Study On The Technology Of Preparing Nano-lignin Based On Acid Precipitation Method And Its Performance

Lignin is the second-largest renewable resource after cellulose in biomass.However,due to its complex composition and structure,it has not yet been fully utilized.Because of its high surface area and volume ratio,nano-lignin has higher activity in the application process,which provides a potential strategy in solving the problem of low lignin application ratio.However,the current methods for preparing nano-lignin still have problems such as complicated processes,high energy consumption,long preparation time,and use of large amount of organic solvent.At the same time,nano-lignin performance is not ideal in terms of stability,yield,particle size and its distribution.To solve these problems,the following investigation was conducted:(1)Lignin from corn stalks was extracted with 1,4-butanediol alkaline solution.The extraction solution was used as the initial feedstock for nano-lignin preparation.The effect of dilution times and acid concentration on nano-lignin formation in the process of acid precipitation was studied.After analyzing and comparing the obtained nano-lignin from different conditions,it was found the particle size presented the trend of decreasing at the early stage and then stabilizing as the dilution times increased,while the polydispersity coefficient(PDI)gradually increased and the yield was getting lower and lower.Three times dilution was considered as the best condition after comparing comprehensively.In addition,the acid concentration was observed to be a less affecting factor for the formation of nanoparticles since there were only small changes in particle PDI and particle size at a higher acid concentration.(2)The effect of different p H on the particle size,PDI,Zeta potential,and yield of the obtained nano-lignin was investigated.The results showed that the particle size gradually increased as the p H value decreased.The trend for the PDI was firstly decrease followed by increase.The particle size at p H=5 was observed to be 160.1nm with PDI of 0.278.The stability of the nano-lignin at this p H was improved when it was re-dispersed into water.Compared to the original nano-lignin solution(-13.7m V),the Zeta potential of the re-dispersed solution dropped to-30m V,which could maintain stability at a salt concentration lower than 100mmol/L.At the same time,infrared,~1H-NMR,and molecular weight analysis were used to investigate the influence of lignin molecular structure on the formation of nano-lignin.The results shows that molecules with more carboxyl groups and alcoholic hydroxyl groups tend to form nanoparticles at higher p H.(3)The influence of different biomass including poplar(hardwood)and pine softwood on the preparation of nano-lignin was studied.After comparing the nano-lignin formation condition between these two biomass,it was found that the optimal p H for the nano-lignin preparation from poplar and pine were different,which were 6.0 and 5.7,respectively.The particle size,PDI,Zeta potential and yield were615.1nm,0.309,-16m V,19.63%(poplar)and 202.9nm,0.211,-22m V,12.25%(pine),respectively.Compared with poplar,the nano-lignin prepared from pine had a smaller particle size and better stability.In addition,the nano-lignin was characterized with lower phenolic hydroxyl groups content and higher alcoholic hydroxyl groups content.The molecular weight of the nano-lignin particles from poplar was lower than that of non-nano lignin,while pine wood-based nano-lignin showed the opposite result.