Preparation And Dissolving Of Low Molecular Weight Chitosan And Study On Structure And Properties Of Alginate Fibers Coated With Chitosan

Alginate fibers prepared via wet spinning method have excellent hygroscopicity,biocompatibility,biodegradability,natural flame retardancy,beauty face and skin care effects.However,the application of alginate fibers in garment fabric field is limited due to its gelation in salt solution,no resistance to acid or alkali and difficulty to dye.In this study,chitosan solutions were prepared by dissolving low molecular weight chitosan in carbonic acid solution,coated by which the salt resistant alginate fibers with excellent mechanical properties and antibacterial properties were obtained.The salt-free dyeing of direct fast scarlet dyes 4BS on the alginate fibers coated with chitosan was realized.The kinetics and thermodynamic properties of dyeing were investigated.The low molecular weight chitosan was prepared byenzymatic hydrolysis of chitosan using cellulase and the low molecular weight chitosan with different molecular weight were collected using step-by-step sedimentation method.The optimum conditions of enzymolysis were as follows: temperature 50 ℃,pH value 5.0~5.5,enzyme dosage0.06~0.08 g per gram chitosan.The cellulase is a kind ofendonuclease and function on chitosan randomly.There is no derivative reaction during hydrolysis process.The chemical and physical structure of chitosan with different molecular weight was consistent.The enzymatic hydrolysis of chitosan by cellulase was conducted in steps.Six kinds of low molecular weight chitosan with different molecular weight were prepared by controlling molecular weight of raw chitosans and enzymolysis time.Then the low molecular weight chitosan was made into fine powder,of which the particle diameter is ranging from 200 to 600 nm.There is no chemical reaction during the refining process,while the molecular weight and crystallinity of chitosan both decreased to some extent.With the decreasing of chitosan’s molecular weight,the particle diameter of chitosan fine powder was smaller,the antimicrobial activity was stronger,the bulk density became larger,the water absorption increased,the pH stability was enhanced while the viscosity of the solution decreased significantly.The transparent chitosan solution with a certain viscosity and good stability was prepared using carbonic acid solution.There was no derivative or degradation reaction during the dissolution and regeneration of chitosan.However,the crystallinity of regenerated chitosan decreased.The dissolution of chitosan in carbonic acid solution was conducted by two ways according to the molecular weight: the chitosan with molecular greater than 12 KDa was prepared into chitosan gel firstly and then dissolved in carbonic acid solution since it cannot be directly dissolved in carbonic acid solution;the chitosan with molecular less than or equal to 12 KDa was immersed in carbonic acid solution firstly and then dissolved in carbonic acid solution with the assistant of ultrasound.The dissolution of chitosan gel began from the inside.The optimum dissolution temperature was 10 ℃.The dissolution speed was fast when the optimum moisture content was92.1% and the dissolution time was 3~5 min.The dissolution of chitosan powder was conducted from the surface to the interior slowly and the dissolution time was about 90 min.The optimum dissolution conditions were as follows: pretreatment temperature 5 ℃,pretreatment time 30 min,dissolution temperature 10~15 ℃,ultrasonic power100 W.The optimum preparation conditions of alginate fibers coated with chitosan were as follows: concentration of NaOH during pretreatment 0.3 wt%,pretreatment time 30 min,concentration of chitosan 3 wt%,coating processing time 50 min.The salt resistance of the alginate fibers coated with chitosan and the swelling degree in the salt solution decreased to 55.36% while the breaking strength increased to 1.46 cN/dtex.The antibacterial rate wasabove99% while the moisture absorption ability decreased.Theadsorption isotherm ofalginate fibers coated with chitosan belonged to Freundlich type.The optimum dyeing conditions were as follows: dyeing temperature 80℃,concentration of dyeing solution 2%~4%,dyeing time 90 min,concentration of chitosan solution 2%.The dye up-take of alginate fibers was improved from 20.32% to 82.4%.The washing colorfastness of dyed fibers was good and the retention rate was 92.3%.