Study On The Preparation, Structure And Properties Of Chitosan Fibers With High Tenacity

Chitosan has attracted great attention in the area of biological medical materials duo to its unique biological properties and, at the same time, the research on its physical and chemical structure has made tremendous progress. Chitosan fiber can be used to prepare medical dressing, human body absorbable suture, support material for tissue engineering etc., but its lower tenacity greatly hinders its application area. Therefore, the modification to improve the mechanical properties of chitosan fiber has been as an important research direction in this area in recent years. The purpose in this dissertation is to ameliorate the mechanical properties of chitosan fiber by using dry-jet wet spinning and cross-linking reaction. The rheological behavior of chitosan dope was studied and the effect of spinning technology on the fiber tenacity was discussed. Glyoxal was used as a cross-linking agent to deal with chitosan fiber and the cross-linking mechanism was approached. The effect of cross-linking technology on the fiber tenacity was systematically studied and the chemical structures, crystal structure as well as the heat endurance of the cross-linked fiber were characterized. Based on above research works, the main results obtained are as follows:1. The rheological behavior of chitosan /acetic acid at various shear rate γ and temperature was studied. The results showed that the apparent viscosity η a of chitosan dope is increased with increasing chitosan content and reaches its critical concentration C* at about 3%. Above the C*, the entanglement of macromolecular chains is significantly intensified and thus the n a is remarkably increased. The saturation concentration of spinning dope is about 3.8%. There is a yield stress τ_y, similar to Bingham fluid, appearing in the high concentration, low temperature and lower γ region of the flow curves. When shear stress τ is less than τ y, γ approaches to 0. The dope exhibits Newdonian fluid behavior with n about 1 at lower γ region. With the γ increasing, the dope exhibits a behavior of pseudoplastic fluid with shear thinning character (nl) and the orientation of chain segments created during nozzle channel by shear stress was strengthened in the air gap, as a result, the fiber tenacity was increased whereas if the dope thread was negatively drawn (draw down ratio