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314 Refining Biomass Residues for Sustainable Energy and Bioproducts

ozonolysis of maize stover but reduces 42% of xylose yield (Li et al., 2015b). In
the case of wheat straw, the washing step was found to reduce the hydrolysis dura-
tion (Schultz-Jensen et al., 2011).

14.2.4 Characteristic and structural changes on ozone-pretreated
lignocellulosic biomass

The chemical characterization of ozonated products was done by Bule et al. (2013).
The lignin structure was found to have significant changes in the nuclear magnetic
resonance (NMR) analysis due to degradation of aromatic rings in different lignin
subunits. The signal corresponding to the aromatic carbon is diminished in the ozo-
nated sample as shown in the spectrum in Fig. 14.4 (Sega et al., 2010). Methoxy
group changes could also be observed due to the possible breakdown of ester link
structures.
On the other hand, the destruction of aromatic rings and the formation of alde-
hydes and ketones on ozonated aspen sawdust are described in Fourier-transform
infrared (FTIR) spectroscopy (Mamleeva et al., 2009). The partial oxidation reac-
tion of lignin and hemicellulose leads to formation of aliphatic carbon acids and
carbonyl compounds. Souza-Corrˆ ea et al (2013) supported the Criegee mechanism
of ozone attack toward lignin double bonds using mass spectrometry and FTIR
spectra (Souza-Corrˆ ea et al., 2013). The surface chemical changes of ozonated
wheat straw were studied by Ka ´da ´r et al. (2015) using attenuated total reflectance-
FTIR spectroscopy, found significant reduction in peak intensity attributed to the
aromatic skeletal vibrations from the lignin degradation as shown in Fig. 14.5
(Ka ´da ´r et al., 2015).
In terms of crystallinity index, Yu et al (2011) has analyzed ozonated loblolly
pine and mixed southern hard wood chips using X-ray powder diffraction and found
a general augmentation resulting from a reduction in the amount of amorphous
components attributed to the degradation of lignin and hemicellulose. Travaini et al
(2013) analyzed the ozonated sugarcane bagasse using scanning electron micros-
copy (SEM) and found a disturbed structure and nanoscopic fibrous morphology as
shown in Fig. 14.6. The lignin removal was shown in some areas especially at the

Figure 14.4 NMR spectra of (A) control and (B) ozone-treated wheat straw samples (Sega
et al., 2010). NMR, Nuclear magnetic resonance.