Study On The Construction And Properties Of Sulfated Nanocellulose Based Conductive Composite Materials

In the context of the"Double carbon"strategy,combined with the key task of developing bio-based materials in the"14th Five-Year Plan",the development of advanced conductive composites based on biomass nanocellulose has important implications for promoting the green and high-end development of the raw materials industry.Nanocellulose-based conductive composites combine the advantages of nanocellulose and conductive media,and have significant application value in frontier fields such as flexible electronics,sensors,energy conversion and storage.However,the insufficient of dispersion and interface properties between nanocellulose and conductive media limits the full play of their own advantages,resulting in the failure of nanocellulose-based conductive composites to meet the high-performance requirements for advanced functional materials.Carbon nanotubes（CNTs）and poly（3,4-ethylenedioxythiophene）（PEDOT）are two representative types of conductive media,and this article aims to address their shortcomings of poor dispersibility and weak interfacial binding force in constructing nanocellulose-based conductive composites.Specifically,the article develops sulfated nanocellulose with abundant surface chemical groups as a platform to enhance the dispersion and interface properties between nanocellulose and CNTs or PEDOT,and further optimizes the composite process and microstructure control to construct high-performance nanocellulose-based conductive composites.Based on the structural and functional characteristics of sulfated nanocellulose-based conductive composites,the article explores their potential applications in fields such as conductive inks,sensors,electromagnetic shielding,electric heating,and thermoelectricity.The main research contents and conclusions are as follows:（1）Sulfated nanocellulose（SNC）is prepared by combining chemical pretreatment with sulfamic acid/DMF system and high-pressure microfluidization mechanical treatment using pine pulp as a cellulose source.The resulting SNC has a nanofibrous structure with diameters distributed between 2-6 nm and lengths less than 1μm.The degree of sulfate substitution of SNC is as high as 0.5 owing to the high efficiency of the sulfamic acid/DMF system.The surface of SNC has abundant negatively charged sulfate groups,and the surface charge density is as high as 2362μmol/g.The high surface charge density enables the Zeta potential of the SNC dispersion to reach-108 m V,and exhibits excellent dispersion stability and redispersibility.（2）SNC is used as a highly efficient dispersant to construct a CNT-SNC（CSNC）dispersion system.The high surface charge density of SNC allows for strong interactions between SNC and CNTs to overcome the van der Waals forces between CNTs,resulting in the CSNC dispersion system with a high dispersion limit of 80 wt%CNTs and excellent dispersion uniformity and stability.The adaptability of the CSNC dispersion to the printing substrate and the compatibility with the printing process indicate its potential application in green conductive inks.Based on the film-forming property of SNC and the high CNTs content,CSNC dispersion can form flexible self-supporting composite films with high electrical conductivity（1140 S/cm）by solution casting.The high electrical conductivity of the CSNC composite film enables it to achieve a high Joule heating temperature of greater than 170°C at a low voltage of 2 V.The excellent thermal stability and rapid temperature response demonstrate the outstanding thermal management performance of the CSNC composite film.Based on the high humidity sensitivity of SNC,the CSNC composite film exhibits excellent responsiveness to human respiration-related humidity behavior.（3）Based on SNC as a high-efficiency dispersant for CNTs and a green adhesive for rotary-cut basswood veneers,the delignified veneers are assembled layer by layer through the plywood manufacturing process to prepare high-performance carbon nanotube-nanocellulose bulk materials（CCNB）.After the delignification process,the rotary-cut basswood veneers retain the highly oriented structure of cellulose fibers,and form a CNT conductive multilayer structure through the layer-by-layer assembly process.CCNB exhibit excellent mechanical properties（tensile strength of 547 MPa,elastic modulus of 31.8 GPa）and good electrical conductivity（54.2 S/cm）.The Joule heating temperature of CCNB at 2.5 V voltage can reach 177°C,which combines with the fast,stable and controllable temperature response reflects the excellent thermal management performance of CCNB.In addition,the conductive multilayer structure of CNTs in CCNB enables it to achieve an electromagnetic shielding effectiveness of more than40 d B and a shielding efficiency of 99.99%at a low CNTs loading（<3.5 wt%）.（4）A novel PEDOT:SNC dispersion system is constructed by in-situ polymerization using SNC as a dispersant instead of poly（styrene sulfonate）（PSS）.PEDOT:SNC dispersion system shows excellent stability and good redispersibility even at a high EDOT/SNC mass ratio（1:1）,owing to the rich negative sulfate groups and colloidal stability of SNC.Compared to the PEDOT:PSS-cellulose conductive composite system,PEDOT:SNC dispersion system without PSS shows advantages in both manufacturing process and electrical conductivity.Since PEDOT:SNC dispersion exhibits good printability on various substrates and high mechanical durability of the conductive coating,it can be applied to high-performance green conductive inks.PEDOT:SNC dispersion can also directly form flexible,self-supporting conductive composite films with excellent responsiveness to external stimuli such as humidity,liquids,and strain,benefiting from the good plasticity and film-forming ability of SNC.（5）Tunicate cellulose is used instead of pine pulp as cellulose raw material to prepare tunicate sulfated nanocellulose（TSN）with excellent aspect ratio.Based on mussel-inspired polydopamine（PDA）as the interfacial modification layer to enhance the interface interaction between PEDOT and TSN,PEDOT is induced to assemble on the TSN surface,forming a PEDOT:PDA:TSN（PPTSN）conductive nanofiber with a core-sheath structure.The superior aspect ratio of TSN compared to SNC contributes to the formation of the PEDOT conductive sheath structure.Meanwhile,the abundant negative sulfate groups on the TSN surface endow PPTSN with excellent dispersion stability.Due to the inheritance of the mechanical properties of the TSN fiber core and the conductivity of the PEDOT sheath layer,the flexible self-supporting PPTSN composite film prepared by solution casting has excellent mechanical properties and electrical conductivity（～90 S/cm）.The PPTSN composite film with high electrical conductivity and low thermal conductivity exhibits good thermoelectric performance with a power factor of up to 2.6μW m^-1K^-2.Based on the humidity responsiveness of the PPTSN composite film,combined with the humidity-related behavior of the human body,the PPTSN composite film can be applied to non-contact sensors in breathing monitoring sensors and human-machine interaction systems.