Study On Biomimetic Construction Of Bio-based High-performance Fiber And Its Performance Of Pyrolysis To Carbon

In recent years,the problems of environmental pollution and the exhaustion of oil resources have become increasingly severe,posing severe challenges to the sustainable development of society.Therefore,exploring the use of green and renewable resources has essential research significance.Cellulose is the most abundant natural polymer material in nature.Because of its excellent mechanical properties,biocompatibility and biodegradability,it is considered to be the primary raw material for future energy and chemical industries.However,due to its high crystallinity,intermolecular and intramolecular hydrogen bonds and other aggregate structure characteristics.Natural cellulose can neither melt nor dissolve in conventional solvents.The anodization of cellulose and the construction of a macro-scale material system through the assembly of nano cellulose provides a new way for the green processing of cellulose.Among them,the macro-scale filament constructed by nano cellulose（CNF）is a vital research hotspot.And because of the excellent properties of nanocellulose,the constructed nanocellulose filaments are expected to be used in biomedicine,intelligent textiles and other fields.However,the performance of the CNF filament constructed in the current literature reports is insufficient.To prepare high-performance CNF filaments,many methods have been reported in the literature to bulid CNF filaments.At present,the most essential ways are wet spinning,microfluid assisted spinning and polyelectrolyte complex spinning.However,the low orientation of CNF filaments prepared by wet spinning leads to poor mechanical properties,and the organic solvents in the coagulation bath are not environmentally friendly.Although the filaments prepared by microfluid-assisted spinning have good tensile strength,the toughness of the prepared filaments is insufficient due to the rigidity of cellulose.Polyelectrolyte complex spinning is gelled due to the interaction of CNF and chitosan,which hinders the highly oriented assembly of CNF.The prepared CNF filament has poor mechanical properties.This study is different from the traditional spinning method reported in the literature.Self-designed microfluid-assisted interface polyelectrolyte complex spinning device.CNF filaments and lignin/CNF filaments were prepared by complexing with chitosan in situ polyelectrolyte.To obtain better performance and bionic structure than traditional spinning methods,the main research contents and results are as follows:This article uses the TEMPO oxidation method to prepare nanocellulose.By selectively oxidizing the hydroxyl groups on the cellulose surface C₆ to carboxylates,a negatively charged CNF hydrogel is obtained after homogenization.The acid-base titration of CNF hydrogel was carried out,and the charge density on the CNF surface was calculated to be 1.6 mmol/g.The high charge density indicates that almost all of the hydroxyl groups on the surface of nanocellulose are oxidized to carboxyl groups.The nano-cellulose hydrogel was characterized by an ultraviolet spectrophotometer,and the transmittance of ultraviolet-visible light was above 95%in the range of 300-1100 nm.It shows that the prepared nanocellulose hydrogel does not have impurities and agglomeration.The size of nanocellulose was characterized by TEM and AFM,and the statistics showed that the width,thickness and length were 6.0±0.13 nm,1.95±0.08 nm and 483.4±9.66nm,respectively.The critical lap concentration of nanocellulose hydrogel was obtained by rheological analysis,and the aspect ratio of nanocellulose was calculated to be 91.By combining the advantages of microfluid-assisted spinning and interfacial polyelectrolyte complex spinning,a spinning device is designed.Preparation of CNF filaments with high performance and biomimetic structure.Studies have found that when the concentration of chitosan in CNF filaments is 0.5 wt%,CNF filaments have the best mechanical properties.The tensile strength is 1289 MPa,and the toughness value is 88.9k J/m³.The excellent strength and toughness are due to the solid interfacial interaction caused by the ionic and hydrogen bonds between the highly oriented nanocellulose and chitosan molecules.Using Ca²⁺for further synergistic cross-linking,the tensile strength of the filament is further increased to 1627 MPa,exceeding the value reported in the literature.To explore the breaking mechanism of filaments.The breaking mechanism of nano-cellulose filaments in the tensile breaking process is simulated by molecular dynamics.It was found that during the relative slippage of nanocellulose and chitosan,the ionic and hydrogen bonds at the interface were broken and recombined at the same time.This process dissipates the tensile deformation energy and improves the toughness.Studies have found that CNF filaments have excellent biocompatibility.To overcome the shortcomings of lignin challenging to spin and hard to crystallize after carbonization.Combining the advantages of microfluid-assisted spinning and polyelectrolyte complex spinning in the research,the prepared lignin/CNF filament has a highly oriented and tightly assembled microstructure,which is a very suitable precursor for carbon fiber.After stabilization and carbonization,bio-based carbon fiber is obtained.Bio-based carbon fiber is composed of fine graphite crystals,and the carbon lattice is highly oriented along the fiber direction,which significantly improves the mechanical properties and electrical conductivity.The study found that when the lignin content in the lignin/CNF filament is 75 wt%,the tensile strength of the carbon fiber is 1648 MPa and the electrical conductivity is 185.33 S/cm,exceeding the highest reported value in the literature.The carbonization mechanism of the lignin/CNF precursor was further studied by TG-FTIR combined technology.