The Preparation And Functionalization Of Nano-cellulose Hydrogels With Metal Ions Synergistically Enhancement

Conductive hydrogels can be attached to textiles or human skin for disease diagnosis and health monitoring,due to its high flexibility,stable conductivity and excellent tensile properties.It can be used in electronic skin,human movement monitoring and personal health.There are broad application prospects in management and other fields,and it is gradually replacing traditional rigid materials to become a research hotspot.When researching as a sensor,the ion conductive gel must not only have good mechanical strength and high sensitivity,but also have excellent self-healing,stretchability,frost resistance,antibacterial and adhesion stability.This paper mainly studies the use of nano-cellulose（including nano-cellulose microcrystals and nano-cellulose fibrils）as the reinforcing phase,and the use of coordination bonds and hydrogen bonds between cellulose and metal ions and solvents to build an interface enhancement mechanism,and it is combined with Am,PVA,CS and other functional polymers are compounded to prepare multifunctional hydrogels.By analyzing the type and concentration of nanocellulose,the type of coordination ions and the influence of solvent environment on the mechanical properties of hydrogels,the study of nanocellulose-metal ion synergistic enhancement effect;at the same time,the mechanism of synergistic enhancement structure for self-healing,electrical conductivity,antifreeze,antibacterial and other functional enhancement mechanisms is explored.Specific experiments are as follows:study using nano cellulose filaments and nano cellulose microcrystals as variables,adding nano-cellulose to PVA,Zn²⁺,Ca²⁺and PB for mixing and polymerization to form hydrogels;using metal ions as variables,adding PVA,Am and nano cellulose are mixed and polymerized to form a hydrogel.A series of ionic hydrogels were prepared with different nanocellulose concentrations;with different ratios of glycerol/water solvent conditions and different nanocellulose concentrations as variables,PVA,Am,CS were added,and ammonium persulfate was used as initiator,N’,N’-Methylene bisacrylamide is a cross-linking agent for mixing and polymerization to form a hydrogel.Finally,SEM,FTIR,rheometer,universal testing machine and other instruments and equipment are used to analyze and compare the physical and chemical properties of the hydrogel.The conclusions were showed as below:Nano-cellulose has a significant strengthening effect on PVA hydrogel.With the increase of nanocellulose,the density of nanocellulose hydrogel gradually increases,and the water content gradually decreases.And with the addition of nanocellulose,the hydrogel exhibits good morphological stability and can be molded into different shapes.When the concentration of nanocellulose is 0.6%,the maximum storage modulus of PVA/CNF ion hydrogel is 7.56 k Pa and the tensile strength is 27 k Pa,which are three times and one time of PVA/CNC,respectively.Its hardness,elastic modulus and adhesion strength are generally higher than that of PVA/CNC hydrogel.Therefore,CNF has a stronger reinforcing effect on PVA hydrogel than CNC,forming a denser and firmer hydrogel network structure.Due to the abundant chemical functional groups such as coordination bonds and borate bonds in the nanocellulose ion hydrogel,it can form bonds with different materials,such as skin,wood,metals,etc.,to achieve good adhesion.PVA/CNF ionic hydrogel has a large number of reversible covalent bonds,such as borate ester bonds and metal coordination bonds,so that it can be quickly repaired in the event of damage.At the same time,the ions in the ionic hydrogel can conduct stable conduction,and can be used to measure the bending changes of the finger at different angles stably and accurately during the strain sensing test,which has broad application prospects in the strain sensing field.With the introduction of metal ions and the coordination effect formed between polymer chains and metal ions,the formation of hydrogels has a dense and stable pore structure,which significantly enhances the physical and mechanical properties of the hydrogels.When subjected to external forces,Shows strong anti-destructive performance.And compared with Ca²⁺、Zn²⁺and Al³⁺,the hydrogel polymer network is more stable resulting in different chemical interactions.The PVA/PAAm metal ionic hydrogel forms a stronger intertwining effect,a higher crosslink density,and a stronger network structure.The mechanical strength of PVA/PAAm ionic hydrogels is generally higher than that of hydrogels without added metal ions.Therefore,the metal ions have a significant enhancement effect on the PVA/PAAm hydrogel.Because the PVA/PAAm ionic hydrogel polymer network contains a large number of coordination bonds,hydrogen bonds,and amide groups,the formation of bonds enhances the adhesion strength.At the same time,because the PVA/PAAm ionic hydrogel has good mechanical strength,the metal ions in it give the hydrogel stable electrical conductivity.Through sensing experiments,it can be known that the hydrogel can accurately measure the dynamic bending process of the finger at a bending angle of 0°to 90°,and can be widely used in limb movement monitoring.The introduction of glycerol can promote the formation of hydrogen bonds between the hydrogel network and glycerol and water,thereby improving the mechanical properties of the hydrogel and giving the hydrogel antifreeze properties.When the volume ratio of glycerol to water is 4:26,the organohydrogel forms a denser and firmer network structure.When the ratio of glycerin/water solvent is fixed at 4:26,different concentrations of CNF can significantly improve the mechanical strength of the hydrogel.The interactions in the hydrogel network structure,such as hydrogen bonding and coordination,have been increased,and the mechanical properties of the hydrogel have been significantly enhanced.By introducing Fe Cl₃ to dissolve chitosan,at the same time it forms a coordination with the carbonyl group on nanocellulose,and hydrogen bonds with chitosan and PAAm,and is uniformly dispersed in the organohydrogel to strengthen the polymer network and give the organic water coagulation.Adhesive conductivity,antibacterial properties,self-healing properties,good adhesion and mechanical properties.And combined with its good frost resistance,strain sensing can be achieved under low temperature conditions（-20°C）.Used to monitor finger movement by assembling sensors.When kept at-20°C for 5 days,the impedance value of the strain sensor remains relatively stable,which proves that the organic hydrogel has excellent low temperature tolerance and conductivity stability,and has certain application potential in the field of low temperature sensing.In summary,combined with Am,PVA,CS,the coordination bond and hydrogen bond between cellulose,metal ions and solvents are used to construct an interface enhancement mechanism and prepare conductivity,frost resistance,self-repair,and adhesionl properties.Multifunctional hydrogels have potential application value in strain sensing.