DMAc),1-allyl-3-methylimidazolium chloride/dimethyl sulfoxide([AMIM]Cl/DMSO),potassium thiocyanate/ethylenediamine(KSCN/EDA),Na OH/urea/water,it was observed that G100 fibers were completely dissolved in the copper ethylenediamine system,Li Cl/DMAc system,and [AMIM]Cl/DMSO system.LF fibers only dissolved completely in the [AMIM]Cl/DMSO system,while A100 fibers dissolved completely in the KSCN/EDA system,Na OH/urea/water system,and [AMIM]Cl/DMSO system.All three types of Lyocell fibers dissolved completely in the [AMIM]Cl/DMSO system,with a dissolution time of 72 hours.Based on this,the dissolution systems for Lyocell fibers with different types of crosslinking were established.By applying the Lyocell fiber dissolution system,the degree of polymerization(DP)of Lyocell fibers with different types of crosslinking was compared using absolute viscosity as an indicator.It was found that the arrangement order of polymerization degree(DP)for Lyocell G100,LF,and A100 fibers was LF > G100 > A100..Then,through the design of an orthogonal experiment,it was found that the treatment temperature during alkali treatment had the most significant effect on the fiber weight loss rate,and the weight loss rate of A100 fibers was significantly higher than that of LF and G100 fibers.By varying the concentration of sodium hydroxide,the changes in weight loss rate,water retention value,carboxyl content,crystallinity,crystal structure,and grain size of Lyocell fibers with different types of crosslinking after different concentrations of Na OH treatment were compared.It was observed that the fiber structure did indeed change to some extent after Na OH treatment,and relatively speaking,the changes were more pronounced in crosslinked Lyocell fibers.By comparing the changes in polymerization degree,viscosity of the dissolution system,and shear stress with shear rate after different concentrations of Na OH treatment for Lyocell fibers with different types of crosslinking,it was found that there was indeed crosslinking between the cellulose macromolecular chains in crosslinked Lyocell fibers.This crosslinking phenomenon could become ineffective when treated with higher concentrations of Na OH solution.Finally,by using reactive dyes and direct dyes to dye Lyocell fibers with different types of crosslinking,it was found that when using reactive dyes with different dyeing systems,the order of dye uptake percentage and color fastness was A100 > G100 > LF for the three types of crosslinked Lyocell fibers.Moreover,in the initial stage of dye uptake and color fastness,the rate was relatively high,which easily led to uneven dyeing.All three types of crosslinked Lyocell fiber fabrics exhibited good dyeing enhancement,with A100 and G100 showing better dyeing enhancement compared to LF.When using direct dyes to dye the three different types of crosslinked Lyocell fibers under the same conditions,it was observed that the initial dyeing rate was high for all types of Lyocell fibers.The order of dye uptake percentage at equilibrium was A100 > G100 > LF.The order of K/S values for same-bath dyeing of Lyocell fiber fabrics with reactive dyes was A100 > G100 > LF,while for same-bath dyeing with direct dyes,the order of K/S values was G100 > A100 > LF.