Preparation And Properties Of Nanocellulose/Nanochitin Multidimensional Composites

As one of the representative substances of renewable resources,cellulose can be dispersed into nanocellulose by chemical modification or mechanical exfoliation.Nanocellulose has many advantages,such as excellent mechanical properties,high transparency,biocompatibility,high aspect ratio,high specific surface area,and outstanding dispersion.It has been widely used in many fields.Chitin is the second largest biomass resource after natural cellulose relay.Its can also dispersed to nanometer level by chemical modification or mechanical exfoliation.Chitin exhibits excellent biodegradability and biological phase because of the source organisms.Which are easy to modified due to its active groups such as amino groups,and widely used in biomedical products and materials.Nanocellulose and nanochitin have their own advantages and disadvantages.The nanocellulose membrane has poor water resistance,and the nanochitin membrane has good hydrophobicity.Nanocellulose has a higher aspect ratio than nanochitin,with better enhancement properties,etc.In order to comprehensively utilize the advantages of nanocellulose and nanochitin,and further expand the application fields of nanocellulose and nanochitin.This thesis uses nanocellulose and nanochitin as raw materials,and based on its unique structural characteristics and chemical properties,through the structure-function integrated design,the one-dimensional conductive wire,two-dimensional superhydrophobic membrane material,three-dimensional hydrogel material,four-dimensional shape-photothermal double-responsive material wrer prepared.These materials pioneering the application of nanocellulose and nanometer chitin in new fields,and increasing the added value of cellulose and chitin basic raw materials,providing scientific basis and new ideas for the deep development and comprehensive utilization of biomass resources.（1）The TEMPO/NaBr/NaClO oxidation system was used to obtain the negatively charged（-COO^-）TOCNF.The partial deacetylation ofα-chitin by NaOH,and the protonation were carried out at acidic environment to obtain positively charged(-NH³⁺)α-DECHN.Theα-DECHN charge is+44.40 mV,the pure TOCNF charge is-40.30 mV,the prepared TOCNF has a width of 10-20 nm,the length is 800-1100 nm,theα-DECHN diameter is about 12 nm,the length is 500-600 nm.The TOCNF andα-DECHN have a very high transmittance,and have good thermal stability without thermal decomposition at 220°C.（2）TOCNF/MWCNTs suspension was extruded inα-DECHN by linear extrusion-crosslinking method using TOCNF dispersed multi-walled carbon nanotubes（MWCNTs）andα-DECHN as cross-linking molding agent.The charge cross-linking obtained the TOCNF/MWCNTs/α-DECHN composite one-dimensional conductive wire.The results showed that TOCNF has good dispersibility to MWCNTs.MWCNTs has little effect on the zeta potential of TOCNF.The TOCNF/MWCNTs/α-DECHN composite conductive wire has a rod-like structure,and the surface is firmly connected to each other without pores.The surface is rough and high and low undulations shows a certain directionality,the arrangement is arranged along the length direction of the conductive wire.The cross-sectional structure is high and low undulating and closely connected to each other,and shows the flexible fractures.The inner part of the wire is relatively flat without the linear direction.The addition of MWCNTs improves the thermal stability of composite wires.The addition amount of MWCNTs is suitable at 12.0 wt%,and the electrical conductivity of the composite wire is1.56×10^-33 S?cm^-1,and the LED lamp can be lit at a voltage of 1.62 V.（3）Preparation of TOCNF/α-DECHN composite transparent membrane by low-power ultrasonic self-assembly with positive and negative charges,combined with casting method.The modification of nano-SiO₂ with 1H,1H,2H,2H-perfluorodecyl dimethylchlorosilane to prepare F-SiO₂.TOCNF/α-DECHN/F-SiO₂ composite superhydrophobic transparent membrane was prepared by coating F-SiO₂ on the surface of TOCNF/α-DECHN composite membrane by surface deposition method.The results showed that TOCNF/α-DECHN composite transparent membrane macroscopically is smooth and flat,and it has hydrogen bonding and positive and negative charge electrostatic attraction.The contact angle of TOCNF membrane is almost 0°,which is completely hydrophilic.The contact angle ofα-DECHN membrane is 112°,which is hydrophobic membrane.The contact angle of TOCNF-5:α-DECHN-5 membrane is 52°,which indicates that theα-DECHN composite TOCNF can improve the hydrophobic properties of the pure TOCNF membrane.Increased F-SiO₂ reduces the light transmittance of the composite membrane.Under the premise of ensuring the optical transparency and superhydrophobicity of the TOCNF/α-DECHN composite transparent membrane,the addition of F-SiO₂ is suitable at 2.0 wt%.At this ratio,the TOCNF/α-DECHN/F-SiO₂ composite membrane has a contact angle of 150°and a transmittance of 68.5%.（4）The negatively chargedα-DECHN and the positively chargedα-DECHN are used as hydrogel assembly materials.The TOCNF dispersion is added dropwise to theα-DECHN dispersion with a slight agitation to trigger assembled and intertwined of the negative charge TOCNF and positive chargeα-DECHN.The TOCNF/α-DECHN hydrogel was formed,which was applied to the sustained release of the anticancer drug 5-FU.The results showed thatα-DECHN-40%:TOCNF-60%mixture has the closest to the neutral amount of charge and has the largest elastic modulus（G’）and viscous modulus（G"）.The TOCNF/α-DECHN hydrogel has a different pore structure from TOCNF andα-DECHN.Withα-DECHN ratio is gradually increased,the pore structure of the TOCNF/α-DECHN hydrogel is transformed by a dense pore radial network-like pore size,and a hydrogel with a finer porous structure is obtained.α-DECHN-40%:TOCNF-60%,the hydrogel has the highest swelling rate,and the drug sustained-release tendency of TOCNF/α-DECHN hydrogel is very close to the swelling of TOCNF/α-DECHN hydrogel.Theα-DECHN-40%:TOCNF-60%hydrogel has minimal surface charge and the strongest physical cross-linking shows a loading amount（M5-FU）of5331μg/0.1g absolute dry gel,loading efficiency（LE5-FU）was 53.31%.（5）Theα-DECHN/TOCNF composite membrane was used as the matrix material.The preparation of the thermo-variable color-responsive ink and the optically variable color-responsive ink,which were co-dissolved with the temperature-deformation material PNIPAM to form a co-solubilized system,which was screen printed on the TOCNF/α-DECHN composite membrane.The printed composite structure were cured by UV-light or heat to obtain TOCNF/α-DECHN composite membrane-based thermotropic deformation-photochromic double-response material and TOCNF/α-DECHN composite membrane-based thermal deformation-discoloration double response material.The results showed that the composite double-response material has shape deformation after heating at65°C,and the shape recovers after cooling to room temperature.The deformation and recovery of TOCNF/α-DECHN composite membrane-based thermodeformable material is a reversible process.For the light-changing color response portion,magenta is generated when UV is irradiated,the composite material gradually turns white after the UV is removed,or the heating 60℃rapidly fades to white,and the light-changing color response process is reversible.For the heat-change color response part,when heating,the composite material turns green,the heating is removed,the green color of the composite material gradually fades,and the thermal color change response is reversible process.