Study Of Efficient Treatment And Utilization Of Natural Peach Gum To Prepare UV-responsive Peelable Pressure-sensitive Adhesives

Wearable ultrathin electronics are increasingly applied for routine physiological monitoring and human-machine interfaces.The adhesives developed for the non-destructive fabrication of ultrathin electronics are usually UV-responsive peelable pressure-sensitive adhesives（PSAs）.The main components of existing UV-responsive peelable PSAs include polyacrylates,polyurethane acrylate（PUA）oligomers,and photoinitiators.The above PSAs have high adhesion strength to fix electronics without UV irradiation.When the oligomers in the PSAs are cured by UV light,a cross-linked network structure forms inside,and the peel strength is dramatically reduced,thus achieving the damage-free peeling of ultrathin electronics.Despite successful designs and applications,fully petrochemical-based PSAs are not sustainable and may harm the environment.Therefore,it is desirable to transition from petroleum to biomass as the source of raw materials.Natural peach gum is an exudate secreted from the peach trees due to mechanical damage or microbial attack.It is mainly composed of arabinogalactan-type polysaccharides possessing a high molecular weight（>10³ k Da）and a highly branched molecular structure.The monosaccharide composition of peach gum includes arabinose,galactose,xylose,mannose,rhamnose,and uronic acid,with arabinose and galactose being at the most prominent levels.Mainly composed of polysaccharides with abundant hydroxyl and carboxyl groups,peach gum is endowed with strong adhesion strength when used as a binder for cartons,envelopes,building materials,etc.Exudate collected from the trunks and branches of peach trees is usually called raw peach gum（RPG）.RPG always has a very complex structure and high molecular weight,resulting in a very poor solubility,significantly limiting its application in practice.Therefore,it is essential to propose a brand-new method for peach gum’s efficient treatment and utilization.N,N-dimethylacetamide/lithium chloride（DMAc/LiCl）,a widely used direct solvent system for the dissolution of cellulose.In this work,DMAc/LiCl system was innovatively applied to the dissolution of peach gum and successfully obtained a 30 wt%of pretreated peach gum（PPG）solution,which significantly increased the percentage of peach gum as a dissolved substance in the solution,greatly facilitating the utilization of peach gum.However,simply obtaining a PPG solution is not enough yet,as PPG’s compatibility with many other substances is still insufficient.Herein,a H₂O₂ solution was added to the PPG solution and exposed to UV light to generate·OH at room temperature,facilely obtaining a solution of degraded peach gum（DPG）,which improves the compatibility of peach gum with other components.As for PUA oligomers,in this work,sorbitol,a type of carbohydrate considered polyol found in many fruits,was employed as a polyol in synthesizing a hexafunctional sorbitol-based polyurethane acrylate（SPUA）,an oligomer possessing good UV curing properties,which is the functional component causing the fundamental transformation of PSA from‘sticky’to‘non-sticky’under the initiation of UV light.Herein,the bio-based UV-responsive peelable PSAs were obtained by mixing a photoinitiator and multiple components originating from biomass sources,including DPG,SPUA,rosin,and epoxidized soybean oil（ESO）,and the PSAs possessed strong peel strength（244.4 N/m）before UV irradiation and negligible peel strength（7.3 N/m）after UV curing and were successfully applied for non-destructive fabrication of ultrathin electrodes.