Comparison on structural modification of industrial lignin by wet ball milling and ionic liquid pretreatment

• Two pretreatment methods were investigated to improve the quality of industrial lignin.
• ILP significantly reduced the average molecular weight and polydispersity of lignin.
• The methoxy group of lignin showed obviously decrease after ionic liquid pretreatment.
• ILP with [Emim][OAc] is an effective way to enhance the quality of industrial lignin.

As the most abundant aromatic compounds, lignin is still underutilized due to its relatively low quality. In order to improve its quality, two pretreatment technologies, wet ball milling (WBM) and ionic liquid pretreatment (ILP) were tested on the industrial lignin and evaluated on the average molecular weight and polydispersity, surface morphology, and functional groups changes. The results showed that the lignin pretreated by the WBM with phosphoric acid presented dramatic decrease of polydipersity (23%) and increase of phenolic hydroxyl content (9%). While, the ILP treated samples exhibited the significant reduction of the average molecular weight and polydispersity. The decrease on the particle size and the emergence of the porous structure were found when treated with [Emim][OAc]. In addition, the remarkable reduction of the methoxy groups were observed to be 50% and 45% after treated with [Bmim]Cl and [Emim][OAc], respectively.

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