Synthesis And Properties Of Tough Hierarchical Polyvinyl Alcohol/Gum Xanthan Hydrogel

The unique layered structure of the dense outer layer of articular cartilage and the porous center endows the cartilage with excellent self-lubrication,wear resistance and toughness.Inspired by this structure,the research and development of cartilage bionic structure hydrogel materials with excellent lubrication and mechanical properties has become an international research hotspot.As a hydrogel material with biocompatibility,permeability,hydrophilicity and low friction coefficient,polyvinyl alcohol（PVA）hydrogel has shown great advantages in intelligent materials such as artificial skin and soft robots.However,PVA hydrogels prepared by conventional methods generally have poor mechanical properties,and the bacterial growth caused by their high water content makes them lack stability in practical applications,which greatly limits the application of PVA hydrogels in new smart materials.In view of the single function of PVA hydrogel,poor chemical stability and fatigue resistance,and easy growth of bacteria,this thesis is inspired by the hierarchical structure of cartilage,by introducing xanthan gum（GX）with a double helix structure,and fusing freeze-thaw circulation and sodium silicate induction strategy to construct a polyvinyl alcohol/gum xanthan（PVA/GX）bionic hydrogel with hydrogen bond network cross-linking;The effect of process factors such as raw material ratio,coagulation bath concentration and temperature on the microstructure,chemical structure,water content,mechanical properties,chemical stability and thermal stability of PVA/GX hydrogel has been systematically studied,and its mechanical enhancement mechanism has been explored.In order to expand the functional application of biomimetic structure PVA/GX hydrogels in smart materials,aminated cellulose（ACe）is further introduced to prepare PVA/GX/ACe antibacterial hydrogels,which are prepared by sodium citrate（Na₃Cit）/glycerin mixed solution.Impregnation treatment to obtain PVA/GX/ACe conductive hydrogel with both high strength and toughness and antibacterial properties.The influence of the amount of ACe on the water retention,mechanical and antibacterial properties of the hydrogel was explored,and the conductivity of the PVA/GX/ACe conductive hydrogel and its response to human motion signals were preliminarily evaluated.The specific research results are as follows:1.Preparation and performance of tough polyvinyl alcohol/gum xanthan biomimetic hydrogel:Using polyvinyl alcohol（PVA）and xanthan gum（GX）as raw materials,a strong and tough PVA/GX hydrogel with a cartilage-like layered structure was successfully prepared under the induction of sodium silicate（SS）coagulation bath.The addition of GX can significantly improve the mechanical properties of the hydrogel,and as the concentration and temperature of the coagulation bath increase,the thickness of the dense layer on the surface of the gel will increase,and its mechanical strength will be further enhanced,with the maximum tensile strength as high as 6.39 MPa and the modulus of elasticity reaches 4.73 MPa.After 400 compression cycles,the elastic modulus can still be maintained at 3.5 MPa.After the hydrogel is rubbed with a 9 N metal probe for 30 times,its fracture stress is 5.6 MPa,showing excellent wear resistance;After treatment with strong acid and alkali（pH=1-14）,the fracture stress is still 6.17-6.5 MPa,and the elastic modulus remains at 4.3-4.5 MPa,showing significant acid-base resistance.In order to explore the enhancement mechanism of the hydrogel,the orientation and crystallization of the hydrogel molecular chains were analyzed by two-dimensional X-ray diffraction.It was found that the diffraction ring of the PVA/GX hydrogel was complete,and the crystal area was more perfect,showing highly directional diffraction.The crystallinity of the hydrogel has been effectively improved due to the addition of GX,from 1.47%to 2.8%,and as the tensile strain increases,the crystallinity of the gel increases.2.Preparation and performance of polyvinyl alcohol/xanthan gum/aminated cellulose antibacterial conductive hydrogel:In order to realize the functional application of PVA/GX hydrogel in smart materials,rod-shaped aminated cellulose（ACe）was further introduced as an antibacterial component,and after induction by SS,it was further treated with sodium citrate/glycerin to successfully prepare PVA/GX hydrogel.GX/ACe antibacterial conductive hydrogel.Thanks to the hydrogel’s own hydrogen bond network and a more complete crystal structure and the synergistic enhancement of ACe,PVA/GX/ACe hydrogels exhibit more excellent flexibility and mechanical strength.When the ACe content is 0.1%,At 0.2%and 0.3%,the maximum tensile strength is 7.39,8.00 and 9.42 MPa,respectively.Due to the Schiff base structure of ACe and the large number of amino active groups on the surface,the hydrogel exhibits good antibacterial properties.When the ACe concentration is 0.3%,the antibacterial rates against S.aureus and E.coli are 54.78%and 82.11%,respectively.As an ionic conductor,sodium citrate can enhance the conductivity of the hydrogel.Under a strain of 25-100%,the resistance change rate of the conductive hydrogel becomes proportional to the tensile strain;There is almost no hysteresis in the 60%strain and 500 compression cycles,and there is almost no attenuation of resistance,indicating good stability and cyclability.PVA/GX/ACe conductive hydrogel as a strain sensor has high sensitivity and can effectively detect different degrees of bending of the human index finger and wrist,and the signal output is stable.In this thesis,polyvinyl alcohol（PVA）and xanthan gum（GX）are used as raw materials,and a strong,chemically stable and wear-resistant PVA/GX bionic structure hydrogel is successfully prepared through the induction of SS coagulation bath,and through the introduction of ACe and After treatment with sodium citrate,a new type of PVA/GX/ACe antibacterial conductive hydrogel with strong toughness and stable conductivity was prepared.The introduction of amino cellulose not only improves the mechanical properties and cycle stability of the hydrogel,but also successfully imparts certain antibacterial properties to the hydrogel.The combination of hydrogel and sodium citrate as an ionic conductor has good conductivity stability and circulation,and can detect deformation caused by bending of fingers and wrists,and has broad application prospects in the field of wearable sensors.