Co-dissolution Of Cellulose/Silk Fibroin And Regeneration Of The Blended Fibers

Protein fibers have many advantages such as smoothness, softness and moisturepermeability. However, the production of natural protein fibers which can be directly utilizedis limited and the price of such protein fibers is high. Meanwhile, it is difficult to produceregenerated protein fibers due to the strong intra-and inter-action in the proteinmacromolecules. In order to improve the spinnability of the protein solution and the propertyof regenerated protein fibers, the protein is often to be modified by grafting to syntheticpolymer or blending with other polymers. In the thesis, the natural, renewable polymersincluding cellulose and silk fibroin were chosen to be dissolved in1-butyl-3-methylimidazolium chloride ([BMIM]Cl). The phase morphology of the blendsolution was studied and the cellulose/silk fibroin blend fibers were prepared by dry-jet wetspinning.The miscibility of cellulose and protein in the regenerated blend fibers could be tracedback to the phase morphology of the blend solutions. However, there are few researchmethods on phase morphology of polymer blend solutions. In this dissertation, the effect ofcellulose/silk fibroin blend ratio, temperature and shear rate on the rheological properties ofthe blend solutions were studied. And also the phase morphology of cellulose and silk fibroinin the blend solution were analyzed by comparing experimental results with the calculateddata from the log-additivity rule. It is found that silk fibroin could be dispersed with smallerphase size in the continuous phase of cellulose due to the lower viscosity of silk fibroinsolution when the cellulose/silk fbroin blend ratio is larger than0.5. As the ratio of silkfbroin increased, the solution turned to negative deviation and the change of phasemorphology occurred, thus the larger sized of discrete phase of cellulose could be imaged.The phase sizes of cellulose and silk fibroin decreased, the dispersion of cellulose and silkfibroin in the blend solution was improved by increasing shear rates. Results showed that thephase morphology of cellulose and silk fibroin in the blend films agreed with the ones fromrheology.In order to illustrate the stability of cellulose/silk fibroin/[BMIM]Cl solutions during preparation, storage and forming, the effect of temperature on the rheological properties ofcellulose/silk fibroin/[BMIM] Cl was further studied. The temperature dependence of losstangent (tan) followed the sol-gel transition law, as it was described by Winter andChambon. The sol–gel transition of cellulose/silk fibroin/[BMIM]Cl was thermoreversible.The gelation temperature (Tgel) and gel compactness increased along with the increase ofcellulose/silk fibroin concentration. The concentration of6wt%cellulose/silk fibroin waschosen to study the effect of cellulose/silk fibroin blend ratio on the sol-gel transition. TheTgeldecreased and gel structure of the mixture system was loosened along with the increaseof silk fibroin content, which suggest that the gel structure was mainly formed with cellulosechains and the silk fibroin did not form gel during this process.Based on the research on blend solution properties, the cellulose/silk fibroin blend fiberswere fabricated by dry-jet wet spinning. The effect of coagulants (water, ethanol/[BMIM]Cl,water) and coagulation temperature on the composition, phase morphology and property ofcellulose/silk fibroin blend fibers were studied.The conformation of regenerated silk fbroinwas random coil and a-Helix when water was chosen as coagulant. Such regenerated silkfibroin is water-soluble and the protein content in the blend fiber is low. When ethanol waschosen as coagulant, the conformation of regenerated silk fbroin was β-sheet. Thisregenerated silk fibroin was insoluble in water and existed stably in the blend fiber. Theprotein content in the blend fiber increased when proper blend ratio of ethanol/[BMIM]Clwas used as coagulant. The phase morphology of cellulose and silk fibroin in the blend fiberswas traced by laser confocal microscope (LSCM), the silk fibroin existed as―fibril-like‖in theblend fibers when ethanol was used as coagulant. The dispersion of silk fibroin along the radialdimension became more uniform when ethanl/[BMIM]Cl was coagulant. The coagulationtemperature decreased, leading to the increase of viscosity of the blend solution as well as thedecrease of diffusion of silk fibroin and [BMIM]Cl. The protein content in the blend fiberincreased, the dispersion of silk fibroin along the radial dimension became more uniform andthe tensile strength and the initial modulus increased as well.On the basis of the optimization of coagulation kinetics conditions, the effect ofcellulose/silk fibroin blend ratio and draw ratio on the phase morphology, structure andproperty of cellulose/silk fibroin blend fibers were also studied. Regenerated silk fibroin existedas“fibril-like”in cellulose, in which the radial dimension of silk fibroin phase was0.5–1.0μmand increased with increasing of silk fibroin content. Although the tensile strength and initialmodulus of blend fibers decreased with increasing silk fibroin content, the tensile strength of blend fibers containing37.2wt%of silk fibroin was up to191MPa and met the demand oftextile. With the increase of draw ratio, the tensile strength and initial modulus increased andthe elongation decreased. This is related to the crystallinity and orientation of the blend fibers.Further more, the distribution of two draw ratios on the structure and property of the blendfibers were studied. The effect of distribution of two draw ratios on the mechanical propertieswas not obvious under the same total draw ratio. The tensile strength of cellulose/silk fibroinblend fibers could be up to398.8MPa when the blend fiber contains16.1wt%silk fibroinwith draw ratio of5.