The Study On The Green Synthesis And Resource Utilization Of Functionalized Lignin Nanospheres

As an important component of new green materials,lignin has the characteristics of anti-oxidation,antibacterial,and good stability,showing broad application prospects.In particular,lignin itself contains a large number of phenolic hydroxyl and methoxy functional groups,which makes it have certain antioxidant and ultraviolet protection capabilities and can be used in the field of sun protection.However,due to the complex structure,high polydispersity,low solubility and high coloration of lignin macromolecules,the development of lignin in the field of sunscreen is limited.Previous studies on lignin sun protection have obtained lightcolored lignin that can be used in the field of sun protection through ultraviolet irradiation or acetylation modification methods,but these methods are all implemented in the form of blocked phenolic hydroxyl groups,which reduces the sun protection performance of lignin.In the field of nanomaterials,nanoparticles can achieve some of their difficult-to-achieve properties without changing the structure of the bulk material itself,such as color and mechanical properties.Therefore,this experiment intends to realize the retention or even improvement of the phenolic hydroxyl content of lignin without modification,and these lignin with high phenolic hydroxyl content can be used to synthesize nanospheres,which not only meets the standard of light-colored lignin,but also meets the requirements of high sunscreen performance.The specific research content includes three experiments:(1)The light-colored lignin was extracted from gramineous agricultural waste(bamboo chips)with less Syringa units(S-unit)and more p-phenylhydroxyl units(Hunit)by mild organic solvent.Various lignin fractions with gradually reduced molecular weight and gradually increased solubility and phenolic hydroxyl content are obtained after fractionation with acetone.The high solubility and phenolic hydroxyl content lay the foundation for the subsequent synthesis of lignin nanospheres.(2)By virtue of the high solubility and phenolic hydroxyl content of the low molecular weight lignin fraction,the self-assembly of lignin is made use of its amphipathy to synthesize nanospheres.And by controlling a single factor to study the influence of some external conditions such as the initial concentration of lignin,pH,molecular weight and stirring speed on the synthesis of nanospheres,and discussed the synthesis mechanism.(3)By mixing the synthesized light-colored nanospheres with the commercial pure cream,the sunscreen performance of various nanospheres and the influence of nanospheres addition on the ultraviolet transmittance of the synthesized sunscreen agent were studied.It was found that the nanospheres obtained from unrefractioned lignin mixed with emulsion(0.5: 1 wt%)can isolate more than 50% of ultraviolet rays,while the nanospheres obtained from fractionated lignin with the same dose can isolate ultraviolet rays more than 90%,especially for UVA ultraviolet rays.It lays a foundation for the wider practical application of lignin in the field of sun protection.