Preparation And Performance Study Of Functionalized Gels With Sodium Lignosulfonate

Flexible wearable strain sensors convert various physical signals into electrical signals for information acquisition and transmission and have a large potential for application.Conductive hydrogels have excellent electronic properties,such as flexibility,high electrical conductivity,and biocompatibility,making them ideal candidates for flexible wearable strain sensors.However,existing hydrogels usually exhibit poor mechanical properties in practical applications,which affect signal stability and sensitivity.In addition,the water in the hydrogel network inevitably freezes in extremely low-temperature environments or evaporates in high-temperature environments,resulting in significant degradation of its mechanical properties and a significant decrease in electrical conductivity,which affects the normal use of hydrogels.Therefore,the preparation of hydrogel sensing materials with multiple functions such as excellent mechanical properties,electrical conductivity,and frost resistance remains a great challenge.Lignin is the second largest renewable resource after cellulose in biomass fraction,rich in catechol-like structure,with cheap and easy to obtain,degradable,and green and safe features.Green multifunctional composite biomass conductive gel can be prepared by using lignin-modified hydrogel.In this thesis,water-soluble sodium lignosulfonate was used as the raw material to reduce composite nanosilver to activate ammonium persulfate to complete the free radical polymerization reaction;self-assembled into nanospheres to enhance the mechanical properties and UV-protection of the gel.In addition,the anti-freeze,moisture,and antibacterial multifunctional properties of the composite gels were also explored.On this basis,the sodium lignosulfonate-based gels were applied to skin sense to expand the new applications of water-soluble lignin in the field of functional materials.The main research of this work is as follows:（1）Multifunctional cellulose nanocrystals-sodium lignosulfonate-silver-polyacrylamide nanocomposite hydrogels were prepared by free radical polymerization in ten minutes.The sodium lignosulfonate-silver（Ls-Ag）redox pair can effectively activate ammonium persulfate（APS）,which triggers free radical polymerization,resulting in rapid polymerization of acrylamide（AM）to form hydrogels.The morphology,mechanical properties,and UV-blocking properties of the hydrogels were characterized by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,mass spectrometer,and solid-state UV spectrophotometer.The results showed that the hydrogels have excellent tensile strength（406 k Pa）,super tensile properties（1880%）,and self-recovery and anti-fatigue properties.Due to the presence of metal ions and polyphenol-like structured lignin,the composite hydrogel exhibits excellent adhesion（especially to metal substrates:36.8 k Pa）,electrical conductivity(9.5 m S cm^-1),UV-blocking performance（100%shielding in the UV spectral region）and bacterial inhibition（over 98%inhibition）.In addition,the hydrogel-based sensor has high sensitivity（sensitivity coefficient of 2.46）to accurately monitor large or subtle changes in human movements,and can also be used as a bioelectrode to collect human electromyographic signals and ECG signals.This study provides a theoretical basis and application support for the high-value utilization of sodium lignosulfonate in the field of hydrogel sensors.（2）In this chapter,lignin nanospheres（LNSs）were first prepared using the DMSO/H₂O binary system.The particle size of the prepared LNSs was 140 nm at the DMSO/H₂O ratio of 1/4,and it became larger with the increase of DMSO content.From the morphological analysis,it was known that the LNSs were regular spherical with good dispersion and no obvious aggregation.The binary solvent containing LNSs was compounded with polyvinyl alcohol（PVA）without chemical cross-linker,and the aqueous organogels with excellent mechanical properties,anti-freezing and UV-blocking properties could be prepared after freeze-thawing,and DMSO lowered the freezing point of the organogels by regulating the hydrogen bonding between water molecules so that the sodium lignosulfonate-PVA organogels showed excellent performance in a wide temperature range.The organogels were characterized by mechanical properties,freezing resistance,self-recovery properties,and UV-blocking properties.The results showed that the maximum stress,strain,and toughness of LNSs-PVA organogels reached 1.02 MPa,530%,and 2.07 MJ m^-3,respectively.LNSs-PVA organogels exhibit excellent frost resistance and can still reach a stress of 0.73 MPa at a low temperature of-90°C,which is about 72%of the stress at 20°C.LNSs-PVA organogels can shield 100%of UV light at200～400 nm while maintaining high transparency.LNSs-PVA organogels can be assembled into wearable strain sensors to accurately monitor and differentiate between large and subtle movements of the human body,broadening the application of strain sensors under extreme conditions.（3）To further improve the mechanical properties and electrical conductivity of the organogels and to impart antibacterial properties,silver ions were introduced on the gel surface by impregnation method based on LNSs-PVA organogels,and then the ascorbic acid（VC,C₆H₈O₆）solution was used to reduce the silver ions adsorbed on the gel surface so that the organogel surface was coated with a layer of dense silver nanoparticles（Ag NPs）.The organogels were characterized for mechanical properties,electrical conductivity,frost resistance,and antibacterial properties,and the results showed that the prepared LNSs/Ag-PVA organogels have excellent mechanical strength（1.58 MPa stress,680%tensile strain）,frost resistance（-90°C）and antibacterial properties（over 98%antibacterial rate）.Moreover,the organogel conductivity can still reach a high value of1.9 m S cm^-1 at the ultra-low temperature of-90°C.In addition,the LNSs/Ag-PVA organogels exhibited high strain sensitivity（GF=0.71）,a fast response time（440 ms）and recovery time（430 ms）,and excellent resistance stability for complex flexible wearable electronic devices,providing theoretical support for the application of lignin-based conductive,antifreeze organogels.