During the ethanol fractionation process, the effect of severity parameter on crystallinity of lignocellulosic material is not fully defined. Under mild conditions, the degradation of carbohydrates mainly occurred at the amorphous region, resulting in the removal of hemicelluloses and amorphous cellulose, but cellulose in the crystalline region is resistant to degradation. This was supported by the comparative analysis of solid state CP/MAS 13C NMR spectra of the treated and the untreated Miscanthus x giganteus [18]. Pan et al. [19] reported that the crys­tallinity of cellulose increased with increased severity of ethanol fractionation pretreatment of Lodgepole pine, suggesting that cellulose in amorphous region was more easily degraded than that in crystalline region. In another investigation on Pine (Pinus radiata) fractionation by formic acid, a decrease of crystallinity after the treatment was also shown [38]. However, a more serious severity was capable of disrupting the crystallinity of cellulose, resulting in the decrease of CrI, as reported in the ethanol fractionation of Buddleja davidii [39]. The degradation results in cellulose with a decreased degree of polymerization (DP) and a narrow molecular weight distribution. In addition, it has also been found that crystalline cellulose dimorphs (Ia/Ib) are converted into para-crystalline and amorphous type.

Carbohydrates in lignocellulosic materials undergo decomposition under acidic conditions during the auto — or acid-catalyzed ethanol fractionation process. Car­bohydrates are first hydrolyzed into oligosaccharides and monosaccharides, and the resulting monosaccharides further dehydrate to generate furfural (from pen­toses) and hydroxymethylfurfural (HMF) (from hexoses). Furfural and HMF undergo further degradation to form levulinic acid and formic acid, respectively. In addition, the products, i. e., furfural, HMF and levulic acid, tend to condense and form polymers such as humins [40]. The contents of furfural and HMF increase with increased severity parameter. But the overall effect of severity is minor due to the low yield of these products. At a high temperature and a high pressure, water can act as an agent for the degradation of carbohydrates [41]. These effects con­tribute a lot in the hot compressed water and dilute acid treatment of woody biomass. However, they are reduced largely by ethanol fractionation because of the elimination of strong acid and the high water content [40].