Fractionation Of Lignin And Its Applica-tion And Properties In Sunscreen And Natural Eucommia Ulmoides Tubber

With the increasing energy crisis and environmental pollution,sustainable and renewable environment-friendly materials are increasingly favored by researchers.Lignin,as the second largest biomass resource on earth,is polymerized by the structure of phenyl propane and has certain UV and aging resistance.However,the complex structure of lignin,high molecular weight polydispersity,and different types and contents of the functional groups contained make ligninbased products less stable.In order to further investigate the influence of molecular weight and functional groups of lignin on the anti-UV and anti-aging properties of the products,this paper uses grading technology to grade industrial lignin and obtain lignin with different molecular weight and functional group contents.The purpose of this paper is to study the effects of different molecular weight lignin on the anti-UV performance of sunscreen and the anti-UV and anti-aging performance of natural eucalyptus gum,and to explain the mechanism of lignin structure against UV and anti-aging,so as to lay the theoretical foundation for the high-value utilization of lignin resources.The main research results are as follows:(1)100% and 70%(v/v)ethanol solutions were used to grade the raw lignin EL0,and three different lignin grades-EL100,EL70 and ELR were obtained.test results showed that the molecular weight of the graded lignin was inversely proportional to the ethanol concentration,and the molecular weight of ELR was the largest(4022 g/mol).The EL100,EL70 and ELR The structural characterization showed that grading did not affect the core structure of lignin,and the content of lilyl unit/guaiacyl unit,aryl ether bond,carbon-carbon bond and monomer with conjugated structure were proportional to the molecular weight of lignin after grading,but the content of hydrophilic group was inversely proportional to the molecular weight of graded lignin.(2)Using the graded lignin obtained above,lignin-based sunscreen products were prepared by the co-blending method.The results showed that the UV resistance of the lignin-based sunscreen was directly proportional to the lignin content.The SPF values of the sunscreens prepared by EL70 and ELR were48.88 and 51.79 at 10% lignin addition,indicating that the UV resistance of lignin-based sunscreens is proportional to the lignin molecular weight.A computational model using density flooding theory(TD-DFT)to simulate the UV absorption of lignin molecules demonstrated that the UV resistance of lignin-based mainly depends on the π-π stacking of benzene ring in the lignin structure that can reduce the electron leap energy gap and the conjugated structure between the unsaturated group of the side chain and the aromatic ring.Combined with the structural characterization of lignin,EL70 and ELR with relatively larger molecular weights have more structures related to UV resistance than EL100,and thus have better UV resistance properties.(3)In order to further improve the anti-UV performance of graded lignin anti-UV materials and expand the lignin application scenario,lignin/dustin gum composite films were prepared by solvent casting method and characterized for the related properties.The results showed that the synergistic conjugation of lignin and eucalyptus gum further improved the UV resistance of the composite films in comparison with lignin-based sunscreens.The UV transmittance of the lignin-added composite films decreased to less than 10% in all wavelength bands.Meanwhile,the resistance to thermal and oxygen aging and UV aging was proportional to the phenolic hydroxyl content of lignin,as shown by the increase of the main thermal degradation temperature of the composite films with 4%EL100 and EL70 from 290 ℃ to 371 ℃ and 372 ℃ in pure EUR films and the good mechanical properties of the composite films after 96 h of high power UV irradiation.The mechanism study showed that in addition to the UV resistance of lignin and the molecular weight of lignin,the anti-aging property,thermal stability and mechanical properties of the films were also positively related to the phenolic hydroxyl content of lignin.