Preparation And Study Of Cellulose Composite Adhesives With High Strength And Water Resistance

Nowadays,adhesives are widely used in various industries and are an indispensable part of people’s lives.However,most of the adhesives currently used are mainly derived from petroleum,which is a non-renewable resource.What’s more,during the production and the use of petroleum-based adhesives,a lot of polluting and toxic substances will be produced,causing great harm to the environment and the human body.Therefore,it is of great significance to develop a non-toxic,non-polluting,and environment-friendly adhesive.As a biomass material,cellulose nanofiber（CNF）is widely used in various aspects because of its rich source,high aspect ratio,biodegradability,and biocompatibility.Meanwhile,a lot of hydroxyl groups on the surface of CNF endow it with bonding properties to polar surfaces,having huge application prospects in adhesives.However,it is the hydroxyl groups of the CNF that have low bonding strength and are easily combined with water molecules resulting in low cohesion and interfacial adhesion with the substrate,which limits the application of CNF adhesives in wet environments and underwater.In order to solve the above problems,water-resistant substances and network structures were introduced to enhance the bonding strength and water resistance of CNF adhesives,broadening the application of CNF composite adhesives.The specific research work is as follows:Firstly,polyethyleneimine（PEI）formed chain entanglements with CNF and reacted rapidly with tannic acid（TA）to form chemical bonds.With the help of PEI,TA was introduced to the surface of CNF to improve the interfacial adhesion and water resistance of CNF adhesives.CNF/TA/PEI adhesives with different bonding strengths and water resistance were prepared by adjusting the content and ratio of TA and PEI.Through the test and the characterization of the structure and properties of the cellulose-based adhesive by different experimental instruments,it was found that the water resistance and the bonding strength of the adhesive were significantly improved after the introduction of TA.When the total content of TA and PEI reached 80 wt%of CNF and the ratio between them was 60:40 w/w,the dry and wet shear strengths of the adhesive were both the highest,which were 394.1±17.8 kPa and 178.5±17.6kPa,respectively.And the water absorption rate of the adhesive was 21.6±2.5%.The adhesion strength of the adhesive with long-term stability can still be stabilized at about 60 kPa,after being soaked in water for 28 days.In addition,CNF/TA/PEI adhesives can be used on a variety of material surfaces,having broad application prospects.Secondly,to further improve the underwater bonding strength and reduce the curing time of the CNF adhesive,CNF was firstly blended with PVA-SbQ to prepare CNF/PVA-SbQ adhesive with a network structure,where PVA-SbQ can form a network structure through photodimerization under ultraviolet light.The effect of the ratio of CNF to PVA-SbQ on the structure and properties of CNF/PVA-SbQ adhesive was studied,and the optimal ratio of CNF to PVA-SbQ was obtained.Then,TA was introduced to the surface of CNF by the self-aggregation deposition method to obtain TA-CNF.After mixing TA-CNF and CNF,a CNF/TA-CNF composite suspension was obtained.The prepared CNF/TA-CNF suspension was mixed with PVA-SbQ to prepare CNF/TA-CNF/PVA-SbQ adhesive with excellent underwater bonding strength.Through the test and the characterization of the structure and properties of the adhesive by different experimental instruments,it was found that in the CNF/TA-CNF/PVA-SbQ adhesive,the introduction of TA and the formation of the cross-linked network structure could significantly improve the cohesion and interfacial adhesion of the adhesive,thereby further improving the bonding strength and water resistance of the adhesive.When the ratio of CNF to TA-CNF was 0:100 and the ratio of TA-CNF to PVA-SbQ was 1:8,the wet shear strength of TA-CNF/PVA-SbQ adhesive was the highest,reaching 332.5±31.5 kPa,which was86.3%than that of the first system.And the water absorption rate of TA-CNF/PVA-SbQ adhesive was 81.5%higher than that of the first system,reaching 39.2±3.5%.Even after the adhesive was soaked in water for 28 days,the bonding strength could still be stable at about160 kPa,which had long-term stability.Thirdly,aiming at the problem that CNF is prone to agglomeration,PVA-SbQ/CNF hydrogel adhesive was firstly prepared to study the effect of CNF content on the structure and properties.The optimal dosage of CNF was obtained as 3 wt%.Then,TA-CNF（the dosage was3 wt%）obtained by self-polymerization deposition was introduced into the PVA-SbQ hydrogel adhesive to prepare PVA-SbQ/TA-CNF hydrogel adhesive by photocrosslinking.Finally,after being immersed in a 0.4 mol/L FeCl₃ solution,Fe³⁺was introduced by the solvent exchange to prepare PVA-SbQ/TA-CNF/FeCl₃ hydrogel adhesive with a double network structure,where its structure and performance were studied in detail.The results showed that in the PVA-SbQ/TA-CNF/FeCl₃ hydrogel adhesive,PVA-SbQ formed the first network through photodimerization,and the second network was formed through chelation between TA-CNF and Fe³⁺.Except for the enhancement of the mechanical and bonding properties,the double network structure formed by covalent and coordination also endowed the adhesive with electrical conductivity.The tensile strength,elongation at break,and bonding strength of the PVA-SbQ/TA-CNF/FeCl₃ hydrogel adhesive were 0.83±0.07 MPa,595.9±29.7%,and 6.96±0.9 kPa,respectively.The electrical conductivity also reached 1.29±0.02 S/m,broadening the application of hydrogel adhesives in the fields of sensors and smart wearable devices.