Surface characterization of dilute acid pretreated populus deltoides by ToF-SIMS

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to analyze the molecular constituents on cross sections of juvenile poplar (Populus deltoids) stems before and after dilute acid pretreatment (DAP). Bulk analysis of milled and 50μm thick cross sections of poplar before and after DAP was shown to be chemically equivalent by FT-IR and carbohydrate analysis. ToF-SIMS analysis of dilute acid pretreated material indicated significant changes in relative contents of cellulose, xylan, and lignin occurred upon pretreatment. The relative content of xylan after DAP increased by 30% on the surface of the poplar stem by ToF-SIMS, while bulk carbohydrate analysis showed that the relative concentration of xylose decreased 10-fold in comparison with untreated poplar wood. The relative content of cellulose and G-lignin units doubled on the surface of the poplar stem sections, while the bulk glucose concentration and Klason lignin increased 40% and 5%, respectively, as determined by bulk carbohydrate and Klason lignin analysis. The spatial distributions of the major lignocellulosic components on the surface of juvenile poplar stem before and after DAP were examined by SIMS and this data was processed into mapping images. Scanning electron microscopy (SEM) was used to evaluate the morphological changes of the cell wall layers before and after DAP, which was also correlated with the results of ToF-SIMS analysis.