Study On Liquid Crystalline State In Composite Polysaccharide Nanofibers By Electrospinning

Cellulose,chitin and chitosan are natural polymer resources of current interest.Owing to their excellent biocompatibility and biodegradability,they have seen extensive use in the production environmentally friendly composite materials.Moreover,the facile preparation and application of these unlimited resources have attracted both academic and industrial interest making them front-runners in the nanotechnology field today.In the present thesis,the aim of this study was to effectively characterize the structure and properties of nanofibers produced via electrostatic spinning process.Here,3 materials;cellulose nanocrystals(CNCs),chitin nanocrystals(CNW),chitosan nanofibers(CSF)were directly dispersed into PVA matrix to fabricate environmental-friendly polysaccharide-based nanofibers.Different spinning conditions such as voltage,rotational speed,concentration,flow rate and collection distance,etc were employed to fabricate different fibers.The obtained fibers were examined using POM,SEM,XRD,and tensile test.The results showed composite fibers with smooth and uniform size distribution.The liquid crystalline nanofibers showed significant birefringence and higher crystallinity when CNC content was 50%and also applied as a shell.The tensile strength of the free-oriented PVA/CNC composite fibers was improved and reached about-1.10 times higher than PVA mats.Meanwhile the elongation at break was reduced by 3.8 times.By improving the collection device,temperature,voltage,distance between nozzle and roller,translational velocity,rotation speed,etc,oriented PVA/CNC fibers were obtained.Electrospun nanofibers were examined using POM,SEM,XRD,polarized FTIR,and tensile test.The results showed that the highly oriented fibers with uniform and continuous.CNCs were arranged in the axial direction of the oriented fibers.The degree of orientation was highest when the content was 50%and the tensile strength of the orientated PVA/CNC composite fibers was improved 1.24 times when compared to random fibers and the elongation at break increased by 4.36 times.The elongation at break of CNC@PVA fibers compared with PVA@CNC fibers increased by 65.72%.Also,spinning conditions such as voltage,flow rate,spinning distance,speed,temperature etc were investigated and orientated,random PVA/CNW and coaxial nanofibrous mats were obtained.The composite fibers were examined using POM,SEM,XRD,tensile test.The diameter distribution was also subsequently analyzed.The results showed PVA/CNW fiber with smooth and smaller diameter.The liquid crystalline fibers showed significant birefringence and higher crystallinity when CNW content was 10%.Moreover CNW content of 1%exhibited the highest mechanical properties.Meanwhile the introduction of aqueous ethanol solution caused an improvement in the clarity of PVA/CNW nanofibers with high transparency(?85%).By employing chitosan,CSF were obtained by mechanical treatment and later dispersed into PVA matrix to prepare PVA/CSF composite nanofiber mats.Spinning conditions such as solution concentration,voltage,flow rate,spinning distance,speed,temperature etc were investigated and random PVA/CSF nanofibrous mats were obtained.The composite fibers were examined using POM,SEM,XRD,tensile test.The results revealed that the fiber exhibited better morphology.However the PVA/CSF fibers did not show birefringence behavior under polarized conditions.Tensile strength of the PVA/CSF(1%,w/w)was 75.57 MPa and this was improved about 10 times higher than PVA mats.With the increase of chitosan nanofibers,the tensile strength and elongation at break of the fibers were significantly reduced.