壳聚糖/纤维素纳米晶复合纤维的制备与表征OA北大核心CSTPCD

Cellulose is the most abundant naturally occurring macromolecule on earth,and cellulose nanocrystals(CNCs)are obtained by removing the amorphous regions in cellulose to retain the crystalline regions.The high aspect ratio and high specific surface area of CNCs give them excellent mechanical properties.Meanwhile,as a typical bio-derived nanorod with chirality,they exhibit strong birefringence phenomenon and produce colorful and unique structural colors,so they are commonly used in anti-counterfeiting responsive sensors and so on.Chitosan(CS)is the only alkaline cationic macromolecule containing free amino groups in nature.Chitosan fibers are commonly used in the medical field because of their unique properties such as good biocompatibility,degradability,and rapid hemostasis.However,due to the high surface charge density and high dispersion of CNCs,fibers are difficult to form by wet spinning,and the generally low strength of CS fibers limits their practical application in life.Therefore,the two can be synergized to promote the spinning and forming of CNCs in CS as an effective way to prepare functional fibers.Currently,some researchers have also used CNCs as reinforcement base to compound with bio-based functional materials in order to expand the application areas of CNCs,but little research has been done on the characteristics of CNC assembly in composite fibers that would result in structural coloration.On this basis,this paper innovatively prepares chitosan/cellulose nanocrystalline(CS/CNC)composite fibers by wet spinning method,and compares the mechanical properties and unique optical characteristics of the CS/CNC blended fibers and CS/CNC sheath-core composite fibers prepared by different blending and coaxial spinning methods. In this paper,the effects of different concentrations and temperatures on the tensile theological properties of CS solutions were firstly investigated,and it was found that 2.5％CS solution was suitable for spinning at 60 iC.Secondly,different concentrations of sisal CNCs were used to prepare CS/CNC sheath-core composite fibers to analyze the effect of CNCs concentration on the mechanical properties of the fibers,and the results showed that the mechanical properties of the fibers prepared with 2.0％concentration of CNCs were the most suitable.Therefore,2.5％CS solution with 2.0％concentration of CNCs was selected for the preparation of subsequent wet spinning. To compare the structure and properties of composite fibers prepared by different spinning methods,the structure of CS/CNC composite fibers was analyzed by infrared spectroscopy.The comparison results showed that the FT-IR spectra of CS/CNC composite fibers were similar to those of CS fibers,with the main peak changes occurring in the characteristic absorption peaks between 3 650-3 200 cm-1.Due to the formation of new hydrogen and ionic bonds between CNC and CS,it is easy to form a network structure.Scanning electron microscopy was used to characterize the morphological structure of the fibers.The results showed that the cross-sectional CNCs of the CS/CNC blended fibers were assembled chaotically and twisted,whereas the diagonal cross-section of the CS/CNC sheath-core composite fibers had a distinct skin-core structure and the CNCs were assembled in the core layer into a lamellar structure.To further investigate the lamellar structure of the core layer assembled with CNCs,polarized light microscopy and circular dichroism spectroscopy tests were performed,and the CS/CNC sheath-core composite fibers showed two distinct positive peaks at 388 nm and 608 nm.It confirms that the core layer of CS/CNC sheath-core composite fibers has a left-handed helical nematic phase structure with uniform and orderly arrangement,and the fiber as a whole shows bright and orderly iridescent colors.The tensile mechanical properties of the fibers were tested,and the results showed that the mechanical properties of the CS/CNC sheath-core composite fibers were superior to those of the CS/CNC blended fibers,with an initial modulus of 489.40 cN/dtex,an elongation at break of 9.65％,and a breaking strength of 0.647 cN/dtex.The analysis by heat loss analysis and swelling property test showed that the thermal stability of CS/CNC composite fibers was more similar to that of CS fibers,and the network structure formed in the composite fibers could effectively impede the penetration of water molecules and improve the water resistance of CS/CNC composite fibers. The above results indicate that the CS/CNC sheath-core composite fibers prepared by the coaxial spinning method not only improve the mechanical properties of the fibers,but also have the unique optical characteristics,showing bright and orderly iridescent colors under polarized light.They are expected to be used for anti-counterfeiting clothing fabrics so as to further expand the application scope of CNC.