The broad peak at 1520 cm−1 in the spectra of SH and TSH are indicative of the presence of lignin and attributed to the C C vibra- tion (Sun et al., 2005). This peak disappeared in WSH30, further indicating the removal of the corresponding groups from lignin. The tiny peak at 1205 cm−1 in the spectra of WSH30 is related to S O vibration, due the esterification reaction, as reported in previous literature (Lu and Hsieh, 2010).
The peaks at 1061 and 897 cm−1 are associated with cellulose the C–O stretching and C–H rock vibrations of cellulose (Alemdar and Sain, 2008), which appeared in all of the spectra. The growth of these peaks showed the increase in the percentage of cellulosic components. The differences in the spectra of TSH and WSH30 indicate that these samples have higher cellulose content, suggesting that they are almost pure cellulose.