Preparation And Regulation Mechanism Of Lignosulfonate Nanoparticles

With the depletion of fossil resources and the deterioration of environment,it is imperative to find a kind of renewable resources that can partially replace fossil resources.At the same time,biomass resources have large reserves and wide sources,and are considered as the most potential renewable resources.Lignin is the second most abundant natural polymer and the most abundant aromatic compound in nature,so it is of great significance to expand its application.Lignin-based nanomaterials have attracted wide attention in the field of functional materials due to their green and sustainable properties.However,how to control the morphology,size and long-term stability of lignin nanoparticles is a challenge.As an important derivative of lignin,lignosulfonate(LS)is not widely used in biomass-based materials due to its wide molecular weight distribution.In this study,different ethanol/water systems were used to classify LS,and the molecular weight and chemical structure of different fractions were characterized.Lignin nanospheres and nanorods with uniform size and long-term stability were prepared by using LS grade as raw material by antisolvent self-adsorption method.In addition,the micromorphology of LS nanoparticles is regulated by the chelation mechanism of metal ions,which is of great significance for the application of lignin-based nanomaterials.(1)The classification of lignosulfonates was achieved by different proportions of ethanol and water.LS90,LS70 and LS40 are obtained by continuous grading of LS with 90%,70%and 40%ethanol/water solutions.The method was green,simple and efficient,and the total yield is 94.4%,among which the highest yield of LS70 was 68.6%.The fractions were characterized by elemental analysis,infrared spectroscopy,molecular weight analysis,functional group content analysis and sugar content analysis.The results showed that the lignosulfonate fractions could be separated efficiently by water and ethanol system.The molecular weights of LS90,LS70 and LS40 increased in turn,and the polydispersion coefficients were relatively small(PDI is 1.5?3.6).The content of S,sulfonate functional group and methoxy functional group increased with the increase of molecular weight,while the content of phenolic hydroxyl functional group and sugar decreased with the increase of molecular weight.(2)Lignin sulfonate nanoparticles were prepared from different LS(LS90,LS70,and LS40)by the process of self-adsorption and reassembly by antisolvent dialysis.Nanoparticles were studied by SEM,TEM,EDS,particle size analysis,Zeta potential and ultraviolet spectrum.The results show that the LS nanoparticles are spherical and the particle size distribution is not uniform,and when the LS concentration is greater than 1.5 mg/m L,the stability of nanospheres in ethanol solution is poor and precipitation is easy to form.On the contrary,lignosulfonate showed obvious advantages for preparing nanomaterials after grading.For LS90,the hemicellulose forms a large amount of surface charge around LS90,which hinders the?-?interaction between aromatic structures and makes it difficult to form nanoparticles.For LS70,the ellipsoidal conformation in aqueous solution randomly aggregates during the self-assembly process,forming small and uniformly dispersed nanospheres,of which the smallest nanospheres can be distributed at 28.3 nm.For LS40 with high molecular weight,it aggregates along the long side of the ellipsoid during the process of self-adsorption reassembly,resulting in the formation of rod-like nanoparticles with a length of about 200?600 nm and a width of about 30?50 nm.Lignin sulfonate nanoparticles,LS70nanorods and LS40 nanorods,were formed by fraction-self-adsorption and showed excellent stability.In a certain temperature range(20?60 ^oC)and common organic solvents(methanol,?-valerolactone,isopropanol),both of them show good long-term stability.In addition,the separation of solid nanoparticles can be achieved by high-speed centrifugation.(3)The morphology of LS40 nanoparticles was controlled by chelation of metal ions.The results show that the morphology of LS40 nanoparticles can be regulated by adding different kinds(Ca Cl₂,Na Cl)and different proportions(3%,5%,7%,10%)of metal ions.The metal ions(Ca²⁺)with chelation can affect the initial conformation of LS40,causing its original ellipsoid configuration to be bent.LS40 is wrapped around Ca²⁺in the adsorption process,and forms homogeneous and stable spherical nanoparticles after dialysis treatment.When the concentration of Ca²⁺increased gradually,the proportion of nano-spheres formed gradually increased,and the size of the nanorods did not change significantly.When the concentration of Ca²⁺continues to increase to 10%,no nanorods are formed in LS40.At this time,lignin nanospheres with a diameter of about 207.8 nm are formed in all LS40 classes.On the contrary,Na Cl without chelation has no effect on the morphology of the nanorods,and the different addition ratio of Na Cl has no obvious effect on the length and width of the nanorods.In addition,the nanospheres formed by Ca²⁺chelation showed long-term stability in different organic solvents(methanol,?-valerolactone,isopropanol)systems and at room temperature(25 ^oC)for 60 days.