Study On Preparation And Application Of Multifunctional Polyvinyl Alcohol Hydrogel

In recent years,conductive hydrogels have been widely used in flexible electronic devices due to their excellent electronic stability,adjustable mechanical properties and special biological functions.However,the hydrogel is easy to be damaged when it is used,and the adhesive is required to stick on the surface of the object,affecting the sensitivity.Therefore,it is of great significance to prepare hydrogels with both self-adhesion and self-repair properties.In this paper,multifunctional polyvinyl alcohol hydrogel was prepared,and its self-repairing,self-adhesive and conductivity were studied.Finally,their applications were carried out.1.Firstly,we modified cellulose nanocrystals（CNC）with tannic acid（TA）under alkaline conditions.TA@CNC solution is mixed with polyvinyl alcohol and heated at high temperature,and then borax is added to form polyvinyl alcohol borax tannic acid modified cellulose nanocrystalline（PBT）hydrogel.In this system,TA@CNC endows the hydrogel with excellent self-adhesive and self-healing properties,which can firmly adhere to various materials.The adhesion to Al is up to 55.2KPa.After 60s of self-healing,the tensile strength of the hydrogel can reach 99.4%of the initial tensile strength.However,the mechanical properties of the obtained hydrogel are too weak,so the PVA chain is crystallized by freezing and thawing,so that PBT hydrogel can obtain more excellent mechanical properties.The tensile strength of PBT-2-0.60-1 is 3.43 times that of PBT-2-0.60-0.However,after freezing and thawing,the breaking elongation,adhesion and self-healing performance of the hydrogel are greatly reduced.2.Polyvinyl alcohol conductive hydrogel was prepared based on PBT hydrogel.The two-dimensional material MXene with good stability,flexibility,hydrophilicity and conductivity was selected as the conductive material to add to the PBT hydrogel.MXene has functional groups such as-F,-OH,-O on its surface,which can interact with PVA and TA@CNC Strong bonding is achieved through hydrogen bonding interactions.In this system,the conductivity,mechanical properties and self-adhesive properties of the hydrogel were adjusted by changing the mass ratio of MXene to PVA.The experimental results show that by optimizing the mass ratio of MXene/PVA,the tensile strength is135.8KPa,and the elongation at break is 397.3%.The current of the cut hydrogel can be restored to 96.7%of the initial current after 0.3 seconds of re splicing.In addition,the water gel also has self-adhesive performance.We can use it as a wearable sensor directly on the human skin to achieve effective detection of human motion signals.3.In the work of Chapter 3,the adhesion of PBTM hydrogel decreases after freezing and thawing,and the self-healing performance greatly decreases.We reduce the crystallinity of PVA chains by shortening the freeze-thaw time and the metal coordination bond formed by Al³⁺,PVA and TA is used to strengthen the hydrogel.The tensile strength of PBTM-Al³⁺-1h hydrogel can be restored to 87.3%of the initial tensile strength 24 h after being cut off,and the recovery rate of tensile strength can reach 91.1%after four cycles under 200%strain.Compared with Chapter 3,the prepared hydrogel sensor is more sensitive.It can not only detect the large motion signal of the human body,but also detect the micro strain of the human body,such as the facial expression changes（smile,anger）,and can detect the pulse on the wrist and the throat strain when speaking.