3.2 Impact of the third constituent in ChCl-DHBA DES system on cellulose degree of polymerization
According to the previous study, the size of cellulose (e.g., degree of polymerization) is a crucial factor in biomass conversion.38 The cleavage of cellulose generates more reducing ends which is beneficial in many biomass conversion processes. The degree of polymerization (DP) of cellulose isolated from untreated and pretreated WT and TG sorghum stover is presented in Figure 2 are tabulated in Table S2 in the Supplementary Materials. The weight-average degree of polymerization (DP) of cellulose in untreated WT and TG sorghum stover were 2,042 and 1,805, respectively. The dispersity (Đ) of cellulose in untreated WT and TG biomass were 11 and 9, respectively. All three pretreatments substantially reduced cellulose DPw in this study. The cellulose of WT biomass was more significantly depolymerized than the one in TG biomass. The highest reduction of cellulose DPw of WT biomass was 35% by the binary ChCl-DHBA DES pretreatment. Binary DES cleaved more cellulose chains in WT biomass (1,338) than in TG one (1,598), while both ternary DES pretreatments were more effective in reducing the cellulose DPw in TG biomass (1,479-1,489) than in WT one (1,499-1,599). Overall, the impacts of binary and ternary DESs on cellulose DP were not significantly different, indicating that the third component was not significantly modified glycosidic bond cleavage. Compared to dilute acid pretreatment, where up to 90% of reduction in cellulose DP could be achieved,39 ChCl-DHBA DES pretreatment showed much less modification on cellulose, which is consistent with the high cellulose retention.