Preparation And Application Of Lignin-based Bionic Adhesive Materials Based On Catechol Structure

As a green and safe natural polymer,lignin has good biocompatibility and degradability.The natural phenylpropane skeleton,large numbers of phenolic hydroxyl groups and other conjugated functional structures endow lignin with excellent ultraviolet absorption and oxidation resistance properties,as well as a certain adhesion property.Because of that,lignin has been widely used in the field of functional materials.However,the bioadhesive ability of extracted lignin is weak,which greatly limits the application efficiency of lignin based functional materials.In view of the above problems,bionic adhesion modification of lignin was carried out.The bioadhesive ability of lignin was strengthened by introducing catechol structure.On this basis,the biomimetic adhesive modified lignin is applied to prepare microcapsules and hydrogels,which are used in sun protection and electronic sensing,expanding the new applications of lignin in the field of functional materials.Firstly,a series of biocompatible polydopamine-grafted lignin(AL-PDA)were synthesized through free radical addition of catechol-structured dopamine(DA)and alkali lignin(AL)to enhance the bioadhesion property,and compatibility of lignin.Infrared spectroscopy,nuclear magnetic resonance,and gel chromatography were used to investigate the grafting sites and grafting numbers.AL-PDA were then used to emulsify organic UV filters and further crosslinked to form nanocapsules through ultrasonic cavitation.The effects of raw material ratio on the molecular weight of AL-PDA,adhesion ability and morphology of the prepared materials were investigated.The results showed that the nanocapsules had good bioadhesion when the added mass ratio of dopamine hydrochloride(HDA):AL reached 1:1.After washing,the retention rate on the skin surface reached 87%,and the permeability was negligible.Atomic force microscopy(AFM)quantitative analysis showed that when the average number of DA grafts was 4,AL-PDA nanocapsules could maintain effective adhesion to the skin,with a critical adhesion of 0.32 m N/m.The capsules were used as the sole active ingredient for formulating sunscreen,whose sun protection factor(SPF)value could reach 195 with a dosage of 10 wt% and last for over 8 h under UV radiation.The excellent bioadhesive ability of the prepared nanocapsules effectively solves series of potential safety problems caused by the penetration of UV filters in sunscreens.Further,AL was demethylated using cyclohexane(ICH)to systhesize demethylated alkali lignin(DAL)with dopamine-like structure.Then,DAL was used to reduce graphene oxide(GO)to prepare lignin/reduced graphene oxide composites(DAL/r GO).After that,the prepared DAL/r GO were added to a sodium alginate/polyacrylamide(SA/PAM)gel to prepare sodium alginate/polyacrylamide/lignin/graphene double network hydrogel(SA/ PMA/DAL/r GO).Experiments show that the phenolic hydroxyl content of DAL increased to 3.25 mmol/g,and the distance between r GO was reduced to 0.37 nm.After optimizing the hydrogel preparation process,the weak hydrogen bonds in the gel network could be dynamically broken and recombined during stretching,giving the hydrogel elastomer properties.When the dosage of DAL/r GO reached 3%,the breaking strain of the hydrogel could reach 1307%.The catequinone/catechol structure in the network endowed the hydrogel with good reversible adhesion performance on skin,reaching 13.99 k Pa.Considering the characteristics of the resistance change during stretching process,the hydrogel was used as human body sensor.When the addition amount of DAL/r GO was 3%,the conductivity of the hydrogel reached 0.15 S/m,which could detect most movements of the human body.When the strain reached 500%,the gauge factor of the reached 7.97.The good biocompatibility and bio-adhesive property of lignin-based hydrogel lays a good foundation for the application of lignin-based hydrogel in the field of wearable and medical equipment.