Preparation And Dry Spinning Of Nano-chitin

Chitin has good application prospects in the field of biomedical materials due to its excellent biocompatibility and degradability,but its insoluble and nonmelting properties make processing relatively difficult,especially the forming of chitin fibers,which has complex process and heavy pollution.Therefore,it is of great significance to develop a green process for preparing chitin fibers.Nano-chitin is a kind of fibrous or rod-shaped nano particles prepared by hydrolysis,tempo oxidation or mechanical stripping of chitin.It obtained by different methods has different apparent morphology and chemical structure.Nano-chitin has the advantages of high modulus,low density,large specific surface area,wide sources,bacteriostasis and good biocompatibility.It can be used as reinforcing filler to improve mechanical and biological properties of materials and it can also be used as a building unit to build macro chitin products,so as to avoid the processing problems caused by chitin dissolution zone.In this paper,nano chitin(ChNF)was prepared by chemical mechanical method.The effects of deacetylation degree of chitin and mechanical treatment conditions on ChNF were discussed.The dry spinning process was simulated,and the chitin fiber was spun with ChNF aqueous dispersion as the spinning dopes.The effects of spinning solution composition,concentration,syringe needle length and diameter on the fiber were discussed.The main research work is as follows:1.Firstly,the partially deacetylated chitin(Chi)was prepared by heterogeneous alkali method,and then the partially deacetylated chitin was treated by ultrasound and centrifugation to obtain nano chitin(ChNF).During the testing of Chi and ChNF by FTIR,Zeta Potential,XRD and TEM,the effects of deacetylation degree and ultrasonic treatment conditions on the yield and morphology of ChNF were discussed.The results showed that with the extension of ultrasonic time or the improvement of deacetylation degree,the yield,length and aspect ratio of ChNF increased to a certain extent.Considering the cavitation effect and the influence of too long alkali treatment time on the preparation of ChNF,it was determined that alkali treatment of 4h and ultrasonic treatment of 3h were the optimal process conditions for the preparation of ChNF.Through the analysis of FTIR,XRD and Zeta Potential of ChNF,it was found that with the increase of deacetylation degree,the number of amino groups in the system increased,the diffraction peak intensity of ChNF at2?=9.3° gradually increased,it symbolizes the gradual formation of a new crystal form,ie,chitosan crystals.2.By comparing the mechanical properties and water resistance of a series of nano-chitin cast films,it is found that the components of ChNF and ChNF+CS/LA+TA form films by dry method after deacidification,and then obtain better mechanical properties and water resistance after heat treatment.Therefore,ChNF aqueous dispersion with reverse dialysis to neutral and ChNF+CS/LA+TA composite system with chitosan / lactic acid(CS/LA)and tannic acid(TA)and reverse dialysis to neutral were selected as spinning dopes,and heat treatment was selected as fiber treatment process to explore dry spinning.3.Rheological analysis of the spinning dopes were carried out in order to provide guidance for dry spinning of ChNF.The effects of deacidification treatment,spinning dopes concentration and different spinning dopes components on its rheological behavior were discussed.The results show that deacidification can enhance the shear thinning behavior,increase the stress required to achieve the flow dynamics,and improve the storage modulus.6wt%,7wt% of ChNF spinning dopes and 7wt% of ChNF composite spinning dope have good viscoelasticity,among which7wt%-ChNF spinning dope and 7wt%-ChNF composite spinning dope have relatively good spinnability.4.Chitin fiber was prepared by extrusion spinning with syringe needle,simulating dry spinning process.The effects of spinning solution concentration,syringe needle length and diameter,spinning dopes composition and other factors on the mechanical properties of the fiber were discussed.The results showed that 7wt%-ChNF fiber obtained better mechanical properties.On the basis of determining the spinning dopes concentration,reducing the needle diameter,increasing the needle length and introducing chitosan(CS)and tannic acid(TA)can further improve the strength of the fiber,among which,the 7wt%-ChNF-CS/LA-TA fiber extruded and spun from a 26 mm long and 0.41 mm caliber 22 needle has the highest strength after heat treatment,which can reach 130.80 ± 8.10 MPa.Finally,the chitin fiber was characterized by SEM,TGA and other characterization methods,the surface and cross-sectional morphology of chitin fiber were observed,and the effect of heat treatment on the thermal stability of chitin fiber was discussed.The results showed that there was no obvious orientation of ChNF in the dry spinning process,and the thermal treatment effect would improve the thermal stability of chitin fiber to a certain extent.