Preparation And Performance Study Of High Performance Nanocellulose Materials

The problems of resource depletion and environmental pollution caused by social development are becoming increasingly serious,and mankind will focus more on sustainable development and environmental protection.Cellulose is the most abundant natural macromolecule in the world,with advantages such as low cost,high mechanical rigidity,and high biocompatibility.It is the preferred alternative to traditional plastics.Nanocellulose has high specific surface area and high aspect ratio,and after alignment,it has excellent mechanical properties.This paper prepared high-performance nanocellulose composite fibers and thin films based on three types of cellulose raw materials,and conducted in-depth research on the structure-activity relationship between the orientation degree and mechanical properties of nanocellulose.The preparation of high-performance nanocellulose composite materials could expand the application of nanocellulose in the field of high-performance materials and provide ideas for the research and development of the next generation of environmentally friendly materials.The specific content is as follows:1.There are differences in the structure and properties of cellulose from different sources.In this chapter,the 2,2,6,6-tetramethylpiperidine-1-oxy radical（TEMPO）/Na Br/Na Cl O system was used to oxidize three cellulose raw materials:hardwood bleached pulp fiber（HBKP）,softwood bleached pulp fiber（SBKP）,and microcrystalline cellulose（MCC）.The results showed that the carboxyl content of the three types of TEMPO oxidized cellulose reached above 1 mmol/g,and the yield exceeded 70%.Oxidation had a small impact on the morphology of cellulose,but it would cause degradation in the amorphous region,ultimately increasing the crystallinity of oxidized cellulose.After ultrasonic dispersion,HBKP derived nanocellulose（H-CNF）and SBKP derived nanocellulose（S-CNF）exhibited similar linear structures,the length size of S-CNF fibers was larger than that of H-CNF,with aspect ratios of85.2 and 65.8,respectively.Compared to these two,MCC derived nanocellulose（M-CNF）was thicker and shorter,with a aspect ratio of 14.9.The difference in tensile strength between H-CNF and S-CNF films was relatively small,at 96.3 and 105.9 MPa,respectively,while M-CNF film had the lowest tensile strength of 65.8 MPa.The flexibility of the three types of nanocellulose films was poor,and their tensile elongation at break was lower than 1.5%.2.Nanocellulose（CNF）and sodium alginate（SA）were mixed to prepare CNF/SA composite fiber by wet spinning process with calcium chloride solution as coagulation bath.The effects of SA addition,glucose addition,CNF type and stretching ratio on the morphology,structure,orientation and mechanical properties of CNF/SA composite fiber were studied.The results showed that SA as a thickening agent and crosslinking agent,was rapidly crosslinked with Ca²⁺during wet spinning.With the addition of SA increasing to 0.8%,the gel rate and orientation degree of CNF in CNF/SA composite system were significantly improved,and the structure of CNF/SA gel fiber was more compact and the shape was more regular.Glucose could thicken colloids and inhibit the formation of wrinkles on the surface of fibers.It could also form hydrogen bonds with CNF and SA molecular chains,and appropriate addition could improve the tensile strength of composite fibers.Among the three types of nanocellulose,H-CNF/SA composite fibers had the best mechanical properties,with tensile strength,elongation at break,and orientation of 179.9 MPa,4.99%,and 25.23%,respectively.The mechanical properties of S-CNF/SA composite fibers were similar to those of H-CNF/SA,while the tensile strength and elongation at break of M-CNF/SA composite fibers were lower than those of S-CNF and H-CNF composite fibers.S-CNF composite fiber was easy to break in the wet spinning stage,and gel fiber had many defects.M-CNF composite fiber was most easy to form in the wet spinning stage,and gel fiber had smooth surface and no defects.The stretching of wet CNF/SA composite fibers could effectively improve the orientation and tensile strength of cellulose.After 20%stretching,the mechanical properties of H-CNF/SA composite fibers were the best among the three types of nanocellulose,with their tensile strength,elongation at break,and orientation increased to 331.6 MPa,3.37%,and 30.77%,respectively.3.Oriented CNF/Gly composite films were prepared by shear casting technique by mixing CNF with glycerol（Gly）.The effects of Gly content,CNF type and CNF content on the morphology,mechanical properties and orientation of CNF/Gly composite films were studied.Research showed that Gly was used as a plasticizer and crosslinking agent.When the amount of Gly added increased from 5%to 20%,the tensile strength of CNF/Gly films first increased and then decreased,and the elongation at break increased.Among the three types of nanocellulose,the mechanical properties of S-CNF/Gly composite films reached their maximum at a Gly addition of 10%,with tensile strength,elongation at break,and orientation of 117.1 MPa,3.73%,and 10.85%,respectively.The mechanical properties of H-CNF/Gly composite films were similar to those of S-CNF/Gly,while the mechanical properties of M-CNF/Gly composite films were much lower than those of these two films.The mechanical properties of S-CNF/Gly composite films were significantly improved by controlling the addition amount of Gly to 10%,and increasing the amount of CNF from 1.2%to 2%,when the content exceeded 1.8%,the mechanical properties did not change much.When the addition of S-CNF increased to 2%,the mechanical properties were the best,with its tensile strength,tensile elongation at break,and orientation increased to 130.7 MPa,6.23%,and 10.25%,respectively.